Issued 11 August 2020
Please note that the values presented in this report are based on preliminary data. They will change when the final data are processed, but will not be replaced on these pages.
National Drought Highlights
- Based on the Palmer Drought Index, severe to extreme drought affected about 11% of the contiguous United States as of the end of July 2020, an increase of about 6% from last month. About 22% of the contiguous U.S. fell in the severely to extremely wet categories.
- About 20% of the contiguous U.S. fell in the moderate to extreme drought categories (based on the Palmer Drought Index) at the end of July.
- On a broad scale, the 1980s and 1990s were characterized by unusual wetness with short periods of extensive droughts, the 1930s and 1950s were characterized by prolonged periods of extensive droughts with little wetness, and the first two decades of the 2000s saw extensive drought and extensive wetness (moderate to extreme drought graphic, severe to extreme drought graphic).
- A file containing the national monthly percent area severely dry and wet from 1900 to present is available for the severe to extreme and moderate to extreme categories.
- Historical temperature, precipitation, and Palmer drought data from 1895 to present for climate divisions, states, and regions in the contiguous U.S. are available at the Climate Division: Temperature-Precipitation-Drought Data page. These filenames begin with "climdiv".
- According to the weekly U.S. Drought Monitor (USDM), as of July 28, 2020, 32.72% of the contiguous U.S. (CONUS) (27.41% of the U.S. including Alaska, Hawaii, and Puerto Rico) was classified as experiencing moderate to exceptional (D1-D4) drought.
Detailed Drought Overview
The atmospheric circulation over North America during July 2020 consisted of sub-tropical high pressure across the southern states, a stronger-than-normal trough over eastern Alaska and adjacent northwest Canada, and a vigorous storm track in between across the U.S.-Canadian border. Anomalous ridging extended northeastward from the high pressure ridge over the southern states into eastern Canada and the northeastern CONUS. There was some variation week to week, especially as strong Pacific systems traversed the continent, but this overall circulation pattern accounted for the unusually warm temperatures over the Southwest and southern Plains region, and Great Lakes to Mid-Atlantic and Northeast region, as well as the cooler-than-normal month over northeast Alaska. Pacific weather systems moved along the storm track, dragging fronts and surface low pressure systems along with them. The fronts and lows mostly moved across the northern states, frequently reaching the central Plains and Ohio Valley when particularly strong upper-level troughs migrated through the region, and occasionally reached into the southeast states. The high pressure ridge inhibited precipitation across much of the CONUS, but the fronts and lows were strong enough to generate intense thunderstorms along their path. These rains left parts of the Plains and Midwest with above-normal precipitation for the month, but they were spotty in some cases with nearby areas missing out. Afternoon convection triggered spotty showers and thunderstorms along the Gulf of Mexico coast; Tropical Storm Fay brought rains to parts of the Northeast at mid-month; Hurricane Hanna moved across the Gulf, drenching southern Texas with heavy rain late in the month; and Hurricane Douglas brushed parts of Hawaii with rain. Hurricane Isaias, as a tropical storm, drenched Puerto Rico with heavy rain right as the month ended.
The extremely hot temperatures, especially in the Southwest, southern to central High Plains, and Northeast, increased evapotranspiration (ET) (as seen by such indices as the ESI and EDDI). The high ET in these regions exacerbated drought conditions for the areas that had below-normal rainfall (as seen, for example, by the Palmer Z Index). The high ET and low precipitation further dried soils (as seen in satellite observations of soil moisture [SMOS; SPoRT LIS 0-10 cm depth, 0-40 cm depth, 0-100 cm depth, 0-200 cm depth, RSM], field reports [USDA NASS reports], and models [VIC, CPC, NLDAS, NASA GRACE surface soil moisture and root zone soil moisture, and Leaky Bucket]) and stressed vegetation (VegDRI, QuickDRI). This was especially true in the Southwest, southern to central High Plains, and Northeast, but also in the Ohio Valley, Iowa, parts of the Southeast, and other parts of the West. Many of the streams and groundwater levels (GRACE satellite estimates, USGS observations) were low in these areas. Dozens of large wildfires broke out across the West and Plains (wildfire maps for July 1, 7, 15, 19, 23, 29, 31), with just over 2 million acres burned nationwide so far this year, according to a July 31 National Interagency Coordination Center report. Reports received from the CoCoRaHS Condition Monitoring Resource (for July 14-21 and 21-28) included crop and livestock issues (reduced yields and pasture/forage, plant/animal stress, drying ponds and lakes, insect infestations and invasive species), increased fire risk, and dry lawns.
As a result of these conditions, drought or abnormal dryness expanded or intensified across much of the West, Midwest, and Northeast, and parts of the Plains and Southeast. Drought or abnormal dryness contracted in other parts of the Plains, Midwest, and Northeast, as well as parts of Hawaii and Puerto Rico. Drought expansion exceeded contraction with the USDM-based national moderate-to-exceptional drought footprint across the CONUS rising from 25.5 percent at the end of June to 32.7 percent at the end of July (from 21.4 percent to 27.4 percent for the 50 States and Puerto Rico). According to the Palmer Drought Index, which goes back to the beginning of the 20th century, about 20.2 percent of the CONUS was in moderate to extreme drought at the end of July, an increase compared to the end of June.
Drought conditions at the end of July, as depicted on the July 28, 2020 USDM map, included the following core drought and abnormally dry areas:
- Moderate (D1) to severe (D2) drought, with areas of extreme (D3) drought, extended from the West Coast to Rocky Mountains and into the adjacent High Plains. The percent area of the West experiencing moderate to extreme drought, according to USDM statistics, increased from 45.2 percent at the end of June to 58.9 percent at the end of July. The percent area of the West (from the Rockies to the West Coast) in moderate to extreme drought (based on the Palmer Drought Index) increased to about 37.7 percent. A few areas from California to the Pacific Northwest were wetter than normal, and a weak Southwest Monsoon gave parts of Colorado and New Mexico above-normal precipitation, but most of the West was well below normal for July. The short-term dryness just added to longer-term dryness (last 6, 12, 24 months), making matters worse. New Mexico ranchers were seeing cumulative impacts on the landscape of the dryness over the last 24 to 36 months. According to local reports, Elephant Butte Reservoir was down to 11.7 percent of capacity late in the month, and continuing to decline; county commissioners issued a drought declaration for De Baca County; and the New Mexico Interstate Stream Commission noted that, if not for the additional releases going on that were approved under the Rio Grande Compact, the Rio Chama (a major tributary) and the Rio Grande from Albuquerque down to Elephant Butte Reservoir would be dry completely from natural flow. Even with the releases, the Rio Grande isn't continuous from Albuquerque to Elephant Butte now. According to reports from Wyoming, parts of the state have gone into regulation with some areas back to Territorial and earlier water rights. In the Buffalo area, producers were paying for the water (from a reservoir feeding Clear Creek) to irrigate with. The newer water rights have been shut off in the Buffalo area since Clear Creek is at a trickle downstream at Arvada and the producers there were not able to irrigate. There were numerous reports from the field of infestations (grasshoppers, crickets, etc.), fires, low water, drying streams, and dried out pastures.
- Drought expanded in some parts of the Plains and contracted in other parts. Abnormal dryness (D0) to extreme drought continued in the southern to central High Plains, moderate to severe drought expanded and extreme drought developed in parts of the northern High Plains (especially Wyoming), and abnormal dryness to moderate drought contracted in other parts of the northern Plains (Dakotas).
- Moderate drought continued in the Upper Mississippi Valley, moderate drought developed in the Ohio Valley and southwest Missouri, and moderate to severe drought developed in western Iowa.
- Moderate drought expanded and areas of severe drought developed in the Northeast.
- Abnormal dryness expanded with pockets of moderate drought developing in parts of the Southeast.
- Abnormal dryness to severe drought contracted slightly in Hawaii.
- Abnormal dryness returned to southern Alaska.
- In the Caribbean, abnormal dryness to severe drought continued in Puerto Rico (as of July 28, pre-Isaias), while extreme drought disappeared and moderate to severe drought contracted in the U.S. Virgin Islands.
- In the U.S.-Affiliated Pacific Islands (USAPI), drought conditions improved in some areas, although extreme drought continued in parts of the Marianas and northern Marshall Islands, while severe drought continued in southern Micronesia at Kapingamarangi.
Palmer Drought Index
The Palmer drought indices measure the balance between moisture demand (evapotranspiration driven by temperature) and moisture supply (precipitation). The Palmer Z Index depicts moisture conditions for the current month, while the Palmer Hydrological Drought Index (PHDI) and Palmer Drought Severity Index (PDSI) depict the current month's cumulative moisture conditions integrated over the last several months. While both the PDSI and PHDI indices show long-term moisture conditions, the PDSI depicts meteorological drought while the PHDI depicts hydrological drought. The PDSI map may show less severe and extensive drought (as well as wet spell conditions) in some parts of the country than the PHDI map because the meteorological conditions that produce drought and wet spell conditions are not as long-lasting as the hydrological impacts.
Used together, the Palmer Z Index and PHDI maps show that short-term drought occurred across much of the West and southern High Plains, expanding and intensifying long-term dry conditions and, in southern parts of the West, eliminating long-term wet conditions (PHDI maps for July compared to June). Short-term drought in the Southeast, Iowa,and western Ohio Valley and southern Great Lakes reduced or pushed back long-term wet areas. The short-term drought in the Northeast began areas of long-term drought there. Short-term wet conditions in parts of the northern and central Plains, and western parts of the Ohio Valley, intensified or expanded long-term wet conditions there.
Standardized Precipitation Index
The Standardized Precipitation Index (SPI) measures moisture supply. The SPI maps here show the spatial extent of anomalously wet and dry areas at time scales ranging from 1 month to 24 months.
The SPI maps illustrate how moisture conditions have varied considerably through time and space over the last two years. Dry conditions are evident across large parts of the West at the 1- to 12-month time scales, with specific regions varying. Parts of the Pacific Northwest are dry at 1 month and 6-24 months; much of California and the Southwest to southern and central Rockies are dry at 1-12 months, except for southern portions of California to New Mexico at 6-12 months; and much of northern New Mexico to southern Wyoming is dry at all time scales. Parts of the northern Plains are dry at 1-9 months. The southern High Plains (west Texas) to central High Plains (eastern Colorado and eastern Wyoming) are dry at the 3-12 month time scales and partly at the 1-2 month time scales. Western Iowa is consistently dry at the 1- to 9-month time scales. Southern Texas is dry at 12 months. Parts of the Southeast are dry at 1-3 months. Parts of the Ohio Valley (eastern parts) to Northeast are dry at 1 to 9 months. Parts of the Upper Mississippi Valley show dryness at 3-9 months. Most of the country east of the Rockies is wet at 24 months; wet conditions dominate from the northern Plains to Southeast at 12 months; and the Southeast is mostly wet at 6 to 9 months.
Standardized Precipitation Evapotranspiration Index
The SPI measures water supply (precipitation), while the SPEI (Standardized Precipitation Evapotranspiration Index) measures the combination of water supply (precipitation) and water demand (evapotranspiration as computed from temperature). Warmer temperatures tend to increase evapotranspiration, which generally makes droughts more intense.
Temperatures during July 2020 were significantly warmer than normal across the West Coast to southern Plains, all along the Eastern Seaboard, and into the Ohio Valley and Great Lakes. Some parts of the Southwest and Mid-Atlantic to Northeast had a record warm July. These included Virginia, Maryland, Delaware, Pennsylvania, New Jersey, Connecticut, and New Hampshire. All of these states have had much-warmer-than-normal temperatures in July for most of the last eleven years. July precipitation was below normal in much of these regions, with parts of the Southwest and central High Plains to central Rockies having a record dry July. The combination of hot and dry conditions resulted in a much more severe SPEI than SPI for July in parts of the southwestern CONUS, southern and central High Plains, Ohio Valley, and Mid-Atlantic to Northeast. Ohio had the eighth driest SPEI for July compared to the 16th driest SPI.
The pattern of anomalously hot and dry conditions in the Southwest to central Rockies, and southern to central High Plains, extends back three to four months (temperature anomaly maps for May-July and April-July, precipitation anomaly maps for May-July and April-July). This has resulted in SPEI values that are more severe than the SPI values for these areas (SPEI maps for the last 2, 3, 4, 5, 6 months) (SPI maps for the last 2, 3, 4, 5, 6 months). Arizona ranked third driest and second warmest for May-July 2020. New Mexico had the 11th driest and second warmest May-July in the 1895-2020 record. These combinations gave Arizona the driest SPEI for May-July compared to third driest SPI and New Mexico the third driest SPEI for May-July compared to 18th driest SPI. Arizona had the second driest SPEI for April-July compared to fourth driest SPI and New Mexico the third driest SPEI for April-July compared to 11th driest SPI. Even out to seven months, Arizona's January-July SPEI ranked 14th driest compared to 43rd driest for the SPI.
Much of the West has experienced persistent warmer-than-normal temperatures for most of the last nine years. The unusual warmth has made the SPEI more extreme than the SPI for those dry areas in the West at the longer time scales (SPEI maps for last 24, 36, 48, 60, 72 months) (SPI maps for last 24, 36, 48, 60, 72 months). For example, for Arizona, the 5-year (60-month) SPEI ranked 21st driest compared to 77th driest (or 46th wettest) for the SPI. For New Mexico, the 5-year SPEI ranked 16th driest compared to 57th driest for the SPI.
Hurricane Douglas tracked just north of the Hawaiian Islands late in the month, far enough away as to cause minimal damage but close enough to bring some rain to the islands. July 2020 was generally drier than normal in the southern Hawaiian main islands and wetter than normal in the northern islands, although there were a few exceptions. Drier-than-normal conditions mostly dominated for the last two to four months, especially at the windward stations. Most stations were wetter than normal at the 5- to 7-month time scales. A mixed anomaly pattern prevailed from 9 to 24 months, with wetter-than-normal conditions dominant at longer time scales (last 1, 2, 3, 4, 6, 7, 9, 10, 12, 24, 36, 48, 60 months). Temperatures were mostly warmer than normal for the last three months (last 1, 2, 3 months). Streamflow had a mixture of gauge anomalies, with above-normal streamflow on Kauai and below-normal streamflow dominating on Oahu and Maui. Drought and abnormal dryness expanded in some parts of Hawaii during July and contracted in others. The statewide moderate to severe drought area shrank to 21.0 percent by the end of the month.
July 2020 had a mixed precipitation anomaly pattern across Alaska. Western, northern, southern coastal, interior, and interior southeastern areas were drier than normal, while the panhandle and a few stations in the interior and southwest were wetter than normal. The panhandle to interior regions were wetter than normal at 2 to 3 months, while the northern, northwestern, and especially Aleutian to south coastal areas were drier than normal. Most of the state was wetter than normal, with dryness continuing along the Aleutian to south coastal areas, at 4 to 12 months. The south-central coastal to panhandle areas were drier than normal at longer time scales (low elevation station precipitation anomaly maps for the last 1, 2, 3, 4, 6, 7, 9, 10, 12, 24, 36, 48, 60 months) (high elevation SNOTEL station precipitation maps for last 1 and 10 months, and SNOTEL basin maps for last 10 months) (gridded precipitation percentile maps for the last 1, 3, and 7 months) (climate division precipitation rank maps for the last 1, 3, 6, 7, 12 months) (station percent of normal maps from ACCAP for the last 1 and 3 months) (Leaky Bucket model precipitation percentile map). July and June-July temperatures were cooler than normal in the north to northeast and warmer than normal along the coast from the southwest to northern panhandle. The northeast was cooler than normal while warmer-than-normal temperatures dominated across the southwestern two-thirds of the state at the 3- to 4-month time scales. The warmer-than-normal areas shrank in size with the colder-than-normal temperatures expanding across the eastern interior at 6 to 7 months, then the cold areas shrank and the warm areas expanded at 10 to 12 months (low elevation station temperature maps for the last 1, 2, 3, 4, 7, 10, 12 months) (gridded temperature percentile maps for the last 1, 3, and 7 months) (climate division temperature rank maps for the last 1, 3, 6, 7, 12 months) (Leaky Bucket model temperature percentile map). Modeled soil moisture and satellite-based soil moisture estimates showed drier-than-normal conditions in southern coastal and northeastern areas, and streamflow was mostly near to above normal at most gauges. Several large wildfires burned from the southwest, across central Alaska, to the northeast (wildfire maps for July 1, 7, 15, 19, 23, 29, 31). According to the National Interagency Fire Center's (NIFC) National Interagency Coordination Center, as of July 31st, 179,238 acres have been burned in Alaska so far this year. Abnormal dryness developed this month on the Aleutian peninsula to south coastal areas, covering 5.2 percent of the state on the July 28th USDM map.
Puerto Rico and U.S. Virgin Islands
Tropical Storm (later Hurricane) Isaias moved across Puerto Rico and the U.S. Virgin Islands (USVI) during the last couple days of July, just after the valid period for the July 28 USDM map. The heavy rains from Isaias immediately ended the drought which was affecting Puerto Rico up to that point (radar-estimated precipitation for July 29, 30, 31). Isaias dropped less rain on the USVI. As a result, monthly precipitation for July was above normal for Puerto Rico and the northern USVI, but still below normal for St. Croix in the USVI. But drier-than-normal conditions were still evident at longer time scales, even at 2 months for southeastern sections of Puerto Rico, and especially for St. Croix. The dryness was significant for the USVI and southeastern Puerto Rico for the last 3 to 4 months, and was still evident at 6 to 12 months. Drier-than-normal conditions covered more of Puerto Rico as well as all of the USVI at 24 months, but Puerto Rico was wetter than normal at longer time scales (radar-based precipitation anomaly estimates for the last 1, 2, 3, 6, 7, 10, 12 months) (low elevation station precipitation maps for the last 1, 2, 3, 4, 6, 7, 9, 10, 12, 24, 36, 48, 60 months). (climate engine model percent of normal precipitation map for July 1-28, July 1-31, April 1-July 31).
Temperatures across Puerto Rico and the USVI have been unusually warm during the last four months, and even extending back for the year to date, increasing evapotranspiration and worsening drought conditions (low elevation station temperature anomaly maps for the last 1, 2, 3, 4, 7 months). Root zone analyses indicated that soil conditions were very dry along the southern coastal areas of Puerto Rico and extending northward across the central part of the island up to July 28; soil conditions improved considerably by July 31. There were some low streams pre-Isaias, but end-of-July streamflow was near to above normal across nearly all of Puerto Rico. Moderate to severe drought covered 45.2 percent of Puerto Rico on the July 28th USDM map, but it was gone from the following week's (August 4) USDM map. Conditions at the end of July improved in the USVI compared to June, with abnormal dryness on St. Thomas and moderate drought on St. John and St. Croix on the July 28th USDM map; the depiction was unchanged on the August 4th USDM map.
CONUS State Precipitation Ranks
July 2020 was drier than normal across most of the West, parts of the Great Plains, and much of the Ohio Valley, Southeast, and Northeast. Fifteen states in these regions had a precipitation rank in the driest third of the 126-year historical record for July, including Arizona which ranked sixth driest and Nevada which ranked 11th driest.
May-July 2020 was drier than normal from the Southwest to southern and central Rockies, across most of the High Plains, in parts of the Midwest and Southeast, and across most of the Northeast. Parts of the Southwest were record dry. Fifteen states had a rank in the driest third of the historical record, including Arizona (at third driest), New Mexico (11th driest), and Maine (12th driest).
The last six months (February-July 2020) were drier than normal in much of the Northeast, parts of the Great Lakes and Gulf of Mexico coast, much of the Upper Mississippi Valley, and most of the West to High Plains. Fourteen states ranked in the driest third of the historical record, including Colorado which ranked eighth driest.
The year to date (January-July 2020) had a similar precipitation anomaly pattern — drier than normal in much of the Northeast, parts of the Great Lakes and Gulf of Mexico coast, much of the Upper Mississippi Valley, and most of the West to High Plains. Fourteen states ranked in the driest third of the historical record, including Colorado which ranked eighth driest, again, and Utah at 11th driest.
The last twelve months (August 2019-July 2020) were drier than normal across much of the West to the southern and central High Plains, parts of the Mid-Atlantic to New England states, and parts of the Gulf of Mexico coast, northern Indiana and Ohio, and western Iowa to northeast Nebraska. Nine states ranked in the driest third of the historical record, including, again, Colorado (third driest) and Utah (11th driest).
During July 2020, the Primary Corn and Soybean agricultural belt experienced a mostly warmer-than-normal temperature anomaly pattern with a mixed precipitation anomaly pattern. The month ranked as the 22nd wettest and 23rd warmest July, regionwide, in the 1895-2020 record.
March marks the beginning of the growing season for the Primary Corn and Soybean agricultural belt. March-July 2020 temperatures were near to warmer than average and precipitation was mostly wetter than average. The period ranked as the 32nd wettest and 28th warmest March-July, regionwide.
As of July 28, drought affected approximately 26 percent of winter wheat production, 28 percent of cattle inventory, 21 percent of hay acreage, 8 percent of spring wheat production, 19 percent of corn production, and 16 percent of soybean production. Except for spring and winter wheat, these were all increases compared to the end of June.
As reported by the U.S. Department of Agriculture (USDA), at the end of July (July 27), topsoil moisture was short or very short (dry or very dry) across 100 percent of Rhode Island, 88 percent of Connecticut, 61 percent of New Hampshire, 58 percent of Maine, 66 percent of Pennsylvania, 54 percent of Ohio, 56 percent of Michigan, 60 percent of Georgia, 71 percent of Texas, 55 percent of Oklahoma, 80 percent of New Mexico, 75 percent of Wyoming, 67 percent of Colorado, 55 percent of Utah, 75 percent of California, 71 percent of Oregon, and 62 percent of Washington, and between 30 and 50 percent of Nevada, Idaho, Montana, Kansas, Nebraska, Iowa, Arkansas, Mississippi, Tennessee, South and North Carolina, Virginia, West Virginia, Indiana, Delaware, New Jersey, and New York. Subsoil moisture was short or very short across 75 percent of California, 70 percent of Colorado, 88 percent of Connecticut, 56 percent of Georgia, 62 percent of Maine, 60 percent of Massachusetts, 50 percent of Michigan, 66 percent of New Hampshire, 85 percent of New Mexico, 58 percent of Ohio, 61 percent of Oklahoma, 70 percent of Oregon, 57 percent of Pennsylvania, 100 percent of Rhode Island, 67 percent of Texas, 54 percent of Utah, 52 percent of Washington, and 78 percent of Wyoming, and between 30 and 50 percent of Arkansas, Delaware, Idaho, Indiana, Iowa, Kansas, Mississippi, Nebraska, Nevada, New York, North and South Carolina, Tennessee, Virginia, and West Virginia. Pasture and rangeland were in poor to very poor condition in Arizona (32 percent), California (55 percent), Colorado (40 percent), Connecticut (86 percent), Nevada (30 percent), New Hampshire (33 percent), New Mexico (50 percent), New York (30 percent), Oregon (69 percent), Rhode Island (100 percent), Texas (43 percent), and Wyoming (50 percent). Nationwide, 37 percent of the topsoil and 35 percent of the subsoil was short or very short of moisture, 30 percent of the pasture and rangeland was in poor to very poor condition, and 16 percent of the cotton crop, seven percent of the corn crop, six percent of the soybean crop, and six percent of the spring wheat were in poor to very poor condition. As seen in the early August (August 3) report, the national statistics changed very little, although the statistics for some states went up while some others went down.
U.S.-Affiliated Pacific Islands
The NOAA National Weather Service (NWS) offices, the Pacific ENSO Applications Climate Center (PEAC), and partners provided reports on conditions across the Pacific Islands.
In the U.S. Affiliated Pacific Islands (USAPI) (maps — Federated States of Micronesia [FSM], Northern Mariana Islands, Marshall Islands [RMI], Republic of Palau, American Samoa, basinwide), July 2020 was drier-than-normal in the Marianas, northern Marshalls, Palau, and FSM. It was wetter than normal at Majuro (RMI) and Pago Pago (American Samoa).
Monthly precipitation amounts were below the monthly minimum needed to meet most water needs (4 inches in the Marianas and Pago Pago, and 8 inches elsewhere) at Yap, Chuuk, and Kapingamarangi (FSM) and Wotje (RMI). July precipitation was above the monthly minimums at the rest of the USAPI stations — Koror (Republic of Palau); Ulithi, Woleai, Fananu, Lukonor, Nukuoro, Pohnpei, Pingelap, Mwoakilloa, and Kosrae (FSM); Ailinglapalap, Majuro, Mili, Jaluit, and Kwajalein (RMI); Guam, Rota, and Saipan (Marianas); and Pago Pago (American Samoa). The 4- and 8-inch thresholds are important because, if monthly precipitation falls below the threshold, then water shortages or drought become a concern.
The first seven months of 2020 were drier than normal across most of Micronesia. Of the primary stations, only Majuro (in the RMI), Kosrae (in the FSM), and Pago Pago (in American Samoa) had a wetter-than-normal January-July 2020.
As measured by percent of normal precipitation, Chuuk, Kapingamarangi, Koror, Kwajalein, Lukonor, and Yap were drier than normal in the short term (July and the last 3 months [May-July 2020]) and long term (year to date [January-July] and last 12 months [August 2019-July 2020]). Guam, Pohnpei, and Saipan were drier than normal in the short-term and for the year to date, but near to wetter than normal for the last 12 months. Kosrae was drier than normal for July and the last 12 months, but wetter than normal for the other two time periods. Majuro and Pago Pago were wetter than normal for all four time periods. It should be noted that the monthly normal precipitation amount can vary significantly from month to month due to the strong seasonality of equatorial Pacific precipitation resulting from the seasonal migration of the Inter-Tropical Convergence Zone (ITCZ) and occurrence of tropical cyclones. Most of the stations in Micronesia have July monthly normal precipitation amounts that are above (and in some cases well above) the monthly minimum threshold for drought. As a result, it is possible for a station to have below-normal precipitation this time of year and still be above the monthly minimum for drought.
Based on percent of normal average (instead of normal median values), in the Marianas Islands, precipitation was drier than normal at the primary stations in July and all time scales from the last 2 to 9 months. At longer time scales, it was wetter than normal at the southern stations (on Guam) but continued drier than normal at the stations to the north (percent of normal precipitation maps for the last 1, 2, 3, 4, 6, 7, 9, 10, 12, 24, 36, 48, 60 months). In the Marshall Islands, the precipitation anomaly pattern was mostly drier than normal for July and mostly mixed for the last 2 to 10 months. The western islands were generally drier than normal and eastern islands wetter than normal at longer time scales (percent of normal precipitation maps for the last 1, 2, 3, 4, 6, 7, 9, 10, 12, 24, 36, 48, 60 months).
According to the July 31st USDM produced for the USAPI, drought continued across parts of northern Micronesia. Saipan and Rota (in the Marianas) and Wotje (RMI) were experiencing extreme drought (D3). In the southern FSM, Kapingamarangi was in severe drought (D2). Abnormally dry (D0) conditions continued at Kwajalein (RMI). The rest of the stations in Micronesia, and Tutuila in American Samoa, were free of drought and abnormal dryness. The National Weather Service office in Guam issued two Drought Information Statements for the drought in July (on July 10 and July 24) discussing the conditions in the USAPI. Drought impacts during July included stressed vegetation and crops, especially in the northern islands. Agricultural impacts were noted across the northern Marshall Islands and the Mariana islands. The wildfire risk across Saipan and Tinian was high early in the month but was reduced later in the month. Water catchment tanks were low. Residents of Kapingamarangi reported household water tanks were around 25% of capacity and residents of Wotje reported water tanks around 50% of capacity. Wotje and Utirik had reverse osmosis units on site to help mitigate the effects of the drought. By early August, wildfire occurrences continued to diminish on Saipan with greener foliage across the island, and residents of Kapingamarangi reported household water tanks had increased to more than half full.
The last eight to nine months have been especially dry at many of the islands in Micronesia (based on monthly and seasonal precipitation ranks). July 2020 was the fifth driest July in a 31-year record at Kapingamarangi, fifth driest in a 70-year record at Yap and Pohnpei, seventh driest at Chuuk (70-year record) and Wotje (36 years), and ninth driest in 37 years of data at Jaluit and Nukuoro. Going back farther, Pohnpei had the driest June-July (69 years), Kapingamarangi the driest May-July (24 years), Saipan the driest March-July (39 years), and Chuuk the sixth driest February-July (69 years). Looking at the last 12 months, Lukonor had the second driest August-July in a 23-year record and Yap the seventh driest August-July in 69 years.
The following analysis of historical data for the USAPI stations in the Global Historical Climatology Network-Daily (GHCN-D) dataset, augmented with fill-in data from the 1981-2010 Normals, helps put the current data into historical perspective by computing ranks based on the period of record. The table below lists the precipitation ranks for July 2020, February-July 2020 (last 6 months), and August 2019-July 2020 (the last 12 months). Some stations have a long period of record and their dataset is fairly complete, while other stations have a shorter period of record and the dataset has some missing data.
|Station||July 2020||Feb-Jul 2020||Aug 2019-Jul 2020||Period of Record|
SPI values for seven time periods for Pacific Islands, computed by the Honolulu NWS office.
NOAA Regional Climate Centers
More information, provided by the NOAA Regional Climate Centers and others, can be found below.
As summarized by the High Plains Regional Climate Center, after the continuation of above-normal temperatures from June into the first part of July, temperatures moderated and ended up being near normal for the month for much of the region. As for precipitation, it was a tale of two extremes. Above-normal precipitation occurred across portions of the Dakotas, Nebraska, and Kansas. The heavy rainfall proved to be beneficial for drought-stricken areas such as western North Dakota and western Kansas, improving drought in these areas, but it was also responsible for overland flooding and rises on local waterways in portions of Kansas and South Dakota. In contrast, dry conditions persisted across areas of Wyoming, Colorado, and western and eastern portions of Nebraska. Locations in this area received, at best, 50 percent of normal precipitation. Some embedded pockets received less than 5 percent of normal precipitation. Casper, Wyoming had its driest July on record. The dryness contributed to further expansion of drought across these areas. Impacts continued to mount due to the dryness, such as the degradation of pasture and rangeland conditions, leading to the continuation of cattle sell-offs and increased irrigation. Crop conditions were generally in good shape across the region. By the end of July, corn was faring well in Nebraska, North Dakota, and South Dakota, with over 70 percent of the crop rated as in good to excellent condition. Corn was faring worst in drought-stricken Colorado, with 25 percent of the crop in poor to very poor condition. Soybeans were doing quite well region-wide. However, pastures and rangeland were struggling in Wyoming and Colorado due to worsening drought conditions. Compared to early July, topsoil moisture improved in Nebraska and Kansas but worsened in North Dakota, South Dakota, Wyoming, and Colorado. The biggest change occurred in Kansas, where the percent of topsoil moisture rated short to very short improved from 47 percent to only 19 percent. In areas where crops are struggling due to drought, receiving ample precipitation in August will be critical; otherwise, there is likely to be significant yield loss.
Streamflows were both above and below normal across the region during July. Streamflows were below normal across western Colorado, portions of Wyoming, and southwestern Nebraska as persistent dryness continued in this area. Some of the lowest streamflows were located along the Republican River in southwestern Nebraska. Streamflows were generally near normal across the western Dakotas, eastern Colorado, and western and eastern areas of South Dakota. Above-normal streamflows were prevalent across much of Kansas, central and southeastern Nebraska, and the eastern Dakotas. Precipitation amounts in excess of 200 percent of normal during the month of July were largely responsible for the above-normal streamflows in these areas.
This month, drought conditions expanded and intensified in portions of the High Plains, but there were other parts of the region that experienced improvements. According to the USDM, the area experiencing drought (D1-D4) in the region increased slightly by approximately 2.5 percent between June 30th and July 28th. A continuation of below-normal precipitation in portions of Colorado, Wyoming, and Nebraska led to worsening conditions in these areas. Extreme drought conditions (D3) developed over parts of north-central Wyoming at the end of the month. Severe drought (D2) was also introduced across Wyoming and the Nebraska Panhandle. Areas of moderate drought (D1) conditions were introduced to northeastern Nebraska and eastern areas of South Dakota. Abnormally dry conditions (D0) also increased in coverage across portions of the High Plains region, including areas of Colorado, Nebraska, and South Dakota. However, drought conditions improved in southwestern Kansas, which was due to precipitation amounts of up to 200 percent of normal during July. By the month's end, D3 conditions and exceptional drought (D4) conditions had been completely removed in southwestern Kansas, with D4 conditions also being removed in southeastern Colorado. D3 conditions also decreased slightly in eastern Colorado. There were also improvements across much of western North Dakota as well, with drought conditions being removed.
As explained by the Southern Regional Climate Center, temperatures for the month of July were primarily above normal across the Southern region and precipitation varied spatially across the region. At the end of the month, drought conditions both improved and deteriorated across the Southern region. Extreme drought conditions persisted across northwestern Oklahoma and northern Texas, with new areas developing or expanding across western Texas. Severe drought classifications reduced in size across central and western Oklahoma as well as parts of northern Texas, but severe drought conditions developed or expanded across southwestern Oklahoma as well as northern and western Texas. Moderate drought classifications decreased across central and western Oklahoma as well as northern and western Texas, but moderate drought conditions developed or expanded across western and central Texas as well as western Tennessee. There was an increase in the overall area experiencing abnormally dry conditions, with conditions expanding or developing across eastern and western Tennessee, northwestern and western Mississippi, northeastern and northwestern Arkansas, eastern and southwestern Louisiana, southeastern Oklahoma, and eastern, central, and western Texas.
As described by the Midwest Regional Climate Center, July temperatures were above normal for nearly all areas in the Midwest, though a few areas in the western parts of the region were near normal. Average temperature for the region was 75.2 degrees F (24.0 C) which was 2.6 degrees F (2.5 C) above normal. July precipitation was primarily from thunderstorms that brought variable amounts across the region. On average the region totaled 4.68 inches (119 mm) which was 0.62 inches (16mm) above normal. This ranked as the 21st wettest July on record (1895-2020). There were two swaths across the Midwest with above-normal precipitation, with some areas with more than twice their normal amounts, including much of Minnesota, Wisconsin, and northern Michigan in one swath, and northern Missouri, much of Illinois, southern Indiana, and much of Kentucky in another. Drier-than-normal conditions fell between those swaths, including Iowa, parts of southern Minnesota, northern Illinois, northern Indiana, southern Michigan, and much of Ohio. Southern Missouri and parts of Kentucky also were below normal in July. The driest area was in central Iowa where less than half of normal July precipitation was recorded.
Drought expanded in the Midwest in July. Drought had returned to the region in early June in Minnesota after the region was drought-free since November. In late June, parts of Wisconsin and Missouri also had drought development. In July, moderate drought expanded to parts of all nine Midwest states. Well below-normal precipitation, and July heat, led to severe drought in about 12 percent of Iowa, primarily in western Iowa. Soils and crops in these areas were stressed as the corn and soybean crops reached important stages of development.
As noted by the Southeast Regional Climate Center, temperatures were above average across much of the Southeast region and Puerto Rico for the month of July and precipitation was highly variable across the region with a few wet and dry extremes recorded. The driest locations were found across the eastern Carolinas, eastern Virginia, and northern Georgia. Monthly precipitation totals ranged from 70 to less than 25 percent of normal across these locations. In contrast, the wettest locations were located across the Florida Panhandle, eastern Florida and Puerto Rico. From the 29th through the 30th, Tropical Storm Isaias impacted parts of Puerto Rico. Heavy rain triggered flash flooding in several areas. San Juan, PR received over 6 inches (152 mm) of rain from the storm, and Juncos, PR received over 9 inches (229 mm).
Drought conditions have increased slightly across the Southeast for July while slightly decreasing in Puerto Rico. A small pocket of moderate drought conditions (D1) emerged in eastern Georgia and northern Virginia. Abnormally dry conditions (D0) expanded across Georgia, Virginia, eastern Alabama, and western Florida. Throughout the month, drought conditions changed very little for Puerto Rico, and by the end of July (July 28 USDM map), severe drought (D2) reduced in coverage through southern Puerto Rico and the eastern part of the USVI. Most of eastern Puerto Rico is under moderate drought conditions (D1), with abnormally dry conditions (D0) stretching westward. Although this drought is expected to improve with the recent rainfall from Tropical Storm Isaias (on the August 4 USDM map). The citrus growing region in Florida continued to experience warm conditions, however rainfall helped contribute to normal grove activities. Rainfall and warm temperatures helped improve row crop conditions throughout much of the Florida Panhandle and northern peninsula. However, some isolated fungus issues were reported in the peanut crop. Most crops were progressing well in Georgia, despite the very hot and dry conditions. Tobacco was being harvested with some drought pressure shown in the crop. Producers ran irrigation due to the hot and dry conditions in the eastern half of Alabama, however row crops remained in mostly good condition. Meanwhile, several pastures were reporting dry fields, but cattle continued to be in mostly good condition. In some South Carolina counties, the heat and dry conditions continued to damage crops that were already stressed, while in other counties, frequent summer storms prevented saturated fields from drying out. Heavy rain in the Midlands region of the state washed out some recently planted fall vegetable fields that will need to be replanted; however overall fall vegetable field preparations and planting were proceeding at a good pace.
As explained by the Northeast Regional Climate Center, the Northeast had its hottest July since regional records began with an average temperature of 73.7 degrees F (23.2 degrees C), which was 4.1 degrees F (2.3 degrees C) warmer than normal. Six of the 12 Northeast states also recorded their hottest July on record: Connecticut, Delaware, Maryland, New Hampshire, New Jersey, and Pennsylvania. July precipitation totaled 3.94 inches (100.08 mm), 93 percent of normal, in the Northeast. State precipitation ranged from 50 percent of normal in Rhode Island to 155 percent of normal in Delaware, with nine states wrapping up July on the dry side of normal. The persistent warmth increased water temperatures during July. Preliminary data from NOAA's Great Lakes Environmental Research Lab showed the average surface water temperatures of Lakes Erie and Ontario in early July were more than 6 degrees F (3 degrees C) warmer than normal, ranking among some of the lakes' hottest water temperatures on record (since 1995).
The USDM released on July 2 showed 14 percent of the Northeast in a moderate drought and 31 percent was abnormally dry. During July, the general trend across the region was worsening drought and abnormally dry conditions. Severe drought was introduced in northern Maine and northern New York. Moderate drought expanded in Maine and eastern/northern New York and was introduced in the western half of Pennsylvania, northern West Virginia, central/southeastern Maryland, and eastern Long Island, New York. Abnormal dryness also expanded to encompass nearly half the region. The July 28 USDM released on July 30 showed 29 percent of the Northeast in a severe or moderate drought and 42 percent was abnormally dry. There were numerous impacts across the region, particularly in New England and New York. On July 2, the water level of Lake Champlain at Burlington, Vermont, was around 95 feet (29 m), more than a foot (0.3 m) below normal and a level more typical of mid-to late August. Due to this, low-water obstacles could be a problem for boaters earlier than usual. Maine officials warned the state's lakes could experience more harmful algal blooms this summer due to the hot, dry conditions. Water restrictions were in place for numerous locations in Massachusetts and several locations in Connecticut and New York. Vermont's online map showed a few wells went dry in early July. Through much of July, water levels of Aquarion's Greenwich and Bridgeport, Connecticut, reservoirs were near their 2016 drought levels. A July 14 press release from Aquarion said, "Despite receiving some beneficial rainfall over the last few weeks, high temperatures and high water demands continue to reduce water reservoir levels in Connecticut. 2020's below average rainfall has resulted in Southwest Fairfield County hitting its second drought trigger this summer." As of July 30, 132 public water systems in New Hampshire had restrictions in place. Some Maine farmers noted they were watering crops frequently and that crops such as corn were behind schedule, with one farmer losing a large portion of their pea crop. A press release from Maine Emergency Management Agency noted northern Maine had seen "impacts to crops, including hay, potatoes, wheat and barley as well as an increase in invasive species due to the lack of rain..." Growers in New York noted variable crop conditions due to hit-or-miss rainfall during July. In a few locations, corn was curling and turning blue due to moisture stress. The condition of corn and soybean crops generally improved in areas that saw beneficial rains. However, hay yields were expected to be lower in several parts of New York. Dry conditions in northern and eastern West Virginia led some cattle farmers to thin their herds due to deteriorating pasture conditions. Crops were also suffering due to hot, dry conditions in western Maryland. Dry conditions in Maine caused a fungus that kills the pupa of the browntail moth caterpillar to grow too late this year. This allowed the caterpillar, which defoliates trees and can cause a skin rash, headaches, and breathing difficulty, to spread farther into central Maine. Stressed grass turned black in parts of Maine due to a fungal disease. In early July, New Hampshire and interior Massachusetts continued to see an enhanced fire risk, with New Hampshire officials noting an increased amount of dry vegetation that could fuel wildfires and Massachusetts officially saying, "As drought conditions increase, fires can be expected to burn deeper into the ground fuels, making it challenging for firefighters to extinguish fires and taking multiple days to contain them." St. Lawrence County, New York, extended its burn ban in July due to dry conditions and numerous brush fires but allowed the ban to expire on July 17.
As summarized by the Western Regional Climate Center, an anomalous area of low pressure centered over the northern Rockies near the US-Canada border persisted for much of the month. The continental air mass had limited moisture and resulted in below-normal precipitation for most of the western US. Below-normal temperatures were found throughout Idaho and Montana with above normal temperatures in Arizona, New Mexico, Colorado, western Nevada, and northern California. Development of the Southwest Monsoon, which peaks in July for some locations, has been inhibited largely due to the position of low pressure over the northwestern US which has prevented the formation of the Four Corners High — one of the primary atmospheric circulation patterns that pumps moisture into the monsoon region. However, various portions of the region including central and eastern New Mexico observed above-normal precipitation while most of Arizona experienced below-normal precipitation. Over Arizona and New Mexico combined, about 75% of the area received below normal (less than 75%) monsoon precipitation (beginning June 15) through the end of July based on data from the University of Arizona Monsoon Tracker.
The combination of persistent hot and dry conditions in July in the Southwest led to the intensification and expansion of drought conditions regionally, according to the USDM. The percent area in drought for the western US expanded from 45% on June 30th to 59% on July 28th with 7% of the area classified as Extreme Drought (D3). Despite an average or above average winter snowpack in much of the Upper Colorado River Basin, the July unregulated observed inflow into Lake Powell was just 0.26 million acre-feet (24% of normal) and the April-July inflow was 3.7 million acre-feet (52% of normal). Major reservoirs in the Rio Grande Basin were well below normal and much lower than last year due to drought, poor summer runoff, and a weak Monsoon. Elephant Butte was 14% of average (8% of capacity) compared to 45% of average (25% of capacity) last year. All seven of the reporting reservoirs in the basin were less than 64% of average at the end of July. Several large wildfires ignited in July that were still burning at the end of the month with Type 1 and Type 2 Incident Management Teams deployed. In Northeastern California, a cluster of fires were started by lightning strikes in mid-July with the July Complex being the largest at over 83,000 acres burned and prompting evacuations near the community of Copic in Modoc County. In southern California, the Apple fire started on July 31st in Riverside County and has burned over 27,000 acres with 12 structures being destroyed including four homes.
In the Hawaiian Islands, Hurricane Douglas narrowly missed the island chain during the last week of July passing just to the north as a Category 1 hurricane. Minimal impacts (high surf, localized street flooding) were observed, but it did bring some beneficial rain to some of the drought-stricken areas. After a 77-day dry streak with no precipitation at Kahului, Maui, 0.01 in (0.25 mm) of rain fell on July 25th and another 0.27 in (6.9 mm) on July 26th in association with the passing of Hurricane Douglas. This was the 5th longest dry streak since 1905. Despite the rain, much of the island remained in moderate or severe drought. Kauai saw above normal precipitation for the month with 4.66 in (118.4 mm; 249% of normal) observed at Lihue. Central and eastern portions of the Big Island were very dry with 5.27 in (133.9 mm; 49% of normal) recorded at Hilo; the 11th driest July since 1950.
In Alaska, temperatures were generally above normal in the southern half of the state, below normal in the northern half, and near normal in Southeast Alaska. Across much of the state (Far North, Interior, Southwest), precipitation was above normal while Southeast Alaska observed above-normal precipitation.
State/Regional/National Moisture Status
A detailed review of drought and moisture conditions is available for all contiguous U.S. states, the nine standard regions, and the nation (contiguous U.S.):
|Northeast U.S.||East North Central U.S.||Central U.S.|
|Southeast U.S.||West North Central U.S.||South U.S.|
|Southwest U.S.||Northwest U.S.||West U.S.|
|Contiguous United States|