November 2018 Drought Report

The U.S. Drought Monitor drought map valid December 4, 2018.

During November 2018, the upper-level circulation pattern consisted of a longwave trough over the central to eastern CONUS and ridge over the West Coast which persisted for extended periods throughout the month. Shortwave ridges and troughs migrated through the jet stream flow, with the troughs and their associated fronts and surface lows bringing above-normal precipitation to the northern High Plains, East Coast, and South, and, later in the month, to parts of the West. But, as a result of the longwave trough, a northwesterly flow dominated the central CONUS. This northwesterly flow and its corresponding ridge out West kept much of the western CONUS and Great Plains drier than normal. By the end of the month, the precipitation contracted drought and abnormal dryness in parts of the northern and central Plains, Northeast, and Southeast, but drought and abnormal dryness expanded in the persistently dry areas of the West, southern Plains, and Southeast, and where impacts increased. The wet season in Hawaii got off to a wet start last month, but recent weeks have been dry, so abnormal dryness returned to the leeward areas. Improvement in parts of the Southwest, where November was drier than normal, was a reassessment due to longer-term wet conditions. Drought contraction essentially balanced expansion this month, so the USDM-based national moderate-to-exceptional drought footprint across the CONUS expanded slightly from 22.0 percent of the CONUS at the end of October to 22.2 percent of the CONUS at the end of November (from 18.8 percent to 18.9 percent for all of the U.S.). According to the Palmer Drought Index, which goes back to the beginning of the 20^th century, about 20.5 percent of the CONUS was in moderate to extreme drought at the end of November, decreasing about 1.4 percent from the 21.9 percent at the end of October.

Drought conditions at the end of the month, as depicted on the December 4^th, 2018 USDM map, included the following core drought and abnormally dry areas:

• A large area of abnormal dryness (D0) to severe (D2) drought stretched across the West, with centers of extreme (D3) drought in the Pacific Northwest and southern California, and extreme to exceptional (D4) drought in the Southwest (Four Corners States). —
  • According to the USDM, more than half (54.5 percent) of the West was experiencing moderate to exceptional drought at the end of November. This is an increase from last month's 52.8 percent. The percent area of the West (from the Rockies to the West Coast) in moderate to extreme drought (based on the Palmer Drought Index) grew slowly in the fall 2017 then rapidly increased in December and continued to increase in January and February, growing from 18.7 percent at the end of October 2017 to 62.4 percent of the West at the end of February 2018. Above-normal precipitation improved conditions in California and Nevada in March, so the Palmer percent area in drought shrank to 50.2 percent by the end of March. April was wet in northern California and northwest Nevada, and Washington to the northern Rockies, and May was wet in Nevada to southern California, but extremely dry conditions occurred along the coast in May, especially in Oregon and Washington; California to Colorado were dry in June; the Pacific Northwest to northern and central Rockies were dry in July; several parts of the West were dry in August; and most of the West was very dry in September. The dry conditions were coupled with unusual warmth in parts to much of the West during May, June, July, August, and September which increased evapotranspiration, thus exacerbating drought conditions (5-month SPEI vs. SPI). As a result, the Palmer Drought Index measure of drought area expanded to 85.5 percent of the West by the end of September, approaching values that have been exceeded only a few times in the past — 1934, 1977, and three times since 2000 (2002, 2003, and this year). But October was wetter and cooler than normal across much of the West, especially the Southwest, which shrank the Palmer measure of drought area to 64.7 percent of the West. November started out quite dry across the West. A series of Pacific storms near the end of November brought beneficial rain and snow, but even with this precipitation, most of the West ended up drier than normal for the month. By the end of November, mountain snow pack had improved and the percent area of the West in drought fell slightly to 60.8 percent.
• Abnormal dryness to severe drought continued in Alaska, mainly in the panhandle.
• There were a few areas of moderate (D1) drought in parts of the northern and southern Plains and southern Florida. Spots of abnormal dryness lingered in the Northeast and Puerto Rico, and abnormal dryness was making a comeback in Hawaii.




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 shows 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 dry conditions continued in November in the Pacific Northwest over areas that were in drought at the end of October, intensifying or expanding long-term drought. Short-term dry conditions continued over Florida which had neutral long-term conditions in October, with long-term drought conditions developing in November. Short-term wet conditions occurred across much of the Southwest (California to the Four Corners States), reducing the intensity of some previous areas of long-term drought. Short-term wet conditions occurred across much of the country east of the Mississippi River, expanding or intensifying previous areas of long-term wet conditions.





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. Dryness dominates much of the Pacific Northwest at all time scales except 24 months, and even at 24 months parts of Oregon are dry. The dryness spreads into northern California and the Great Basin at 2 to 6 months, and across California and the Great Basin at 12 months. The Four Corners States are dry at 1 month and 6 to 24 months. Parts of the northern and central Rockies are dry at 3 to 12 months. Dryness stretches across the roof of the northern Plains at 24 months. Southern Florida has very dry conditions at 2 to 6 months. Parts of the southern Plains are dry at the 1-month time scale.









Regional Discussion





Map of November 2018 percent of normal precipitation for Hawaii.

Hawaii:

After a wet summer and early fall, November 2018 was drier than normal across much of the Hawaiian Islands. There are a few dry areas for the last few months (last 2, 3, 4 months), but wetter-than-normal conditions dominate at these time scales out to the last 12 months (last 5, 6, 8, 11, 12 months). Some stations were drier than normal at longer time scales (last 24 and 36 months), but other stations were wetter than normal at these time scales. Streamflow was still well above-normal across the island chain. Abnormal dryness returned at the end of November, covering about 41 percent of the islands on the December 4^th USDM map.





Alaska gridded precipitation percentile map, January-November 2018.

Alaska:

November 2018 was drier than normal across the southern panhandle and across the western and some interior areas. The dryness in these areas was more severe and widespread at the 2- to 3-month time scales. Wetter-than-normal conditions dominated in interior Alaska, with dryness in the panhandle and along the northwest coast, at 4 to 11 months. The panhandle was consistently dry for the last month to 3 years (low elevation station precipitation maps for the last 1, 2, 3, 4, 5, 6, 8, 11, 12, 24, and 36 months) (high elevation SNOTEL station precipitation maps for last 1 and 2 months, and SNOTEL basin map for 2 months) (gridded precipitation percentile maps for last 1, 3, 11 months) (climate division precipitation maps for last 1, 3, 6, 11, 12 months) (Leaky Bucket model precipitation percentile map for November). Temperatures during November were unusually warm across the state. The unusual warmth was apparent throughout the last 12 months, with record warmth in the west at the 3- to 12-month time scales (low elevation station temperature maps for the last 1, 2, 3, 4, 11, 12 months) (gridded temperature percentile maps for last 1, 3, 11 months) (climate division temperature maps for last 1, 3, 6, 11, 12 months) (Leaky Bucket model temperature percentile map for November). Snow pack was below average along the southern coastal area into the interior due to the warmer-than-normal conditions, and in the panhandle due to warmer- and drier-than-normal conditions. Streamflow was mostly near to above average. Abnormally dry to severe drought conditions continued in the panhandle. About 5.8 percent of the state was in abnormally dry to severe drought conditions on the December 4^th USDM map.





Puerto Rico percent of normal precipitation map, November 2018.

Puerto Rico:

The northwestern coast and part of the northeastern coasts were wetter than normal, but drier-than-normal conditions dominated Puerto Rico during November 2018. There was some dryness in the northwest for the last 2 months, but drier-than-normal conditions dominated along the south to east at the 2-, 3-, 6-, and 11-month time scales. Soils continued dry along the southern coast and a little toward the interior in the southeast. Streamflow averaged for the month was mostly near normal with a few below-normal flows, but below-normal streamflows were more widespread for the last half of the month. As seen on the December 4^th USDM map, abnormal dryness expanded across the south central and northwest coastal regions, covering about a fourth (26.2 percent) of the island.






CONUS State Precipitation Ranks:




The November 2018 precipitation pattern was variable enough, with wetter-than-normal areas occurring next to drier-than-normal areas within some states, that no state was top ten driest. Only four states (Oregon, Arizona, New Mexico, and Oklahoma) ranked within the driest third of the 1895-2018 record.

Dryness across much of the West and in Florida ranked five states in the driest third of the historical record for the last three months (September-November 2018). These included Oregon (at 12^thdriest), Washington, Idaho, Wyoming, and Florida.

June-November 2018 was drier than normal across much of the West, putting five states in the driest third of the historical record. These included Oregon (at tenth driest), Washington, Idaho, Nevada, and California.

For the year to date (January-November 2018), the West was still dry, but the focus shifted a bit. There were still five states in the driest third of the historical record, but they included Oregon again (at tenth driest), Idaho, Utah, Colorado, and New Mexico.




For the last 12 months (December 2017-November 2018), dryness was widespread across the West. Most western states ranked in the driest third of the historical record, including Oregon (this time at fourth driest), Colorado (eleventh driest), Washington, Idaho, California, Nevada, Utah, and New Mexico.




Agricultural Belts




Primary Hard Red Winter Wheat Belt precipitation, November, 1895-2018.

Primary Hard Red Winter Wheat Belt precipitation, October-November, 1895-2018.




November 2018 was near to drier than normal across the Primary Hard Red Winter Wheat agricultural belt, with cooler-than-normal temperatures. The month ranked as the 42^nd driest and 19^th coolest November, regionwide, in the 1895-2018 record.

October marks the beginning of the growing season for the Primary Hard Red Winter Wheat belt. October-November 2018 was wetter and cooler than normal across the region. The 2-month period ranked as the sixth wettest and 14^th coolest October-November, regionwide, on record.

As of December 4^th, drought was affecting only one percent of corn production and one percent of soybean production, 11 percent of hay acreage, 11 percent of cattle inventory, eight percent of winter wheat production, and 15 percent of spring wheat production. Except for spring wheat, these values changed little since a month ago. Nationwide, ten percent of the topsoil moisture and 16 percent of the subsoil moisture was dry or very dry, and 13 percent of the winter wheat crop was rated in poor to very poor condition; these values are less than a month ago. Conditions were worst in the West, where (as of November 26, before the bulk of the recent precipitation came) 80 percent of the topsoil moisture and 75 percent of the subsoil moisture was dry or very dry in California, with the statistics 64 percent topsoil/84 percent subsoil for Oregon, and 80 percent topsoil/85 percent subsoil for Nevada. Even North Dakota still had 24 percent of topsoil and 35 percent of subsoil dry to very dry, and Florida's numbers were creeping up at 33 percent for topsoil moisture and 20 percent for subsoil moisture.




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), November 2018 was drier than normal at Guam, Saipan, Lukonor, Pohnpei, Kosrae, and Majuro, and wetter than normal at Koror, Yap, Chuuk, Kapingamarangi, Kwajalein, and Pago Pago.

It was a dry month in terms of drought at Rota (Marianas); Woleai, Fananu, Lukonor, and Mwoakilloa (FSM); and Ailinglapalap, Jaluit, and Utirik (RMI), with rainfall amounts below the minimum thresholds (4 or 8 inches) required to meet most monthly water needs. It was a wet month (above the minimum thresholds) at the rest of the regular reporting stations in the USAPI. The 4- and 8-inch thresholds are important because, if monthly precipitation falls below the threshold, then water shortages or drought become a concern.

November 2018 was the sixth driest November in a data record spanning 62 years at Guam, 51 years at Kosrae, and 17 years at Utirik. Woleai had the seventh driest November and Lukonor the eighth driest, both in 35 years of data. At Majuro, it was the eleventh driest November in 65 years of data. Jaluit had the second driest November in 35 years, although instrument exposure may have contributed some to the low rainfall totals at Jaluit.

As measured by percent of normal precipitation, Lukonor been drier than normal in the short term (November and the last 3 months [September-November 2018]) and drier than normal in the long term (year to date [January-November] and last 12 months [December 2017-November 2018]). Kosrae was drier than normal at three of the time periods and near normal for the year to date. Majuro and Pohnpei were drier than normal in the short term but wetter than normal in the long term. Guam and Saipan were drier than normal for November but wetter than normal at the other three time periods. Kwajalein and Yap were drier than normal for the last 3 months but wetter than normal at the other three time periods. Chuuk, Kapingamarangi, Koror, and Pago Pago were wetter than normal at all four time periods, although Koror was missing data for the long-term time scales.

• Percent of Normal Precip
• Precipitation
• Normals

Pacific Island Percent of 1981-2010 Normal Median Precipitation

Station Name	Dec 2017	Jan 2018	Feb 2018	Mar 2018	Apr 2018	May 2018	Jun 2018	Jul 2018	Aug 2018	Sep 2018	Oct 2018	Nov 2018	Dec- Nov
Chuuk	120%	99%	175%	131%	45%	124%	143%	107%	96%	158%	93%	142%	112%
Guam NAS	88%	23%	90%	68%	316%	240%	88%	146%	149%	183%	78%	61%	105%
Kapingamarangi	420%	95%	222%	171%	127%	92%	67%	142%	67%	128%	158%	223%	137%
Koror	160%	82%	105%	37%	113%	92%	66%	87%	N/A	63%	119%	140%	N/A
Kosrae	123%	100%	147%	181%	105%	136%	74%	106%	159%	65%	34%	58%	92%
Kwajalein	71%	458%	159%	662%	229%	332%	227%	90%	193%	81%	63%	107%	160%
Lukonor	70%	129%	106%	84%	56%	61%	67%	123%	83%	96%	89%	78%	76%
Majuro	172%	204%	120%	343%	189%	216%	151%	142%	102%	94%	67%	69%	143%
Pago Pago	94%	115%	271%	60%	189%	96%	61%	192%	181%	132%	128%	117%	119%
Pohnpei	130%	167%	219%	440%	102%	85%	92%	130%	166%	93%	100%	74%	139%
Saipan	60%	117%	87%	49%	332%	384%	161%	88%	146%	172%	90%	83%	129%
Yap	132%	182%	163%	270%	67%	94%	97%	105%	100%	109%	46%	136%	108%

Pacific Island Precipitation (Inches)

Station Name	Dec 2017	Jan 2018	Feb 2018	Mar 2018	Apr 2018	May 2018	Jun 2018	Jul 2018	Aug 2018	Sep 2018	Oct 2018	Nov 2018	Dec- Nov
Chuuk	13.52"	10.01"	12.70"	10.86"	5.60"	14.01"	16.67"	12.77"	12.33"	18.55"	10.66"	15.02"	152.7"
Guam NAS	4.49"	0.94"	2.72"	1.40"	7.99"	8.15"	5.42"	14.84"	21.89"	23.17"	8.87"	4.51"	104.39"
Kapingamarangi	41.30"	8.71"	20.59"	19.60"	17.39"	11.08"	9.17"	20.15"	5.47"	12.67"	12.98"	20.71"	199.82"
Koror	17.89"	8.38"	9.03"	2.75"	8.25"	10.91"	11.60"	16.19"	N/A	7.37"	14.12"	15.92"	N/A
Kosrae	19.85"	16.62"	19.03"	29.00"	18.45"	24.16"	10.77"	15.83"	22.60"	9.19"	3.70"	8.09"	197.29"
Kwajalein	4.72"	14.46"	4.20"	15.55"	12.05"	22.33"	15.75"	8.88"	18.81"	8.65"	7.05"	12.12"	144.57"
Lukonor	7.90"	10.83"	9.50"	7.76"	6.28"	7.14"	7.83"	19.66"	11.70"	9.79"	10.06"	7.12"	115.57"
Majuro	19.59"	15.76"	8.29"	22.54"	17.79"	21.81"	16.62"	15.88"	11.96"	10.46"	8.53"	9.29"	178.52"
Pago Pago	12.06"	15.37"	32.47"	6.36"	17.76"	9.26"	3.24"	10.68"	9.76"	8.60"	11.83"	11.90"	149.29"
Pohnpei	20.86"	22.03"	20.94"	57.92"	18.80"	16.91"	13.58"	20.11"	23.61"	11.70"	15.31"	10.97"	252.74"
Saipan	2.31"	2.97"	2.25"	0.93"	8.72"	9.14"	5.83"	7.88"	19.12"	17.39"	9.59"	4.64"	90.77"
Yap	11.27"	11.64"	8.44"	12.29"	3.80"	7.41"	11.67"	15.81"	14.82"	14.65"	5.56"	12.03"	129.39"

Pacific Island 1981-2010 Normal Median Precipitation (Inches)

Station Name	Dec 2017	Jan 2018	Feb 2018	Mar 2018	Apr 2018	May 2018	Jun 2018	Jul 2018	Aug 2018	Sep 2018	Oct 2018	Nov 2018	Dec- Nov
Chuuk	11.25"	10.10"	7.25"	8.32"	12.47"	11.30"	11.66"	11.98"	12.86"	11.71"	11.51"	10.61"	136.77"
Guam NAS	5.11"	4.01"	3.03"	2.07"	2.53"	3.40"	6.18"	10.14"	14.74"	12.66"	11.44"	7.38"	99.09"
Kapingamarangi	9.84"	9.15"	9.27"	11.43"	13.64"	12.08"	13.78"	14.15"	8.13"	9.93"	8.19"	9.27"	145.85"
Koror	11.16"	10.18"	8.56"	7.44"	7.32"	11.83"	17.48"	18.53"	13.50"	11.77"	11.84"	11.39"	152.90"
Kosrae	16.11"	16.67"	12.93"	16.06"	17.51"	17.75"	14.64"	14.91"	14.22"	14.22"	10.94"	13.83"	213.87"
Kwajalein	6.66"	3.16"	2.64"	2.35"	5.26"	6.72"	6.93"	9.87"	9.74"	10.74"	11.18"	11.28"	90.41"
Lukonor	11.27"	8.41"	8.93"	9.26"	11.31"	11.69"	11.65"	15.93"	14.04"	10.15"	11.32"	9.08"	151.36"
Majuro	11.39"	7.74"	6.88"	6.58"	9.42"	10.11"	11.01"	11.17"	11.69"	11.17"	12.73"	13.44"	125.25"
Pago Pago	12.84"	13.34"	12.00"	10.68"	9.39"	9.66"	5.33"	5.55"	5.38"	6.53"	9.26"	10.14"	125.57"
Pohnpei	16.08"	13.18"	9.55"	13.17"	18.41"	19.96"	14.81"	15.43"	14.26"	12.55"	15.27"	14.83"	182.36"
Saipan	3.85"	2.53"	2.59"	1.89"	2.63"	2.38"	3.62"	8.91"	13.13"	10.09"	10.62"	5.61"	70.25"
Yap	8.51"	6.39"	5.19"	4.56"	5.63"	7.85"	12.04"	15.08"	14.82"	13.50"	12.18"	8.83"	120.31"

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 November 2018, June-November 2018 (the last 6 months), and December 2017-November 2018 (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.

Rank, Number of Years with data, and Period of Record for USAPI stations for November 2018, June-November 2018, and December 2017-November 2018.
Rank of 1 = driest.

Station	Nov 2018 Rank	Nov No. of Years	Jun- Nov 2018 Rank	Jun- Nov No. of Years	Dec 2017- Nov 2018 Rank	Dec- Nov No. of Years	Period of Record
Jaluit	2	35	MSG	34	MSG	32	1981-2018
Koror	59	68	MSG	66	MSG	66	1951-2018
Woleai	7	35	10	26	10	23	1968-2018
Yap	55	68	31	67	41	67	1951-2018
Majuro	11	65	27	65	62	64	1954-2018
Mili	16	35	MSG	33	MSG	31	1981-2018
Ulithi	27	37	MSG	35	MSG	32	1981-2018
Ailinglapalap	11	35	10	34	17	32	1981-2018
Kosrae	6	51	4	38	17	31	1954-2018
Lukonor	8	35	7	22	4	22	1981-2018
Saipan	14	38	37	38	28	29	1981-2018
Pohnpei	15	68	36	67	66	67	1951-2018
Kwajalein	42	67	53	67	66	66	1952-2018
Kapingamarangi	28	30	15	17	16	16	1962-2018
Chuuk	54	68	55	67	50	67	1951-2018
Guam	6	62	46	62	36	61	1957-2018
Nukuoro	33	35	12	34	10	33	1981-2018
Pago Pago	30	53	37	53	47	52	1966-2018
Wotje	21	34	MSG	33	MSG	30	1981-2018
Utirik	6	17	7	7	3	3	1985-2018


















SPI values for seven time periods for Pacific Islands, computed by the Honolulu NWS office.

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