Monthly Report Summary Information

National Summary Information - August 2015

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Significant climate events for August 2015

Contiguous US experiences 12^th warmest summer and 9^th warmest year to date

The average temperature for the contiguous U.S. during summer 2015 (June–August) was 72.7°F, 1.3°F above the 20^th century average. Record summer heat impacted the Northwest, while the central US remained cool. The August average temperature for the lower 48 was 73.0°F, 0.9°F above average, and the 31^st warmest on record.

The summer precipitation total for the contiguous U.S. was 9.14 inches, 0.82 inch above average. Driven largely by rainfall early in the season, it was the 16^th wettest summer on record. The August precipitation total for the lower 48 was 2.36 inches, 0.26 inch below average, and the 28th driest on record. Drought and wildfires plagued the West and severe drought emerged in the South.

This analysis of U.S. temperature and precipitation is based on data back to January 1895, resulting in 121 years of data.

U.S. climate highlights: summer (June-August)

Temperature

Jun-Aug 2015 Temperature Departure from Average (top)
and Precipitation Departure from Average (bottom)

• Eleven states across the West and Southeast were much warmer than average. Oregon and Washington each had their warmest summer on record. Oregon's summer temperature was 4.6°F above average, besting the previous record set in 2003 by 0.6°F. Washington's summer temperature was 5.3°F above average, beating the previous record set in 1958 by 1.1°F.
• Near- to below-average temperatures stretched from the Central Plains, through the Midwest, and into the Northeast. No state was record cold. Above-average precipitation across these areas suppressed daytime temperatures, contributing to the cool summer.

Precipitation

• Nine states across the Midwest and Northeast had summer precipitation totals that were much above average. Record precipitation fell across the Ohio Valley during June and July, but a relatively dry August kept the seasonal rainfall totals off the record mark. Above-average precipitation also fell in parts of the West, but this is the dry season for the region and the rainfall did little to improve long-term drought conditions.
• Below-average summer precipitation was observed in the Southeast and Northwest. Washington had its ninth driest summer on record receiving only 52 percent of the seasonal average rainfall. The warm and dry summer in Washington created ideal wildfire conditions. By early September the Okanagan Complex Fire had charred over 300,000 acres and destroyed 176 homes. This is the largest wildfire on record in Washington, surpassing the Carlton Complex Fire that charred 250,000 acres in 2014. According to data form the National Interagency Fire Center, during summer 2015 wildfires burned nearly eight million acres in the U.S., the most since reliable record-keeping began in 2000.

Extremes

• The U.S. Climate Extremes Index (USCEI) for summer was slightly above average. On the national-scale, extremes in warm minimum temperatures and days with precipitation were much above average. The USCEI is an index that tracks extremes (falling in the upper or lower 10 percent of the record) in temperature, precipitation, land-falling tropical cyclones, and drought across the contiguous United States

August

Temperature

August 2015 Temperature Departure from Average (top)
and Precipitation Departure from Average (bottom)

• Five states in the West — Arizona, California, New Mexico, Oregon, and Washington — and five states in New England — Connecticut, Maine, Massachusetts, New Hampshire, and Rhode Island — were much warmer than average during August, no state was record warm. Below-average August temperatures were observed across the Central Plains and Midwest, no state was record cold.

Precipitation

• Below-average precipitation was observed across parts of the West, South, and Northeast where Connecticut and Louisiana were much drier than average. Parts of the Northern Plains and Southeast were wetter than average — North Dakota was much wetter than average. In the Southeast, the remnants of Tropical Storm Ericka brought beneficial rainfall at the end of the month.
• According to the September 1^st U.S. Drought Monitor report, 30.4 percent of the contiguous U.S. was in drought, up 3.3 percent since late July. Drought conditions improved across parts of the Central Plains and Northeast, where it rained. Drought worsened across the Northwest, Northeast, and Southeast. Drought conditions degraded rapidly in parts of the South where hot temperatures and lack of precipitation quickly stressed manmade and natural systems. Drought conditions remain dire in the West, where wildfires charred over one million acres in August.
• Outside of the contiguous U.S., drought changed little in Alaska, Hawaii, and Puerto Rico. The remnants of several tropical systems impacted both Hawaii and Puerto Rico, but the beneficial rainfall did little to improve longer-drought conditions.

U.S. climate highlights: Year-to-date (January-August)

Temperature

Jan-Aug 2015 Temperature Departure from Average (top)
and Precipitation Departure from Average (bottom)

• The year-to-date average temperature for the continuous U.S was 55.5°F, 1.6°F above average, the warmest year-to-date since 2012. Above-average temperatures were observed in the West and Southeast. Thirteen states were much warmer than average, of which California, Nevada, Oregon, and Washington were record warm. Below-average temperatures were observed in the Midwest and Northeast.

Precipitation

• The year-to-date precipitation total for the contiguous U.S. was 22.14 inches, 1.43 inches above average, and the 24^th wettest on record. Above-average precipitation was observed across the central US, where eights states were much wetter than average. Oklahoma had its wettest January-August on record with a precipitation total 156 percent of average.
• Below-average precipitation was observed along both coasts. California, Connecticut, and Oregon each had precipitation totals that were much below-average. California had its fifth driest year-to-date receiving less than half the average precipitation.

Extremes

• The USCEI for the year-to-date was 35 percent above average and the 17^th highest value on record. On the national-scale, extremes in warm maximum and minimum temperatures, one-day precipitation totals, and days with precipitation were much above average. The USCEI is an index that tracks extremes (falling in the upper or lower 10 percent of the record) in temperature, precipitation, land-falling tropical cyclones, and drought across the contiguous U.S.

This month's report also contains, as a supplement, an analysis of recurrent tidal (or sometimes referred to as nuisance) flooding trends at 27 tide gauges along the contiguous U.S. coast and Hawaii. The analysis indicates that the number of days with tidal flooding during 2014 continues to increase as sea levels rise, up three-fold to nine-fold at a majority of locations since the 1960s. The analysis also indicates that El Nino events increase the likelihood for tidal flooding, even above the long-term trend.

For extended analysis of regional temperature and precipitation patterns, as well as extreme events, please see our full report that will be released on September 11^th.