Much Above Normal July Temperatures Help Make May-July 2010 the Hottest on Record for Eastern U.S.

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May-July 2010 U.S. Regional Temperature Ranks

Source: NOAA.

The National Oceanic and Atmospheric Administration (NOAA) released its July 2010 State of the Climate: National Overview on Friday (6 Aug 2010), with data showing that July 2010 temperatures for every eastern state were in the top ten on record.  Persistent warmth over the region has made May-July the warmest such period on record for the southeast and northeast.  Meanwhile, precipitation for the U.S. overall was much above normal with the heaviest precipitation falling in the Great Plains and Midwest.

Nationally it was the 17th warmest July on record and is part of a longer term trend of increasing temperatures in July.  See the figure below.

National (Contiguous U.S.) Temperature, July 1895-2010

We provide below select highlights quoted directly from NOAA's report with some additional illustrations.

Temperature Highlights - July

July 2010 Statewide Temperature Ranks
Source: NOAA.

  • Persistent high pressure systems continued to dominate much of the eastern United States during July, resulting in a nationally averaged temperature that was warmer-than-normal.
  • The intense heat either tied, or shattered, July monthly temperature records in several East Coast cities, including Washington D.C., which recorded an average temperature of 83.1°F (28.4°C). This tied July 1993 for the warmest for any calendar month on record. Other July monthly temperature records were broken, or tied, in Atlantic City, New Jersey and Hartford, Connecticut.
  • It was the hottest July on record for Delaware and Rhode Island. Along the East Coast, each state from Maine to Florida ranked in its top ten warmest. Only Montana, Idaho, and Texas had average temperatures that were below-normal for the month.
  • The Southeast and Northeast climate regions experienced their third and fifth warmest July on record, respectively. Of the nine climate regions within the contiguous U.S., none experienced an average temperature in the below-normal category.

Daily Maximum Temperature Records, July 2010

Source: NOAA.

Temperature Highlights - May - July and Year-to-Date

  • The May–July period was the warmest on record for the Northeast and Southeast climate regions and was the ninth warmest for the Central region. By contrast, the Northwest had its sixth coolest May-July period.
  • The May–July period produced record warmth for: New Hampshire, Massachusetts, Rhode Island, New Jersey, Delaware, Maryland, Virginia, North Carolina, and South Carolina. Conversely, the same period brought below-average temperatures to: Oregon (fifth coolest), Idaho (seventh), and Montana (eighth).
  • In the Southeast, the below-average temperatures from the winter were still evident in the year-to-date (January–July) period, as Texas, Louisiana, Mississippi, Alabama, Georgia, and Florida were below normal. Meanwhile, Maine, New Hampshire, Vermont, Rhode Island, and Connecticut have experienced a record warm January–July, contributing to a record warm such period for the Northeast climate region.

Precipitation Highlights - July

US Precipitation, July 2010 Statewide Ranks
Source: NOAA.

  • Precipitation, when averaged across the country, was much-above-normal, ranking in the top ten percent in the 1895-2010 period. Much of the Plains and Upper Midwest experienced above normal precipitation partly due to moist tropical air which fueled thunderstorms, some of which were severe. These systems stalled out causing major flooding in some areas.
  • Wisconsin had its second wettest July, while Texas had its fourth, Iowa its fifth, and Missouri its eighth. In contrast, it was the tenth driest July for Georgia and Virginia.

Precipitation Highlights - May through July and Year-to-Date

  • From May through July, persistent rainfall made this period the wettest for Wisconsin, the second wettest for Illinois and Iowa, the third wettest for Michigan and fifth wettest for Washington state.
  • The three-month precipitation average of 17.38 inches in Wisconsin was 5.84 inches above their normal for the month, resulting in their wettest May-July period. The 22.01 inches in Iowa resulted in only its second wettest May–July period, which was 9.40 inches above the long-term-mean. Iowa's record wettest May–July period is 24.43 inches, set in 1993.
  • Precipitation, when averaged across the nation, was much-above-normal, ranking as the tenth wettest May–July period. On the regional level, much of the northern tier United States was above normal. The East North Central region had its second wettest May–July. Both the Central and West North Central region had their ninth wettest and the Northwest had its tenth.
  • Precipitation was well-below normal in Louisiana for the year-to-date period (January–July), as drought conditions continued to deteriorate. The state was more than 9.5 inches below the long-term average for the year, its seventh driest such period in 116 years. Conversely, Iowa was nearly ten inches above average, its third wettest January–July.

Other

  • Extremes for the most recent year-to-date period (Jan-Jul) were about eight percent above average. Contributing factors include: a large portion of the country with above-normal minimum temperatures, a wet Palmer Drought Severity Index, extremes in 1-day precipitation and above average number of days with precipitation.
  • The U.S. Drought Monitor reported 8.2 percent of the United States was affected by drought on August 3rd. While slight improvements were seen in the Northern Rockies, Great Lakes area, and eastern Texas, conditions deteriorated around the Mid-Atlantic and Sierra Nevada range.
  • Based on NOAA's Residential Energy Demand Temperature Index (REDTI), the contiguous U.S. temperature-related energy demand was 19.4 percent above average for July. The unusual warmth in the highly populated Northeast and Southeast contributed to the 8th highest July REDTI value in 116 years.

Online Resources:

State of the Climate: National Overview, July 2010From NOAA, 6 Aug 2010.

NOAA: Above-Normal Temperatures and Precipitation in July for U.S. Press release (9 Aug 2010) from NOAA.

WWF Climate Change Blog:

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