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U.S. experiences warmer than average September

Tropical Storm Lee drenches parts of the U.S. while extreme drought conditions persist in the Southern Plains October 7, 2011

Significant events for September 2011.


Significant events for September 2011.

High resolution (Credit: NOAA)

During September, a persistent upper-level weather pattern brought above-average temperatures to the western third of the country, below-average temperatures to the central United States, and above-normal temperatures to the Northeast. The remnants of tropical storm Lee brought significant rainfall from the Gulf Coast into the Northeast, causing above-normal precipitation for most of the eastern United States, and alleviating drought across parts of the Gulf Coast. Dry conditions prevailed across the Plains and into the Northwest, with the national precipitation average near normal.

The average U.S. temperature in September was 66.9 degrees F, which is 1.5 degrees F above the long-term (1901-2000) average. Precipitation, averaged across the nation, was 2.43 inches. This was 0.10 inch below the long-term average, with large variability between regions. This monthly analysis, based on records dating back to 1895, is part of the suite of climate services NOAA provides.

September 2011 precipitation "divisional rank" map.


September 2011 temperature "divisional rank" maps.

High resolution (Credit: NOAA)

U.S. climate highlights - September
 

  • Above-normal temperatures dominated the western United States, with five states - California, Idaho, Nevada, Oregon, and Washington - having one of their ten warmest Septembers on record. A persistent upper-level low pressure system was associated with 14 states having below-normal September temperatures across the central United States. Mississippi tied its ninth coolest September on record.
  • Eight states in the Northeast had September temperatures among their ten warmest -Connecticut, New Hampshire, New Jersey, New York, Maine, Massachusetts, Rhode Island, and Vermont.
  • Precipitation averaged across the Nation during September was near normal, with most of the rainfall during the month coming from Tropical Storm Lee. It made landfall along the Louisiana coast on September 4 and moved along a frontal boundary into the Ohio Valley and eventually into the Northeast. Rainfall totals over 10 inches were widespread along the track of the storm.
  • A string of eleven adjacent states from Louisiana to New York had a top ten wet September, partially attributable to tropical storm Lee. Across Pennsylvania, 9.71 inches fell during the month, 6.25 inches above average, marking the wettest September on record for the state. The Northeast climate region had its second wettest September on record, with 6.70 inches of rain. This total is shy of the record of 8.04 inches from 1999 when Hurricane Floyd impacted the region.
  • Dry conditions prevailed across the Plains states. Kansas, Minnesota, Montana, South Dakota, and Texas had precipitation totals during September rank among their ten driest since 1895. Nine other states from the Plains to the Northwest also had below-normal precipitation totals during the month.
  • Record breaking drought, combined with strong winds, created ideal wildfire conditions across eastern Texas the first half of the month. Three large wildfires burned approximately 94,000 acres and destroyed over 1,600 homes during September.
  • At the end of September, about a tenth of the United States remained in the worst category of drought, called D4 or exceptional drought, which has remained fairly constant since early summer 2011. Nearly all (97%) of Texas was in extreme to exceptional (D3-D4) drought, which is a record, and more than three-fourths (79%) of Oklahoma was in extreme to exceptional drought

September 2011 precipitation "divisional rank" map.


September 2011 precipitation "divisional rank" map.

High resolution (Credit: NOAA)

July-September and year-to-date





  • During the July-September period, the United States as a whole experienced much above normal temperatures. The nationally averaged temperature of 73.4 degrees F ranks as the second warmest July-September on record.
  • New Mexico and Texas had record warm temperatures during the three month period, with temperatures of 3.5 degrees F and 4.2 degrees F above average, respectively. Twenty-two additional states had three-month average temperatures in the top third of their historical record. Six states, across the central and southeastern United States had near-normal temperatures during the period, while no state had below-normal temperatures.
  • July-September precipitation for the United States was 0.72 inch below normal, but with significant regional variability. Below-normal precipitation was widespread across the central and northwestern United States while wetter-than-normal conditions were prevalent across the Northeast. Vermont, New Jersey, and Maryland had a record wet July-September. The Northeast climate region was record wet during the period, with 17.62 inches of precipitation.
  • For the first nine months of 2011, the U.S. average temperature was 1.0 degree F above average. Above-normal temperatures were anchored across the Southern Plains and along the Eastern Seaboard, while parts of the Northern Plains and Northwest were cooler than average. The Texas statewide average temperature for January-September tied as record warm at 70.8 degrees F, 2.9 degrees F above average.
  • Precipitation totals were mixed for January-September 2011, and the nationally averaged value was 0.5 inch below average. Above-normal precipitation was widespread across the northern tier of the country, particularly the Northeast, while below-normal precipitation was reported across the southern tier.
  • New Mexico and Texas, as well as the Southern region, all experienced record dry conditions during January-September. Conversely, Vermont, New York, New Jersey, Pennsylvania, Ohio, and the Northeast climate region were record wet during the nine-month period.

NCDC's monthly reports are based on preliminary data, which are subject to revision. Additional quality control is applied to the data when late reports are received several weeks after the end of the month and as new scientific methods improve NCDC's processing algorithms.

NOAA's mission is to understand and predict changes in the Earth's environment, from the depths of the ocean to the surface of the sun, and to conserve and manage our coastal and marine resources. Join us on Facebook, Twitter and our other social media channels.

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