WASHINGTON — 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, which is 1.5 degrees Fahrenheit 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.
Above-normal temperatures dominated the western United States, with five states — California, Idaho, Nevada, Oregon, and Washington — having one of their 10 warmest Septembers on record.
Eight states in the Northeast had September temperatures among their 10 warmest — Connecticut, New Hampshire, New Jersey, New York, Maine, Massachusetts, Rhode Island, and Vermont.
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.
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 Sept. 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 10 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 10 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 more than 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 percent) of Texas was in extreme to exceptional (D3-D4) drought, which is a record, and more than three-fourths of Oklahoma was in extreme to exceptional drought.