Monthly Report Summary Information

National Summary Information - September 2013

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Contiguous U.S. had sixth warmest and 12^th wettest September

Contiguous U.S. had warmest September since 2005; Drought conditions eased in parts of the Plains and West with record flooding along the Colorado Front Range

The average temperature for the contiguous U.S. during September was 67.3°F, 2.5°F above the 20^th century average. Warmer-than-average conditions dominated in the central and western U.S., while parts of the Northeast were cooler than average.

The nationally-averaged precipitation total for September was 2.99 inches, 0.51 inch above average, tying with 2004 as the 12^th wettest September on record. The West was wetter than average, as well as parts of New England. The Western Great Lakes, Mid-Atlantic, and Southeast had below-average September precipitation.

Significant climate events for September 2013. Click image to enlarge, or click here for the National Overview.

U.S. climate highlights: September

• The West, Great Plains, and much of the Gulf Coast were Nebraska.
  
  September 2013 Statewide Temperature (top) and Precipitation (bottom) ranks
• In the East, near-average and below-average September temperatures were observed. No state had September temperatures that ranked among the 10 coolest on record.
• The nationally-averaged precipitation total for September was 2.99 inches, 0.51 inch above average, tying with 2004 as the 12^th wettest September on record.
• Washington each had their wettest September on record. Seven additional states, from New Mexico to North Dakota, had September precipitation totals that ranked among the 10 wettest on record.
• Between September 9^th–16^th, a cut-off low pressure system situated over the Great Basin pumped deep tropical moisture into the Colorado Front Range, resulting in record-breaking precipitation. The heaviest precipitation totals were reported in and around Boulder, Colorado, where 9.08 inches accumulated on September 12^th alone, setting a new 24-hour precipitation record for the city. Boulder also broke its monthly and annual precipitation records due to the event. Streams and rivers approached and exceeded record levels with widespread flooding reported. Additional information on this flooding event can be found here:
  • National Weather Service Rainfall Map
  • Exceedence Probability Analysis of Rainfall
  • Earth System Research Lab Analysis
  • National Weather Service Analysis
  • Univeristy Corporation for Atmospheric Research Analysis
  • Climate.gov rainfall and flooding maps
• Maryland both had a top 10 dry September.
• According to the October 1^st U.S. Drought Monitor report, 41.2 percent of the contiguous U.S. experienced drought conditions, down 8.9 percent since the beginning of September. Over the course of the month, the percent area of the contiguous U.S. in severe, extreme, and exceptional drought all shrank. Drought conditions improved, and in some areas quite drastically, across the Intermountain West and the Central Plains. Drought conditions remained unchanged for much of the Great Basin and California, while drought expanded and intensified across the Upper Midwest.

U.S. climate highlights: warm season (April-September)

• The warm season average temperature for the contiguous U.S. was 65.9°F, 1.0°F above the 20^th century average and the 22^nd warmest April-September on record.
• Below-average temperatures stretched from the Upper Midwest, through the Mississippi River Valley, and into the Southeast.
• The April-September contiguous U.S. precipitation total of 18.76 inches was 2.73 inches above the 20^th century average and the second wettest warm season on record. The record wettest April-September occurred in 1915, when 18.85 inches of precipitation was observed. Florida, had warm-season precipitation totals ranking among the 10 highest.

U.S. climate highlights: year-to-date (January-September)

• 
  January-September 2013 Statewide Temperature (top) and Precipitation (bottom) ranks
  The year-to-date contiguous U.S. temperature was 55.9°F, 0.8°F above the 20^th century average and the 28^th warmest January-September on record. Below-average temperatures were observed across much of the southeastern quadrant of the Lower 48.
• The year-to-date contiguous U.S. precipitation total of 24.76 inches was 2.09 inches above average and the 11th wettest January-September on record for the nation. This also marked the wettest January-September since 1998.
• Much of the contiguous U.S. had Michigan had its wettest January-September on record with 29.69 inches of precipitation, 5.68 inches above average.
• California had its driest year-to-date on record with 5.72 inches of precipitation, 9.36 inches below the 20^th century average, and 1.21 inches below the previous record dry January-September of 1898.