September 2011 Climate Summary

For a printable version of the climate summary which includes more figures, data tables, and state summaries, click here. 

Temperature Summary

September 2011 temperatures were generally below normal in the eastern portion of the High Plains Region and above normal in the western and northern areas of the Region. Temperature departures were up to 6.0 degrees F (3.3 degrees C) below normal in Kansas, Nebraska, and South Dakota. The cooler than normal temperatures allowed many locations across eastern Nebraska to be ranked in the top 10 coolest Septembers on record. Lincoln, Nebraska had its 6th coolest September with an average temperature of 61.5 degrees F (16.4 degrees C) which was 4.5 degrees F (2.5 degrees C) below normal (period of record 1887-2011). Lincoln’s coolest September occurred in 1993 with an average temperature of 59.9 degrees F (15.5 degrees C). Meanwhile, Colorado, Wyoming, North Dakota, and pockets of western South Dakota and the panhandle of Nebraska had temperature departures which were up to 6.0 degrees F (3.3 degrees C) above normal. Some locations in Wyoming ranked in the top 10 warmest Septembers on record. For instance, Yellowstone National Park, Wyoming tied for its 6th warmest September on record with an average temperature of 57.0 degrees F (13.9 degrees C) (period of record 1894-2011). The warmest September occurred in 1990 with an average temperature of 58.9 degrees F (14.9 degrees C).

Precipitation Summary

September was a quiet month for the High Plains Region. Severe weather was reported on only a few days this month and the majority of the Region was dry. Much of Kansas, Nebraska, South Dakota, North Dakota, and Wyoming received only 50 percent of normal precipitation and many areas received less than 25 percent of normal precipitation. Several of these locations ranked in the top 10 driest Septembers on record and a few even broke records. For instance, Sioux Falls, South Dakota had its driest September on record with only 0.20 inches (5 mm) of precipitation (period of record 1893-2011). The old long-standing record of 0.21 inches (5 mm) occurred in 1899. Boysen Dam, Wyoming, which is located in the central part of the state, received no precipitation this month and tied for its driest September (period of record 1948-2011). Interestingly, the other driest September occurred just last year (2010) which makes two Septembers in a row without precipitation.

Pockets of Colorado and North Dakota had precipitation which was more than 150 percent of normal. This month’s wet location was Colorado Springs, Colorado. Colorado Springs had its wettest September on record with 5.91 inches (150 mm) of precipitation (period of record 1894-2011). The old record occurred in 2008 with 4.97 inches (126 mm). An impressive 4.50 inches (114 mm) of the monthly total fell in one day, September 14th. Not only did this set a record for the day, the September 14 precipitation set a new record for the highest one-day precipitation total on record (for any day of any month)! The old record of 4.29 inches (109 mm) occurred on September 11, 2008.
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Climate Outlook

La Niña conditions are present in the equatorial Pacific and are expected to strengthen and continue into winter. The temperature outlook indicates a higher probability of above normal temperatures for most of the Region, including Colorado, Kansas, Nebraska, the majority of Wyoming, and southern South Dakota. Equal chances of above, near, or below normal temperatures are predicted elsewhere in the Region. The precipitation outlook indicates a higher probability of below normal precipitation for Colorado, Kansas, southeastern Wyoming, and the panhandle of Nebraska. Equal chances of above, near, or below normal precipitation are predicted elsewhere in the Region. The seasonal outlooks combine the effects of long-term trends, soil moisture, and when applicable, the El Niño Southern Oscillation cycle (ENSO).  More information about these forecasts can be found here.

Drought Watch

There were many changes to the U.S. Drought Monitor this month. Areas of improvement include northeastern Colorado and the Black Hills region of South Dakota where abnormally dry conditions (D0) were erased. East central Kansas had a one category improvement from extreme drought (D3) to severe drought (D2) while a pocket of exceptional drought (D4) in south-central Colorado was downgraded to D3. D0 expanded to include much of eastern South Dakota and two pockets of moderate drought (D1) expanded there as well. In addition, an area of D0 expanded through parts of central Nebraska and the panhandle. Meanwhile, the ongoing drought in eastern Colorado and western Kansas remained largely unchanged. According to the U.S. Seasonal Drought Outlook drought conditions in western Kansas and eastern Colorado were expected to improve somewhat. The drought conditions in central Colorado, western Kansas, and eastern South Dakota were expected to persist, while drought conditions in western Colorado were expected to develop.