May 2011 Climate Summary

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

Temperature Summary

Temperatures were cool across the High Plains Region this month.  Average monthly temperatures were near normal in Kansas and up to 8 degrees F (4.4 degrees C) below normal across Wyoming, the panhandle of Nebraska, and the Dakotas.  Each of these areas had locations which ranked in the top 10 coolest Mays on record.  In Wyoming, record and near record temperatures were widespread as many locations ranked in the top 5 coolest Mays on record.  Medicine Bow, Wyoming, which is located in southern Wyoming, had an average temperature of 43.4 degrees F (6.3 degrees C) which was 6.7 degrees F (3.7 degrees C) below normal.  This broke the old record of 43.5 degrees F (6.4 degrees C) which was set just last year (period of record 1949-2011).

The cool weather has slowed planting activities and crop progress across large portions of the Region.  By the end of the month, crop development was behind average in Nebraska, South Dakota, and North Dakota.  According to the National Agricultural Statistics Service, the average starting date for field work in North Dakota was May 7th which was the latest spring start date since 1979.  While the cooler weather was a hindrance to much of the planting and crop progress, these conditions helped improve the declining winter wheat crop in Kansas.

Precipitation Summary

Precipitation varied somewhat across the High Plains Region this month.  In general, heavy precipitation occurred from about central Kansas northward, and little to no precipitation fell across parts of southern Colorado and Kansas where drought conditions persisted.  Several locations near the Colorado/Kansas border received less than 5 percent of normal precipitation this month and exceptional drought conditions (the highest intensity of drought according to the U.S. Drought Monitor) developed there.

However, ample precipitation fell in areas of Wyoming, Nebraska, northeastern Colorado, eastern South Dakota, and western areas of the Dakotas.  Precipitation in some locations even ranged from 200-300 percent of normal.  The recent heavy precipitation, along with mountain snowpack and cool temperatures has increased flooding concerns throughout the High Plains Region.  According to the Wyoming State Climate Office, statewide snow water equivalent (SWE) topped 327 percent of normal.  In comparison, at the end of last month, the statewide SWE was about 150 percent of normal.  Much of the increase in SWE resulted from cooler temperatures which delayed melting.  May precipitation also contributed to the increase in SWE across the state and many locations received both rain and snow this month.  Lander, Wyoming had its wettest May on record with 6.79 inches (17 cm) of precipitation.  This beat the old record of 6.13 inches (16 cm) set in 2008 (period of record 1891-2011).  Interestingly, the May 2011 precipitation was also the 3rd wettest month on record in Lander.  The record was set in April 1900 with 7.19 inches (18 cm).

According to the U.S. Army Corps of Engineers, reservoir releases from Missouri River reservoirs are forecast to reach unprecedented levels.  People living along the Missouri River have already been encouraged to evacuate as significant flooding will impact towns and agricultural lands in the Dakotas.  Flooding is also anticipated along the Missouri River down to the Mississippi River.  Unfortunately, flooded areas have the potential to be inundated for several months.

Climate Outlook

A transition from La Niña conditions to El Niño Southern Oscillation cycle (ENSO)-neutral conditions is currently underway.  ENSO-neutral conditions are expected to develop soon and continue through summer.  The temperature outlook indicates a higher probability of above normal temperatures for most of Colorado and southwestern Wyoming.  Meanwhile, the eastern half of North Dakota, portions of eastern South Dakota, and a small sliver of eastern Nebraska and Kansas have a higher probability of below normal temperatures.  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 the majority of Wyoming.  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, ENSO.  More information about these forecasts can be found here.

Drought Watch

The U.S. Drought Monitor had many changes throughout the month of May.  Early in the month, persistent extreme dry conditions caused an expansion of drought across east-central Kansas.  Extreme drought conditions (D3) were introduced in central Kansas and even exceptional drought conditions (D4) expanded along the border of Colorado and Kansas.  The main impact from these dry conditions was the decline in the winter wheat crops.  But, towards the end of the month, much needed rains fell in many parts of the drought stricken areas.  Abnormally dry conditions (D0) were eliminated from Wyoming and nearly all parts of Nebraska.  Northeastern Colorado and north-central Kansas had one to two category improvements as well. According to the U.S. Seasonal Drought Outlook released May 19th drought conditions across Colorado and Kansas were expected to improve.