...15 May through 31 August 2009 Summer Outlook...

 

Synopsis...

As of late April, weak La Nińa conditions continued across the central Pacific. The Climate Prediction Center forecasts that this La Nińa will dissipate during May, with Enso-Neutral conditions expected for June through August. These oceanic conditions, along with recent weather patterns, were used to develop our prediction of the general weather pattern across the northern high plains for this May through August.
 

Outlook...

We expect precipitation to be near or slightly above long term averages from May through August, with the best chances of above average precipitation in May and June. Temperatures are expected to continue to be near or slightly below long term averages through the summer for most of the area, with slightly above average temperatures possible across northeastern Wyoming.
 

Impacts...

Across northeastern Wyoming and the Bear Lodge Mountains, rainfall is expected to be 100 to 110 percent of normal. Rainfall for May through August averages 7 to 9 inches on the plains of northeastern Wyoming and 9 to 11 inches in the Bear Lodge Mountains. Based on our outlook, this could result in a 0.75 to 0.90 inch rainfall surplus on the plains, and a 0.90 to 1.10 inch surplus in the Bear Lodge Mountains.
 
In western South Dakota, rainfall is expected to be 100 to 110 percent of normal. Rainfall for May through August averages 9 to 11 inches on the plains and 11 to 14 inches in the Black Hills. Based on our outlook, this could result in a 1.10 to 1.40 inch rainfall surplus in the Black Hills, and a 0.90 to 1.10 inch surplus on the plains.
 
Heavy rains over the past 11 months have filled reservoirs and stock ponds across western South Dakota. If the anticipated rainfall for May through August occurs, then above average stream and river flows can be expected to continue.

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