Monday, August 13, 2012

Midwest Gets A Break From The Heat, But Not The Drought

It has been a brutally hot summer from the Midwest to the southern Plains.  Add to this the lack of rainfall and you have the recipe for a devastating drought.  What was expected to be a record year for corn is likely to be the worst in decades.  The drought expanded quickly as all-time record highs were being set; some dating back to the Dust Bowl.

Look at two cities caught in the heat wave and drought.  Oklahoma City has endured 28 days from late June to mid August of 100 degree temperatures.  St. Louis has recorded 21 days during the same period.  Both cities tied their all-time record high temperatures at some point during the heat wave.

Now Mother Nature is about to give the central and eastern parts of the country a break from the heat.  A low pressure is going to develop aloft and become centered just south of Hudson Bay by early next week.  As the map below shows winds in the upper atmosphere will dip south into the U.S. bringing a cooler Canadian air mass.  If this were winter there would be talk of a cold wave, but this is summer and we will call it refreshing.

The forecast for winds at 500 mb (about 18,000 ft) for Monday, August 20, at 18z.  Click on the image for a larger view for all of the graphics.  Image Credit: NOAA/NCEP.

The 6 to 10 day outlook from the Climate Prediction Center shows a rather high chance of cooler than normal temperatures for this time of year for the period of August 19th through the 23rd.  The coolest air will be centered over the upper Midwest.

The 6 to 10 day temperature outlook for August 19-23.  Image Credit: NOAA/CPC.
This will be welcome relief from the heat, but there will only be a limited amount of rain.  Thus, the drought which now covers about 70% of the contiguous U.S. will likely continue unabated.  About 52% or about half of the country is rated in a moderate drought or worse.

US Drought Monitor as of August 7, 2012.  Drought classes are incipient, moderate, severe, extreme, and exceptional.  Image Credit: USDA.

Record heat helped drive moisture out of the ground and the evaporative stress index showed the areas of greatest water needs.  It has been persistent over the past three months leading to the flash drought over much of the Midwest.  Much of Oklahoma and western Texas were still recovering from last year’s heat wave and drought.  Their drought never ended, but persisted for a second year.

Image Credit: USDA.
There has been more rain over parts of the Southeast during the past couple of months.  In fact two tropical storms brought much of northern Florida and southeast Georgia out of drought.  This has been replaced with heat, humidity, and lots of mosquitoes in those areas.