Friday, July 12, 2013

Westward Ho! A Potential Drought Denter

500 millibar map (~20,000 ft) for 7:00 a.m. CDT July 12, 2013
Normally weather systems tend to move in a general west to east direction across the U.S.  However,over the next five days an upper level low that was located over West Virginia this morning is forecast to retrograde, or move west, to the Desert Southwest.  That's quite a trek, and not one I can ever remember seeing before.  The system that retrograded from the Ohio Valley back to the Plains did not make as long a trip as this low is forecast to make.

The upper trough been responsible for rain in the east the past few days. Rain was falling this morning from New Jersey and southeastern Pennsylvania south along the Atlantic coast. As it this low moves west the next few days it will be responsible for unsettled weather over much of the country east of the Rockies, and will eventually help kick the southwestern monsoon into gear. The eastward moving wave along will have ample Gulf moisture available to work with. East of the wave sultry summer weather will take hold and most of the eastern half of the U.S. will be dealing with highs from the upper 80s to the 90s as an upper level ridge builds in behind the trough.. Meanwhile temperatures will be cooling in west Texas and in the southwest as clouds and rain become more prevalent.

Here is a loop of the 500 millibar level for every 12 hours from today through the morning of July 17 showing the upper low moving west into Texas and New Mexico.

Some hefty rainfall amounts are indicated in the model forecasts. Rainfall amounts may reach three inches from Oklahoma into southeastern New Mexico.

7-day Quantitative Precipitation Forecast (QPF) for the period from 7:00 p.m. CDT July 12 to 7:00 p.m. July 20, 2013

This system won't be a drought breaker, but it will put a small dent in the drought in those locations that get the rain.  The bottom line is that the long-term drought will need long-term precipitation to be reversed.

Of course, the final path of the low and its strength (and the associated weather) may change in future forecast model runs, so this rainfall forecast will likely change. If you would like to keep tack of the updates to the QPF visit the NWS Weather Prediction Center web site.

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