Wednesday, May 8, 2013

Lumbering Low Lingers

The major upper level trough that brought snow to the Rockies, Midwest and as far south as Arkansas the first two days of the month is still producing rainfall in the eastern U.S. a week later.

The trough developed a closed circulation on May 3 and the closed low has been slowly, very slowly, making its way east through the southern half of the country.

Animation of the 7:00 a.m. CDT 500 millibar map for May 2-7, 2013

This morning the upper low was centered over northern Virginia and was responsible for more than two inches of rain in the mid-Atlantic region in the past 24 hours.

The path of this system can be seen in both the precipitation and temperature patterns for the past 7 days.  Precipitation from the Plains through the southeastern U.S. has been much above above normal as you might expect. The persistent cloudy, rainy, and cool weather has significantly delayed spring planting.

Total 7-day precipitation ending the morning of May 8, 2013.
Map from the NWS Advanced Hydrologic Prediction Service.
The low's progress across the country can also be discerned from the temperature departures over the last week.  Temperatures were much below normal along the storm's path. The ridge of high pressure over the northeastern U.S. kept temperatures much above normal from the Great Lakes through New England. Temperatures were also warmer than average along the west coast and in the Pacific Northwest where a high pressure ridge was also situated.

The closed low will continue moving northeast the next two days, and will finally dissipate as it moves off of the New England coast on Friday.

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