PROLONGED & MAJOR RAIN EVENT FOR ALL EAST COAST AUG 16-21

Posted by wxrisk | GENERAL | Thursday 12 August 2010 9:11 pm

It doesn’t take a meteorologist for anyone to know how beastly hot the Summer of 2010 has been across the Commonwealth. And not just over Virginny…. but for all of Maryland Delaware the Carolinas and through the Deep South it’s been a beastly hot Summer.  And not surprisingly it also been quite dry with much of the mid Atlantic region moving into various drought stages as date to date by  folks at   USDA  / NOAA’s drought monitor index.

At Richmond June and July 2010 set the record for the most 100+ degree days ever recorded (now at 11) .   But all that is about to change and it is  very probable— but not yet certain— that the period from say August 15/16  to August 30 will not see any more of these 100+ degree  max temperature days.

The change to a much much wetter  pattern  begins when a Major Low pressure develops over Hudson’s Bay and Eastern Canada on AUG 13 and 14.   This Low will carve out a Major trough in the Jet stream over the eastern half of the Conus and send a strong cold front sweeping south and east through the Midwest. This front will reach the Appalachian Mountains AUG 15-16.   At this point the cold front will stall on a line from Georgia to New York State and in doing so this stalled front will become a focusing mechanism for widespread heavy showers and thunderstorms up and down the front.

In this prolonged interval ….from say AUG 15-16 to AUG 20-21… it is NOT going to rain ALL the time.   But in this type of pattern the strong inflow from the Gulf and Atlantic Ocean off the SE Coast will feed abundant moisture into this front. At times the rainfall especially from I-95 west into the mountains will be the very heavy.

This link shows the POSSIBLE rainfall from the Wednesday Midday GFS ensemble mean just for the period from AUG 16 to the 20th.     More importantly  as  we move closer to the  event  the   model data is  increasing the   rainfall amounts and coverage . Some areas of this 7 day period   could see 5-10″ of rain  and more over the elevated terrain in Northern GA far northern SC western NC and western half of VA.    There are of course of several aspects to this unfolding event that are uncertain. . First is possible that the front could move through North Carolina Virginia and Maryland faster than what the model data right now is depicting. If that happens… it would end the rains much but significant rains are still fall across the most of commonwealth NC MD DE eastern PA and southern NJ.

It is also quite possible that the front will stay stalled over the East coast as the Bermuda High/western Atlantic Ridge builds into the East coast. Indeed this is what the 12z GFS and European weather models are depicting to occur after August 21. This would continue the rainy pattern fpr a few more days.