Sep 2 US Extended Forecast Discussion through Sep 9

Extended forecast discussion
NWS Hydrometeorological Prediction Center Camp Springs MD
150 pm edt Thu Sep 02 2010

Valid 12z Sun Sep 05 2010 - 12z Thu Sep 09 2010

Medium range model guidance remains in agreement and consistent
Thru day 5 with an amplifying short wave dropping sewd thru b.c.
And into the pac northwest and nrn rockies days 3 and 4 while
Downstream hts slowly rise as a deep vortex over canada lifts out
Into davis strait and ridging rebounds from the tx gulf coast into
The mid atlc states region day 5 tuesday. All guidance indicates a
Second pac shortwave dropping down the b.c./pac nw coast carving
Out a deep but progressive trof swinging thru the southwest with
H500 hts at least 3 standard deviations below normal. Meanwhile
Downstream the first pac nw shortwave is ejected ewd thru the
Great lakes rergion with the 00z gfs and ecmwf amplifying the trof
As it swings thru new eng late days 6 and day 7 wed/thu. This is
Not supported by ens means of either gfs or ecmwf which keep up
More ridging and higher hts over ern conus and are in good
Agreement. Hpc morning updated solution is a blend of ecmwf/gfs
And ens means of both thru day 5 tues then an increased blend into
The ens means days days 6 and 7 wed/thu.

A mostly dry period over much of conus with showers over mt
Rockies and far nrn plains as the first shortwave moves eastward.
Second stronger shortwave digging into the west will add in
Moisture return thru the srn and central plains mid to late week
And nwd into the upper ms valley/wrn great lakes region. Below avg
Temps will dominate wrn conus this period especially as the deeper
Wrn trof amplifies thru the west while rising hts will bring a
Return of above to well above avg temps from the mid atlc states
Region to the srn plains

Over the tropics ts gaston forecast to be hurricane by monday and
May threaten the lesser antilles days 6 and 7 wed/thu. See nhc
Forecasts and discussions.
Rosenstein


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