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fxus61 klwx 060015 
afdlwx 


Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia 
715 PM EST Thursday Nov 5 2009 


Synopsis... 
an upper level disturbance will continue to move off the middle 
Atlantic coast tonight. High pressure in place over the area Friday 
through early next week. Chilly temperatures are expected for 
tonight and Friday night...while a warming trend will begin over 
the weekend. 


&& 


Near term /until 7 am Friday morning/... 
500mb trough axis drifting east off the eastern Seaboard...taking the shortwave 
energy with it. Northwest flow has opened the fetch from Western Lake Erie to 
the Allegheny Front where snow showers are occurring /nrn half of 
Grant Colorado...western Mineral...and western Allegany co/. Up to a 
half inch of snow is possible above 2500 feet elevation...mainly 
before midnight. 


Scattered clouds pushing east of the Allegheny Front to dissipate 
through the night...resulting in mostly clear skies /all clear 
south of kshd-kcho line/. Middle to upper 30s tonight east of the 
Blue Ridge...though dew points remain low enough to not allow for 
frost development. Strong northwest flow along to keep surface somewhat 
coupled through the midnight hour. 




Short term /7 am Friday morning through 6 PM Friday/... 
high pressure will build eastward over the County warning forecast area during the day 
tomorrow. Any lingering cloudiness from middle level shortwave energy 
will decrease in the morning. 


Took a blend of mav/met MOS numbers for maximum T. 


&& 


Long term /Friday night through Thursday/... 
a pattern change is in store behind the departing upper low over eastern 
Canada. Upper ridge and surface hipres will build across the eastern 
Seaboard...lasting through the beginning of next week. 
Accordingly...long term period will feature mainly quiet and dry 
conditions with upper ridge. 


Surface hipres will move ovrhd Friday night. Under clring skies...calm winds 
and a dry airmass in place...temperatures should effectively radiate into 
the upper 20s along and west of the Blue Ridge...lm30s east of the mts. 
Have issued a freeze watch for most counties along and east of I-95 
where the growing season has not ended yet. At this time the highest 
confidence for a killing freeze is in the northestern Maryland and the northern 
Piedmont of Virginia. However if temperatures drop only a few degrees cooler than 
currently forecasted...a killing freeze could occur across the remaining 
areas under a freeze watch. 


Near normal temperatures Sat will moderate a bit sun into early next week as 
southerly return flow develops around hipres. Next chance for precipitation 
appears to be midweek as a cold front approaches. Chances appear 
low at this time. 


&& 


Aviation /00z Friday through Tuesday/... 
occasional gusts in the 20 to 25 knots range with strong northwest flow 
aloft as an upper trough pushes off the middle Atlantic coast. Ewinds 
will remain northwest during the day tomorrow...with strong gusts around 
25 knots early morning as surface recouples. Sustained wind speeds then 
decrease midday through the afternoon...clear conditions Friday. 


VFR conditions expected this weekend into early next week as hipres 
controls the weather pattern. 


&& 


Marine... 
Gale Warning in effect for lower tidal Potomac and all of the Bay 
and tributaries through the night. The majority of gusts are 
expected in the 25 to 30 knots range...but gusts to 35 knots are 
possible through the rest of the night. Winds to begin to diminish 
early Friday morning...but small craft conditions will remain 
likely through the day. 


Pressure gradient will weaken Friday night as hipres settles ovrhd. Winds 
should will remain light through the weekend and early next week. 


&& 


Lwx watches/warnings/advisories... 
District of Columbia...freeze watch from late Friday night through Saturday morning 
for dcz001. 
Maryland...freeze watch from late Friday night through Saturday morning 
for mdz006-007-011-013-014-016>018. 
Virginia...freeze watch from late Friday night through Saturday morning 
for vaz054>057. 
WV...none. 
Marine...Small Craft Advisory until 6 PM EST Friday for anz535-536. 
Small Craft Advisory from 6 am to 6 PM EST Friday for 
anz530>534-537>543. 
Gale Warning until 6 am EST Friday for anz530>534-537>543. 


&& 


$$ 
Update...baj 
previous discussion...nwl/jrk