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afdlwx 


Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia 
254 PM EDT Thursday Mar 18 2010 


Synopsis... 
high pressure will remain over the area through Friday and will 
promote continued warmth and dry weather. A strong upper level 
disturbance and its associated cold front are expected to impact 
the region late Sunday through Monday. 


&& 


Near term /through 6 am Friday/... 
high pressure both at the surface and aloft will remain over the 
region through Friday. Light winds and mainly clear skies will 
allow for radiational cooling tonight...bringing seasonably 
chilly conditions with min temperatures ranging from near freezing in 
some of the colder valleys to the middle and upper 40s in downtown 
Washington/Baltimore. 


&& 


Short term /Friday/... 
plenty of sunshine and a downsloping westerly flow will bring 
even milder conditions Friday...with maximum temperatures ranging from near 
60 in the mountains to the upper 60s and 70s across most other 
locations. 


&& 


Long term /Saturday through Thursday/... 
a number of weekend in recent months have had one form of inclement 
weather or another...snow/wind/cold. This coming weekend will be 
quite different. Daytime highs on Sat afternoon /for instance/ peaking 
into the l/m70s will be some of the warmest since last fall - early 
Nov '09. Clear skies for much of the day...light southerly winds - 
pleasant all-around for the middle Atlantic. The nice weather though is just a 
pre-cursor to the next low pressure system...that will be developing 
across the Southern Plains during our nice weekend. 


This feature is a bit more intense than previous runs have indicated - 
mainly because the system will be in the form of a cut-off upper low 
that is very deep for this time of the season. Much of the energy of 
the system will be given-off as the low makes its furthest southward 
extent over the Ozark mountains/Red River valley. The low will then be 
picked by the longwave over southern Canada and drift toward the southern 
Appalachians late sun/early Monday. Clouds will be on the increase during the 
day Sunday...which won't have much of an effect on temperatures - maybe a 
couple of degrees cooler overall. As the atmosphere begins to 
moisten...a few isolated showers will move through the area toward 
evening - more scattered activity into the overnight hours. 


The surface low looks to make a trek across the central Appalachians and Potomac 
Highlands during the day on Monday - a bit slower than previous runs 
showed. The minimal convective potential will be south and east of 
the low - but mainly east of the Virginia Blue Ridge and especially closer to 
the coast west/ the more unstable elevated layer and a bit better wind 
sheer values. Still...these elements will be marginal across the middle 
Atlantic - much better down across the southern Atlantic coast. As the still cold 
upper cut-off low moves across the region overnight Monday into early 
Tuesday. Some of this cooler air will be mixed down toward the surface which 
will take temperatures back down into the M/l30s. A mix of rain/snow will 
be possible across the western zones. Another wave of light rain may 
slide through the area on Tuesday afternoon as the upper low finally makes it/S 
exit off the Atlantic. 


Another couple of high pressure days before the next low pressure 
system gears up over roughly the same area. Too early to tell how 
far south this system will develop and then move. 


&& 


Aviation /19z Thursday through Tuesday/... 
VFR conditions through Friday. Light winds through tonight will 
become west-northwest Friday with occasional gusts around 10 to 15 
knots. There will be occasional high clouds through Friday. 


VFR conditions /skc-light winds/ all-day Sat and much of Sunday. 
Middle-upper cloud decks will move in late sun...W/ another low 
pressure system moving through on Monday - exiting on Tuesday. Breezy surface 
winds...sub-VFR clouds and occasional showers west/ this system on 
Monday. High pressure for the middle part of next week. 


&& 


Marine... 
onshore winds this afternoon will become northwest tonight into 
Friday morning. Winds will turn onshore during the afternoon hours 
Friday. No flags are anticipated through Friday. 


Mainly light winds this weekend over the waters. A low pressure 
system will approach late sun into early Monday. Southerly winds will 
increase...which may create intermittent Small Craft Advisory conditions - lasting 
through the exit of the low on Tuesday. Then...high pressure will build 
into the region. 


&& 


Lwx watches/warnings/advisories... 
District of Columbia...none. 
Maryland...none. 
Virginia...none. 
WV...none. 
Marine...none. 


&& 


$$ 
Synopsis...bjl 
near term...bjl 
short term...bjl 
long term...gms 
aviation...bjl/gms 
marine...bjl/gms