748 
fxus61 klwx 201830 
afdlwx 


Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia 
230 PM EDT Wednesday Aug 20 2008 


Synopsis... 
high pressure will continue to build across the region for the 
remainder of this week before drifting off the coast this weekend. 
The next cold front will move into the region early next week and it 
will stall out near the region for the middle of the week bringing 
the next chance for precipitation. 
&& 


Near term /through tonight/... 
hipres over eastern Great Lakes...ridging down eastern seabrd. Across County warning forecast area...flow pttn 
has a northeasterly component...which will veer Ely through night as surface high drops 
southeast and ridging aloft slides eastward closer to area. Few clouds District of Columbia east have mixed 
out. Addtl diurnal clouds in the applchns and cirrus seen streaking across 
southwestern County warning forecast area. Although most of these will melt by/soon aftr dusk...suspect 
the Ely component to the wind will spoil true sky clear...especially southwestern County warning forecast area 
where flow pttn will rslt in upslope conds. Will go for scattered-lclly broken 
clouds SW...and mostly clear-clear elsewhere. 


Little spread in MOS guidance...and blend accepted. Unseasonable dewpoints in 
the upper 40s-middle 50s will lead to comfy min-T. Lclzd radl fog possible... 
especially in river valleys. At this time feel threat too ltmd for any grid mntn. 
&& 


Short term /Thursday/... 
upa ridging over County warning forecast area...W/ surface ridge sliding into western Atlantic. Flow will continue 
veering...to the southeast. That will spread in a bit more moisture...though by Aug 
standards it will still be comfortably dry. Only forecast implication will 
be scattered clouds. Maxt not far from today/S values. 
&& 


Long term /Thursday night through Wednesday/... 
a middle-level ridge of high pressure will remain entrenched over the 
region through Friday bringing dry conditions. Surface high will 
slowly drift off the New-England coast allowing for a return flow to 
set up. Maximum temperatures Friday will range from the upper 70s in the 
Potomac Highlands to the middle 80s in the Washington and Baltimore 
metropolitan areas. With a return flow from the east-southeast...it 
will turn out a bit more humid. 


Surface high will continue to move off the coast this weekend while 
the middle-level ridge of high pressure slowly breaks down. These two 
systems should still remain close enough to bring dry conditions 
along with some sunshine each day. However...am concerned about low 
clouds/fog later Friday night into Saturday with an easterly flow. 
Did tweak sky cover a bit overnight Friday into early Saturday to 
reflect this...especially across the central and western County Warning Area. 


The next cold front will slowly move into the region Monday bringing 
the chance for showers/T-storms. This front will likely stall near 
or over our County Warning Area. Latest long range guidance also suggests that some 
moisture from Fay may get drawn into our area from a southwest flow 
aloft. This may enhance the chance for showers and T-storms sometime 
towards the middle part of next week. 
&& 


Aviation /18z Wednesday through Monday/... 
VFR conditions through early tmrw afternoon....except MVFR conditions 
at cho early Thursday where the best probability for br as indicated by sref 
model. P6sm sky clear. NE winds will become light and vrb tonight and east 
Thursday. 


Generally VFR conditions expected for Thursday night and Friday. 
However...patchy br may bring subvfr visibilities late Thursday night into 
early Friday morning. An easterly flow may bring a better chance for 
low clouds/fog later Friday night into Saturday morning. 


The next chance for showers/T-storms is expected Monday as a cold 
front approaches from the north. 
&& 


Marine... 
Ely flow tonight becomes southeasterly tmrw. Winds mostly at or below 10 knots. 


Surface high will slowly drift off the coast Thursday night and 
Friday allowing a return flow to set up. High pressure will remain 
just off the coast this weekend and the next cold front will bring a 
chance for showers and thunderstorms Monday. 
&& 


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


&& 


$$ 
Synopsis...bjl 
near term...heights 
short term...heights 
long term...bjl 
aviation...Klein/bjl 
marine...hts/bjl