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fxus61 klwx 231059 
afdlwx 


Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia 
559 am EST Monday Nov 23 2009 


Synopsis... 
low pressure develops off the southeast coast today. The low will 
track up the coast and southeast of Long Island tonight. High 
pressure will build in behind this system Tuesday and Tuesday 
night. A storm system will approach from the northwest Wednesday. 
A stronger system will move across the area Thanksgiving and 
Friday. 


&& 


Near term /today/... 


Did a quick update - traffic cam on Afton Montana sure looks lake some 
wet snow at the edge of the Rd...and Wintergreen ski area is 
34/34. Calls to eoc's did not reveal any snow reps...but for next 
couple of hours have added mention of snow above 022 feet. 


With high pressure over northern New England and moisture tracking up from 
the southeast my first impression was "i'm glad it's not a little later in 
the yr" or else I fear we'd be looking at a freezing rain situation. But 
it's not cold enough at the surface for that to be a consideration 
today. 


Low pressure developing off the Carolina CST is pushing moisture into southern 
Virginia. This is running into the surface high...which in turn is slowing 
the northward progression. 


Moisture will continue to work into the County Warning Area..and by this afternoon we'll have 
Cat probability of precipitation across the entire area. Highest quantitative precipitation forecast between 1/4-1/2" east of 
I-95...elsewhere up to 1/4". Under xtnsv cloud cover and nerly winds 
temperatures will do little climbing - ranging from the m40s Highlands to lm50s 
along the Bay. 


&& 


Short term / Tuesday through 6 am Tuesday/... 
tonight the low will be tracking NE of the area. Will have Cat probability of precipitation in the 
extreme NE corner of the County Warning Area for the evening hours...dropping to chance 
everywhere aftr mdngt. Skies will remain cloudy. Again little moderation west/ 
the temperatures - expect the lows tonight to range from a40 in The Highlands to 
a50 along the Bay. 


&& 


Long term /Tuesday through Sunday/... 
weak hipres will build over the area behind the departing low off 
the New England coast. Despite hipres ovrhd...cloudy conditions will 
continue midweek as low level moisture remains trapped below subsidence 
inversion. Cannot rule out patchy drizzle with light southerly flow at llvls 
supporting weak isentropic lift in shallow moist layer. 


Leading upper shortwave energy embedded in c Continental U.S. Longwave trough 
will track over the Midwest Tuesday and the Great Lakes Wednesday. Although 
this weakening system should track well northwest of the area...enough lift 
aided by DPVA/warm air advection will develop to mention low chances for showers 
Wednesday/Wednesday night. 


The trailing shortwave trough drops southeastward while amplifying across the 
c Continental U.S. Thursday. With strengthening height falls ahead of the cutoff 
low...surface development is forecast to occur somewhere along the southeast coast. 
Best County warning forecast area-wide chance for rain or showers appears to be Thursday afternoon 
into Thursday night with the surface low tracking through the middle Atlantic region. 
With the thermal gradient tightening...strong cold air advection will ensue behind 
the surface low once the attendant cold front crosses the Appalachians 
late Thursday into Friday. 00z GFS BUFKIT soundings support a rain/snow mix for 
the higher elevations in the Potomac Highlands Thursday night and Friday. 


Cyclonic westerly flow around the upper low will lead to seasonably cold 
temperatures across the entire area while prolonging the chances for 
upslope snow showers across the western slopes of the Allegheny Front and 
Potomac Highlands through Sat. Hipres builds back into the area sun. 


&& 


Aviation /12z Monday through Friday/... 
clouds have been incrsg/lowering over the past few hours. Am xpctg the 
clouds to continue to lower through the morning hours as the low develops off 
the NC CST...dropping into the IFR range at most taf sites by 
sunrise and then remaining throughout the day and into tonight. 


Periods of sub-VFR ceilings and dz possible through midweek as marine 
moisture remains trapped at the llvls. A storm system will track northwest 
of the terminals Wednesday but close enough to bring chances for rain showers. A 
stronger disturbance is expected to move through Thursday into early Friday. 


&& 


Marine... 
winds already into marginal Small Craft Advisory values on the Bay at 3 am. As the 
low develops off the CST these will no doubt continue today and tonight over the 
Bay and lower part of the ptmc. 


Winds will be light during the middle part of the week with hipres 
ovrhd. The pressure gradient will tighten late in the week as 
developing lopres tracks up the middle Atlantic coast. Small Craft Advisory conditions 
appears possible Thursday afternoon and night as the low tracks over the region. 
Strong cold air advection behind the low and associated cold front will allow for 
widespread Small Craft Advisory conditions to continue into the first half of the 
weekend. 


&& 


Tides/coastal flooding... 
tidal anomalies range from near normal to one foot above normal 
today and tonight. 


&& 


Lwx watches/warnings/advisories... 
District of Columbia...none. 
Maryland...none. 
Virginia...none. 
WV...none. 
Marine...Small Craft Advisory until 5 am EST Tuesday for anz531>534-537- 
539>541-543. 
Small Craft Advisory until 8 PM EST this evening for anz530- 
538-542. 


&& 


$$ 
Products...Woody!/Jrk