047 
fxus61 klwx 072000 
afdlwx 


Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia 
300 PM EST Sat Nov 7 2009 


Synopsis... 
high pressure will dominate the weather through early next week. 
A weak pressure trough will bring a wind shift to the area 
tomorrow...but will have little effect on temperatures. The next 
cold front will approach the region late Tuesday into Wednesday. 
&& 


Near term /through tonight/... 
hipres centered just off the Carolina coast will slowly build 
southeastward but remain in control of the middle Atlantic weather pattern. A very 
weak low level shortwave and surface pressure trough will move through the 
region late tonight. Westerly flow aloft will advect warmer air from the c 
Continental U.S. Into the region...resulting in a fairly strong thermal 
inversion in the first 3 kft above the ground. This inversion 
combined with mixing...especially across higher elevations of the 
Blue Ridge and Potomac Highlands...will result in much higher min 
temperatures compared to cooler sheltered valleys. Forecast lows range from 
around 40f in locations below 1 kft to near 50f for elevations at or above 
2 kft. 


&& 


Short term /Sunday/... 
aforementioned weak surface pressure trough will push through by the early 
in the period. Surface flow will shift northwesterly in wake of trough but will 
become light as hipres ridge settles ovrhd. With mostly sunny skies 
and a warmer airmass in place...maximum temperatures will generally be in the 
mu60s with a few spots climbing into the l70s. 


&& 


Long term /Sunday night through Saturday/... 
high pressure will remain the dominant weather feature across the 
County warning forecast area through early Tuesday. A cold front is still prognosticated to move 
through the middle Atlantic region late Tuesday into early Wednesday. 
The GFS is now bringing moisture northward from the Gulf of Mexico 
ahead of the front. There is a wide spread between guidance numbers 
for this period...so will opt to go with persistence and keep the 
slight chance probability of precipitation in the forecast for now. High pressure builds 
back in for the remainder of the week into the early part of the 
weekend. 


Looks like until the frontal passage late Tuesday/early Wednesday temperatures in the 
higher elevations could remain a bit higher than the valleys. 
Also...breezy conditions are anticipated behind this front Wednesday 
and even into early Thursday. 
&& 


Aviation /20z Saturday through Thursday/... 
VFR conditions tonight and sun. Southerly winds around 5-10 knots with a few 
gusts to 15 knots will relax towards sunset. A subtle pressure trough 
will push through overnight...shifting the winds west-northwesterly sun. 


No restrictions to visibility/ceilings are expected through early next week. A 
cold front is expected late Tuesday/early Wednesday. Not much 
precipitation can is expected with this boundary...but breezy 
conditions are possible Wednesday into Thursday. 
&& 


Marine... 
Small Craft Advisory has been extended through 02z this evening in the Maryland chesepeake Bay and 
lower tidal Potomac. Southerly channeling will prolong 20 knots gust 
potential through the evening before the winds relax late this evening. Winds 
will become light overnight into sun as hipres settles ovrhd. 


Some channeling up the Bay is possible later Tuesday ahead of an 
approaching cold front...and gust potential may approach small craft 
criteria. Small craft conditions are likely behind the front 
Wednesday into Thursday. Will have to continue to monitor...winds 
aloft could be strong enough for a brief period of gales during this 
period. 
&& 


Lwx watches/warnings/advisories... 
District of Columbia...none. 
Maryland...none. 
Virginia...none. 
WV...none. 
Marine...Small Craft Advisory until 9 PM EST this evening for 
anz530>534-537>543. 


&& 


$$ 
Klein/listemaa