Weather

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fxus61 klwx 291833 
afdlwx 


Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia 
233 PM EDT Friday Aug 29 2008 


Synopsis... 
low pressure near Washington District of Columbia will lift slowly to the northeast 
through tonight. A cold front will move across the area 
Saturday...then high pressure will build in behind this front and 
hold through much of next week. 


&& 


Near term /through tonight/... 
surface analysis at 15z has an area of low pressure over east 
central Virginia with a ridge extending southwest from New England. 
Regional radar still shows light to moderate rain moving north over 
the eastern half of the forecast area. The Loop actually points out 
a mesoscale low that could very well be the remnant low of Fay. Either 
way...it is providing some much needed rainfall across the region. 


The low will continue to lift north overnight. A continuation of 
easterly will allow moisture to remain trapped over the area. This 
is leading to a cloudy and foggy forecast overnight into Saturday 
morning. While a brief break and lift in clouds and fog is expected 
this evening...low clouds and fog will return late tonight. 
Therefore have included areas of fog in the grids overnight. Both 
mav and met MOS are indicating visibilities below a mile...so a 
dense fog advisory may be needed. Not quite confident enough on the 
area of the lowest visibilities at this time...so will need to let 
the evening shift re-evaluate. 


As for temperatures...went slightly warmer than mav and met MOS 
given cloud cover and current dew points. Low temperatures should be 
similar to Friday morning lows...with not much of a diurnal curve. 
Will also maintain a slight chance for showers given the proximity 
to the low as well as abundant moisture. 


&& 


Short term /Saturday/... 
a cloudy and foggy start to the morning...then a cold front will 
come in and clear this out. Instability is not exceptionally 
impressive...and morning clouds and fog will help to limit daytime 
heating. Kept chance probability of precipitation for showers and thunderstorms during the 
afternoon. If clouds and fog can break during the late 
morning...storms would be stronger and convective available potential energy near 1000 j/kg would be 
possible. 


Went cooler than mav and met MOS given expected morning clouds and 
afternoon convection. MOS has been too cool over the past few days 
as well...so went slightly warmer than todays highs. 


&& 


Long term /Saturday night through Friday/... 
cold front moves through the area Saturday evening...putting an end 
to any scattered showers and possible thunderstorms with it. After 
that...a stretch of dry weather will take hold as high pressure sets 
up shop for the rest of the weekend and most of next week. This will 
allow temperatures to be above normal...with high temperatures 
starting Tuesday likely above 90 degrees. Tropics will obviously 
have to be watched due to moisture from Gustav and Hanna...but high 
pressure would most likely keep any moisture away from our County Warning Area 
through the week. 


&& 


Aviation /19z Friday through Wednesday/... 
low clouds and visibilities will improve briefly during the 
evening...but then deteriorate yet again overnight into Saturday 
morning. Widespread IFR and localized LIFR are expected across all 
terminals. Confidence is higher given the mav and met both indicate 
predominant groups of 1/4sm fog and ceilings of 100 feet. Did not go 
that pessimistic with the 18z tafs. 


Skies and visibilities will gradually improve as a cold front 
crosses the area during the afternoon. The more breaks in the 
clouds...the stronger the storms could be. Storms would be later in 
the day Saturday...so no convection mentioned in the 18z tafs. 


Front will move across the area Saturday evening brining an end to 
any convection. Thereafter...no significant weather is 
expected. 


&& 


Marine... 
Small Craft Advisory remains in effect through late tonight across 
the lower tidal Potomac River and the Maryland Chesapeake Bay from 
Drum Point to Smith Point. Confidence is lower since the WRF-arw 
came in with slightly lighter winds. Will let it stand for now...but 
advisory seems much more marginal. 


Northerly flow bears watching early next week as gusts could tease 
small craft criteria...otherwise next week will feature high 
pressure in control. 


&& 


Tides/coastal flooding... 
easterly flow and a tightened pressure gradient has allowed tides to 
reach about a foot above predicted levels. This trend will continue 
through the next 24 hours as low pressure lifts north and a cold 
front approaches the area. At this time...it appears levels will 
stay below minor flooding thresholds...therefore no headline at this 
time. Will continue to monitor...especially for high tide early 
Saturday. 


&& 


Lwx watches/warnings/advisories... 
District of Columbia...none. 
Maryland...none. 
Virginia...none. 
WV...none. 
Marine...Small Craft Advisory until 11 PM EDT this evening for 
anz532>534-537. 


&& 


$$ 
Synopsis...peloquin 
near term...sar 
short term...sar 
long term...peloquin 
aviation...sar/peloquin 
marine...sar/peloquin 
tides/coastal flooding...sar