196 
fxus61 klwx 151854 
afdlwx 


Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia 
254 PM EDT Monday Mar 15 2010 


Synopsis... 
low pressure will slowly move away from the middle-Atlantic coast 
tonight. High pressure will build across the region for the middle 
and latter part of the week...bringing dry conditions and moderating 
temperatures. The next cold front is expected to impact the region 
next weekend. 
&& 


Near term /until 6 am Tuesday morning/... 
upper low and surface low pressure remain several hundred miles east 
of th Delaware-Maryland-Virginia peninsula. Both features will slowly move to the 
southeast...away from the eastern Seaboard...overnight. Scattered 
showers on the backside of the surface low continue to affect the 
eastern portion of the County warning forecast area. Precipitation will gradually end overnight for 
most locales. 


Occasional drizzle will be possible along the western facing slopes 
of the Allegheny. Currently thinking is that temperatures will stay above 
freezing overnight...so not including any wording for freezing 
drizzle. 


&& 


Short term /6 am Tuesday morning through 6 PM Tuesday/... 
low pressure will continue to move out to sea Tuesday while high 
pressure builds in from the north. Low-level moisture will continue 
to wrap around the low...bringing mostly cloudy skies through 
midday. However...drier air will slowly work its way into the region 
from north to south during the afternoon hours. This will allow for 
clearing from north to south later in the afternoon. Maximum temperatures will 
range from the 40s in the Potomac Highlands and Blue Ridge mountains 
to the lower and middle 50s elsewhere. 
&& 


Long term /Tuesday night through Monday/... 
high pressure will build overhead Tuesday night through the end of 
the week...bringing dry conditions along with a moderating trend in 
temperatures. Maximum temperatures by Thursday and Friday will be in the middle 
and upper 60s across most locations. 


High pressure will bring more dry and mild conditions Saturday...but 
another cold front will pass through Sunday into Monday...bringing a 
chance for showers. Chillier conditions are expected behind the 
front. 
&& 


Aviation /19z Monday through Saturday/... 
MVFR ceilings at most of the terminals currently...with the exception of 
kcho. Expect ceilings to remain in the MVFR range tonight. Guidance 
tries to bring ceilings down below 1 kft overnight...but will hold off 
putting in the tafs for now. Winds will remain up overnight...and 
out of the north at around 10 knots. Some higher gusts are possible at 
mountain...BWI and dca. 


Low pressure will continue to move away from the terminals Tuesday. 
There will be enough moisture wrapping around the low for MVFR ceilings 
through midday. Skies will clear out from north to south later in 
the afternoon. Northerly winds will gust around 15 knots during the 
day Tuesday. 


High pressure will build overhead for the middle and latter part of 
the week...bringing VFR conditions along with light winds. 
&& 


Marine... 
solid small craft conditions across the waters this afternoon. No 
adjustments to the headline are needed at this time. Winds will 
remain out of the north/northwest at 10 to 15 knots with gusts between 20 and 25 
knots. 


Low pressure will continue to move away from the waters 
Tuesday...but the gradient associated with this low and high 
pressure to the north will bring Small Craft Advisory winds across the waters during 
the morning hours. Small Craft Advisory winds will continue into the afternoon hours 
across the Chesapeake Bay and lower tidal Potomac. However...winds 
will diminish later Tuesday and Tuesday night as high pressure 
builds overhead. High pressure will remain in control through the 
end of the week. 
&& 


Hydrology... 
water levels have crested across all of the waters and they continue 
to recede this afternoon. River flooding continues along the Potomac 
River from Harpers Ferry southward. Harpers Ferry is expected to go 
below flood stage tonight. Moderate flooding is currently occurring 
below Harpers Ferry. Water levels will drop to levels below 
thresholds for moderate flooding tonight...and eventually below 
flood stage Tuesday. 
&& 


Tides/coastal flooding... 
water levels remain elevated across the area...but values have 
decreased below critical thresholds along the western shore of the 
Chesapeake Bay. Moderate coastal flooding continues along the tidal 
Potomac. 


Will make some adjustments to the headline for the afternoon. 
Observations at Annapolis are currently below both the 
cbofs/extratropical model forecasts at this time. Will go ahead and 
cancel the advisory for Anne Arundel and Calvert counties since 
overnight model forecasts are just below any minor threshold values. 


Positive tidal departures remain around 4 feet across the tidal 
Potomac. Will leave the warning in place for the overnight high tide 
cycle. Evening shift will have to evaluate whether or not to extend 
or downgrade the warning after tonights high tide cycle. Northwest winds of 
10 to 15 miles per hour should help push the water out. 


&& 


Lwx watches/warnings/advisories... 
District of Columbia...coastal Flood Warning until 11 PM EDT this evening for dcz001. 
Maryland...coastal Flood Warning until 11 PM EDT this evening for mdz013- 
016. 
Coastal Flood Advisory until 11 PM EDT this evening for mdz017. 
Virginia...coastal Flood Warning until 11 PM EDT this evening for 
vaz052>055-057. 
WV...none. 
Marine...Small Craft Advisory until 4 PM EDT Tuesday for anz530>534- 
537>543. 
Small Craft Advisory until noon EDT Tuesday for anz535-536. 


&& 


$$ 
Listemaa/lasorsa