901 
fxus61 klwx 141503 
afdlwx 


Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia 
1103 am EDT sun Mar 14 2010 


Synopsis... 
low pressure will move across the middle Atlantic today...and off the 
eastern Seaboard tonight and Monday. High pressure will build across 
the area for Tuesday through the remainder of the week. 


&& 


Near term /until 6 PM this evening/... 


Lopres across the lower Chesapeake Bay will gradually push offshore 
this afternoon. Wide band of light/MDT showers rotating southwestward around 
low impacting areas between Blue Ridge and Potomac River. Expect this 
area of rain to continue to impact the same region through much of 
afternoon...with 0.25-0.5 quantitative precipitation forecast. Nwwd moving area of heavy showers 
approaching upper chesepeake Bay and will impact areas North/East of balt 
through early afternoon. 


With saturated ground and precipitable waters  near 1 inch...isolated urban/small 
stream flooding is still possible...aside from ongoing river flooding. 
See hydrology section for more information on river flooding...and 
coastal flood section for information on tidal flooding. 


With County Warning Area locked on cool north side of surface low...expected temperatures to remain in 
u40s/l50s through the day. 


&& 


Short term /6 PM this evening through Tuesday/... 
tonight and Monday...center of deep cutoff/closed low to be east of 
the Chesapeake Bay by this evening with north-northwesterly flow and cold air 
advection increasing and chances of rain showers continuing. Cloud 
cover remains...keeping min temperature tonight in the low 40s and maximum 
temperatures Monday near 50f north to low to middle 50s S /may see near 60f in 
Nelson County with some sun break out and downsloping northwesterly flow/. 
Breezy Monday with afternoon gusts in the 25 miles per hour range. 


High pressure begins to build on Tuesday with enough subsidence for 
at least partly sunny conditions by late afternoon. 


&& 


Long term /Tuesday night through Saturday/... 
high pressure will build across the area through the end of the 
week. Temperatures will be slightly above normal...and dry 
conditions are anticipated. 


&& 


Aviation /15z Sunday through Thursday/... 


With exception of kcho...taf sites will remain in IFR/LIFR ceilings through 
the day...with intermittent -shra. Visibility expected to gradually become MVFR 
as -dz tapers off and light northwesterly flow becomes established. 


Chances of rain continue for tonight and Monday with MVFR conds as 
low pressure center drifts further east from the terminals. North-northwesterly 
winds with gusts 20 to 25 knots for Monday. High pressure then builds 
Tuesday with continued northerly flow and VFR conds. 


&& 


Marine... 
lopres spinning across southern Chesapeake Bay...drifting eastward. Winds 
light/variable through early afternoon...becoming north at or below 10 knots lt toward evening. Isolated 
thunderstorms possible across Upper Bay this afternoon...otherwise scattered showers may 
lead to brief visibility reductions. 


Low pressure center drifts east of the waters tonight and Monday 
with north-northwesterly flow intensifying and continued chances of showers. 
Small Craft Advisory for Monday will likely need to be extended 
through Monday night for all waters...then into Tuesday for the Main 
Channel of the Bay. High pressure and more tranquil conditions for 
middle to late week. 


&& 


Hydrology... 
river flood warnings continue across numerous points...mainly on the 
Potomac River basin...although the Rappahannock at Remington and 
Shenandoah at Millville and Front Royal will also be in flood today. 
Most of the flooding is forecast to be minor to moderate...however 
Point of Rocks remains forecast to reach major flood stage. 


Please refer to the latest flood statements...which detail the 
latest observed stages and forecast crest times for the affected 
basins. 


&& 


Tides/coastal flooding... 
coastal Flood Warning now extended to 1 PM tomorrow...with MDT flooding 
expected across upper tidal Potomac with both this evening and tmrw morning high 
tides. Minor/MDT tidal flooding expected elsewhere along tidal 
Potomac and western shore of Maryland Chesapeake Bay. Water levels continue to 
run near 4 feet above normal along Potomac in District of Columbia metropolitan. 


With freshwater effects across upper tidal Potomac...MDT flooding may 
continue into tmrw afternoon/evening high tide. Elsewhere...northwesterly winds and 
departure of lopres to east should allow for tidal anomalies to fall 
below those that would cause MDT flooding. 


&& 


Lwx watches/warnings/advisories... 
District of Columbia...coastal Flood Warning until 1 PM EDT Monday for dcz001. 
Maryland...coastal Flood Warning until 1 PM EDT Monday for mdz007-011-013- 
014-016>018. 
Virginia...coastal Flood Warning until 1 PM EDT Monday for vaz052>055-057. 
WV...none. 
Marine...Small Craft Advisory from 7 am to 7 PM EDT Monday for 
anz530>543. 


&& 


$$ 
Synopsis...bpp 
near term...sbk/bpp 
short term...baj 
long term...nwl 
aviation...baj/sbk/bpp 
marine...baj/sbk/bpp 
hydrology...sbk/bpp 
tides/coastal flooding...sbk