Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 270858

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
458 AM EDT Mon Mar 27 2017

A warm front will positioned over southern Virginia will
track north through the Mid Atlantic this morning. A cold front
will cross the area late Tuesday. High pressure will build over
the region Thursday.


Given ground observations and traffic cams showing dense fog
over the northeastwastern part of the forecast area a dense for
advisory has been issued. It runs through 9 am.

Overnight surface analysis shows low pressure centered over
Michigan with a warm front extneding down the Appalachians into
northern NC. The result for this forecast area is - overnight
easterly winds, low clouds, fog, drizzle.

The front is expected to progress northward through the Mid
Atlantic this morning. Light rain will be possible as the front
makes its move; afterwards warming is expected as the spring
temperature roller coaster brings us back upward: yesterday only
reached the upper 40s, it may take some time but expect this
afternoon to reach the mid 70s over much of the region.


While we will be forecasting "chance of showers" overnight
believe for the most part the nighttime hours will be dry. If it
does the best chances will probably be late ahead of the
approaching short wave. Lows generally in the mid 50s.

Tuesday could see thunderstorm activity as the shortwave tracks
through the Mid Atlantic. SPC has placed much of the forecast
area east of the mountains in a marginal risk of severe storms.
Neither the CAPE or helicity look particularly impressive for

Chances for precipitation should be ending Tuesday evening as
the shortwave moves off the coast. High pressure will return
overnight and for Wednesday. Back on the roller coaster...
temperatures Wednesday should be almost ten degrees cooler than
the previous two days.


High pressure will be building into the Northeastern United States
Wednesday night, sliding east on Thursday. This will lead to drier
and cooler weather, although still near climatological normals. Good
radiational cooling night Wednesday night will lead to widespread
lows in the 30s, with highs rebounding back through the 50s on

Meanwhile, a strong closed low will be moving northeastward out of
the southern plains on Thursday, into the Mid-Mississippi Valley
Thursday night, and towards the Mid Atlantic states by later Friday,
becoming vertically stacked and gradually weakening. Model guidance
is in relatively good agreement with this progression and timing. As
the system makes its way to the eastern seaboard, some redevelopment
off of the Mid-Atlantic coastline Friday night into Saturday morning
is also projected.

Therefore, chances for rain showers increase Thursday night into
Friday morning with initial warm air advection, followed by bulk of
the rainfall likely coming Friday and Friday night with main frontal
push and any subsequent redevelopment. A drying trend should develop
on Saturday, with the chance for some lingering showers as the low
pulls away. High pressure will then build in for Sunday.

Temperatures in the Thursday night - Sunday time period will be
relatively seasonal, skewing slightly above normal. Lows will be
mainly in the 40s. Highs coolest on Friday in the 50s with
clouds/showers, rising into the 60s for the weekend.


Very poor early morning conditions as the Mid Atlantic sits on
the north side of a warm front. LIFR conditions will persist
until at least sunrise. After that the level of improvement and
the speed of it will be dependent upon the how fast the front
pushes to the north as well as how much the sun can work on the
low level moisture. This will need to be watched.

But conditions are expected to reach VFR this afternoon. There
will be chances of rain showers late tonight at all TAF
sites..and then possible thunderstorms Tuesday afternoon. DCA
has the best chance for strong gusty winds.

VFR Tuesday night and Wednesday.

VFR expected Wednesday night and Thursday, but chances for sub-VFR
conditions increase Thursday night and Friday with rain and low
clouds as next system moves into the area. Winds light Wednesday
night into Thursday will increase out of the southeast later
Thursday and Friday.


Winds have been below SCA levels so far overnight. Pushed the
SCA back to after sunrise when the warm front is expected to
make a rapid advance north through the waters.

Thuderstorms will be possible Tuesday afternoon, some of which
could produce SMW level winds. This will need to be monitored.

Sub-SCA conditions expected Wednesday night and Thursday. Potential
for SCA then increases Thursday night and Friday with increasing
southeasterly winds ahead of an approaching system.


DC...Dense Fog Advisory until 9 AM EDT this morning for DCZ001.
MD...Dense Fog Advisory until 9 AM EDT this morning for MDZ004>006-
VA...Dense Fog Advisory until 9 AM EDT this morning for VAZ038>040-
MARINE...Small Craft Advisory from 9 AM this morning to 6 PM EDT this
     evening for ANZ533-534-537-541>543.


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