Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 221858

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
258 PM EDT Wed Mar 22 2017

High pressure will build across the area tonight, and move
offshore Thursday night. A warm front will cross the region
Friday. Low pressure may affect the area Sunday.


High pressure over the Great lakes this afternoon will crest
over the forecast area by Thursday morning. That will lead to
decoupling of the wind field (the gradient has already started
to relax) and radiational cooling. The best cooling will occur
in the mountains, where lows will be in the teens. However, the
entire area will be in the 20s by sunrise tomorrow. Ultimately,
the extent of radiational cooling will depend upon when winds
diminish. With dewpoints near 10 above, there is plenty of room
for cooling, and the source of the uncertainty.


Warm advection will commence by Thursday afternoon, and the axis
of the high will move offshore by Thursday night. It is less
certain whether the warming will be realized at ground level
during the day. Therefore, forecast highs will be similar to
today. The warming will begin to mix to the surface Thursday
night. The ECMWF has been (and continues to be) much wetter than
other guidance late Thursday night into early Friday morning near
a warm front. Given warming aloft, that suggests a freezing
rain threat. The ECMWF is alone in this solution; other guidance
is all dry. Have reduced PoPs a pinch (have 20-30% in database).
Am reluctant to remove PoPs outright, but at the same time am
skeptical whether this will pose an impact.

Forecast area will be on the warm side of the upper ridge on
Friday. Highs near 60; lows 45-50.


Warm southerly flow over our area as a high pressure sits
offshore- will allow for well above normal temperatures on
Saturday... reaching the 70s for most locations... 60s

Backdoor cold front pushes south Saturday night into Sunday and
stalls near or above our CWA into Monday as low pressure approaches
the southern Great Lakes. PoPs will be increasing as this low
continues to move ENE through the front Sunday into Monday.

There seems to be a drier period sometime Monday night into early
Tuesday before a cold front pushes through the area Tuesday into
Tuesday night as PoPs increases. Dry conditions return on Wednesday.
High temperatures Sunday into Tuesday will be in the 50s and 60s,
and in the 40s on Wednesday behind the front.

VFR flight conditions will prevail through the valid TAF period.
Gusty northwest winds are diminishing, with gusts 20-30kt
through sunset. Winds will continue to diminish, with winds less
than 10 kt overnight. Few if any clouds through this period.
Mostly clear/clear skies and light winds will continue through

South/southwesterly flow Thursday night into Friday. Clouds will
overspread during this period. Do not anticipate flight
restrictions during this period. Precipitation should remain
north of the terminals. There is a slight chance that precip
could move in before all cold air departs-- this would affect
only MRB. Have low confidence that this would occur.

Dry/VFR and warm conditions expected on Saturday. A front
pushes south and stalls over our area Sunday and increases
probability of precip over our region into Monday with possible
sub-VFR periods.


Winds continue to diminish. Will replace all Gale Warnings with
Small Craft Advisories. The Small Craft will be able to be
trimmed through the evening. WInds will be light Thursday and
Thursday night. Southerly flow will increase again Friday.

Dry and warm conditions expected on Saturday. A front pushes
south and stalls over our area Sunday and increases probability
of precip over our region into Monday with possible. Winds are
expected to remain below the SCA threshold trough this period.


MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ530-
     Small Craft Advisory until 4 AM EDT Thursday for ANZ532>534-
     Small Craft Advisory until 8 PM EDT this evening for ANZ535-


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