Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 240124

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
924 PM EDT Sun Oct 23 2016

High pressure will remain centered over the Gulf Coast tonight. A
clipper system will push through the northeastern U.S. late
tonight with the associated cold front crossing the central Mid-
Atlantic Monday morning. High pressure will return to the region
through midweek. Low pressure will cross to the north late in the
week with the cold front crossing the area Thursday night.


As of 9pm, a shortwave low is over Lake Erie and will track east
to the southern New England coast overnight. This will allow
pressure gradient to tighten overnight. Winds will become
gusty...especially at higher elevations...where gusts of 30 to 40
mph will likely overnight. The cold front will reach the MD/PA
border late tonight.

Lows generally around 50F inland and mid 50s near shore. This is
much warmer than last night and about 10 degrees above normal -
due to mixing overnight as well as some clouds associated with the
shortwave coming in.


High pressure builds into the Mid Atlantic Monday-Tuesday night.
Expect a comfortable day Monday with highs of 65-70. Monday night
will see temps drop to the lower 40s...cooler at the higher
elevations...warmer in the cities.

Tuesday night high pressure will settle overhead providing
excellent radiation conditions. Have added patchy frost along the
M-D Line and west of the Blue Ridge as temps will likely fall into
the mid 30s. Would not be surprised to see frost advisories issued
with later releases.


Guidance is in reasonable agreement through Thursday, but begins
to diverge after that. At the beginning of the long term, we have
a deep closed low over Atlantic Canada and a weak ridge
extending from western Florida north to the Great Lakes, with a
shortwave further west in the upper Mississippi Valley. By Thursday
morning, all of these features shift east, with the closed low
moving into the western Atlantic, the ridge axis just east of our
region, and the shortwave over the Ohio Valley. By Friday, the first
shortwave passes northeast and a second stronger one is crossing the
area. By Saturday and Sunday, models diverge significantly, with
solutions ranging from a closed low to fast moving shortwaves.

In regards to sensible surface weather, high pressure will be off to
the north on Wednesday, likely leading to radiational cooling and at
least some areas of frost, if not perhaps a freeze in some spots.
Wednesday will then features some increase in high clouds looking
likely ahead of the next system. Clouds continue to thicken and lower
Wednesday night as a front approaches, with showers possible in
western areas late at night. This front then crosses the region late
Thursday or Thursday night with a continued chance of showers. The
front is east on Friday with high pressure trying to build back in,
though guidance showing a closed low is slower. Another weak
northern stream system may affect the area later in the weekend.

Temp-wise, we will remain seasonable to a bit below normal through
the long term as the Canadian influence and northern stream remain
more dominant in our weather.


VFR conditions expected tonight through Tuesday. SWly flow around
10 kt overnight, quickly shifting NWly with gusts to 25 kt Monday
morning behind a cold front. Strong NWly flow persists through
Monday evening before easing late Monday night. NWly flow then
continues through Tuesday.

VFR to start Wednesday, but sub-VFR cigs and vis possible Thursday
as a frontal system moves through with rain. Improvements likely


SWly flow across the waters generally 10 to 15 kt with 20 kt gusts
across the MD portion of the Bay and lower Tidal Potomac where an
SCA is in effect overnight. SCA for all waters starting 9am Monday
as winds shift NW and gust around 25 kt behind a cold front.

SCA remains in effect for all waters Monday until midnight
Tuesday when it drops for the middle/upper Tidal Potomac. SCA
possible for most of the waters Tuesday in continued NWly flow.

Sub-SCA likely Wednesday, then SCA possible Thursday and Friday with
another frontal passage.


Fire wx parameter update for tomorrow since we`re in our
secondary peak in fire season and we`re expecting a dry frontal
passage around 12Z Mon. Min_Rh today at IAD was 31% and 24-hr Rh
model trends for tomorrow show very little change from today.
Winds appear could be a little stronger than today which would
meet the RFW criteria, but the Min_Rh would fall just short. Dead
fuel moisture has dropped below 10 percent for all areas east of
the Potomac Highlands. These will drop further in continued dry
winds Monday. An SPS may be warranted Monday to indicate an
elevated fire threat.


MARINE...Small Craft Advisory until 6 AM EDT Tuesday for ANZ530>534-
     Small Craft Advisory from 9 AM Monday to midnight EDT Monday
     night for ANZ535-536.


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