Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 231836
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
236 PM EDT Tue Aug 23 2016

.SYNOPSIS...
High pressure remains over the region through much of the week
with a cold front moving through on Friday. High pressure returns
for the weekend.
&&

.NEAR TERM /THROUGH TONIGHT/...
Even though high pressure is resting atop forecast area this
afternoon, residual low level moisture has allowed for a decent
cumulus field to blossom. Virginia and West Virginia are more
affected than Maryland. Think that increased subsidence and then
nocturnal cooling will permit a decrease during the mid-late
afternoon hours. Therefore, will not forecast these clouds entering
Maryland.

Otherwise, there is not much to discuss from a synoptic standpoint.
Mean layer RH less than it was last night/this morning. Believe
there will be mostly clear skies, so radiational cooling will be a
bigger driver. That is reflected in low temperature forecast. Since
dewpoints still low, fog should be limited to patches in typical
mountain valleys.
&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
Surface high pressure will slowly be working offshore Wednesday and
Thursday. As a result, we should embark upon a warming trend. Upper
80s/near 90 for high temps seem likely again by Thursday. Dewpoints
will start to creep upward too, but still at tolerable levels (lower
60s Tue, mid 60s Wed).

As humidity increases, instability levels will rise as well on the
back side of the ridge. NAM continues to place more emphasis on the
westerlies across the northern half of the country. Consequently,
more shortwave advection would be affecting area based on this
solution, primarily Wednesday night and Thursday. GFS is far more
reserved, and seems to be the more plausible scenario.

Am keeping all areas dry Wednesday and Wednesday night, but with
added clouds in the mountains.  Although temps will be a little bit
warmer, do not believe there will be adequate forcing for
thunderstorms to develop. By Thursday, believe there will be a
ribbon of instability, confined mainly west of the Blue Ridge. Going
forecast has 30-40% chance of showers/thunderstorms in this area,
which should address threat well.
&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
A weak cool front is expected to stall across the region Friday
and Friday night. A spotty shower cannot be ruled out along the
boundary. Temperatures will be on the warm side too with highs
reaching the lower to middle 90s.

High pressure will build in behind the front Saturday and Saturday
night. Drier and cooler air expected. Temperatures will be closer to
normal.

This high will move east and weaken Sunday and Sunday night. Dry
conditions will prevail Sunday. We can`t rule out a shower or
thunderstorm in the west Sunday night as the next cold front moves
across the lower Great Lakes. Temperatures remaining near normal.

The cold front will move across the region Monday and Monday night.
A chance of showers and thunderstorms will ensue through the period.
Temperatures normal.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
There is a vigorous cu field across Virginia and West Virginia this
afternoon, with bases (some cigs) 050-060. Believe this will erode
prior to sunset. VFR through the evening.

There may be some patchy fog overnight, but air mass quite dry...so
am doubting how widespread it will be. Have limited MVFR to climo-
preferred locations.

VFR conditions should generally prevail Wednesday and Thursday as
high pressure departs. Fog may be a little more pervasive by
Thursday with added humidity. In addition, a few thunderstorms would
be possible in the afternoon and evening, especially near MRB.

VFR conditions expected Friday through Friday night. A brief
period of MVFR or IFR is possible in any isolated thunderstorms
near CHO, MRB, and IAD...mainly Friday evening. Winds southwest
around 5 knots Thursday night becoming northwest around 5 knots
Friday and Friday night.

&&

.MARINE...
Winds light and variable over the waters this afternoon as high
pressure is overhead. flow will become southerly over the next
couple of days as the high pulls offshore. For the most part winds
will be 10 kt or less. However, may have some gusts up to 15 kt due
to channeling Wed and Thu nights.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$
SYNOPSIS...RCM
NEAR TERM...HTS
SHORT TERM...HTS
LONG TERM...KLW
AVIATION...HTS/KLW
MARINE...HTS/KLW



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