Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 241847

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
247 PM EDT Wed Aug 24 2016

High pressure remains over the region through Thursday. A cold
front will cross the region on Friday. High pressure will return
for the weekend.

A ridge of high pressure extends from North Carolina to the
Delmarva peninsula this afternoon. A cumulus field has developed,
although it`s not especially vigorous anywhere. Due to that and
the upper level subsidence, do not believe there will be any
thunderstorms developing late today into this evening. Dewpoints
have crept up into the mid 60s, so there will be a hint of

Although vorticity advection should be scarce tonight, believe
there could be some lift from isentropic upglide. As such,
scattered clouds likely to persist well into the evening if not
through the overnight hours. Consequently, low temperatures will
be a bit higher than past couple of days.


As the theta-e ridge strenthens over the forecast area, a ribbon
of instability will work its way up the Appalachians during the
afternoon Thursday and spread east in the evening. The added
warmth, instability, and terrain circulations suggest that
thunderstorms should be able to develop by midday in the mountains
and spread east during the afternoon. Believe the initial storms
will be confined to points west of the Blue Ridge due to limited
CAPE east of there. When the instability improves along I-95,
daytime heating will be dwindling. Therefore, will keep chance
PoPs west but only slight chance to the east. Think the overnight
hours should be dry in spite of low level confluence.

The latest solutions (12z 24th) as a bit quicker in taking the
surface front through the forecast area (am hesitant to call it a
cold front). There is rather strong subsidence from the mid level
(h8-5) ridge, leading to rather poor lapse rates. But, there will
be a boundary lingering coincident with a hot and reasonably
humid air mass. Therefore, have painted in a corridor of 20 PoPs
across the central Shenandoah valley up along I-95. Have low
confidence in storms firing, but 1 or 2 may.

As mentioned, temperatures will slowly be warming through the
period. Friday will be the warmest of the week, with temperature
likely reaching 90 degrees tomorrow and into the mid 90s Friday.



High pressure will build in behind the front Saturday and Saturday
night. Drier and slightly 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 Potomac Highlands Sunday night as the next
cold front moves across the lower Great Lakes. Temperatures
remaining near normal.

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

The front is expected to stall Tuesday. Showers and thunderstorms
could become more prominant. Temperatures a couple of degrees warmer.

A shower or thunderstorm could linger in the region Wednesday as a
weak disturbance rides along the stalled front. Temperatures a few
degrees above normal.

VFR conditions expected tonight into tomorrow morning. Scattered
clouds (FL050) and south winds (at or below 10 kt) should prevent
fog development overnight.

There will be increasing instability on Thursday. Anticipate
thunderstorms will develop over the mountains during the midday
and spread east in the afternoon. MRB most likely to be affected.
However, there will be limited forcing east of the Blue Ridge.
Therefore strength/coverage concerns raises doubts whether any
airfield would receive an impact.

A weak cold front will cross the terminals Friday. Winds may shift
more to the west, but the front otherwise will be hard to
distinguish. An isolated thunderstorm would be possible, but have
low confidence in that forecast.

VFR conditions expected Friday night. A brief period of MVFR or
IFR is possible in any isolated thunderstorms near CHO and mainly
Friday evening. VFR conditions at all terminals Saturday and
Saturday night. Winds northwest around 5 knots Friday and Friday
night. Winds becoming northeast at 5 knots Saturday, then
southeast at 5 knots Saturday night.


Southerly flow will continue through Thursday night. Winds this
afternoon and early evening mainly around 10 kt (there may be an
onshore component til sunset). The increase in speeds will be more
noticiable Thursday evening, when channeling will be possible.
Will be raising a Small Craft Advisory for portions of the mid

Winds will be veering west Friday as a weak surface boundary
crosses the waters, eventually becoming northwest by late in the


Increased southerly flow will cause water levels to rise tonight
into Thursday. By Thursday night, caution stage will be reached at
several sites on the Bay. Annapolis could approach minor flood,
although not all guidance sources support that solution.

Winds will become west on Friday, so there should not be a concern
beyond the Thursday night cycle.


MARINE...Small Craft Advisory from 6 PM Thursday to 2 AM EDT Friday for


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