Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 212317

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
717 PM EDT Wed Jun 21 2017

High pressure will remain west of the area through Thursday. A
cold front will cross the area late Friday night into Saturday,
with tropical moisture streaming into the Mid Atlantic ahead of
the cold front.



Thunderstorm activity that came out of southern PA into
northern MD produced a measured gust to 50 mph in Perry Hall,
but stayed below the 50 kt severe limit. Storms will be
diurnal, and will see a rapid decrease by sunset.

We will be in ridging/subsidence tonight. Suspect there will be
enough mid-level moisture for some clouds, but not enough for a
solid cloud deck. We will have a dewpoint gradient overhead,
which will influence low the 60s.



For the most part, ridging will hold for the day Thursday.
However, warm advection/isentropic lift will be knocking on the
door of the western ridges by afternoon. Add in terrain
circulations, and have chance PoPs for the mid-late afternoon
hours. Believe we will be a degree or two warmer for high
temperatures, which places highs around 90 degrees.

There are two windows of opportunity for heavy rain: Thursday
night into early Friday and again Friday night. The former will
be on the nose of the theta-e ridge. Precipitable waters will
rise to in excess of 2 inches inside the ridge axis.

Then, assuming even some clearing, there will be the opportunity
for some significant instability to develop. While this is
conditional, GFS MUCAPE progs indicate 1500-2500 j/kg possible.
This will be in a sector with a 30-35 kt 925-700 mb jetlet and
500 mb flow reaching 55 kt, so more than ample shear will be
present as well. We will keep to see how details pan out, but
severe weather threats will need to be monitored over the next
day or two.

The second window of heavy rain/storms would be associated with
the cold front that drops toward the forecast area Friday night.
Given the possibility for saturated soils and prolific warm rain
processes, this would be the period that flood concerns most
likely will need to be assessed in the cycles to come.


A cold front, likely entangle in the remnants of Cindy, will move
away from the area early Saturday. This should lead to much drier
and more comfortable (less humid, warm but not hot) conditions for
much of the weekend.

A secondary cool front may drop through the area early next week,
which should keep near to slightly below normal temperatures and
humidity through at least the middle of next week.


VFR conditions through Thursday. Showers and perhaps some
thunderstorms will approach Thursday night. Friday and Friday
night look unsettled as moisture from the remnants of Cindy
stream northeast ahead of a cold front. Local flight
restrictions likely, but its difficult to time specifics at this

Sub-VFR likely Sat AM, then VFR through Sun. Patchy fog
possible Sat night. Winds W 5-10 kts.



Some mesoscale guidance suggesting the southerly channeling may
occur again tonight on the mid-Bay. If it happened, it would be
a few gusts to 20 kt for several hours. Have limited forecast
just under Advisory criteria at this time.

A similar wind regime will continue through Thursday night.
Gradient flow increases by Friday as the remnants of Cindy
stream north ahead of a cold front. Small Craft Advisories seem
likely at this time.

Gusts should subside quickly Saturday and remain below Small
Craft Advisory levels through the rest of the weekend.


Water levels a few inches above astronomical normals this
afternoon. These will slowly increase over the next couple of
days. There is the potential for minor flooding by Friday at
sensitive sites, in the gradient flow ahead of a cold front
which would be merged with moisture from the remnants of Cindy.




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