Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 211857

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



The trough axis presently over New York and Pennsylvania this
afternoon. A line of thunderstorms can be noted at the base of
the trough. There are also a few showers and perhaps a
thunderstorm from around Fredericksburg across southern Maryland
to the eastern shore. This area received sufficient heating
to reach convective temperatures. There is also more than ample
effective shear (50 kt) in this zone as well. Did increase PoPs
to accommodate these trends. Believe that this activity will be
largely diurnal, and am forecasting a rapid decrease by sunset.

We will be in ridging/subsidence in the wake of the trough
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 on 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 anticipated 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.


Southwest flow under Small Craft thresholds this afternoon.
However, there are a couple of showers/maybe a thunderstorm near
the waters which may contain gusty winds. A couple of Marine
Warnings may be required.

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. Will pass concerns on
to the next forecaster.

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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