Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 161540

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1140 AM EDT Wed Aug 16 2017

An area of high pressure will build into the region through
tonight. A warm front will move northward Thursday into
Thursday night followed by a cold front that should pass through
the region Friday night into early Saturday. Weak high pressure
will build into the area during the rest of the weekend.


All fog has dissipated and rest of day should generally be
tranquil. Ridge of surface high pressure moving eastward
from the Great Lakes will crest near the region this afternoon.
This will provide for mainly dry conditions and partly-mostly
sunny skies. Guidance continues to hint that there may be a
spotty shower or t-storm, but the vast majority of the area is
not expected to see any measurable rainfall, so at this point
have kept pops just below 15 percent. Temperatures should still
reach the upper 80s to locally near 90F by late in the


For tonight, surface high will be slow to exit so another night
of light winds and mostly clear skies will be in store to start.
We`ll be one day removed from significant rainfall however, so
while areas of fog and stratus are likely again, coverage/density
should be less than this morning. Another factor may be an
increase in mid clouds late tonght as the next system
approaches, so bottom line is that we are not expecting another
dense fog event. Lows from the mid 60s to low 70s.

High pressure shifts offshore for Thursday allowing for the
return of southerly flow. As an approaching low pressure
system lifts through the Great Lakes, a warm front will lift
northward and into the region by Thursday afternoon. This and a
developing area of broad low level convergence will serve as a
focus for shower/thunderstorm development on Thursday. MLCAPE
south/west of the warm front is currently progged to be in the
1000-2000 J/KG range, which is quite sufficient for thunderstorm
development. Further examination of the modeled forecast
soundings would indicate potential for both an isolated severe
and isolated flood threat, with the presence of a low level
boundary, directional shear along the boundary, 0-6KM shear of
around 30 knots, and precipitable water values 2-2.25 inches.
Initial focus likely to be west of I-95, with propagation
eastward during the evening/overnight hours. Highs Thursday
should reach into the mid/upper 80s, with lows Thursday night in
the low to mid 70s.

The area of low pressure will push into southern Canada on Friday,
with its trailing cold front entering the Mid-Atlantic states
during the day. This will serve as another focus for scattered
showers/thunderstorms during the day Friday. A potential severe
threat will exist again on Friday, as temperatures and low
level moisture surge out ahead of the front, leading to the
development of 1500-2500 J/KG of MLCAPE, with 30-35 knots of
shear moving overhead. Highs upper 80s to around 90F. Convection
will wane Friday night.


Weak high pressure will build toward the area for Saturday and
Sunday. Most areas will remain dry with less humidity.
However...a pressure trough will likely be hung up near the
Chesapeake Bay into southern Maryland. Humidity may remain
across these areas along with an isolated shower/t-storm...but
much of the time will be dry.

High pressure will move offshore for Monday and Tuesday. Hotter
and more humid conditions are expected.


Conditions VFR rest of today under high pressure.

Potential for additional fog/stratus exists tonight, although
coverage/density should be less than this morning.

Next weather concerns will be the possibility of scattered
showers/thunderstorms both Thursday and Friday, where brief
reductions of both ceiling/visibility are possible.

High pressure should bring VFR conditions most of the time for
Saturday and Sunday.


Sub-SCA conditions expected through Thursday. South winds will
then be on the increase late Thursday through Friday ahead of a
frontal system, and Small Craft Advisory conditions are
expected across the middle portion of the bay and lower tidal
Potomac. Have issued SCA for late Thursday-Thursday night
period, and this will likely need to be extended through Friday.
Isolated to scattered showers and thunderstorms are also
possible both Thursday and Friday, mainly in the
afternoon/evening, and Special Marine Warnings may be necessary.

A pressure trough will remain near the waters during the
weekend. Wind speeds should be below SCA criteria for the most
part since the gradient will be week. A return flow from the
south will develop early next week as high pressure moves


A light northerly flow allowed anomalies to drop this morning.
However...southerly winds will increase for Thursday through
Friday night ahead of a cold front. Minor tidal flooding is
possible near high tide Thursday night into Friday morning and
again Friday night into Saturday morning for sensitive areas.


MARINE...Small Craft Advisory from 4 PM Thursday to 6 AM EDT Friday for


TIDES/COASTAL FLOODING...BJL/RCM is the U.S. government's official web portal to all federal, state and local government web resources and services.