Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 200052

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
852 PM EDT Wed Jul 19 2017

Weak high pressure will build into the region through Thursday,
followed by the potential for weak disturbances Friday through
Sunday. An upper level trough of low pressure will move over the
northeastern US to start the new week.


A few showers present across southern PA this evening and have
been weakening as they approach the MD border. Warm and humid
conditions expected tonight. A few showers and thunderstorms can
not be ruled out tonight due to the present instability however
most places will stay dry into Thursday morning.

Lows in the 70s in many areas and upper 70s in urban areas

As heights rise a bit more and h85 temps rise into the low 20s
(C), expect even less convective coverage Thursday than today.
In addition, a light w to nw sfc flow will develop lowering sfc
dewpoints and boosting temps in the mid to upper 90s hottest
over western MD, ern WV panhandle and wrn VA. Due to advection
of lower dewpoints, heat indices will likely fall below any heat
advisory criteria. Still hot nonetheless.


Slight risk of some nocturnal MCS activity to make it into
western MD, but activity is likely to dissipate as it crosses
the Appalachians.

Hotter on Friday as h85 temps peak at 22C. A light sw flow over
Fredericksburg, southern MD and the urban areas will likely keep
sfc dewpoints higher with heat indices filtering around the 105
degree threshold. Temps west of the Blue Ridge could hit the
century mark with heat indices filtering with the new heat index
criteria there of 100F. Some convection can`t completely be
ruled out, but model guidance do not show good chances.


A front will stall across central Virginia Saturday. There is a
chance for showers and thunderstorms along this front. Highs will
once again reach the middle 90s in many areas.

The front will move north of the region as a warm front Saturday
night, keeping the chance for showers and thunderstorms present over
much of the region.

Upper level energy from the west will set up a trough of low
pressure on the leeside of the Appalachians Sunday into Sunday
night. Additional showers and thunderstorms could form along this
trough but could mainly be isolated to scattered. Highs will reach
the middle to upper 90s.

A cold front will approach the region Monday before pushing across
the region Monday night. Showers and thunderstorms will develop
along and ahead of this front. Some thunderstorms could be strong to
severe as wind shear increases some. Highs will reach the be in 90s
again, until the front ushers in cooler and drier air Monday night.

Broad high pressure will build in from the west and northwest
Tuesday through Wednesday. Temperatures will be nearly 10 degrees
cooler than previous days with a comfortable relative humidity with
respect to mid-Summer days and nights.


VFR conditions tonight through Fri with light and variable

Mvfr to ifr conditions possible with showers and thunderstorms
Saturday through Sunday night. Ifr conditions would be mainly in
heavy thunderstorms. Winds southwest 5 knots Saturday. Winds light
and variable Saturday night. Winds southwest 5 to 10 knots Sunday,
becoming northwest around 5 knots Sunday night.


Isolated t-storms possible today through Fri. Most activity will
be in the afternoon and early evening.

No marine hazards expected Saturday through Sunday night. Winds
southwest 5 to 10 knots Saturday and Saturday night. Winds southwest
10 knots Sunday and Sunday night.




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