Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 201858

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
258 PM EDT Wed Jul 20 2016

High pressure will build southeast over the area through tonight
before drifting offshore through Thursday. A cool front will sag
into the area Friday night before stalling to our south over the
weekend. High pressure will be in control of the area weather
Saturday through Monday. A cool front looks to enter the area
Monday night and linger just south of the area into the midweek.


As of 3pm, upper 50s to low 60s dewpoints have settled over the
area with 1025 mb surface high pressure just SE of Lake Erie. This
high will shift southeast and overhead tonight. Clear and calm
overnight with typical valley and piedmont fog/ground fog. Min
temps low 60s inland (around 60F west of the Blue Ridge) with low
to mid 70s along the shoreline (water temps low to mid 80s).

High pressure shifts east offshore Thursday with a Sly return flow
developing in the afternoon across the area. Moisture returns. Max
temps around 90F with dewpoints rising to the mid 60s, just a
couple degrees heat index. 850mb temps rise to 20C west of the
Blue Ridge by 00Z Friday, closer to 17C east at that time.


Tranquil Thursday night with high pressure still over the region.
Light Sly flow with a warmer night than tonight, upper 60s inland
and mid 70s nearshore.

Low pressure tracks east across northern Quebec Friday into
Friday night. Associated cold front will be quite strung out by
the Mason-Dixon line Friday evening. Ahead of this front, expect
850mb temps to increase to 20 to 22C with max temps mid 90s, upper
90s possible in best mixing. Dewpoints mid to upper 60s with heat
indices around 100F in the coastal plains. May need a very
targeted heat advisory for urban centers.

PoPs delayed to Friday evening with the weak forcing from the cool
front enough to cause scattered thunderstorms. Severe
thunderstorms are possible any time the temperature reaches the
mid 90s with dewpoints in the 60s. Any activity should wane in the
late overnight.


Extended stretch of hot and humid weather over the weekend into at
least early next week as broad ridge that has been across the CONUS
noses into the mid-Atlantic. High temperatures near 100F combined
with dewpoints AOA 70F will combine to create heat index values near
105F...with heat related headlines possible during this time. Urban
areas will also see little nighttime relief as lows remain well into
U70s in the humid airmass. Shower/Thunderstorm chances remain low
over the weekend...with best chances with terrain induced

Vort max passes well to our north Monday into Tuesday...allowing for
H5 heights to fall some and for a cold front to approach the area.
While the uncertainty regarding how far cold south front makes into
our area is rather high, nearby frontal boundary could allow for
some afternoon/evening showers and thunderstorms Monday and
Tuesday, which could provide some relief from the heat.


VFR through Friday night under high pressure that builds tonight
and lingers offshore Thursday afternoon through Friday night. Best
fog chances tonight, though not expected to be more than ground
fog at TAF sites.

VFR prevails this weekend through early next week under high
pressure. Thunderstorm chances are low over the terminals during
this time.


High pressure builds southeast across the area through tonight
with a north wind 5-10kt in advance. Light return southerly flow
begins Thursday afternoon. Southerly flow continues through Friday
night. Channeling may require an SCA Friday afternoon into the

High pressure in control over the weekend, with southerly channeling
developing overnight leading to elevated winds near SCA criteria.




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