Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 211910
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
310 PM EDT Thu Jul 21 2016

.SYNOPSIS...
High pressure over the area will drift offshore this afternoon. A
system will push north of the region on Friday, followed by a
front moving into the area Friday night into Saturday. High
pressure will be in control of the area`s weather Sunday before
another front enters the area Monday night.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 3pm, 1021mb mslp is across the central Mid-Atlantic, down a
millibar since this morning as the high pressure center shifts
east offshore. Flow is generally 10 mph or less and Sly. Dewpoints
have been slow to rise, mid 50s north to mid 60s south. Dewpoints
increase to the upper 60s to 70F over the next 24 hrs.

MCS has made it to Nrn IN and SErn MI. All guidance, including CAMs
have struggled with this feature all day. 17Z HRRR kills the
activity over OH this evening. 500mb flow would keep it west of
the area. The lack of moisture advection thus far into the area
has limited thunderstorm development and would limit potential of
any activity advecting in.

Mostly clear tonight with min temps in the 60s inland to low to
mid 70s urban/nearshore.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
Interaction of heat dome spreading east from the central CONUS and
low pressure tracking across northern Quebec will determine
weather for Mid-Atlantic Friday and Friday night. Heat is expected
with heat indices approaching 100F. Trough from the low will
approach from the north Friday evening and should provide enough
forcing for scattered thunderstorms into the overnight. However,
given mesoscale activity, the timing and location cannot be
certain until the activity develops.

A remnant frontal boundary from overnight activity should set up
near of over the area Saturday. This will be more of a
moisture/dew point boundary with areas south having dewpoints over
70F, perhaps mid 60s north. Temperatures expected to be a degree
or so higher, highs mid to upper 90s. Good chance for 105F heat
indices. With temperature and moisture this high, any
thunderstorms could easily become severe.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Hot and often humid weather continues through the long term, with
little "true" relief from the heat through Thursday (>90F forecast
each day). Hottest weather expected Sunday through early next week,
with H85 temperatures exceeding 20C as upper ridge noses into the
area. Guidance is suggesting that dewpoints could drop some Sunday,
as slightly drier air filters into the area, which would keep heat
indices near 100F. However, any respite from the humidity would be
short-lived, as dewpoints rise back well into the 70s by
Monday...with heat headlines possible as heat indices approach 105F.
Only low thunderstorm chances Sunday, as aside from terrain
circulations forcing remains weak. Approaching cold front increases
thunderstorm chances Monday, as storms develop to our N/NW and
propagate toward the area.

H5 heights begin to sag south Tuesday in response to wave moving
along with the northern stream. At the same time, aforementioned
cold front will approach the area from the NW, which could offer
some relief from the oppressive humidity as drier air possibly
filters into the area. However, as is always the case this time of
year, forward progress of the front remains unclear, which reduces
forecast skill with remainder of forecast.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
VFR under high pressure into Friday. Isolated to scattered
showers/thunderstorms around both Friday and Saturday. Light and
variable winds this morning turn light southerly this afternoon,
southwest Friday, and then westerly Saturday.

Primarily VFR Sunday. May have some early morning fog, with a low
chance at late day thunderstorms.

Thunderstorm chances improve Monday, but coverage still appears to
be scattered.

&&

.MARINE...
Sub-SCA conditions expected into Friday. Light southerly through
tonight. Winds turn southwest Friday, and a SCA may be needed for
Srn MD waters Friday night as southwest winds increase. Winds
then turn west on Saturday.

High pressure remains in control Sunday, with southerly channeling
possible overnight leading to elevated winds near SCA criteria.
Gradient winds will increase Monday ahead of cold front.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$
SYNOPSIS...BAJ
NEAR TERM...BAJ
SHORT TERM...BAJ
LONG TERM...MSE
AVIATION...BAJ/MSE
MARINE...BAJ/MSE



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