Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 191420 AAA

Area Forecast Discussion...UPDATED
National Weather Service Baltimore MD/Washington DC
1020 AM EDT Wed Jul 19 2017

High pressure will build into the region today and Thursday,
followed by the potential for weak disturbances Friday and the
weekend. An upper level trough of low pressure will move over
the northeastern US to start the new week.


Upper level trough over the Carolinas has shifted considerably
south and east of the local area this morning as compared to
past few days putting local area under mid-upper level ridging.
Experimental GOES-16 low-level water vapor 7.3 micron channel
shows that dry air has spread a bit farther east today to near
the I-95 corridor even though 12Z IAD sounding came in with
higher PW values at 1.72 inches as compared to past two
mornings. Hi-res models show considerable less convective
activity today than past two days and this seems reasonable
given trends seen in water vapor imagery. In addition, h5 temps
have warmed up a deg or two C since yesterday which should tend
to cap things off a bit. Still isolated t-storms are expected
over the Blue Ridge mtns into northeast MD along the Chesapeake
Bay due to orographic lift and sea breeze convergence

Not anticipating any heat headlines today and are not likely
tomorrow either. Heat headlines will probably be needed Fri and
possibly Sat.


Building heat Thursday and Friday. High pressure centered over the M
id-South states will direct organized thunderstorm development/MCSs
from the Lake Erie area to the central Mid-Atlantic. Thursday night
looks to be the first threat time for MCS activity.

Heat advisory for portions of the area (mainly along the Bay
shoreline and south of DC) Thursday with an advisory for most of the
area likely Friday. 100F heat index criterion west of the Blue Ridge
should allow greater advisory coverage than last year when the
criterion was 105F out there.


Historically the latter part of July is the hottest period of
the year in the Mid Atlantic, and this weekend will definitely
fit that descriptor. Highs Saturday will be in the 90s over much
of the area, with the cities reaching the upper 90s. With
dewpoints around 70 this will push afternoon heat indicies of
100 to 105. Heat advisories will be likely. With this much
heat/humidity in place afternoon/evening thunderstorms will be
possible, especially over the mountains.

"Sultry" will be a good decriptor for Saturday night. Lows
generally in the 70s, possibly 80 in the cities.

Sunday will be pretty much a repeat. A short wave moving into
the Upper Great Lakes Sunday night may serve as an initiator for
convection in the Ohio Valley. Whether or not this will be
impact the Mid Atlantic remains to be seen.

The worst of this heat wave should be put to rest Monday as the
short wave tracks over New England. Temperatures will probably
still reach 90 Monday. With the trof passing to the north
there`ll be a chance for thunderstorms.

Tuesday the trof will have moved off the coast, helping to bring
the Mid Atlantic back to more "normal" temperatures with highs
in the mid to upper 80s.


VFR prevails under high pressure through the weekend. Organized
thunderstorm chances Thursday night through the weekend.

Saturday and Sunday VFR with the potential for showers and a
few thunderstorms. Heavy downpours and gusty thunderstorms are
possible in any storms.


Tranquil winds through the weekend, though organized
thunderstorm chances begin Thursday night with high pressure
centered over the Mid-South States.

Winds expected to be below SCA values this weekend.
Afternoon/evening thunderstorms will be possible each day.


We are now at the higher of the two high tides and nowhere is
in danger of reachng minor flood stage, hence there should be no
problems with the daytime high tide cycle.




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