Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 201856
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
256 PM EDT Thu Jul 20 2017

.SYNOPSIS...Weak high pressure will remain over the region
through tonight, followed by the potential for weak
disturbances Friday through Sunday. An upper level trough of low
pressure will move over the northeastern US early in the new
week.

&&

.NEAR TERM /THROUGH FRIDAY NIGHT/...Sultry night on tap with
increasing high clouds keeping temps up overnight. 24-hr model
trends in temperature indicate a 2-4 deg F rise from last night
meaning places like DC and Balt will not drop below 80F. In
fact, Downtown Balt may only drop to mid 80s tonight. For
tomorrow, models don`t indicate much change in MaxT so
temperatures will be as hot as they are today. Moisture might be
a little higher with 850 mb and sfc dewpoints progged much
higher than today. Heat advisories will likely be needed again
for most of the area similar to today. With regards to
convective potential tonight and Fri, hi-res convective allowing
models show weakening MCS tracking across PA into ern WV late
tonight after 06Z, so have low chance PoPs confined only to west
of the Blue Ridge mtns. Late Fri and Fri evening, GFS guidance
shows potential MCS activity crossing the Appalachians and parts
of the fcst area. Risk of t-storms looks definitely a little
higher than today.

&&

.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...Potentially
active convective day during the afternoon and evening. Both GFS
and ECMWF show an MCS over the lower Great Lks moving sewd
across the fcst area Sat afternoon and evening. As always with
summertime convection, details especially with respect to timing
are very uncertain this far out. Continued hot and humid with
heat advisories still likely to be needed.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...

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. Highs will reach the 90s again.

The front could stall just to our south Tuesday, allowing for a
couple of showers or a thunderstorm to develop.

High pressure will build in from the west and northwest Tuesday
night through Thursday. Temperatures will be nearly 10 degrees
cooler than previous days with a comfortable relative humidity.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...Hot and hazy next few
days. Sct-nmrs t-storms mainly Sat.

Mvfr to ifr conditions possible with showers and thunderstorms
Sunday through Monday night. Winds southwest becoming west-northwest
5 to 10 knots Sunday into Sunday night. Winds northwest becoming
southwest 5 to 10 knots Monday and Monday night.

&&

.MARINE...Potential for showers and thunderstorms Fri night and
Saturday and again Sun which may require special marine
warnings.

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

&&

.CLIMATE...

Late July is climatologically the warmest time of the year,
just like six months from now is the coldest time. How has the
heat of 2017 compared with heat waves (up to now) in other
years? I chose "consecutive days that reached 90 and above" as
the criteria.

At DCA there have been two times this summer with stretches of
six consecutive days - beginning June 29 and again July 19. In
terms of ranking (going back to 1871) these are #47 and 48. #1
(18 consecutive days) occurred 145 years ago - beginning
6/27/1872!

For Baltimore there were also six consecutive days beginning
June 29, which puts it in 36th place. #1 was 13 consecutive days
beginning 7/3/1993.

The all-time record for June-Aug: for Baltimore 25 consecutive
days beginning 7/12/1995. For DC there have been two periods of
21 consecutive days - beginning 7/29/1988 and 7/25/1980.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Heat Advisory until 7 PM EDT this evening for DCZ001.
MD...Heat Advisory until 7 PM EDT this evening for MDZ003>006-011-
     013-014-016>018-502>508.
VA...Heat Advisory until 7 PM EDT this evening for VAZ027>031-
     036>040-050>057-501-502-505-506.
WV...Heat Advisory until 7 PM EDT this evening for WVZ051>053.
MARINE...None.

&&

$$
SYNOPSIS...LFR
NEAR TERM...LFR
SHORT TERM...LFR
LONG TERM...KLW
AVIATION...LFR/KLW
MARINE...LFR/KLW
CLIMATE...WOODY!



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