FXUS61 KLWX 210104

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

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


Very warm and humid this evening across the Mid-Atlantic region.
The 8PM ob at DCA came in with 91/77 with a south wind and heat
index of 105. Warm and humid conditions will continue overnight
with temps only dropping into the 70s and low 80s in the metros
and near the Bay.

Showers and thunderstorms have been approaching the region from
PA and the Ohio Valley this evening. Activity has been
weakening as nocturnal inversions set-up. Showers will likely
enter the Potomac Highlands and northern MD tonight but
dissipate as they move further south. Most areas will be dry

A heat advisory is in effect for much of the region east of the
Blue Ridge from 10am-8pm Friday. Heat indices around 105 are
forecast to occur with dewpts climbing into the low 70s. Temps
in the mid to upper 90s expected by afternoon.

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.

Showers and thunderstorms expected to form across the
Appalachian Mtns Friday afternoon and move eastward into the
evening. Shear is still minimal however instability will be high
due to the high dewpts. Isolated thunderstorms may become
strong to severe.


Potentially active convective day Saturday 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.


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.


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.


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

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.


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 10. In
terms of ranking (going back to 1871) these are #47 and 48. #1
(18 consecutive days) occurred 145 years ago - beginning

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.


DC...Heat Advisory from 10 AM to 8 PM EDT Friday for DCZ001.
MD...Heat Advisory from 10 AM to 8 PM EDT Friday for MDZ011-013-014-
VA...Heat Advisory from 10 AM to 8 PM EDT Friday for VAZ037>039-


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