Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 180759
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
359 AM EDT Sun Jun 18 2017

.SYNOPSIS...A very warm and humid air mass will remain in place
through Monday until a cold front clears the area Monday night.
Weak high pressure will build over the area for the middle of
the week.

&&

.NEAR TERM /THROUGH TONIGHT/...A stratus layer has developed
east of the Blue Ridge mountains early this morning as seen on
nighttime microphysics RGB with some patchy fog over some of the
valleys in eastern WV. After morning clouds scatter out, it
will be a sultry Father`s day with temperatures getting into the
mid 90s and dewpoints around 70F resulting in heat indices
around 100F. Afternoon convection will likely remain scattered
at best given lack of sfc and upper level forcing and no
appreciable height falls. The first part of the night is likely
to be quiet with showers or t-storms beginning to move into the
Potomac highlands after midnight. Model guidance now shows
faster progression of showers overnight tonight into Mon
morning, so have increased PoPs somewhat.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...An upper level
trough will be moving across the eastern Great Lks Mon pushing a
cdfnt into the area. As cdfnt intercepts a plume of very high
PWATs aoa 2.0 inches, expect widespread showers and t-storms to
develop and last into the evening except in southern MD where
they will likely last through much of the night. While shear
will be on the increase through the day (0-6km values of 30-35kt)
which would support organized convection, amount of instability
available still remains questionable given thick clouds are
likely to arrive early and there might be showers already by 12Z.
00Z EPS indicate probabilities of CAPE greater than 1000 J/kg
well below 50%. While individual storm cell motion is progged at
30-35 kt, unidirectional wind profiles suggest some
training/repeated convective activity is likely causing some
concerns for flash flooding especially given the very high
PWATs. Still believe the primary threat will be flash flooding
and a flash flood watch may be required for the I-95 urban
corridor of DC and Baltimore.

Cdfnt clears the area late Mon night with showers ending in most
areas except perhaps southern MD. Drier and more seasonable
Tue-Tue night.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...

Low humidity but seasonable temperatures for Wednesday. A departing
broad upper trough will allow for some potential for instability
convection. By Thursday and Friday zonal flow will replace the
trough. Surface features will be fairly benign...but given the low
level flow, some amount of tropical moisture could make it up here
from the Southeast during the late week. Next weekend looks to be
our next cold front, although the timing of which day is uncertain
given the model spread. Dewpoint temps and humidity are expected to
increase day by day Wednesday thru Saturday.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...Low clouds have
developed this morning with IFR conditions expected. This could
repeat itself again tonight, but no fog is anticipated due to
strengthening winds.

Other than possible showers and thunderstorms at times, no
significant aviation concerns Wed through Fri.

&&

.MARINE...Solid SCA winds today through Mon under strengthening
srly winds. T-storms on Monday may require special marine
warnings. Winds begin to diminish late Mon night.

Other than thunderstorms, no significant marine concerns Wed through
Fri.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 AM EDT Monday for ANZ530>534-
     536>543.
     Small Craft Advisory from noon today to 6 AM EDT Monday for
     ANZ535.

&&

$$
SYNOPSIS...LFR
NEAR TERM...LFR
SHORT TERM...LFR
LONG TERM...CAS
AVIATION...CAS/LFR
MARINE...CAS/LFR



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