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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 171945
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
345 PM EDT Fri Aug 17 2018

.SYNOPSIS...
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A cold front will slowly approach from the northwest and
Saturday, then gradually cross the region Saturday night into
Sunday. High pressure will briefly dominate Monday before
another system approaches towards the middle of next week.
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&&

.NEAR TERM /THROUGH SATURDAY/...
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Latest surface analysis depicts high pressure dominating the
western Atlantic and a slow moving frontal boundary extending
from New England southwest across the Great Lakes into the Corn
Belt. Aloft, a ridge dominates the western Atlantic east of
Florida while a closed low is over Chicago.

Tonight, the front will slowly slip southeast toward the region,
but should remain outside the CWA. However, ample CAPE combined
with limited shear and passing shortwave energy combined with
falling heights is resulting in decent storm organization across
our western zones, and this will likely translate east or
northeast through the rest of the afternoon into the evening.
Damaging winds are the main threat, but hail is possible with
the strongest cores.

Storms should gradually weaken late this evening and overnight
as they continue moving northeast, with the overnight hours
turning out mostly quiet. Lows will remain warm, with 70s
common.

The cold front will slowly slide southeast towards the region on
Saturday, but will remain north of the CWA through the day.
Thus, we will remain unstable, and with the upper low opening
into a trough and passing to the north, more storms look likely.
It should start quiet in the morning as well, likely aiding to
destablization, though at this point expect less CAPE due to
greater cloud cover. Otherwise, flash flooding and gusty winds
look to remain a threat. Highs will be a bit cooler than today,
but should approach 90 in much of the area.
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&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
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Front slowly crosses the area Saturday night and Sunday, and
trough axis passes late Saturday night, so overall, expect less
activity on Sunday. However, lingering instability may still
generate some showers and a thunderstorm or two on Sunday. Highs
will be cooler, with 80s common. By Sunday night, some clearing
should take place as high pressure builds southward into the
area. Lows will drop into the 60s.
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&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
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On Monday, a upper level trough will exit the region to the
east. Behind the trough, a weak upper level ridge will build
into the region from the west. A frontal boundary is forecast to
stall off to the south of the region becoming a focus for
precipitation. A high pressure will try to build over the
region. The region is expected to see a brief dry period on
Monday but showers can`t be ruled in the southern parts of our
CWA.

Tuesday into Wednesday, a upper level trough will approach from
the west early on Tuesday. A warm front will move northward
through the region creating a southerly flow and transport warm
and moist air into our area. Thunderstorms and showers will be
possible on Tuesday especially later in the day as a cold front
approaches from the west. These storms have the potential to be
severe and cause localized flooding due to PWAT values over two
inches. The cold front is expected to finally move through our
region early Wednesday morning. Showers and storms will be
possible Tuesday night into Wednesday morning with showers
lingering through Wednesday morning. The best location for
showers on Wednesday will be on the west side of the Blue Ridge
due to a westerly flow creating upslope induce showers. Daytime
high temperatures are expected to be seasonal below average in
the upper 70s and low 80s.

On Thursday, a high pressure system will build over the region
and linger through the early parts of the weekend. Day time high
temperatures look to remain below average in the low 80s. Winds
will be light out of the north.
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&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
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Mainly VFR through Sunday night, but scattered showers/t-storms
will present issues with low cigs/low vis/lightning and gusty
winds, primarily during the afternoon and evening hours. Some
reductions in vis/cig possible during the late night/early
morning hours due to fog development, most likely at MRB/CHO but
possibly at IAD/BWI as well.

On Monday, skies will remain mostly cloudy with only scattered
showers expected.Winds will be light out of the east northeast.
VFR conditions are likely at this time.

On Tuesday, a frontal boundary will approach from the west.
Showers and thunderstorms will be possible with mostly cloudy
skies. Winds will be light out of the south. The transport
moisture into the region will lead to increasing cloud cover.
SubVFR conditions will be possible especially within storms.
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&&

.MARINE...
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Pressure gradient increasing ahead of an approaching cold front
will result in SCA conditions this aft into early Saturday. In
addition, scattered t-storms this aft/even may result in gusty
winds, with the need for special marine warnings. As the front
slowly crosses the region on Saturday and Sunday, the gradient
should diminish, but scattered t-storms will again be possible
each day.

Skies should remain mostly cloudy Monday with light winds out
of the west to northwest. A few showers will be possible over
marine areas near central Virgina. Isolated showers will be
possible.

A cold front will approach from the west Tuesday. Thunderstorms
and showers will be possible with winds out of the south. A
southerly flow could lead to a channeling effect which may lead
to wind gusts above 15 to 20 knots.
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&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 10 AM EDT Saturday for ANZ530>543.
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&&

$$
SYNOPSIS...RCM
NEAR TERM...RCM
SHORT TERM...RCM
LONG TERM...JMG
AVIATION...RCM/JMG
MARINE...RCM/JMG