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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 250759 AAA
AFDLWX

Area Forecast Discussion...UPDATED
National Weather Service Baltimore MD/Washington DC
359 AM EDT Tue Jul 25 2017

.SYNOPSIS...
A cold front will pass through the area tonight. High pressure
will build into the Mid Atlantic Tuesday before moving offshore
Wednesday. Another cold front will approach the area Thursday
before passing through Friday into Friday night. High pressure
is expected to return for the weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Cold front has pushed southeastward of the area as of early this
morning with north/northwest flow taking hold. This has ushered
in a much less humid air mass with dew points as of 3AM in the
mid 50s north and west of the metros. This air mass will
continue overspreading the region through the morning with dew
points by the afternoon from the mid 50s to mid 60s area-wide.
In addition, temperatures will be a good 5-10 degrees cooler
than yesterday, with highs generally in the low to mid 80s.

Otherwise, early morning high clouds will give way to a developing
cumulus deck during the day with more clouds north than south. An
upper level trough moving off the northeast coast may even get
close enough to help spark an isolated sprinkle or shower this
afternoon across far northeast Maryland in conjunction with a
developing westward push of marine air.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/...
As the upper trough pulls away tonight and surface high
translates eastward across New England, push of marine-
influenced air will gradually move westward and towards the
metropolitan areas. Westward extent by morning is still in
question, but there may be some low stratus that move across
portions of the region by sunrise. There may even be a few
isolated light showers that develop and move into
central/eastern Maryland. In addition, some patchy fog is also
possible. Lows tonight 60-70F.

On Wednesday easterly flow will turn southeasterly as surface high
moves offshore. Broken cumulus deck expected again with
temperatures similar to today, mainly low to mid 80s. Could
also be an isolated shower or thunderstorm around, with highest
chances near the Chesapeake Bay and near the Allegheny Front.

Flow will then turn more southerly Wednesday night as the surface
high moves further away and a low pressure system begins to make
its approach from the west. There is potential for some low
clouds/fog again late Wednesday night into early Thursday
morning.

South/southwest flow returns for Thursday and with it, the
return of heat and humidity. Highs will rebound back to near
90F with dew points rising back to near 70F. As the frontal
system approaches late in the day, chances for
showers/thunderstorms increase, and SPC has placed the region in
a Slight Risk for severe thunderstorms. The greatest risk of
severe thunderstorms and heavy rain at this time appears that it
may come Thursday evening/night into Friday morning. See long
term discussion below for more information.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Low pressure and its associated cold front will move into the
area Thursday night before passing through Friday. A southerly
flow ahead of this system will usher in plenty of moisture.
Latest guidance shows PWATs close to 2 inches.

An upper-level low associated with the cold front will also
approach Thursday night before passing through Friday. Deep
layer shear profiles should strengthen during this time. The
forcing from shortwave energy associated with the upper-level
low...the surface low and the cold front should trigger showers
and thunderstorms. Some thunderstorms have the potential to be
severe due to the strengthening shear profiles. Damaging winds
seem to be the primary threat...but the threat for isolated
tornadoes cannot be completely ruled out with the surface low
nearby. There is also a threat for locally heavy rainfall as
well. There is the opportunity for multiple rounds of
thunderstorms Thursday night into Friday...and with PWATS around
2 inches this poses a threat for torrential downpours and
localized flash flooding. Confidence in timing of heaviest
thunderstorms and location remain low this far out...but there
is an elevated threat for severe thunderstorms with localized
flash flooding Thursday night into Friday.

The cold front will drop to the south Friday night and high
pressure will build overhead for the weekend. Drier....cooler
and less humid conditions are likely along with sunshine. The
high will likely move offshore early next week.

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
VFR expected through today. Early morning high clouds will give
way to a broken cumulus deck of clouds this afternoon with
cloud bases generally 3500-5000 feet. May be an isolated shower
at MTN. Winds today out of the northwest 5-15 knots.

For tonight, flow will gradually turn light northeasterly as
low level marine flow develops. This may bring a period of low
ceilings/fog with MVFR/IFR possible late tonight into Wednesday
morning. Confidence in placement/duration is low at this time.
Conditions improve by Wednesday afternoon, with a returning
chance later Wednesday night into Thursday morning. Winds turn
southeast by later Wednesday.

By Thursday, south/southwest flow returns along with increasing
chances for showers/thunderstorms late in the day.

Showers and thunderstorms are possible Thursday night into
Friday. Some storms may be severe and vsbys may be reduced to
IFR levels in heavy rain. High pressure will return for the
weekend with sunshine and VFR conditions.
-- End Changed Discussion --

&&

.MARINE...
SCA is in effect until 10 AM this morning as surge of northwest
winds occurs behind frontal passage. Winds should gradually
subside during the mid/late morning hours and remain generally
sub-SCA through Thursday morning. Wind direction will turn
northeast tonight, southeast on Wednesday, and south/southwest
later Thursday. Winds will increase again by late Thursday,
which should be our next chance of SCA conditions.

Showers and thunderstorms are possible Thursday night into
Friday. Some storms may be severe with damaging winds possible.
Storms may also contain torrential rains that reduce vsbys below
one mile at times. High pressure will return for the weekend. A
Small Craft Advisory may be needed for portions of the waters
Thursday through Saturday.

&&

.TIDES/COASTAL FLOODING...
Minor flooding is expected early this morning near Straits Point
in St. Marys County. A Coastal Flood Advisory is in effect until
5 am.

A northwest flow will cause anomalies to drop a bit today.
However...an onshore flow will develop tonight and persist
through Thursday. Elevated water levels are expected during this
time.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Coastal Flood Advisory until 5 AM EDT early this morning for
     MDZ017.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 10 AM EDT this morning for
     ANZ531>534-537-539>541-543.

&&

$$
SYNOPSIS...BJL
NEAR TERM...MM
SHORT TERM...MM
LONG TERM...BJL
AVIATION...BJL/MM
MARINE...MM
TIDES/COASTAL FLOODING...