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Office: LWX

FXUS61 KLWX 161421

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1021 AM EDT Mon Jul 16 2018

High pressure will remain over the Atlantic through tonight. A
cold front will approach the area Tuesday before passing through
Tuesday night. High pressure will return for Wednesday and
Thursday before moving offshore Friday. Low pressure may impact
the area during the weekend.


High pressure will be positioned in the western Atlantic today,
with the forecast areas impacted by heat and humidity due to
light south flow. Still seeing some mid to high level clouds
across central Virginia and southern Maryland as shortwave
energy moves off to our south. Any early morning mountain valley
fog has dissipated.

Looking for showers and storms to form once again this afternoon
over the mountains, with the bulk of the activity residing mostly
along and west of the Blue Ridge. While CAMs suggest some spread
in coverage, the majority of solutions keep the metro corridor
dry. Will have a 20-30 percent chance along I-95, but greater
odds to the west. With plenty of instability and minimal shear,
thunderstorms likely to be pulsy in nature. Would not rule out
a localized strong wind gusts, but it would be the exception.
Primary impact would be brief heavy rain. Believe recent dry
conditions and at least some flow would preclude a widespread
flood threat.

Temperatures appear on track to reach 90-95. Coupled with
dewpoints hovering in the lower 70s, we will see heat indices
just shy of Heat Advisory criteria. Will continue with a
sub-Advisory forecast...but not by much.

Showers and thunderstorms will decrease in coverage this evening
and overnight, as winds favor a southwesterly trajectory at 5
to 10 mph. This will maintain muggy conditions overnight, and
lows will range in the 70s area wide, with upper 70s likely
along and east of the I- 95 corridor.


The cold front currently over the upper Midwest and western
Great Lakes region will be knocking on our doorstep on
Tuesday. Expect widespread showers and storms, favoring Tuesday
afternoon and the evening hours as the front crosses the area.
Precipitable water values will be in excess of two inches, which
will support at least an isolated threat for localized flash
flooding despite the dry conditions observed over the last few
weeks. There is some indication of the potential for strong to
severe storms, particularly over portions of north central
Maryland where a Marginal Risk of severe storms has been
highlighted by the Storm Prediction Center (SPC). Moderate to
high CAPE values ahead of the front will range in the 2000-3000
J/Kg range, with some modest 0-6km shear will support the chance
for damaging wind gusts. Again, this looks to be an elevated
threat for severe and/or flash flooding, but not a significant
threat at this time.

Model guidance is in general agreement of the front moving east of
the region by around midnight, with drier conditions winning out
in its wake. Lows Tuesday night will range from the upper 50s
over the Allegheny Front to near 70 degrees in the cities.
Canadian high pressure will build in behind the front,
delivering cooler and less humid conditions area wide. Highs on
Wednesday will top out in the lower to middle 80s, with
dewpoints in the upper 50s to near 60 degrees. Lows Wednesday
night will be in the 60s with no threat of rain Wednesday or
Wednesday night.


High pressure will build remain overhead for Thursday, bringing
dry and seasonably warm conditions, but with low humidity.
Dry and mild conditions are expected Thursday night with high
pressure remaining in control.

The high will move offshore Friday and low pressure both at the
surface and upper-levels will cutoff from the jetstream over the
Great Lakes. A return flow will result in slightly more humid
conditions. A warm front associated with the low will remain to
our south, so although a stray shower or thunderstorm is
possible it appears that most areas will be dry on the stable
side of the warm front.

The cutoff upper-level and surface low is expected to remain
nearby over the Great Lakes Friday night through the weekend.
This will allow for the warm front to lift north through our
area. Also, there may even be a coastal low that develops due to
jet dynamics interacting with the Mid-Atlantic Coast. Details
still remain highly uncertain, but with an anamolous upper-
level low to our west and deep moisture advection it does appear
that there will be at least an increasing chance for showers
and thunderstorms during the weekend.


Generally VFR flying conditions this morning at all terminals.
Afternoon showers and storms will ignite once again over the
mountains, with MRB seeing the highest chance of sub VFR
VIS/CIGs. A shower or thunderstorm could impact terminals
further east, but best chances will reside along and west of the
Blue Ridge, thus no mention of SHRA or VCTS for DCA/BWI/MTN at
this time. Any impact will produce brief periods of MVFR/IFR
VIS, with CIGs remaining AOA FL050.

Cold front will approach and cross the terminals Tuesday,
delivering widespread showers and storms, and periods of
MVFR/IFR VIS/CIGs. Favored time period of impact will be Tuesday
afternoon and early evening, with strong gusty winds a
possibility with any stronger thunderstorms. Winds will turn
northwesterly behind the front Tuesday evening, and high
pressure will build over the terminals through Wednesday,
resulting in a return to VFR flying conditions.

High pressure will remain over the terminals Thursday before
moving offshore Friday. VFR conditions are expected during this


Light southerly flow will persist today before increasing this
evening and overnight. This will bring a better likelihood for
SCA wind gusts over portions of the Bay and lower Tidal Potomac.
As such, an SCA will go in to effect from early this evening
into early Tuesday morning. A cold front will approach and cross
the waters Tuesday afternoon and evening, with showers and
thunderstorms expected to impact the waters. Some storms could
be strong, producing gusty winds and the need for Special Marine
Warnings. Be sure to have your weather radio handy to receive
alerts should warnings be issued.

In the wake of the front Tuesday night, wind gusts will near SCA
criteria as winds turn northwesterly. High pressure will build
in behind the front on Wednesday, promoting lighter northerly
breezes and likely sub SCA conditions.

High pressure will remain over the waters Thursday through
Thursday night before moving offshore Friday. Low pressure may
impact the waters during the weekend. Winds may approach SCA
criteria later Friday into the weekend.


A southerly flow will continue to bring elevated water levels
through Tuesday. The flow will be just west of south most of the
time so most high tides should be around caution stage. However,
water levels near minor flood stage are possible for sensitive
areas tonight into Tuesday morning during the higher of the two
high tides.


MARINE...Small Craft Advisory from 5 PM this afternoon to 9 AM EDT
     Tuesday for ANZ532>534-537-540-541-543.