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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
915 PM EDT sun Aug 2 2015

Synopsis...
high pressure will dominate through tonight. A cold front will
approach from the northwest on Monday and enter the area Monday
night. The front will stall in the area Tuesday...slide southeast
Wednesday...then lift back north Thursday. A wave of low pressure
will then ride east along the front Friday. After this low passes
the front will slip south of the area over the weekend.

&&

Near term /through Monday/...
high pressure extends across the middle-Atlantic and central
Appalachians this evening. A cold front is dropping through the
Great Lakes. As the patch of denser cirrus exits to the east...the
bulk of the night will be mainly clear...although some additional
high clouds could enter from the west late. Combined with light
winds...this could lead to some patchy fog in the typical spots in
central Virginia and the western valleys...but the dry airmass looks to
hold firm and limit this potential. It looks like if there is dew
point advection...it will be into the southeastern counties...so
some of the valleys could still radiate out into the 50s.
Otherwise 60s for most and 70s urban centers/Bayshore.

Although the front will approach US Monday...the atmosphere will
not moisten appreciably (westerly flow except at the low levels)
and the bulk of the forcing will remain to the north. Depending on
the model of choice...some convection may sneak into the northern
Potomac Highlands (to perhaps as far east as the Martinsburg area)
by middle to late afternoon. If anything does hold together from the
northwest...the time of arrival looks to be more in the evening
time frame though. The pressure gradient will tighten up so there
could be some gusts around 20-25 miles per hour. The southwesterly flow will
drag warmer air north so highs will rise several degrees compared
to today. Highs will be in the low 90s in most areas with middle 90s
in the hottest spots. However dew points will only rise into the
lower to middle 60s so the heat indices will only be a few degrees
higher than the air temperatures.

&&

Short term /Monday night through Wednesday/...
front moves in Monday night. Shear does
increase...however...moisture will still be relatively limited
and this will in turn limit cape...so this should result in
thunderstorm activity having to advect into the area rather than
develop locally. Best forcing aloft will stay north. Thus...it
appears that storms which develop to our northwest will enter the
County Warning Area during the evening...but appear likely to diminish to showers
overnight...possibly even before reaching the metropolitan area. The
increased cloud cover should hold lows up a bit warmer than
tonight's readings. Places that receive any rain could also see
patchy fog overnight if some breaks in the clouds develop.

Low pressure in southern Quebec will be moving northward while a
Bermuda high persists in the Atlantic Tuesday. A cold front will
be stalled across the middle-Atlantic in the vicinity of the I-95
corridor Tuesday. Due to the time of year...the temperature
gradient is weak but drier air will be moving into the Potomac
Highlands. In vicinity of the front and in the warm/moist sector
isolated-scattered showers and thunderstorms are possible. Forecast soundings at
dca-nhk show 1-2k j/kg of SBCAPE with unidirectional shear. A
stable layer will likely be overcome by late afternoon and some
storms may produce gusty winds especially across S Maryland and
surrounding waters.

The cold front moves off the coast Tuesday night as high pressure
builds into the region from the SW. Dry conditions expected
Wednesday. Warm air advection will begin Wednesday afternoon as
the next system approaches.

&&

Long term /Wednesday night through Sunday/...
medium range guidance is gradually coming into better agreement
with the timing of a wave of low pressure moving along a stalled
boundary across the County Warning Area Wednesday night into Thursday. While finer
scale details remain to be seen...felt confident enough to go with
high chance probability of precipitation as the wave passes. Convection potential will
depend on exact timing/placement of the wave.

Guidance diverges after Thursday...with some solutions suggesting
the front sags far enough south to leave the area dry...while
other solutions keep the front stalled over the area with a second
wave of low pressure Friday into Saturday. Climatology would
suggest a slower southward progression of the front...and as such
have kept chance probability of precipitation in the forecast through the end of the week.

High pressure should attempt to make a return next weekend.

&&

Aviation /01z Monday through Friday/...
high pressure centered over the area tonight. Do not have very
high confidence of visibility reductions in br at the western terminals
but if it does occur cho would have the highest chance. A front
will approach from the northwest Monday...resulting in increasing S/SW wind
gusts to around 15-20 knots...but otherwise no aviation impacts with VFR
conditions expected through the day.

Mrb will have the highest chance of a shower/storm by early Monday
evening. Low confidence on how far S/east (i.E. The metropolitan sites)
this activity makes it before weakening. If it does hold together...sub-
VFR conditions would be possible. There is a low chance of br late
Monday night at mrb/cho as well as any location which sees rain.

A stalled cold front will be near the I-95 terminals Tuesday and
rain showers/thunderstorms and rain possible through Tuesday evening.

Sub-VFR possible in lower ceilings/visibilities associated west/ showers/thunderstorms Wednesday
night- Thursday. Wind direction forecast uncertain and depends on
placement of stalled front...but speeds should be light at or below 10 knots.

&&

Marine...
gustiest winds (up to 15 kt) this evening are over northern
sections of the Bay. Although winds overnight should be fairly
light with high pressure in control...there may be a few continued
gusts to 15 knots due to southerly flow over the Bay.

Winds will strengthen from the south on Monday as the pressure
gradient tightens ahead of an approaching cold front. This will
help winds to reach Small Craft Advisory levels by afternoon. Have kept Small Craft Advisory going
through Monday evening all waters...with the Small Craft Advisory for the Bay and
adjacent waters continuing through Monday night. Thunderstorms may
approach the waters from the northwest Monday evening...but should be on
a weakening trend if they do.

A stalled cold front will be near the waters Tuesday and showers
and thunderstorms are possible in the afternoon and early evening.
Some storms may produce gusty winds that may warrant a smw.
Depending on the location of the gradient...a Small Craft Advisory may be needed
Tuesday afternoon for portions of the waters.

Winds should remain below Small Craft Advisory levels Wednesday and Wednesday
night. Showers and scattered thunderstorms are possible mainly on
Thursday as a wave of low pressure approaches the waters along the
front. Should this wave of low pressure be stronger than what the
current consensus suggest then there is a chance of Small Craft Advisory gusts
Thursday...but confidence in any one solution is low at this time
given model spread.

&&

Tides/coastal flooding...
tidal anomalies remain below a half foot this evening. Southerly
flow ahead of the next front will elevate tidal anomalies on
Monday...but at this point we are not expecting minor flooding.
This possibility will require monitoring however.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory from noon Monday to 6 am EDT Tuesday for
anz530>534-537>543.
Small Craft Advisory from 3 PM Monday to midnight EDT Monday
night for anz535-536.

&&

$$
Synopsis...rcm
near term...ads/rcm
short term...has/rcm
long term...dfh
aviation...ads/has/dfh
marine...ads/has/rcm/dfh
tides/coastal flooding...ads/rcm

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