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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
350 am EDT Friday Jul 25 2014

Synopsis...
high pressure will remain over the region through tonight before
moving off the coast Saturday. An upper-level disturbance will
pass through the area Sunday and a potent cold front will move
through Monday. High pressure will return for the middle portion
of next week.

&&

Near term /through tonight/...
after the Post-frontal reprieve yesterday...our temperatures will make a
slight turn back toward the warmer side that will gradually increase
over the next few days. However...dewpoints will take a slight
downward turn today...leveling-off the temperature increase and making
today less humid than yesterday. The metropolitan areas will see highs
top-out in the m80s...while l80s will be common across the rest of
the County Warning Area. Water vapor imagery at this time shows our region as the "driest"
in the country - at the middle-levels of the atmos. This regional-sized
area of subsidence will eventually mix down some of the drier air
through the boundary layer as the surface High Rolls over the area and
toward the middle Atlantic coast.

As this feature moves east later tonight...winds will turn back
toward southerly and again begin the low-level moisture increase.
Dewpoints later tonight will climb back into the l60s from the shen
valley toward the east over time. No substantial weather-change from this
return flow overnight but it will set-up the area heading into the
weekend for a return to the warmer/humid conditions - and an active
atmos to start the coming week.

&&

Short term /Saturday through Saturday night/...
high pressure will move out into the Atlantic Saturday through
Saturday night. A southerly flow will allow for warmer and more
humid conditions to return. Maximum temperatures Saturday will range from the
70s in the mountains to the upper 80s/near 90 in the Washington
and Baltimore metropolitan areas.

The heat and humidity will lead to an unstable atmosphere
Saturday afternoon and evening. A few showers and thunderstorms
are possible...but with the lack of a strong lifting
mechanism...convection coverage will be isolated or widely
scattered.

A potent shortwave in the westerly flow aloft will approach the
area Saturday night. Most of the forcing should remain to the
west...but a surface trough will strengthen a bit over the area.
Therefore...a few showers and thunderstorms will remain possible
Saturday night. Min temperatures will range from the 60s in the mountains
to the middle 70s in downtown Washington and Baltimore...and it
will feel noticeably more humid.

&&

Long term /Sunday through Thursday/...
the potent shortwave will pass through the region Sunday in the
westerly flow aloft. The forcing from the shortwave will combine
with some instability from a warm and humid airmass to bring a
better chance for showers and thunderstorms. Shear profiles do
support the possibility of severe thunderstorms...but there is a
question regarding the coverage because plenty of high and middle-
level clouds may limit instability. As of now...there is at least
an isolated threat for locally damaging wind gusts. Locally heavy
rainfall is more likely in showers and thunderstorms Sunday. With
precipitable waters over 2 inches and the possibility for training
convection...this does pose a threat for flash flooding.
Again...the extent of flash flooding will be dependent on how much
instability can develop.

The shortwave will move off to the east Sunday night...but an even
stronger shortwave and its associated cold front will approach
from the Ohio Valley. More showers and thunderstorms are possible
Sunday night ahead of this system.

The cold front will pass through the region Monday...bringing the
chance for showers and thunderstorms. If this system is slow
enough...then there will be enough heating for severe
thunderstorms since shear profiles will be extremely favorable.
Damaging wind gusts and large hail would be the primary
threats. Details are still uncertain due to the high uncertainty
with the timing of the front.

High pressure will build in behind the front for the middle
portion of next week...bringing noticeably cooler and drier
conditions.

&&

Aviation /07z Friday through Tuesday/...
light northwest flow persists over the area into the overnight hours. Some
calm ob sites and the typical fog-prone northern Virginia Valley locations west/ the
patchy dense ground fog/low stratus. The kcho area particularly
under the most fog prone conditions tonight after the longer period
of rain showers from yesterday's activity. Confident that most areas
will remain in solid VFR west/ only the kcho area wavering west/ the
recent rainfall...low-level winds decoupling and terrain-induced valley
fog.

Post-sunrise the leftover ground fog will mix-out and temperatures will
stay at a reasonable l-m80s for highs. Only scattered batch of
clouds today and again quiet heading into the overnight hours.

Patchy br is possible Saturday morning...especially across the
western terminals. Otherwise...VFR conditions are expected with a
south-southwest flow. A few showers and thunderstorms are possible
Saturday afternoon and Saturday night...but coverage will be
limited. Patchy br is possible overnight Saturday into early
Sunday. A potent upper-level disturbance will pass through the
terminals Sunday into Sunday evening...bringing a better chance
for showers and thunderstorms. Thunderstorms may contain gusty
winds and locally heavy rainfall that could reduce ceilings/visibilities to
IFR levels at times.

A potent cold front will approach the terminals Sunday night and
pass through Monday. More showers and thunderstorms are possible
ahead of the front. High pressure will return for Tuesday with a
northwest flow.

&&

Marine...
marginal Small Craft Advisory conditions appearing in observation overnight from the weak northerly
channeling over the main Stem of the Maryland Bay. These winds will likely
switch toward southerly overnight tonight as the surface High Rolls over the
region and the off the coast.

Southerly winds are expected around high pressure over the
Atlantic for Saturday and Sunday. Winds may gusts past Small Craft Advisory
criteria over portions of the waters Saturday night into
Sunday. A cold front will pass through the waters Monday and
northwest winds may gust past Small Craft Advisory criteria behind the front Monday
night and Tuesday.

Showers and thunderstorms are possible Saturday through Monday. As
of now...it appears that the best chance for thunderstorms will
Sunday and Monday. Thunderstorms may contain gusty winds and
locally heavy rainfall that could reduce visibilities below a mile at
times.

&&

Climate...
59 degrees is the forecast for BWI early this morning. The record
low for the threaded Baltimore climate record is 59...set in
2008... 1976...1973...and 1876.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory until 8 am EDT this morning for
anz531>534-537-539>543.

&&

$$
Synopsis...bjl
near term...gms
short term...bjl
long term...bjl
aviation...bjl/gms
marine...bjl/gms
climate...bjl/baj/ceb

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