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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
948 am EDT Thursday Jul 31 2014

Synopsis...
surface high pressure remains over the western Atlantic...and will
spread its influence inland. Meanwhile...upper level low pressure
over eastern Ontario continues to send upper level disturbances
eastward. A coastal front will develop Friday night...lasting
through this weekend into early next week.

&&

Near term /through tonight/...
our area will remain between an upper-level disturbance moving
into New England today...and another one passing through the
southeastern Continental U.S.. high pressure will remain along the eastern
Seaboard...and a southwest flow is expected around this high. This
will cause somewhat warmer and more humid conditions compared to
recent days...but still comfortable for this time of year. Maximum
temperatures will range from the 70s in the mountains to the middle 80s
across most other locations.

A stray shower cannot be completely ruled out this afternoon...but
the forecast remains dry. This is due to weak instability along
with little to no forcing since shortwave energy is both to our
north and south. There will be a scattered/broken cumulus deck developing this
afternoon.

Thte ridging and middle-level convergence increase tonight. Thus...would anticipate building
middle deck clouds...rising dewpoints and potl crrdr of precipitation. Both NAM/GFS
have this...though the NAM seems excessively wet for the situation. Have
sided west/ GFS...which brings chance probability of precipitation just east of The Spine of the
blurdg past cho toward District of Columbia. Low level winds in this area southeasterly around periphery
of ridge...which would add a little upslope support for precipitation development. Quantitative precipitation forecast
light...and am keeping probability of precipitation no higher than 30 percent...gnly lt night/overnight
hours. Since dewpoints should be able to crack the 60 degf barrier...min-T
will be in the 60s...and a bit higher than that for dca/dmh.

&&

Short term /Friday through Friday night/...
pttn change will manifest itself Friday...as h9-7 confluence will coax Gulf of Mexico
moisture northeastward. Will still have a thte ridge situated over the mountains...so a
crrdr of favorable isent upglide will reside coindicent west/ low level lift. Will
raise probability of precipitation to likely by afternoon. Soundings look fairly satd throughout...and am
overall not too impressed by cnvctv potl-- rain showers not thunderstorms and rain.

A coastal fnt may develop by evening...W/ a shortwave riding northward lt night. Guidance
struggling a bit west/ its development/placement vs ridging on the back side
down the I-95 crrdr. That will dicate precipitation timing Friday night. Thte seems
to be shunted toward the CST...and since frontogenesis plausible...will
aim probability of precipitation that way.

Per temperatures...maxt Friday will be held down by clouds and possible precipitation. Most
guidance suggesting upper 70s/lower 80s. European model (ecmwf) distinctly lower...especially in
centrl shen valley and ptmc Highlands. Have minimzed range for min-T Friday
night due to wet air mass. Dewpoints led the way.

&&

Long term /Saturday through Wednesday/...
the middle-Atlantic will continue to be influenced by cyclonic flow
aloft through the long term. An upper level trough will approach
the Ohio Valley Saturday. High pressure is expected to lift to
the northern Atlantic while a coastal front remains along the East
Coast. Showers will be possible along the frontal boundary near
the Chesapeake Bay Saturday. Showers and thunderstorms will also
be possible across the Ohio Valley and west of the Blue Ridge
Saturday afternoon as this region will gain instability throughout
the day. The trough will approach the middle-Atlantic Sunday and
large scale forcing will increase across the region as positive vorticity advection
increases and the entrance region of the jet moves close by.
Southerly flow will continue to draw moisture into the region and
showers and thunderstorms are expected. A weak front will cross
the region Sunday night into Monday and showers should move to the
east by Monday midday. Forecast maximum temperatures will be below normal this
weekend...in the low to middle 80s.

The start of the work week looks quiet at this time as high
pressure moves in behind the weak cold front. By Wednesday and
Thursday...return flow begins and showers and thunderstorms will
be possible. Forecast maximum temperatures will be near normal next week.

&&

Aviation /14z Thursday through Monday/...
VFR conds expeceted tda-tngt. A scattered/broken cumulus deck will develop around
5-7kft. These will thicken tonight...W/ ceilings forecast at same range. Fog will
again be a wild card predawn tmrw...but so may scattered rain showers. Due to low
confidence...will be keeping VFR forecast.

Moisture profile increases Friday-Friday night...so rain showers chances increase. These may
prompt flgt restrictions...W/ periods VFR in between.

Rain showers/thunderstorms and rain possible Saturday afternoon and Sunday as an upper level
disturbance approaches. MVFR possible early Sunday morning. High
pressure moves into the region for the start of next work week.

&&

Marine...
southerly flow is expected this afternoon...but wind speeds should
remain below Small Craft Advisory criteria due to the relatively cooler waters. Low level jet
increase tonight. Not sold on Small Craft Advisory conds yet...but WRF suggesting will have a
better chance at it. Have capped grids below Small Craft Advisory...but its not out of the
realm of psbltys.

Winds back Ely Friday-Friday night. Spds not a factor...mainly below 10 knots.
Precipitation chances do increase...which would obstruct visibility.

A coastal front will remain near the Chesapeake Bay Saturday and
Sunday before a weak cold front moves through the region from the
west. Showers and isolated thunderstorms possible on the waters during
this time.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...none.

&&

$$
Synopsis...heights
near term...bjl/hts
short term...heights
long term...has
aviation...bjl/has/hts
marine...bjl/has/hts

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