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

high pressure will remain over the region through Friday...but a
series of upper-level disturbances will pass through during this
time. A coastal front will develop Friday night...lasting through
this weekend into early next week. Upper-level disturbances will
continue to move over the area during this time.


Near term /through Friday/...
an upper-level disturbance is tracking into upstate New York and
New England this afternoon while another tracks through the
Carolinas into southern Virginia. High pressure will remain along
the eastern Seaboard...and a southerly flow is expected around this
high. This has caused 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

The upper-level disturbance to our south will move northeast into
our area tonight. This will bring more moisture with it. The warm
and moist air will overrun the relatively cooler air in
place...resulting in increasing clouds along with a better chance
for showers. Precipitation amounts will still be light due to a
lack of instability. Precipitation amounts will range between a
few hundredths up to a quarter inch. The best chance for
precipitation will be late tonight across central Virginia.

Surface high pressure will remain along the New England and middle-
Atlantic coasts. A southeast flow will continue to usher in
moisture off the Atlantic Ocean...while more warm and moist air
stream in aloft in the southwest flow. A series of upper-level
disturbances will pass through during this time. Showers are
likely...especially near and west of the Blue Ridge where forcing
will be stronger and heights will be lower. Maximum temperatures will range
from the 60s and lower 70s in the mountains to the lower and
middle 80s near Washington and Baltimore.


Short term /Friday night through Sunday/...
a coastal front will develop along the middle-Atlantic coast Friday
night and it will remain nearby through Sunday. The forecast
remains uncertain at this time due to the uncertainty with the
exact location of the front along with timing of upper-level
disturbances that will pass through in the southwest flow aloft.

A potent upper-level disturbance will likely pass through Friday
night...bringing a good chance for showers and perhaps a couple
thunderstorms. Showers will remain possible for Saturday...but the
coverage of the showers will be dependent on the location of the
coastal front. If the front is farther west into our area...then
more instability will result in more showers. However...if the
front is closer to the coast...then it will be more stable with
with showers being widely scattered. Models do converge on
bringing the coastal front farther west Sunday...which should
result in a better chance for showers and thunderstorms.


Long term /Sunday night through Thursday/...
series of weak 500mb troughs and positive vorticity advection will affect County Warning Area through the
period. Upward vertical motion and moisture greatest over Virginia
Tidewater...southern Maryland and Chesapeake Bay Sunday night through
Monday night. Dry airmass will replace surface low pressure trough
and associated moisture by Tuesday. Cold front will enter County Warning Area early
Wednesday. Associated moisture...upward vertical motion and positive vorticity advection will
move over County Warning Area Wednesday morning/afternoon.

Greatest chance of precipitation Sunday night into Monday evening
and again Wednesday.


Aviation /18z Thursday through Tuesday/...
VFR conditions are expected through this evening. Southerly winds
this afternoon will become light and variable. A series of upper-
level disturbances will bring more clouds tonight through Friday
along with a better chance for showers. Subvfr conditions are
possible in showers...especially across kcho.

Moisture will continue to stream in from the Gulf of Mexico and
Atlantic Ocean Friday night through Sunday...bringing a good
chance for showers and even some thunderstorms. Details are still
uncertain this far out. High pressure may briefly build overhead
early next week.


high pressure will remain along the middle-Atlantic coast through
tonight. Southerly winds will channel up the Chesapeake Bay and
lower tidal Potomac River. A Small Craft Advisory is in effect
tonight for the Maryland Chesapeake Bay from Sandy Point to Smith
Point and the lower tidal Potomac River from Cobb Island to Smith

A coastal front will develop along the middle-Atlantic coast Friday
through early next week. A southerly flow is expected most of the
time...but the gradient should be relatively most of the
time winds should remain below Small Craft Advisory criteria.


Tides/coastal flooding...
a southerly flow will continue through Friday. The flow will
strengthen late tonight into Friday morning and this will cause
tidal anomalies to increase. The high tide will be the higher of
the two Friday water levels will be close to minor
flooding thresholds. However...current feeling at this time is
that water levels will remain just below minor flooding thresholds
since the astronomical norms are a bit lower since we are headed
toward the first quarter phase of the moon.


Lwx watches/warnings/advisories...
District of Columbia...none.
Marine...Small Craft Advisory from 6 PM this evening to 6 am EDT Friday
for anz532>534-537-540-541-543.


near term...bjl
short term...bjl
long term...cem
tides/coastal flooding...bjl

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