Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Baltimore Maryland/Washington District of Columbia
929 PM EDT Thursday Sep 18 2014
high pressure will build overhead for late tonight through
Saturday. The high will move off the coast Sunday and a stronger
cold front will pass through the area Sunday night into Monday.
High pressure will return for the middle portion of next week.
Near term /through Friday/...
moisture continues to pool and bank up against the Lee side of the
southern Appalachians and the foothills...while a weak cold front scrapes the
northern edge as it moves toward the coast. The front has allowed
another drier air surge to return from the north. Dewpoints across
the northern half of the County Warning Area are starting to drop into the M-u40s...a
good sign that it will be a cool night there. The stratification
of moisture however makes a decent-sized leap on the eastern side of
the Blue Ridge and particularly along The Lowlands of the I-95
corridor/coastal zones. Dewpoints will hang tight in the
u50s/l60s...keeping these areas more moderated for overnight lows
and down across the cho/I-64 corridor west/ additional dense overcast
skies. Used a blend of the adjmav and local WRF guidance for
high pressure will continue to wedge into the middle-Atlantic through
Friday...bringing mainly dry conditions along with below normal
temperatures. However...the flow will turn onshore and this may
cause clouds to get trapped underneath the subsidence inversion.
The deepest moisture will be across southern Maryland...central
Virginia and the Potomac Highlands where a few sprinkles cannot be
ruled out. Maximum temperatures will range from the lower to middle 60s in
the Potomac Highlands to the lower and middle 70s near Washington
Short term /Friday night through Sunday/...
high pressure will move off the New England coast and the surface
ridge axis will continue to extend south and west toward the middle-
Atlantic coast Friday night through Saturday. An onshore flow will
continue during this time...and it may lead to some low clouds
along with patchy fog...especially late Friday night into Saturday
morning. Clouds should give way to sunshine Saturday...and that
will cause maximum temperatures to be a bit warmer compared to
Friday...ranging from the 70s in the mountains to near 80 across
Washington and Baltimore.
A stronger cold front will approach the area Saturday night...but
the surface ridge axis should remain in place. Areas of low clouds
and fog are possible overnight Saturday into Sunday morning. The
cold will move into the area Sunday afternoon. A southerly flow
ahead of the front will cause warm and humid conditions. A few
showers and thunderstorms are possible Sunday afternoon ahead of
the cold front.
Long term /Sunday night through Thursday/...
a cold front will move across the region to the East Coast Sunday
night. There is a chance for showers along the front...mainly from
the Shenandoah Valley east to the Chesapeake Bay.
An upper level trough of low pressure will sweep across the region
Monday. There could be a few instability showers that develop
enlighten to this trough. For the most part...most areas should be
dry. High pressure will gradually build into the region Monday night.
High pressure should hang on to the middle Atlantic coast Tuesday
before it moves offshore and a surface cold front sags in from the
northwest and north late Tuesday into Tuesday night. With limited
moisture in place...most areas will be rain-free.
A second area of high pressure will build in behind the front and
usher in colder than normal air into the region Wednesday through
Aviation /00z Friday through Tuesday/...
onshore flow will develop late tonight through Friday...and this
may lead to low clouds across kcho. Also patchy br is possible
late tonight into Friday morning for kmrb and kcho.
VFR conditions are expected for most of the terminals Friday...but
low clouds may persist across kcho which could lead to MVFR
conditions. Low clouds may become more widespread late Friday
night into Saturday...and again late Saturday night into Sunday as
an onshore flow persists. A cold front will move into the
terminals Sunday afternoon...and a few showers and thunderstorms
a pressure surge is expected to develop behind an exiting cold
front overnight into early Friday morning...causing winds to
increase and a Small Craft Advisory is in effect for the Maryland
Chesapeake Bay and lower tidal Potomac River. However...it will be
marginal with gusts near 20 knots.
An east to southeast flow will continue Friday through Saturday as
high pressure builds off the New England coast. Wind gusts may
approach Small Craft Advisory criteria at times...but the gusts have been capped at
15 knots for now due to a relatively weak pressure gradient.
A cold front will approach the waters Sunday. A few showers and
thunderstorms are possible late in the day into Sunday night.
Winds will shift to the northwest behind the front...and a Small
Craft Advisory may be needed for portions of the waters Sunday
night into Monday.
tidal anomalies have increased to about 1 to 1.5 feet above normal
from the southerly flow Wednesday. The flow will be continue to be
light through this evening...before increasing and turning
toward the northeast late tonight. With no offshore flow to push
the water out of the Bay...these tidal anomalies are likely to
continue through tonight. A coastal Flood Advisory remains in
effect for the high tide cycle late tonight into early Friday for
Anne Arundel County through St Marys County.
Elsewhere...minor tidal flooding is possible near high tide late
tonight into early Friday. However...confidence is not high enough
for a coastal Flood Advisory at this point.
An onshore flow is expected to continue through Sunday...causing
elevated water levels and the possibility of minor tidal flooding.
District of Columbia...none.
Maryland...coastal Flood Advisory until 2 am EDT Friday for mdz017-018.
Coastal Flood Advisory until 5 am EDT Friday for mdz014.
Marine...Small Craft Advisory from 2 am to noon EDT Friday for