Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
928 PM EDT Friday Aug 22 2014
deep high pressure will remain centered over the deep south
through the weekend. Meanwhile...surface high pressure will build
southwest from New England...with an onshore flow across the
area. High pressure will center over the middle- Atlantic through the
middle of next week.
Near term /until 6 am Saturday morning/...
as of 01z...longwave ridge is across the central Continental U.S. With the axis
just west of the MS river. 1023mb surface high pressure is over
Labrador with a surface ridge extending southwest to the mid-Atlantic.
This is resulting in a backdoor cold front and onshore flow east
of the Blue Ridge. This surface high will continue to build southwest
through the weekend (and the onshore flow will continue through at
least monday). Low clouds spread west across the area overnight.
With stable onshore flow...the only cape remaining is west of the
Blue Ridge and diminishing. Showers and isolated thunderstorms
will persist over the central Shenandoah Valley and vicinity
through the late evening.
Min temperatures middle 60s inland (the onshore flow is actually drier than
the current air)...around 70f for nearshore urban areas.
Short term /6 am Saturday morning through 6 PM Saturday/...
the air mass over the middle Atlantic will remain moist Sat...hence skies will
again have plenty of clouds west/ chances for rain shower in the morning through midday. High
pressure off the New England CST will begin building into the middle Atlantic during
the afternoon. This could trigger some lightning but not xpctg a severe threat.
Skies could begin clearing in northestern Maryland by late afternoon.
Late Aug high temperatures should be in the m80s. Expect temperatures to be a few
degrees below that.
Long term /Saturday night through Friday/...
southward moving upper shortwave trough will push reinforcing
backdoor cold front across the middle-Atlantic Saturday night into
Sunday. Residual moisture before the frontal passage along with upslope flow
and upper trough energy should continue to produce showers across
mainly the Blue Ridge and Potomac Highland Sunday night.
Drier/cooler air pushes in behind the front with high pressure for
Positively tilted upper ridge and surface high pressure will
then dominate through middle next week with slowly moderating
temperatures and humidity. Position of upper flow looks to keep any
tropical system activity offshore the middle-Atlantic next week as
Return flow sets in with temperatures back to normal for Thursday
ahead of a progressive upper trough moving across the northern
Continental U.S.. this deepening trough drags a seasonably strong cold front
through the region for the end of the work week...with Friday
looking to be back in the upper 70s/low 80s at this time. Deep-layer wind
shear and instability may be favorable for some organized convection
with this cold frontal passage.
Aviation /01z Saturday through Wednesday/...
overcast and MVFR/IFR ceilings expeceted to spread west across the terminals
overnight. MVFR ceilings hold on much of Saturday with some rain
chances through the afternoon. Skies clear from increasing high
High pressure/VFR will prevail through midweek before a cold
front pushes through Friday.
backdoor cold front has brought onshore flow...chance of Small Craft Advisory
low...but winds will be around 15 knots through the weekend. Would
not be a surprise to see stronger gusts at times...required
statements and advisories.
Cold front may bring some showers to the Bay Saturday night.
Winds look to stay below Small Craft Advisory levels. High pressure will then build
across the area Sunday through middle week before another cold front
pushes through Friday.
District of Columbia...none.