Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
1038 am EDT Friday Aug 22 2014
an area of low pressure will move along a stalled frontal boundary
across the Middle Atlantic States late today and tonight. The front
will push southwest as a cold front Saturday. High pressure will
build south from New England into the middle Atlantic this weekend
into early next week.
Near term /through Saturday/...
Xpctg M cloudy to overcast skies this afternoon as the boundary remains stalled
across the region. 12z iad sndg shows a light wind field...not uncommon
for this time of yr. If there is a threat today it would likely be any
heavy rain cells that form would not be moving too fast...although not
xpctg flsh fld conds to develop.
Cloudy skies also helping to limit temperatures from rising too quickly.
Highs expeceted to be in the lm80s.
Sunset will again be the start of thunderstorm dissipation west/ only a handful
of showers continuing to slide across the area into the late night
hours. Dewpoints will continue to hover near 70f for another humid
overnight. Batches of middle cloud decks will also help shelter the
area and keep overnight lows moderated near the 70f mark.
Toward sunrise Sat...the dynamic transition will begin to take place
off to our north and east. The upper low sitting over the Great
Lakes for the past couple of days will be absorbed into the upper
flow and help dig the retrograded portion of an upper trough back
over the area on Sat. The last arm of this feature will drift across
the region during the daytime hours and bring more scattered showers
and thunderstorms. High temperatures will be their coolest in days but still
reaching the l80s by middle afternoon. However...the instability profile
will look more like thu's...W/ surface-based convective available potential energy potentially in the
1-1.5k range west/ a cooler upper level temperature profile from the upper
trough passage. Stability may come however in the form of an Ely low
level wind...which could limit the convective initiation potential
if the cap is too strong and surface temperatures don't reach the appropriate
levels - espec closer to the Bay and near the Mason-Dixon line.
Short term /Saturday night through Sunday night/...
Surface hipres will be building down the coast Sat ngt-sun. As 500 mb ridge axis
continues to sharpen...drier air will be entrained...and gradually erode the
low level maritime saturation. That will hppn first along I-95 Sat evening.
Think we/ll need to hold onto probability of precipitation for the mountains all night Sat. First
clearing will come to metropolitan balt Ely sun...and will spread that to the SW
across the remainder of the County warning forecast area throughout the day. Sunday will be a nicer
day than Sat...even for the mountains which may average out as ptsun vs mosun
/or even sunny/.
Since itll be cloudy...and dewpoints will be dropping through the 60s...didnt
lower min-T as much as I could have. Am taking a reserved approach...W/
min-T in the 60s as well. Did go on the cooler edge of maxt guidance for
sun...but believe prolonged Ely fetch will keep temperatures fairly close to
Long term /Monday through Thursday/...
Surface hipres and 500 mb ridge axis continue to build over the middle Atlantic through the
extended period. Flow will be light...but temperatures will gradually be moderating by
A cold front dropping toward the area lt weak will provide the only precipitation risk
during the work week.
Aviation /15z Friday through Tuesday/...
M cloudy skies today...although VFR. Scattered showers and late-day thunderstorms
possible again across the region. Conds will improve again
overnight...though a few isolated showers and more dense cloud
cover is expected into early Sat west/ more shower/thunderstorms expected on
May have some low clouds or patchy fog to start the day sun...otherwise VFR
will prevail through Tuesday.
Small Craft Advisory conditions not anticipated today or tonight. A few thunderstorms
possible this afternoon/evening over the waters. Ely onshore flow will
strengthen into early Sat...W/ some possibly marginal Small Craft Advisory conditions
along the Western Shores and main Stem of the Maryland Bay.
Ely/northeasterly flow will prevail Sat night into sun as hipres drains
cooler/drier air across waters. Guidance suggests winds will remain at or below 15 knots
during this time. Will go that Route in the forecast at this time...but wudnt be
shocked if a few higher gusts approached Small Craft Advisory crit in the Main Channel
of the Middle Bay. Beyond that...winds will lessen as hipres builds.
District of Columbia...none.