Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
355 am EDT Friday Sep 19 2014
high pressure will build overhead 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 Saturday/...
high pressure is centered across Ontario this morning. A weak
frontal boundary will continue to move to the south of the
mid-Atlantic. High pressure to the north will begin to wedge down
the eastern Seaboard today.
Moisture is trapped below the subsidence inversion and against the
Blue Ridge/Virginia Highlands early this morning. Isolated-scattered showers due to
moisture convergence across the Piedmont may brush Nelson-
Albemarle this morning. A weak frontal boundary is located across
the mouth of the Potomac and central Piedmont and light nearly winds
will continue behind the frontal boundary this morning. Drier air
and subsidence has led to clearing across the northeastern half
of the County Warning Area with dewpoints in the upper 40s. Near and ahead of the
frontal boundary dewpoints are in the upper 50s leading to patchy
ground fog. Winds will veer to the east throughout the day as
high pressure noses into the area. Onshore flow will lead to
moisture banking up against the ridge lines across the Virginia Highlands and
central Blue Ridge. Elsewhere...partly sunny conditions expected
with forecast maximum temperatures in the upper 60s to low 70s today.
High pressure will move across New England later this afternoon and
out to sea by evening. Easterly flow will continue across the
region. Coverage of low stratus will increase and move northward
along the Blue Ridge...Shenandoah Valley and Potomac Highlands
High pressure will begin to weaken its hold on the middle-Atlantic
Saturday as it moves further out to sea. As with many cad
setups...stratus will slowly dissipate across the region although
winds become southerly. Sunshine is expected by Saturday afternoon with
forecast maximum temperatures reaching the middle to upper 70s.
Short term /Saturday night through Sunday/...
high pressure axis remains in place across the middle-Atlantic Saturday
night/Sunday morning between an offshore tropical low and a strong
cold front pushing across the Ohio River valley. Shallow low level
moisture present with weak onshore flow could result in patchy
ground/river fog developing overnight...and maintained mention for
favored areas. Warm air advection strengthens Sunday as low level
winds veer and 850 mb temperatures climb to the middle teens celsius. This warmer
airmass ahead of the approaching cold front should result in temperatures
reaching the low to middle 80s. Models now showing a relatively narrow
axis of moisture and instability Sunday afternoon...especially areas
west of the Blue Ridge...and have maintained mention of thunder
through the afternoon period. Will also see increasing deep-layer
shear through the day Sunday as potent short wave in base of long
wave trough swings across the southern Great Lakes. The timing of
the best instability and shear remain disconnected however...but a
few organized storms may be possible Sunday afternoon.
Long term /Sunday night through Thursday/...
instability drops off rapidly Sunday evening as front progresses
eastward. However shear increases so gusty showers are possible
through the evening along and ahead of the cold front. Good cold air
advection looks to begin a big earlier /now on late Sunday night/
and continues through Monday as upper short wave trough moves
overhead. Will see increasing northwest winds and much cooler/drier
air Monday. Should also see downsloping temperature effect for areas
east of the ridges on Monday. Temperatures will be chilly Monday night as
high pressure builds in from the west. This cool and dry airmass
will continue for the first full day of astronomical fall
-Tuesday...as well as Wednesday/Thursday.
Aviation /08z Friday through Tuesday/...
light nearly winds will become easterly today and onshore flow will
allow stratus to bank against the Blue Ridge today. MVFR ceilings are
expected at cho through tonight. Elsewhere...VFR scattered- broken ceilings
are expected. High pressure will continue to wedge across the
eastern Seaboard and MVFR ceilings will expand tonight reaching mrb
and possibly iad by Saturday morning. Ceilings may become IFR at cho
this evening. Winds will veer to the south by Saturday morning
and ceilings will become VFR from south to north Saturday.
A high pressure wedge will be in place for Saturday
night with areas of fog possible late. A cold front will bring the
chance of showers and storms as it crosses the area from west to
east Sunday afternoon through late Sunday evening. Winds will shift
out of the northwest and increase behind the front for Monday. Cool
high pressure will return for Tuesday and Wednesday.
nearly winds will increase behind an exiting frontal boundary this morning.
Winds will increase from north to south across the Bay and lower
tidal Potomac and a Small Craft Advisory is in effect for these zones. East-southeast winds will
continue through Saturday. Some gusts may approach Small Craft Advisory at times
this afternoon but due to the weak pressure gradient across the
waters kept them below at this time.
High pressure will shift south of the region Saturday
night into Sunday as winds veer south. A cold front will push across
the waters Sunday evening...bringing the chance of showers or storms
with gusty winds. Northwest winds will increase early Monday behind
the cold front...and a Small Craft Advisory may be needed for portions of the waters.
High pressure will return to the region for Tuesday and Wednesday.
anomalies have dropped below a foot this morning and coastal
flooding is not expected at this time.
An onshore flow is expected to continue late tonight through Sunday...causing
elevated water levels and the possibility of minor tidal flooding.
District of Columbia...none.
Marine...Small Craft Advisory until noon EDT today for anz530>534-537-