Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
837 am EDT Friday Oct 31 2014
high pressure located over the area will move offshore today. Deep
low pressure will descend from the Great Lakes...crossing the
Carolinas Saturday before strengthening along the New England
coast Sunday. High pressure will then return into Monday followed
by another cold front during midweek.
Near term /through Saturday/...
West.V. Satellite imgry shows short WV has pushed into WI. This will dive
to SC as upper level pattern undergoes substantial amplification
and northern and southern streams phase offshore. Surface low is weak at
this time and will lose definition as energy eventually transfers
a coastal low off the Carolina coast on Saturday. With such a
southward trajectory...forcing will be focused over the mountains
for the first stage of this system. Some rain showers are possible
this afternoon there but much of central Maryland and Virginia will be in a
squeeze play until tonight or Saturday when the system winds up
and broad scale lift will produce showers area-wide.
However...any heavier precipitation from the coastal low will
likely remain to the east of the area.
In terms of any snowfall...at least through Saturday cold advection
will be very minimal with this occluded system. An analysis of
soundings and low level thickness suggest that any snow will be
limited to the very highest elevations of WV...and mostly as a
rain/snow mix at that. The snow will be favored during diurnal
minimums in temperature and any slushy accumulations will be minor.
High temperatures today will range from the upper 40s at higher
elevations to near 60 in The Lowlands. Lows tonight tempered by
cloud cover in ranging from the middle 30s Highlands to middle 40s east.
Precipitation Saturday will be most widespread west of the Blue
Ridge on Saturday and will limit highs a bit more there...well into
the 40s. Still near 50 to the east. Northerly winds will also
increase on Saturday as the low strengthens off the coast.
Short term /Saturday night through Sunday night/...
By Sat night...shortwave energy would have shifted off the Atlantic CST...inducing
cyclogenesis somewhere off Cape Hatteras. In terms of precipitation east of the
aplchns...that pretty much will mark the end...as drier air will work in
on the northwest side of the cyclone. Have opted to hold onto more clouds than
GFS indicating...partly due to timing/uncertainty diffs and the
other part due to low 500 mb heights/positive vorticity advection still pivoting across County warning forecast area. Winds
may be the biggest impact...but the nocturnal timing may prevent the
full 30-40 knots available h9-8 from mixing down. Will be keeping gusts 25-30
miles per hour.
Across the mountains...the air mass will be cooling sufficiently for some snow.
However...the best dynamic cooling will pass S of area. This leaves only
a marginally favorable air mass west/ warm grnd. Have trimmed snow ttls back a little.
Will keep severe weather potential statement mention...as its not out of the qstn that accums
potentially could yield an advisory. Decisions will be made as event nears.
800 mb-5 ridging builds quite quickly Sunday...shutting off upslope shsn.
Downslope flow will erode most of the clouds during the morning. The incrsg
subsidence will take care of the mountains by midday. Will have a tight p-gradient
over area for much of the day...and better mixing. GFS quite
enthusiastic on 35-40 knots winds. That remains to be seen...but do have
30-35 miles per hour gusts in grids.
Am preserving a good amount of forecast continuity for temperature forecasts through this
period. Biggest change comes Sat night...as the strong gradient suggests that
any temperature loss will primarily be advective. That means min-T in the 30s
areawide Sat night/Sun morning...and temperatures struggling to reach 50f Sun
Ridging builds over area Sun night...W/ all the associated features-- clear
skies/dcplg winds/dewpoints in the 20s. Its looking like a hard freeze
for most of the County warning forecast area xcpt for the urban downtowns and communities
near the Bay. That likely will mark the end of the growing season.
Long term /Monday through Thursday/...
the high slides southeast across the Carolinas and near the
southeast coast Monday and Monday night. Temperatures will modify
some during the day but remain a little on the chilly side Monday
High pressure slides offshore Tuesday through Wednesday night to
allow a cold front to gradually slide into the region and bring a
chance for rain showers. Precipitation timing has been pushed back to
Wednesday-Wednesday night. High pressure will build on Thursday.
Aviation /13z Friday through Tuesday/...
A low pressure system will approach from the west today and tonight
but any precipitation should stay west of the taf sites through most
of this period. A VFR ceiling may be prevalent with very few breaks
with the appraoching system.
As low pressure strengthens off the coast on Saturday...northerly
winds will gust up to 20-25 knots and MVFR ceilings will be possible
Winds will provide primary op impact Sat ngt-sun...as an elevated core
of 40+ knots winds cross terminals. The low level jet will reside about 2k feet above surface.
Should have 25-30kt gusts in northwest flow at grnd level...maybe a little higher than
that sun mrng-midday. Any ceilings would be MVFR-VFR Sat night and should clear
by/soon aftr sunrise Sun morning.
VFR Sun afternoon into Tuesday.
East to northeast winds under small craft conditions will prevail
today and tonight as a low pressure system passes west and south of
the area. With the strengthening low moving off the coast on
Saturday...small craft conditions will be met with northerly winds
gusting to around 30 knots.
Gradient increases Sat night. Am not certain if glw will encompass
entire marine area...but it should hit a majority of it. Since the glw
would means a headline ramp-up in the 4th period...have opted to not issue
at this time per policy. Nonetheless...the open waters of the Middle Bay should
experience 35-40 knots gusts. Conds would continue into sun before the
gradient relaxes and winds subside. Small Craft Advisory conds prognosticated to hold on through
Sun night per current forecast.
As hipres builds Ely next week...no hazards expected at that time.
a deep area of low pressure will cross the Carolinas Saturday
morning and then track northeast along the middle-Atlantic coast
Saturday night. Positive departures up to a half foot on the
waters at this time...and these may increase a little bit more through
tonight. Tidal flooding issues would only occur if departures
exceeded a foot. At this point...suspect that wont happen.
Blowout conditions are expected Sat afternoon through Sunday.
District of Columbia...none.
Marine...Small Craft Advisory from 8 am to 8 PM EDT Saturday for