Scientific Forecaster Discussion
fxus61 klwx 060220
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
920 PM EST Thu Dec 5 2019
high pressure will move offshore of the Carolinas through
tonight. A pair of low pressure systems will split the mid-
Atlantic to the north and south Friday, with a cold front in
between crossing the region from west to east by evening. High
pressure will follow for the weekend, before a stronger area of
low pressure develops over the mid-Mississippi Valley and tracks
northeastward toward the eastern Great Lakes early next week.
Near term /until 7 am Friday morning/...
winds have taper off this evening with sporadic gusts up to 15
knots. Some higher clouds have moved into our region but they
remain mostly above 20k feet. Low temperatures tonight will be
in the upper 20s to lower 30s with cooler temps along the
Allegheny frontal range, though the high clouds could thicken
enough to keep it a bit warmer.
Short term /7 am Friday morning through Saturday night/...
a weak area of low pressure moving through the Great Lakes and
a shortwave trough to our south will allow a weak cold front to
move through the County Warning Area Friday night. With high pressure banked
offshore and westerly flow off the surface, not expecting much
in terms of precipitation with this frontal passage for the majority of
the County Warning Area. Any precipitation would be mainly along/west of the
There will be a bit of a warm up ahead of the front, with highs
in the upper 40s and lower 50s. Given above freezing
temperatures, even across the higher terrains prior to the
fropa, any precip would fall mainly as rain, however can't rule
out the possibility of a few wet snowflakes mixing in towards
the end. Behind the front, a large/strong area of high pressure
originating from Canada will build in to start the weekend.
Cold advection will result in lows below freezing in many areas
and highs in the 40s.
Long term /Sunday through Thursday/...
overall, model guidance is in good (above average) agreement
through the long term. A narrow but strong ridge is progged to
build over the eastern Pacific, moving eastward Sunday into the
first half of next week, forcing downstream troughing over the
central Continental U.S.. there are differences in sub-synoptic scale
timing/strength differences, which will ultimately determine the
magnitude of precipitation across our area as a cold front
trailing low pressure over the Midwest encroaches on the region.
Chances for rain are high (above 50 percent) as this system
moves through, most likely peaking in the day 5/Monday period as
warm/moist advection strengthens ahead of the slowly advancing
This system will slowly push eastward, and secondary low pressure
development is possible near or over the area during the middle of
next week before the front finally clears the coast, prolonging
chances for precipitation. Behind the front, there is reasonable
model agreement on well below normal temperatures as the
aforementioned ridge building over western North America dislodges
Arctic cold and sends in southeastward in our general direction.
Aviation /02z Friday through Tuesday/...
VFR conditions expected through Saturday night. High pressure
will move offshore Friday and a southerly flow will develop. A
cold front will pass through Friday evening, and a wind shift to
the northwest is expected behind the boundary. High pressure
will return for Saturday and Saturday night.
Mainly VFR sun, with restrictions in showers becoming increasingly
likely Mon-Tue as a low pressure/cold front approach from the
high pressure will move offshore Friday and a southerly flow
will develop. An Small Craft Advisory is in effect for the waters Friday morning
through the afternoon periods.
A cold front will pass through the waters Friday evening and an
Small Craft Advisory is in effect for the middle portion of the Bay and lower
tidal Potomac River. The Small Craft Advisory may be needed for the upper tidal
Potomac River and Northern Bay as well, but confidence is too
low at this time. High pressure will build overhead Saturday
into Saturday night, and winds should be below Small Craft Advisory criteria most
of the time.
Winds should be relatively light out of the southwest as high
pressure shifts offshore Sunday, but winds will likely increase into
early next week as gradient tightens between departing high and
approaching/strengthening low pressure over the Midwest.
District of Columbia...none.
Marine...Small Craft Advisory from noon Friday to 6 am EST Saturday for
Small Craft Advisory from 9 am Friday to 6 am EST Saturday for
Small Craft Advisory from noon to 6 PM EST Friday for anz530-