Scientific Forecaster Discussion
fxus61 klwx 222119 cca
Area forecast discussion...updated
National Weather Service Baltimore Maryland/Washington District of Columbia
419 PM EST Fri Nov 22 2019
high pressure will build from the Ohio Valley eastward over the mid-
Atlantic through early Saturday as low pressure develops over the
mid Mississippi Valley. High pressure will move offshore Saturday
while low pressure moves northeastward toward interior West
Virginia, then re-develops over southeastern Virginia. Low pressure
will pull northeastward away from the region Sunday, then high
pressure will develop toward the region from the southern United
States through early next week. Low pressure will likely develop
over the mid section over the country and pass to the west and north
of the mid-Atlantic during the middle of next week.
Near term /through tonight/...
latest surface analysis shows the front moving over our area with
the main rain band east and out of the area. A few echoes are still
observed on radar but conditions will be drying soon with northwest flow
and cold air advection. Some of these gusts are between 15 and 25
Winds will be on the decrease as high pressure builds tonight over
our area with clearing skies. Radiational cooling (late) and
northwesterly flow and cold advection (early) will allow low
temperatures to drop into the upper 20s and low 30s. A brief period
of patchy freezing drizzle or freezing fog is possible over the
Allegheny Front this evening as residual moisture lingers and
temperatures drop below freezing.
Short term /Saturday through Sunday night/...
high pressure will be moving offshore early on Saturday for a dry
start. During the same time, a low pressure system will be moving
into the Tennessee Valley ahead of a mid-level trough axis. The low
pressure system will continue to move northeast into our area
bringing plenty of moisture with it. Precipitation will move
into our region from the southwest during the late morning into
the early afternoon, and will continue to expand northeastward
into the evening and night hours.
Precipitation is expected to be rain with this system, but a few
localized spots of freezing rain cannot be ruled out at the mountain
ridges if a below freezing layer is maintained at the surface
(bufkit soundings indicate a near-freezing layer between 1000 and
2000 feet or so; valley floors and ridgetops may stay plain rain
with a narrow area of patchy freezing rain in between). Quantitative precipitation forecast values
will be between a quarter and half an inch west of the Blue Ridge,
and between half an inch to an inch east of it. The low pressure
will be overhead on Saturday night and offshore early Sunday with
precipitation ending behind it.
High pressure will build over our area for Sunday with gusty
northwesterly flow and cold air advection. Snow showers will be
possible west of the Allegheny Front early on Sunday before drier
air moves in.
Long term /Monday through Friday/...
high pressure passing to the south will envelop the region with
moderating temperatures and relatively benign weather Monday and
Tuesday. As the high pushes to the southeast, southerly flow should
help moderate temperatures. However, the warmest day looks like
Wednesday, right before a cold front crosses the region as low
pressure passes by to the west and north. Trends with the front
continue to reduce moisture and pull forcing further north away from
US, so it's looking more and more likely that a dry frontal passage
will occur Wednesday. Since warm air will be drawn northward just
ahead of the front, and downslope winds will occur right behind it,
highs may be propelled well into the 60s on Wednesday. High pressure
building southward from Canada on Thursday and Friday should bring
temps back below seasonable levels, but probably not quite like the
severe cold we saw earlier this month.
Aviation /Friday through Wednesday/...
VFR conditions are observed over the terminals, with some gusting to
20 knots. Winds will diminish tonight with VFR conditions continuing
through Saturday before a low pressure moves through our area
bringing widespread rain over the terminals in the afternoon. MVFR
and IFR conditions are possible at times, especially late Saturday
afternoon into the night. VFR conditions are expected behind this
system late Saturday night into Sunday.
VFR should prevail Monday and Tuesday with high pressure.
a Small Craft Advisory is in effect for this afternoon and evening
over all the waters as winds are increasing behind the front that is
currently moving over the waters. The winds will decrease tonight
with high pressure taking over. A low pressure system will be moving
across our area late Saturday. Winds will increase above criteria
behind this system and another advisory will likely be needed for
Sub-Small Craft Advisory winds should prevail Monday and Tuesday under high
northwesterly offshore flow is expected through this evening behind
a departing cold front, and that will cause a decrease in water
levels. Therefore, any flooding threat appears to be quickly
District of Columbia...none.
Marine...Small Craft Advisory until midnight EST tonight for anz530>533-
Small Craft Advisory until 4 am EST Saturday for anz534-537-