Scientific Forecaster Discussion
fxus61 klwx 181957
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
257 PM EST Mon Nov 18 2019
a pressure trough will cross the area tonight. High pressure
will gradually build in from the west during the middle of the
week. A cold front will cross the region by week's end.
Near term /through tonight/...
coastal low pressure will continue to move to the east this
afternoon while an upper level trough axis approaches from the
west. A second weak surface low and attendant surface trough is
located beneath the upper trough and will cross the area through
tonight. The pressure pattern in between is very weak, and the
air has essentially been stagnant from mrb/hgr through iad,
resulting in the persist low clouds and haze. These clouds have
been eroding away from the west and east, but will quickly be
replaced by additional clouds ahead of the disturbance aloft.
Rain showers have already reached roa/lyh, and will continue to
spread north this evening. There's pretty good model agreement
that the showers will weaken some with northward extent, before
fading/exiting between midnight and 3 am. Some locations
near/east of the central Virginia Blue Ridge could get up to a
quarter inch of rain, but otherwise amounts will be light.
The rain will serve to resaturate the lower atmosphere, so
additional low clouds and/or fog may develop late tonight.
Currently thinking stratus will have formed first and thus will
be predominant, though fog could occur if clearing is quick
behind the rain. There's a low chance of some flurries or light
freezing drizzle in the upslope areas late tonight, but don't
think there will be notable accumulation at this time. Lows will
be in the mid to upper 30s, east of the Blue Ridge, and closer
to freezing to the west.
Short term /Tuesday through Wednesday night/...
any fog/low clouds should mix out by mid morning. However, upper
level troughing will remain overhead on Tuesday and there will
be enough moisture associated with it to likely result in mostly
cloudy skies. The daylight hours should be dry though, with
slightly warmer temperatures in the upper 40s to mid 50s. A vort
Max and weak surface trough will rotate across the area during
the evening. Low level moisture will be lacking, but there could
be enough lift to produce a few light showers or sprinkles,
especially toward central Virginia and out in the mountains.
Light upslope precipitation will continue into Wednesday
morning, with any wintry accumulations being very minimal.
Upper troughing finally pushes to the east Wednesday with
ridging at the surface and aloft building in from the west.
There may be enough moisture in the northwest flow to keep some
clouds around, but should be more sunshine overall than Tuesday.
Temperatures will be fairly seasonal with a more Pacific
airmass, though radiational cooling could allow some below
freezing temperatures Wednesday night.
Long term /Thursday through Monday/...
surface high pressure and ridging aloft will reside over the eastern
Seaboard Thursday before shifting off the coast Thursday night. At
the same time, low pressure will track northeastward from the
central U.S. Into the Great Lakes, lifting a warm front through the
mid Atlantic region. A few showers will be possible Thursday night
as a result, with temperatures running on the mild side for this
time of year. The cold front associated with the aforementioned low
will push into our area on Friday, continuing the chance for showers
as temperatures rise into the 50s & 60s.
Model guidance is at a bit of a disagreement thereafter in terms of
the placement of the frontal boundary as another area of low
pressure tracks northeastward along it. As a result, will maintain
pops in the forecast for the first half of the weekend as the area
of low pressure tracks through the region. Depending on how much
cold air is able to filter in behind the front Friday night, could
see a mix of rain/snow showers, with our mountains areas favored for
any wintry precipitation. Rain showers will be advertised
Saturday/Saturday night with drier conditions expected the second
half of the weekend in the wake of the low/front. Slightly below
normal temperatures can be expected through the weekend.
Aviation /19z Monday through Saturday/...
a weak pressure pattern between offshore low pressure and a
weaker low near pit has resulted in a "stagnant" airmass that
resulted in IFR conditions lasting longer than anticipated. The
clouds have been eroding from the west and east, so it's
plausible iad could finally break into MVFR or even VFR later
this afternoon. However, an upper disturbance is driving and
area of rain showers in southern Virginia that will overspread the
terminals this evening. The rain itself won't be too heavy, but
may bring ceilings back to MVFR, and even a low probability of
IFR. The rain should move out by 05-06z.
However, greater uncertainty lies during the late night period,
when conditions should be calm in the wake of the rain.
Currently thinking stratus will already be in place and
predominate, though if there is clearing, fog could develop
instead. Don't have tafs dropping to IFR at this time due to low
confidence, though there's at least a moderate chance based on
guidance. Conditions should improve to VFR by mid morning.
VFR conditions are most likely for the remainder of Tuesday and
Wednesday as high pressure gradually builds in. Some westerly
wind gusts over 20 kt could occur on Wednesday. VFR conditions
on Thursday with dry conditions and a light southerly flow.
Likelihood of sub VFR conditions increase Thursday night through
Friday as a frontal boundary crosses the terminals, bringing
rain showers and winds shifting west-northwest.
all small craft advisories have been cancelled as winds have
weakened as low pressure pulls offshore. A weak trough will pass
tonight with some light rain showers, but winds should remain
below advisory levels into Tuesday night. After a second trough
passes Tuesday night and strong high pressure builds in from the
west, westerly winds will increase on Wednesday, and small craft
advisories may be needed.
Small Craft Advisory conditions will be possible Thursday night and early Friday,
while looking likely Friday afternoon and Friday night thanks to an
increasing gradient as a frontal boundary nears and crosses the
with northerly flow over our area and becoming lighter, the
high anomalies of around and over 2 feet are starting to spread
north up into the Maryland section of the Bay. A coastal Flood
Warning has been issued for St. Mary's (straits point) and Anne
Arundel (annapolis) counties for this afternoon, evening and
tonight were anomalies are expected to reach moderate flooding
during the next high tide. Coastal flood advisories were issued
over other coastal zones. Anomalies should gradually diminish
Tuesday, but minor flooding is still possible around times of
District of Columbia...coastal flood advisory from 8 PM this evening to 5 am EST
Tuesday for dcz001.
Maryland...coastal flood advisory until midnight EST tonight for mdz018.
Coastal flood advisory from 11 PM this evening to 5 am EST
Tuesday for mdz508.
Coastal flood advisory from 8 PM this evening to 4 am EST
Tuesday for mdz011.
Coastal Flood Warning until 4 am EST Tuesday for mdz014.
Coastal flood advisory until 11 PM EST this evening for mdz016.
Coastal Flood Warning until 11 PM EST this evening for mdz017.
Virginia...coastal flood advisory until 11 PM EST this evening for vaz057.
Coastal flood advisory from 8 PM this evening to 5 am EST
Tuesday for vaz054.