Twitter - Sunday, October 21, 2018

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Do you “see the Day approaching”?

DC Climate Report — DCwx

Last 72 Hours: Observations

Currently: 52°F — Radar — @PatPend • @TerpWeather • @JZTessler • Weather

Hazardous Weather Outlook
Frost Advisory

Today: Mostly sunny, with a high near 53°. Breezy, with a northwest wind 16 to 23 mph, with gusts as high as 43 mph.

Tonight: Mostly clear, with a low around 37°. Northwest wind 5 to 14 mph, with gusts as high as 28 mph.

Monday: Sunny, with a high near 58°. Light and variable wind becoming south 5 to 8 mph in the afternoon.

Monday Night: Partly cloudy, with a low around 44°. South wind 6 to 8 mph.

Tuesday: Sunny, with a high near 65°. West wind 5 to 8 mph.

Tuesday Night: Mostly clear, with a low around 45°.

Wednesday: Sunny, with a high near 56°.

Wednesday Night: Mostly clear, with a low around 37°.

Thursday: Sunny, with a high near 51°.

Thursday Night: Partly cloudy, with a low around 37°.

Friday: Mostly sunny, with a high near 55°.

Friday Night: Mostly cloudy, with a low around 41°.

Saturday: A chance of showers. Partly sunny, with a high near 57°. Chance of precipitation is 30%.

Baltimore/Washington Forecast Office

Forecast Archive | Observations Archive

000
FXUS61 KLWX 210121
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
921 PM EDT Sat Oct 20 2018

.SYNOPSIS...
A strong cold front in the Great Lakes region is crossing the
area tonight, followed by high pressure for Sunday through
Monday. Another cold front will cross the area on Tuesday with
high pressure building again over the region during the middle
of next week.

&&

.NEAR TERM /THROUGH SUNDAY/...
A vigorous shortwave is pivoting across the Mid Atlantic
tonight. Steep height falls and starkly cooler air behind the
boundary will support deep mixing. The steepest lapse rates will
be north of Maryland, but there will be enough forcing for
showers across much of the area. These showers are tapping into
some gusty winds aloft and bringing some 35-40 knot gusts with
them. There has been some sporadic lightning as well, but that
appears to be waning gradually as we head deeper into the night.

The bigger impact will be the winds. Numerous models suggesting
that 40 kt (Wind Advisory criteria) available somewhere within
the mixed layer behind the shortwave trough. Most have 40 kt
within 2000 ft of the surface. However, there are multiple
considerations in the wind forecast late tonight into tomorrow
morning-- elevation, duration, and mixing potential.

While the forcing factors lean heavily on greater than mean
mixed momentum transfer, the time of day suggests that full
mixing won`t occur. So due to topography, the Blue
Ridge/Catoctins/Appalachians will reside within higher winds
and will experience these conditions for longer. In the metro
corridor, the best chance for mixing will be contingent upon the
frontal zone itself. Still am not confident of wind gusts along
I-95 40+ kt. For that reason, issued a Wind Advisory for the
ridges only (10 pm through 8 am). If it appears as though an
Advisory warranted in metro DC/Baltimore, it can be expanded
east.

After winds diminish slightly near sunrise, diurnal mixing will
likely result in an increase once again. Although mixing will be
better, there is less wind in the column. That may result in
another windy but sub-Advisory day.

The cold air rushing in will also result in upslope snow. There
are widely varying solutions wrt qpf. Am not taking NAM verbatim
as it would result in multiple inches of accumulation. Early
season events are highly elevation dependent, and the window of
opportunity here is roughly 6-8 hours. Thus, snow forecasts
hovering around an inch or two for the westernmost zones.

High pressure builds Sunday afternoon, resulting in less
blustery and more sunny conditions. The subsidence will also result
in curtailing the upslope snow potential. However, intense cold
advection will mean a chilly day...with highs in the 40s, except
50-55F Charlottesville-Baltimore southeast.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
The short term will be dominated by high pressure. It will
mainly be a temperature forecast, with Sunday night the coldest
period of this stretch. Even the city centers could drop into
the 30s. More frost possible in the outlying areas. Freeze
watch/warning may be necessary for the next stripe of counties
east of where the freeze occurred Thursday night/Friday
morning, but confidence is low.

Gradual temperature modification Monday as the high slowly works
offshore. Highs in the 50s; lows in the 40s.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Cool and dry conditions will be the theme across the area
through the long term period.

A mid-upper level trough will track across Upstate NY and New
England during the day on Tuesday. We will be displaced off to
the south of this feature, with zonal flow aloft. With all the
forcing for ascent ahead of the trough located well off to our
north, mostly sunny skies are expected across the area.
Temperatures will max out in the low to mid 60s, which is close
to normal for this time of year.

The aforementioned trough will spawn an area of surface low
pressure off the New England Coast late Tuesday, which will
intensify and track toward the mouth of the St. Lawrence River
on Wednesday. As this system intensifies, it will drive a surge
of colder air southward in it`s wake. This surge of colder air
will make it into our area for Wednesday and Thursday, leading
to a period of below normal temperatures. By Friday,
temperatures will moderate slightly as warm advection ensues
aloft ahead of a weak trough approaching from the Midwest.
Conditions will remain dry through the duration of the long term
period.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
VFR flight conditions anticipated for the next several days.
The main operational impact will be from the winds. Gusty
showers with the frontal passage tonight will then be followed
by a wind surge behind it. Gusts 35-40 kt from the northwest
likely between midnight and dawn. Highest confidence of 40 kt at
MRB. Winds will still be gusty after daybreak, with numerous
gusts in the 30s (kt) throughout the morning and midday. Winds
slowly diminishing in the afternoon and evening.

VFR conditions are expected at the terminals each day Monday
through Friday.

&&

.MARINE...
Gales tonight and continuing into Sunday. It is likely that the
Gale Warning will be replaced by a Small Craft Advisory at some
point Sunday afternoon. Do not ramp up and ramp down hazards
within one forecast, but Small Craft conditions will follow the
gales Sun PM.

Winds much lighter on Monday with high pressure overhead.

SCA conditions expected Tuesday ahead of an approaching cold
front with gusty southwesterly winds. The dry cold front will
move through the waters Tuesday night, as SCA gusts turn out of
the northwest. SCA conditions likely to remain through Wednesday
night and potentially into Thursday as northerly breezes remain
elevated as high pressure builds over the Great Lakes. The high
finally settles over the region late Thursday and Friday,
improving the likelihood of winds dropping below SCA criteria.

&&

.TIDES/COASTAL FLOODING...
Strong northwest winds tonight will create blowout conditions
Sunday into Sunday night.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Wind Advisory until 8 AM EDT Sunday for MDZ003-004-501-502.

&&

$$
SYNOPSIS...HTS/RCM
NEAR TERM...HTS/RCM
SHORT TERM...HTS
LONG TERM...KJP
AVIATION...HTS/KJP/RCM
MARINE...HTS/KJP/RCM
TIDES/COASTAL FLOODING...HTS

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