Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 270859
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
359 AM EST Mon Jan 27 2020

.SYNOPSIS...
Low pressure will linger over northern New England and the
Canadian Maritimes through Tuesday. Weak low pressure will pass
south of the region tonight. High pressure will build across
the Northeast and Mid-Atlantic Wednesday through Friday. A storm
system may affect the region next weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Cyclonic flow from low pressure across the Canadian Maritimes
remains the main synoptic feature for the Mid Atlantic region.
Shortwave energy rotating around this low has been responsible
for various periods of cloud cover; another impulse affecting
the area early this morning. Perhaps there could be a bit of a
break, allowing for some sunshine, this morning before
convectively- induced cumulus develops this afternoon. As a
description, skies will be waering between partly sunny and
mostly clouds.

In the mountains, skies will be mostly cloudy at best. Given
southwest/west flow, there`s not a lot of moisture to work with
at this time. Perhaps there could be a few flurries (or early
this morning maybe an isolated patch of freezing drizzle). Will
be keeping a 20-30 PoP, but that`s not high enough for snow
accumulations of any consequence.

A vigorous piece of vort energy, with a weak surface low, will
be diving southeast from the northern Plains, passing south of
the region this evening. The trough axis should be capable of
bringing clouds across the entire area, and reinvigorate
scattered upslope snow showers tonight.

Middle ground between NAM and GFS MOS seems to be a good
solution for high temperature forecasts, and went that way (with
a pinch of persistence) for today`s high. That indicates that
DCA-CHO southeast should again reach 50 degrees. Verification
suggests that ensemble forecasting preferred tonight...lows
upper 20s-lower 30s, except mid 30s downtown DC/Baltimore and
along the Bay.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
In the wake of the trough axis, high pressure will be building
at the surface as well as a ridge axis at 500 mb. Believe that
the area will be receiving cold advection, so temperatures will
be cooler, but not abnormal for late January. Some upslope
scattered showers likely to persist into Tuesday before
subsidence squashes them with the lowering inversion. East of
the ridges, there is a better chance for sunny skies as
downslope flow won`t be fighting as much mid-level energy, not
to mention a drier air mass overall.

Another piece of vorticity and a trough axis will be
approaching from the west coast...arriving by Wednesday night.
There are some evolution/track/timing differences in guidance,
so at this point will restrict impact to just increasing cloud
cover.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Quiet weather conditions will persist Thursday through the daylight
hours Friday, but forecast confidence decreases significantly as we
move toward Friday Night into the weekend. The large scale pattern
across the CONUS will be rather disorganized at the start of the
long term period. Multiple weak disturbances oriented in a chaotic
manner across the center of the country will slowly move to the east
and interact with each other. By Friday into Saturday, a strong
ridge will become established across the western CONUS in response
to repeated cyclogenesis event in the eastern North Pacific. A more
coherent shortwave will descend down the front side of the ridge and
dig toward the Gulf of Mexico. This shortwave will interact with the
disorganized disturbances to form some semblance of a longwave
trough across the eastern CONUS. Exactly when and where this trough
forms, as well as what orientation/tilt it ultimately takes on are
very much up in the air. With multiple complex moving parts, the
forecast for next weekend is highly uncertain, with large amounts of
spread in both deterministic and ensemble guidance. Possibilities
range anywhere from a weak system suppressed far to our south with
little to no precipitation across the region, to a major coastal low
tracking either along the coast or out to sea. Confidence in any
given solution is very low at this time, with both timing and amount
of precipitation next weekend very much up in the air. For now, have
low end chances for precipitation advertised throughout the weekend.
We will monitor trends in the guidance throughout the week and
gradually focus in on a solution as we move closer to the event.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
Mid level energy will support periods of clouds today and
tonight. VFR flight conditions should prevail, with bases (and
occasional ceilings) at two levels: FL040-050 and also at
FL080-100.

High pressure will start to build toward the east coast Tuesday
and Wednesday, but SCT-BKN cumulus likely to continue.

VFR conditions are expected for Thursday and Friday.

&&

.MARINE...
Light southwest/west flow (at or below 10 kt) across the waters
early this morning. Winds will be increasing today, but water
temperatures in the lower 40s should keep higher gusts aloft.

Shortwave energy will be passing south of the waters tonight.
As the associated trough axis crosses the waters, there should
be enough energy to reinvigorate mixing. Further, air
temperatures will be cooler than the water by that time. Have
raised a Small Craft Advisory for the Bay south of Pooles Island
as well as the mouth of the Potomac/Patuxent and most eastern
inlets tonight into Tuesday morning. Have omitted the northern
tip of the Bay, Baltimore Harbor, and most of the Tidal Potomac
as am not quite as certain about mixing in these narrower
waterways.

High pressure will be building Tuesday night into Wednesday. At
this point wind forecasts have been kept below Advisory
thresholds. Sub-SCA level winds and quiet weather conditions
are expected over the waters on Thursday and Friday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 3 AM to noon EST Tuesday for ANZ531-
     532-539-540-542.
     Small Craft Advisory from 11 PM this evening to noon EST
     Tuesday for ANZ533-534-537-541-543.

&&

$$
SYNOPSIS...HTS
NEAR TERM...HTS
SHORT TERM...HTS
LONG TERM...KJP
AVIATION...HTS/KJP
MARINE...HTS/KJP


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