Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 270901

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
400 AM EST Mon Feb 27 2017

High pressure will shift east of the area today. A warm front will
then lift north into the area Tuesday into Wednesday followed by
another cold front Wednesday night. After a brief period of high
pressure Thursday, a weak low pressure will cross the region early


Current surface analysis shows high pressure near Cape Hatteras.
A developing low pressure and attendant warm front is located
over the southern Plains. This system will be the focus of our
attention through the next several days. The main upper level
component of this system is still well to the west near the West
Coast, but well ahead of that, a weak trough aloft with little
surface reflection is currently crossing the mid-Mississippi

As this weak system moves into the area today, clouds wil be on
the increase as warm advection occurs aloft. Low levels remain
dry, but some guidance brings the warm advection precipitation
into our western zones as early as around sunrise, and with
temperatures near or below freezing, some freezing or frozen
precipitation is possible. For now have included a chance of
rain, sleet and snow in the western zones for this morning,
changing to rain as southerly winds bring milder air northward
this afternoon. Will be watching radar trends over the next few
hours to determine if any winter weather headlines need to be
issued, but right now believe odds accumulating snow or ice this
morning are less than 50 percent.

Further east, high pressure and dry air will win out and it
should stay dry, if turning out somewhat cloudy, today.
Southerly flow should bring warmer air back up from the south,
however, so it should turn out to be a milder day compared to
yesterday despite the clouds. Highs in most places will be
around 10 degrees warmer than yesterday, but this is just the

Tonight, weak ridging returns aloft and the chance of any precip
fades. In fact, we may get some clearing, which could again
allow some radiational cooling. However, with the milder
southerly flow, expect lows to also be around 10 degrees warmer
than this morning.


Deep trough from the Pacific hooks up with the developing low in
the southern Plains and sends a maturing storm system
northeastward into the Great Lakes by Wednesday. As this system
develops, increasing southerly flow will bring another surge of
very warm air northward to our region. Warm advection clouds and
then showers will overspread the area Tuesday, but with weak
forcing, it seems coverage and QPF will be rather modest for a
warm front. Southerly flow with the warm front should nudge
highs on Tuesday up into the 60s, with lows staying very mild
Tuesday night, likely well into the 50s. The low and strong
upper trough then pass to our north on Wednesday, dragging the
surface front across our region Wednesday night. Temps look to
surge well into the 70s and perhaps into the 80s ahead of the
front, and this may set the stage for another round of severe
weather. The SPC has placed the entire CWA in slight risk for
Wednesday given this potential. The front should clear the area
near or just after midnight, with drying and cooling on gusty NW
winds after midnight Wednesday night.


Thursday looks to be post-cold frontal with low pressure
lifting north from Maine. Despite rapid growth progged, the
strong wind threat continues only through Thursday morning as
the low center is progged by 00Z GFS and ECMWF to reach Labrador
late in the day. Notable cold air advection from mid-
continental air

Thursday night into Friday. An Alberta clipper system scoots
east across or just north of the area. Will need to monitor this
rare shot at snow in one of the warmest winters on record (see
climate section below). While accumulating March snow in the
central Mid- Atlantic is rare, there has been measurable snow
each of the past four Marches across the area. This is the first
shot at a fifth. Generally raised PoPs to chance for both
Thursday night and Friday with the highest along the Mason-Dixon
line with likelies west of the Allegheny Front. Alberta
clippers lack Gulf of Mexico moisture and thus have maximum
snowfall of a few inches with dusting to one inch most common
result east of the Allegheny Front.

Eastern Region Superblend (our default forecast for Days 4-7)
progs low 50s max temps for the lower southeastern portion of
the CWA Friday despite reinforcing cold air behind the clipper.
Undercut this by a few degrees and made the chance PoPs for
Friday snow showers due to the cold column under the upper

The subtropical ridge then sets back up over the SErn CONUS
with a warming trend through the weekend.


VFR through the next 30 hours. CIGS should stay above 5k ft and
no precip or fog is expected at terminals through early Tuesday.
Rain and sub-VFR threat increases later Tuesday and Tuesday
night. Gusty thunderstorms with sub-VFR cigs and vis are
possible later Wednesday and Wednesday night as a strong cold
front passes. Winds will be increasing out of the south, ligth
today, but steady and gusty by Wednesday afternoon, then turn
gusty from the NW after the front passes at night.

Gusty NW flow behind a Wednesday night cold front eases through
Thursday as cold air spills into the region. An Alberta Clipper
crosses Thursday night/Friday morning with a shot for brief
accumulating snow.


Winds likely to stay sub SCA today and tonight. Southerly flow
may bring SCA by tomorrow afternoon to the bay, but held off on
SCA for now given uncertainty. Southerly winds increase further
just ahead of cold front on Wednesday, with gusty thunderstorms
possible along the front and gales possible behind it.

Gales taper off Thursday (possibly in the morning) as a brief
bout of cold air settles into the region. An Alberta Clipper
crosses the waters Friday morning with a reinforcing shot of
cold air through Friday with another gale possible.


Another period of unseasonably warm weather is forecast
culminate in near record warmth ahead of a cold front late
Wednesday. Here is a list of record daily warm temperatures for
March 1st (Wednesday).

Site   Record High   Record Warm Low
DCA    80 (1976)     57 (1910)
BWI    80 (1972)     53 (1910)
IAD    77 (1972)     43 (1997/1987/1976)




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