Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 klwx 130237 aaa 
afdlwx

Area forecast discussion...updated
National Weather Service Baltimore Maryland/Washington District of Columbia
937 PM EST Tue Dec 12 2017

Synopsis...
an Arctic cold front will move off the coast tonight. Weak high
pressure will build overhead Wednesday. An Alberta clipper will
pass nearby Wednesday night through early Thursday. Developing
low pressure will pass off the East Coast late Friday and high
pressure will return for Saturday. Low pressure may impact the
area early next week.

&&

Near term /through Wednesday/...
infrared satellite imagery shows bkn clouds over the mtns with ekn
obs indicating only light snow falling there with 4sm
visibility. Elsewhere, sct flurries are falling east of the
mtns. Trough axis will cross the area around 06z tonight with
subsidence inversion strengthening overnight with snow showers
over the mtns diminishing rapidly. Up to an inch of additional
accumulation is expected through 06z.

Very cold and windy overnight with temps falling into the teens
east to single digits in the mtns and wind chills in the single
digits east to negative teens in the mtns. Clearing skies are
expected overnight. Gusts around 35kt are expected overnight.

&&

Short term /Wednesday night through Thursday night/...
weak high pressure noses into the region on Wednesday, so the
sun should return, but a steady wind looks likely to remain as
the gradient between low pressure to the northeast and high
pressure to the southwest remains relatively strong. Cold
advection will diminish, but we will be solidly within the cold
air mass, and with very cold mid level temps, surface readings
will struggle to recover. Most places will end up below freezing
all day long, and even the warmest spots probably only reach the
mid 30s.

Wednesday night into Thursday, a clipper will move across the
region. Latest guidance has trended the low track northward,
with most models now sending it along or just north of the
Mason-Dixon line. Typically this means that any accumulating
snow will stay north of our region. There remains some potential
for a wiggle back southward, so did not completely remove chance
of precip, but did nudge it back down somewhat. It is notable
that with the low now expected to pass north, it could
conceivably warm up overnight as south winds behind a warm front
push temps above freezing in parts of the Metro. Highs on
Thursday look like most places get above freezing, with 40
looking more likely in the Metro.

The clipper moves east Thursday afternoon, and we will try to
dry out at night, but a weak vort Max passing through could
cause a few flurries - nothing more, most likely. Lows will drop
back into the sub-freezing category.

&&

Long term /Friday through Tuesday/...
an upper level trough of low pressure will move across the
region Friday into Friday night. Snow shower chances will linger
due to this trough. Temperatures will remain below normal.

A modifying area of high pressure is expected to build eastward
behind the upper level trough Saturday and Saturday night.
Milder temperatures and a southwest wind are expected through
the period.

The next threat for rain or snow showers will be Sunday through
Monday as a cold front sags southward across the region. For
the most part, rain showers should be the story and not so much
the snow showers.

High pressure will build into the region Tuesday and bring
another blast of chilly air to the region.

&&

Aviation /02z Wednesday through Sunday/...
generally VFR thru the period. Any snow shower this
afternoon/evening could briefly reduce cigs/vis to IFR, but
impacts should be brief. Lasting longer will be the gusty winds
from the northwest, which will continue through much of the
night and perhaps into the morning Wednesday.

Clipper crossing the area Thursday night appears more likely to
stay north of the region. Best chance of any impacts will be the
northern terminals (mrb/BWI/mtn), but even here, odds seem to be
decreasing. Will need to monitor however, as a wiggle in the low
track back to the south could make snow more likely in these
areas.

VFR returns or continues later Thursday and Thursday night
behind the clipper.

VFR conditions Friday through Saturday night. Snow showers on
Friday into Friday night could briefly reduce conditions to
MVFR. Winds light and variable Friday into Friday evening,
becoming west 5 to 10 knots late Friday night. Winds west
becoming southwest 5 to 10 knots Saturday into Saturday night.

&&

Marine...
cold front crossing the waters now is resulting in rapidly
increasing winds, with gales likely to start late this afternoon
and continue through Wednesday. Gales are up for all waters
tonight and the more open waters through Wednesday due to this
expectation. Winds should gradually slacken starting late
tonight and then decrease more signficantly Wednesday night as
the flow becomes southerly ahead of an approaching clipper, but
Small Craft Advisory level gusts still expected, so have added Small Craft Advisory for the Open
Bay on Wednesday night.

No marine hazards Friday through Saturday night. Winds light
and variable Friday into Friday evening, becoming west 10 knots
later Friday night. Winds west becoming southwest around 10
knots Saturday and Saturday night.

&&

Tides/coastal flooding...
a strong northwest flow is developing behind a cold front at
present which will continue through Wednesday. Tidal blowout
conditions are possible late tonight through Wednesday.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...Wind Chill Advisory until noon EST Wednesday for mdz501.
Virginia...Wind Chill Advisory until noon EST Wednesday for vaz503-504-
507-508.
WV...Wind Chill Advisory until noon EST Wednesday for wvz501-503-
505-506.
Marine...Small Craft Advisory from 6 PM Wednesday to 6 am EST Thursday
for anz532>534-537-540-541-543.
Gale Warning until 6 PM EST Wednesday for anz530>534-537-
539>541-543.
Small Craft Advisory from 6 am to 6 PM EST Wednesday for
anz535-536-538-542.
Small Craft Advisory from midnight Wednesday night to 6 am EST
Thursday for anz542.
Gale Warning until 6 am EST Wednesday for anz535-536-538-542.
Small Craft Advisory from 6 PM Wednesday to midnight EST
Wednesday night for anz530-531-539.

&&

$$
Synopsis...rcm
near term...lfr

National Weather Service Glossary of Abbreviations