Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
922 am EST Wednesday Nov 26 2014

a low pressure system will move up the Atlantic coast today. An
upper-level disturbance will pass through the area Thursday and
high pressure will build overhead Friday. The high will move off
the coast during the weekend.


Near term /through tonight/...
latest analysis shows low pressure along the North Carolina coast.
A potent shortwave is also moving into the Carolinas this morning.
Precipitation associated with this system has overspread the
area...but and forcing is strong due to the potent dynamics
associated with the shortwave. Colder air is being drawn into the
system and this has caused rain change to snow for locations near
the Mason-Dixon line and also along and west of the Blue Ridge
mountains. Already had reports of 5 to 8 inches of snow along the
ridges of the Potomac Highlands. The latest updates to the
forecast have been to bump up snowfall totals in the mountains
based on the latest reports and radar imagery showing mesoscale
banding across these areas. Elsewhere...little change has been
made to the forecast and the headlines remain the same. A Winter
Storm Warning is in effect for much of northern and western
Maryland and for locations along and east of the Blue Ridge
mountains. A Winter Weather Advisory is in effect for the northern
and western suburbs of Washington and Baltimore. The previous
discussion follows.

There have been reports of rain mixing with snow for the northern
and western suburbs of Washington District of Columbia...but temperatures remain above
freezing. The previous discussion follows.

Temperatures will continue to fall through the day. Rain will change to
rain/snow just east of the Blue Ridge late this morning.
Thicknesses aloft continue to show a transition zone near
Interstate 95. Little change to the snowfall forecast was done
overnight due to the consistency of model runs. Most snowfall
accumulation will be across higher elevations along and west of
the Blue Ridge and near the Mason Dixon line. At this time...using
hi res models to anticipate boundary layer conditions. Although
the surface high to the north will be supplying some cold and dry the low moves northward that supply will diminish and
dynamical cooling will be the best chance for snowfall
accumulation east of the Blue Ridge mountains there is a banding
potential that is shown in the fn vectors in the NAM and GFS for
midday across I-95. If this occurs...all snow would be able to
produce accumulation. It will be likely melt on pavement but
accumulate on grassy surfaces.

Low pressure will move away from the middle-Atlantic late this
afternoon and evening taking the precipitation shield with it. Nearly winds
will become northwest and dry/cold air will filter into the region. Any
showers will likely change to all snow across the entire region by
late afternoon and early evening before tapering off. Forecast min temperatures
will be in the upper 20s to low 30s tonight. This will cause wet
surfaces to freeze.


Short term /Thursday through Thursday night/...
upper trough with embedded shortwave is prognosticated to swing across the
middle-Atlantic Thanksgiving day. Shortwave will produce plenty of
clouds along with scattered precipitation. Initial p-type likely
would be snow...but by afternoon thermal profiles become more
marginal further east through the County Warning Area therefore have rain shower/SW as p-type
east of the Blue Ridge.

Shortwave exits by early evening Thursday...but expect some upslope
snow showers with west/northwest wind behind the shortwave.


Long term /Friday through Tuesday/...
high pressure builds in Friday night then pushes offshore Saturday.
Warm front looks to lift north late Saturday into Saturday night.
This should help temperatures warm above normal for Sunday. This
likely lasts into Monday even though a cold front moves through.
Cooler air is slated for Tuesday.


Aviation /14z Wednesday through Sunday/...
low pressure will move up the East Coast today. Rain and snow
is expected. IFR conditions are expected across most of the
terminals. Snow is expected at mrb for most of the event today
whereas warmer temperatures eastward will lead to a mixture of rain and
snow. There is a chance that precipitation changes to all snow for
a period during the early and middle afternoon hours across these
areas. Nearly winds are expected today with gusts up to 20kts at
iad/dca/BWI/mtn. Precipitation will diminish late this afternoon
into early this evening. Low pressure moves away from the coast
tonight. Ceilings and visibilities will improve to VFR this evening.

Disturbance will bring a chance of SW/rain shower Thanksgiving day...then no
significant weather expected Friday into the weekend with high pressure
generally in control.


low pressure will move up the East Coast today. Nearly winds across
the waters will increase and Small Craft Advisory conditions are expected today. As
the gradient tightens as the low nears...gale force winds will be
possible across the lower tidal Potomac and middle Chesapeake Bay
through the afternoon. Low pressure will move away from the waters
this afternoon and evening. Northwest winds will subside tonight and into

Trough moves through Thanksgiving day...with potential Small Craft Advisory
conditions behind it for Thursday night into Friday. High pressure
builds in thereafter.


records for earliest measurable snow already passed a few weeks
ago...but below is a list of daily maximum snowfall records specific
to the date of November 26th.

Dca 2.2" (1898)
BWI 4.5" (1898)
iad 1.1" (1978)


Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...Winter Storm Warning until 6 PM EST this evening for
Winter Weather Advisory until 6 PM EST this evening for mdz007-
Virginia...Winter Storm Warning until 6 PM EST this evening for
Winter Weather Advisory until 6 PM EST this evening for
WV...Winter Storm Warning until 6 PM EST this evening for
Marine...Small Craft Advisory until 10 PM EST this evening for anz532-
Small Craft Advisory until 11 am EST this morning for anz533-
Small Craft Advisory from 6 PM to 10 PM EST this evening for
Gale Warning until 6 PM EST this evening for anz533-534-537-
Small Craft Advisory until 6 PM EST this evening for anz530-


near term...bjl/has
short term...bpp
long term...bpp

National Weather Service Glossary of Abbreviations