Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Baltimore Maryland/Washington District of Columbia
955 PM EDT sun Mar 16 2014
low pressure over the lower Mississippi Valley will track south
of the area overnight and Monday. A wedge of high pressure is
expected to persist over the area through Tuesday...with a cold
front crossing the region on Wednesday.
Near term /through Monday/...
not much of a ptype-transition period at onset...owing to dry air
in the boundary layer earlier this afternoon. Precipitation spread over the
entire middle-Atlantic fairly quick during the middle-late afternoon - saturating
the column west/in a 1-2hr period for most areas...slightly longer
for the I-95 corridor and east. Radar trends over the past 3-4 hours
have been showing the heaviest snow band directly over I-66
tapering off on either side.
Zooming back out to a more regional-scale...the surface low transition
period is underway. The earlier parent surface feature over the deep
south - from central Alabama to northern Georgia - will weaken as a coastal low
develops off the Carolina coast. Already seeing the frontogenetical
dyan mics of this west/ a couple of hefty snow bands over the eastern half
of the County Warning Area west/ the northern one staying put over the District of Columbia-balt I-95
corridor and stretching back to the Blue Ridge. The other...
centered toward lower southern Maryland and back into north central Virginia. While
plenty of widespread lift exists west/ this entire precipitation region...
stronger and more localized areas will get confined to these
heavier bands. Snow ratios between 8:1-10:1...W/ a general 2-4"
already covering much of the lower shen valley and surrounding
ridgelines...W/ 1-2 east of the Blue Ridge a tier of counties. Part
of this southern band of heavier snow falling into surface conditions at or
above freezing a degree/two.
Some adjustments to the latest snowfall forecast include higher
amnts for the shen valley portions along west/ the higher terrain closer
to the 10-12" range for elvns receiving the most. But even down in
the valleys...not much lower west/ many areas already halfway to their
expected totals west/ several more hours of steady light/moderate snow. Even
a few breaks between now and the predawn hours will still give these
areas a few more additional inches. East of the Blue Ridge...a slower
but steady rate of accumulation over the past couple hours. Over the
next 3-6 hours...the current bands setting up over the District of Columbia/balt metropolitan
should add a bulk of the expected heavier snow accumulations.
Toward the predawn hours...the snow bands will become more NE-SW
oriented and begin drifting over the Bay and areas to the east.
Some lingering and lighter bands will continue to drift over the
rest of the County Warning Area through middle morning Monday.
No headline adjustments expected...though mesoscale banding over
specific areas in the next few hours could change this slightly for
the I-70 portion of northern Maryland/Mason-Dixon line. Does appear like the
tight gradient will be stationed along and just south of the PA/Maryland
Line through the event.
Maximum temperatures Monday will be in the lower 30s across most locations.
Despite the cold temperatures...there should be some melting during the
afternoon hours due to the higher sun angle this time of year.
Short term /Monday night through Wednesday/...
surface high stalls over the St Lawrence Valley with a ridge/wedge
persistent over the middle-Atlantic until the cold front moves through
late Wednesday. Surface ridge axis looks to hold steady Monday night
into Tuesday night which keeps an onshore surface flow and moisture
advection. Areas of snow push east of the area by Monday evening as
the upper trough moves offshore. In fact...an upper trough will build
over the region Tuesday so there will be subsidence. However...the
onshore flow will saturate The Levels below the inversion and
produce light precipitation or drizzle. Temperatures will be near or below
freezing...so freezing drizzle/rain is possible as crystals do not
form well until below minus 4c. Chance probability of precipitation begin late Monday
night...expanding from central Virginia through Tuesday...with
likely probability of precipitation for Piedmont and ridges by Tuesday evening. Again...
precipitation will be light and at times not measurable. However...even
trace freezing rain requires an advisory...so a mention in the severe weather potential statement
will be added for our western segment. Weather grids currently have the
more simple rain/snow instead of wintry mix.
Warm air advection ahead of the next cold front looks to end the
freezing rain potential by Wednesday. Likely probability of precipitation for showers ahead
of the cold front for Wednesday afternoon. Maximum temperatures middle 40s to low
50s in southerly flow.
Long term /Wednesday night through Sunday/...
active northern stream storm track will keep a roller coaster type
forecast for the extended period. Showers with prefrontal trough
look to be ongoing across I-95 and east but pushing east as cold
front and dry wedge pushes in from the west. Cold air advection behind front will
knock temperatures down for Thursday night before return flow sets
in on Friday ahead of the next approaching upper trough over the
southern Great Lakes region. Trailing surface cold front with this
low will push through Saturday...with scattered rain/snow showers
Aviation /00z Monday through Friday/...
ceilings/visibilities hovering in the solid IFR range across much of the area
west/ light-moderate snows spreading over the middle Atlantic. Periodic lower
cats...espec the upper-end LIFR for the next few hours west/ a...then a
steady IFR into midday Monday. Subvfr ceilings may hang around Monday
afternoon but visibilities should improve as the snow ends.
Wedge of high pressure/cold air persists over the region Monday
night into Wednesday with an onshore flow. MVFR/IFR ceilings and light
precipitation (some wintry) Tuesday and Tuesday night). Flow becomes southerly on
Wednesday with increasing showers ahead of a cold front.
Scattered-broken areas of MVFR conditions will be possible
Wednesday night and again Friday night/Saturday due showers along a
couple of cold frontal systems.
strengthening pressure gradient from a coastal low developing off
the Carolina copast will cause winds to increase out of the NE
overnight. A Small Craft Advisory is in effect for much of the
waters tonight into Monday. A Gale Warning is in effect late
tonight into Monday morning for the Maryland Chesapeake Bay from
Drum Point to Smith Point and the lower tidal Potomac River from
Cobb Island to Smith Point.
Northeasterly flow gusts for at least southern Maryland waters continue under a high
pressure wedge...continued the Small Craft Advisory for Maryland waters south of North
Beach for Tuesday night. Small Craft Advisory for portions of the waters through
Tuesday night as flow slowly veers southerly. Cold front approaches on
Small Craft Advisory conditions may be met on Thursday with northwest winds
behind a departing cold front and again on Saturday with southerly
winds associated with another cold front.
a north-northeast flow will strengthen tonight into
Monday...causing tidal anomalies to increase. However...the
astronomical norms are low so water levels should remain below
thresholds for minor coastal flooding.
District of Columbia...Winter Storm Warning until 2 PM EDT Monday for dcz001.
Maryland...Winter Storm Warning until 2 PM EDT Monday for mdz009>011-013-
Winter Weather Advisory until 2 PM EDT Monday for mdz003>007-
Virginia...Winter Storm Warning until 2 PM EDT Monday for vaz025>031-
WV...Winter Storm Warning until 2 PM EDT Monday for wvz050-053-055-
Winter Weather Advisory until 2 PM EDT Monday for wvz051-052-
Marine...Small Craft Advisory until 6 am EDT Tuesday for anz532-533-
Small Craft Advisory until 10 PM EDT this evening for anz534-
Small Craft Advisory from 10 am Monday to 6 am EDT Tuesday for
Gale Warning until 10 am EDT Monday for anz534-537-543.
Small Craft Advisory until 6 PM EDT Monday for anz530-531-538-
Small Craft Advisory until noon EDT Monday for anz535-536.