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Area forecast discussion 
National Weather Service Wakefield Virginia
1051 am EST Wednesday Mar 4 2015

a warm front lingers over the northern middle Atlantic this morning...with
a cold front slowly crossing the region later this afternoon
through tonight. The front will stall over North Carolina on
Thursday...with a wave of low pressure moving along the front into
Thursday night. This will bring another round of wintry weather to
the area...followed by cold and dry conditions by Friday.


Near term /through tonight/...
quick update to reflect issuance of Winter Storm Watch over
Wicomico/Dorchester counties in Maryland. Incoming 12z guidance
bolstering forecast confidence of the going forecast...outlined
in the short term section below. Forecast confidence for winter
storm headlines is sufficient to justify watch over these areas.
Will make advisory/warning decisions this afternoon as 12z data
continues to filter in.

Previous discussion sent 706 am EST...
the current surface analysis shows a quasi-stationary frontal
boundary lingering from the Tennessee Valley through the northern middle-
Atlantic with a residual wedge airmass in place to the Lee of the
mountains. The frontal boundary is situated in between Arctic high
pressure building over the Central Plains and high pressure off
the coast...and is aligned nearly parallel to the upper level flow
and hence it will move very little today. Stratus will linger
through at least middle- morning...with areas of fog
early...especially over southeast Virginia/NE NC. High temperatures will be
very challenging today. There is a potential that far northern portions
stay in the upper 40s...with low 70s across southern portions. Central
portions could experience a spread of at least 10-15f depending on
the eventual position of the frontal boundary. The highest probability of precipitation
today will be across the far northern tier counties in closer proximity
to the boundary...with a sharp gradient across central portions
that tapers to 10-20% across S/southeast portions.


Short term /Thursday through Friday/...
a cold front presently back over the Ohio Valley drops into the area
this evening and tracks north-northwest-south-southeast across the area overnight into Thursday
morning. Meanwhile...a wave of low pressure develops along the front
and tracks across the Carolinas Wednesday night into Thursday. Much
colder air arrives behind the front with most of the area falling
into the upper 20s/low 30s by Thursday afternoon. Forecast soundings show dry
air lingering between 600-400mb any precipitation (in the form
of -ra) will be light. A strong anti-cyclonic jet is presently
located from the middle-Mississippi Valley through Atlantic Canada.
This jet structure will translate eastward through Thursday as a strong trough
digs across the upper Midwest and Great Lakes by later Thursday morning
into Thursday afternoon. It is at this time that deeper moisture will
arrive and rrq forcing will be idealized and trigger the onset of
wintry precipitation from northwest-southeast across the area.

It is not until 21z Thursday to 00z Friday that sub 1540m 850-700mb
thickness values arrive into northwest portions of the area.
this time the strongest uvm will be exiting the coast. Overall it
appears that slr values will be low (perhaps 5:1-8:1) given that
there will be a period of sleet...and that middle-level thicknesses
will be 'warm' during the strongest forcing. The current forecast
has a narrow band of 3-4" from Louisa County to Dorchester County
bordered by a band of 2-3" for other portions of the northwest
Piedmont...Northern Neck...and lower Maryland Eastern Shore. Currently 1-2" is
forecast from the ric metropolitan down through Hampton Roads...with 1" or
less farther S. A brief period of freezing rain is possible during the
transition from rain to snow/ice pellets with any ice accumulate only trace to a few
hundredths of an inch. Confidence is not high enough for a watch
across the far north at this time given that this is a later third
period this will continued to be highlighted in the severe weather potential statement.

Wintry precipitation should taper off Thursday evening...with drier air arriving
from the northwest during the late evening. Temperatures will continue to
plummet with lows Friday morning ranging from the low teens low
20s southeast. Highs Friday will struggle to reach 30-35 Friday under a mostly
sunny sky.


Long term /Friday night through Tuesday/...
extended period will be highlighted by generally dry conditions
and a return to near seasonable normal temperatures.

Medium range guidance in general consensus with the upper flow
through the extended...characterized by ridging/blocking over the western
Continental U.S./Eastern Pacific and broad troughing over the central and eastern
Continental U.S.. to begin the period...cold/dry 1030+mb Arctic high pressure
centers over the middle-Atlantic region. Thursdays cold front locates
off the coast...extending southwestward into the northern Gulf. 850 mb temperatures drop
to around -8c Friday (~-1 Standard dev)...slightly warmer than depicted 24
hours ago. Highs Friday generally in the low-middle 30s inland and upper
20s-low 30s coastal areas. Airmass modifies Friday night-Sat as the
cold/dry air retreats northward. High pressure remains over the region
Sat...with light return flow helping to moderate low level
thicknesses. Temperatures warm into the upper 40s-low 50s inland and low-
middle 40s coastal areas. Sky average mostly sunny-partly cloudy. High
pressure remains over the region sun...resulting in continued dry
and warming conditions. Highs in the low-middle 50s inland and low
40s to upper 40s coastal areas. Attention then turns out
west...where models continue to struggle handling split/blocky
flow and southern stream energy over the desert SW/baja. Good news is
that now the deterministic European model (ecmwf) has trended dry Sun night-early
next week...matching the GFS and ensembles. However...split flow
continues resulting in low confidence early next week. Front over
the Gulf will attempt to amplify and lift northward as southern stream energy
approaches...but will keep probability of precipitation silent. Highs early next week (mon
and tues) continue to warm into the middle 50s inland and low-upper
40s coastal areas thanks to cold water.


Aviation /16z Wednesday through Sunday/...
as of 12z...IFR/LIFR conds are found throughout the area with a
warm front in the vicinity and very moist low levels. The chance of
-ra has diminished this morng but there is still some areas of
-dz. SW winds gusting up to 20-25 knots will continue today ahead of
an approaching cold front. Some improvement in ceilings is expected
this afternoon at most taf sites...but IFR/MVFR is still possible. The cold
front drops into the area this eveng into tonight...with rain and
LIFR/IFR conds expected. During the day Thursday...the precipitation becomes snow
northern portions and mixed precipitation southern portions. Precipitation becomes mainly snow
Thursday evening before ending from the northwest. Any snow accumulations are
expected to be around 1-3 in on average...with possibly more at ksby. A
gusty northerly wind will develop along the coast Thursday. High pressure
then builds in with dry weather Friday through Sunday.


have extended dense fog advisories northward to include the entire
Bay...eastern Virginia Rives and coastal waters to Chincoteague as warm air advection
overspreads cold waters. Warm air advection will wane through the
afternoon...allowing visibilities to improve. May need to extend
the dense fog headlines with the next update. SW winds have
diminished this morning as the strongest gradient winds push
offshore. Seas have subsided below 5 feet except in the southern coastal
waters where southeast swell has helped maintain Small Craft Advisory conditions. Have
opted to issue Small Craft Advisory headlines south of Cape Charles Light for seas will remain 4-5 feet.

Previous discussion...
a cold front approaches from the west today with S/SW flow continuing out
ahead of the front. Winds may come close to Small Craft Advisory thresholds this morng
over the Lower Bay due to a strong low level jet...but warm air advection and cold waters will
cause a sharp inversion that should keep sustained winds up to ~15
knots there. Issued a dense fog advisory for coastal waters S of Cape Charles
Light due to expected visibilities at or below 1 Michigan through the midday hours in
association with very moist low levels. The front slowly drops through
the area late today into tonight as a wave of low pressure develops along the
front. As the front finally pushes S of the area tonight...Small Craft Advisory conds will
commence over the waters. These conds will continue into Thursday night as
well so extended the headlines into the 4th period. Winds may come
close to gale force over southern coastal waters but confidence is not hi enough
to issue a gale watch/warng at this time. Also kept all river zones except
the lower James out of the advisory for now but will continue to
monitor. Waves over the Bay up to 4-5 feet with seas over coastal waters up
to 7-8 feet. Surface hi pressure then builds in for Friday into the weekend leading
to improving marine conds.


Akq watches/warnings/advisories...
Maryland...Winter Storm Watch from late tonight through Thursday evening
for mdz021-022.
Marine...dense fog advisory until 1 PM EST this afternoon for
Small Craft Advisory from 4 am Thursday to 4 am EST Friday for
Small Craft Advisory from 7 am Thursday to 4 am EST Friday for
Small Craft Advisory until 4 am EST Friday for anz656-658.


near term...ajz/mam
short term...ajz
long term...Sam

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