Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
650 am EST sun Dec 8 2013
high pressure centered over Pennsylvania this morning will slowly
retreat off to the northeast to New England by this evening. An
area of low pressure will move northeast just west of the
Appalachians today into Monday morning...while a second low
pressure area tracks northeast just off the middle Atlantic coast.
Another low pressure system will move across the Carolinas Monday
night into Tuesday.
Near term /through tonight/...
have made some minor adjustments to the forecast based on current
observation and radar trends. As expected...radar is beginning to Blossom
across the local area as strong isentropic lift/700-850 mb
frontogenesis is moving in from the west-southwest. Lyh now reporting
freezing rain at 31 f...with -ra at Dan at 35 f (dew pt 27f). Think Dan
will go to freezing rain over the next 2 hours as column cooling/wet bulb
effects take over and this will eventually overspread the akq County Warning Area
after 13z. Looking at observation in our County Warning Area...at 11z...lku now 30 (dew pt
21) with sleet...ric now reporting -ra at 34 (dew pt 23)...akq 36
(dew pt 26). Thus the line between any ice later this morning/early
afternoon will tend to occur about Half Way between ric and akq. Lowered
ice accumulations in grids to the S/east of ric Airport down to
minimal amounts (genly trace to a few hundredths). Will keep
advisories in place...but they will be very marginal across the Maryland
Eastern Shore (especially wicomico) as well as to the east/southeast of ric and
they may be able to be dropped by early afternoon. The warning appears
in good shape...especially as freezing rain appears to be coming in faster
(with less snow/sleet potential). Expect .25" or more of ice across
most of the warned area...with .40-.50" ice possible in
After 18z-21z...the strong isentropic lift and frontogenesis from
700 to 850 mb will slowly push to the north and bulk of any frozen
precipitation across southern 1/2 of the County Warning Area will diminish...while remaining
moderate across northern 1/2.
By 00z...most areas should be above 32 f...the exception being the
western portions of Fluvanna/Louisa/Cumberland where additional ice
accumulations may occur (warning continues). Overnight temperatures will be
steady to slowly rising as the high pressure to the north moves
off the coast and the cold air damming finally ends. Will have
more precipitation intensifying after midnight as better
overrunning develops and pushes back into the area. Expect only
the extreme northwest corner of the area may still be just below
freezing at that time but even there temperatures will go above
freezing by sunrise on Monday.
Short term /Monday through Tuesday night/...
with a ridge holding strong in the Atlantic waters well off the Florida
coast...the next trough pushing into the plains states will become
positively tilted and keep an unsettled wet pattern in place for the
middle Atlantic region Mon/Tue. NAM/GFS/sref/ECMWF into better agreement
than yesterday at this time for general timing and placement of key
features. Best forcing pushes through northern zones Monday
morning...then shifts to the S and east by aftn/evening. Will carry
likely probability of precipitation all zones at some point on Monday. Another wave of
moisture prognosticated to spread precipitation across the area on Tuesday. Critical
thicknesses suggest it may become cold enough in north/northwest zones to mix
with snow before ending in the afternoon so have added that to the
forecast but bulk of heavy precipitation may be done at that point. Otherwise...the
boundary should then push well S of the area Tuesday night...with hi pressure
bldng into the region from the west by Wednesday morng. Maximum temperatures on Monday will
range from the middle 40s northwest to lower 60s across NE NC. Lows Monday night will
range from the middle-upper 30s across the northern cnties to near 50 across NE
NC. Highs on Tuesday will not move much form am lows...and range from
near 40 extreme northern cnties to the lower 50s across NE NC. Lows Tuesday night
will range through the 20s to lower 30s.
Long term /Wednesday through Saturday/...
very cold and generally dry in the extended from Wednesday into next
weekend. The coastal low will be exiting the coast Wednesday and a
few showers could be lingering in the east early Wednesday morning but
have not extended probability of precipitation into Wednesday morning due to a lack of model
consistency. The big story will be the very cold high pressure which
will build in late Wednesday and especially Thursday and Friday. Thicknesses
plummet Thursday and Thursday night with the high settling in overhead Friday.
This will result in a prolonged period of cold weather middle to late
week with lows in the teens and 20s and highs struggling through the
30s to around 40. The very cold airmass looks to loose its grip on
the area some next weekend as the high lifts north and a wave of
low pressure sets up in the Gulf.
Aviation /12z Sunday through Thursday/...
surface hi pressure strengthens just north of the forecast area today with an area of warm air advection
precipitation spreading into the region this morng and continuing through
the rest of the taf period. Mixed precipitation is indicated for both ric and
sby with a tendency toward changing to rain in the afternoon. A light ice
accumulation is possible at ric. Periods of IFR can be expected during
the day...especially with any heavier precipitation...and eventually
transitioning to LIFR later in the afternoon. North/NE winds will average 7-10 knots
and be gusty at times...especially toward the coast.
Outlook...IFR ceilings are likely to persist into Monday with periods
of rain possible into Tuesday. Conditions improve by Tuesday night with
VFR/dry weather then expected through at least Thursday.
surface hi pressure building north of the area will allow strong north/NE flow to
continue today over the waters. Will hold onto the Small Craft Advisory for the lower James
River and Northern Bay until the 12z end time...then re-evaluate if an
extension is needed. Seas over northern coastal waters may drop below 5 feet as
well so will continue to monitor. Otherwise...15-20 knots winds
expected to persist over the southern Bay today with seas up to 6-7 feet over
southern coastal waters. Winds diminish tonight as a wave of low pressure passes through
the waters from the south. Winds then shift to the SW for Monday leading
to improving conditions with waves over the Bay 1-2 feet and seas 2-4
feet. A cold front pushes through the region Monday night/Tuesday morng...with Small Craft Advisory
conditions again possible in association with a nearly surge.
Maryland...Winter Weather Advisory until 7 PM EST this evening for mdz021-
Virginia...Winter Storm Warning until 7 am EST Monday for vaz048-049-
Winter Weather Advisory until 3 PM EST this afternoon for
Winter Weather Advisory until 7 PM EST this evening for
Marine...Small Craft Advisory until 10 PM EST this evening for anz632-
Small Craft Advisory until 7 PM EST this evening for anz630-
Small Craft Advisory until 4 PM EST this afternoon for anz638.