Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
416 am EST sun Dec 8 2013
high pressure centered over Pennsylvania this morning will slowly
retreat off to the northeast. 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/...
current conditions show dew points now dropping into the low 20s
across northern/central zones...middle 20s in the south. Even though
temperatures are still mainly at or above 32f...as precipitation
intensifies later this morning...especially between 12-15z...think
the temperatures will drop several degrees due to column cooling. Current
warning/advisory headlines have been adjusted to add a sliver of
counties in central/S central Virginia to the advisory...mainly for very
light amounts of ice accumulation (genly less than .05"). It will
be marginal but west/northwest portions of these counties in particular are
likely to see a light coating by late morning. Otherwise...no
changes to overall thinking. Latest sref does suggest the
potential for a little less ice and a little more sleet/snow across
northern areas. Made only minor grid adjustments to reflect
this...still expect .25" of ice across most of the warned area and
locales that receive a little less may see up to 1 inch of
snow//sleet with temperatures through 18z below 32f.
After 18z-21z...the strong isentropic lift develops 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 come to an end. So
expect the precipitation to start off fairly heavy later this
morning then gradually become lighter during the afternoon. Also
looking at BUFKIT soundings see some drier air aloft coming in
during the afternoon which will also decrease the intensity of the
Precipitation to the northwest of Richmond will probably begin as
sleet and snow mixed before changing to freezing rain. From
Richmond and northeast could see precipitation begin as a mix of
snow and sleet but quickly change to a brief period of freezing
rain before temperatures rise above freezing during the morning. Expect
largest ice accumulations over Fluvanna Goochland and Louisa with
some areas receiving around a half inch of ice.
Late tonight 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. 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 /09z Sunday through Thursday/...
VFR conditions to start off the taf period as surface hi pressure
strengthens just north of the forecast area. Area of warm air advection precipitation spreads
across the region later this morng and continues 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. North/NE winds will be
gusty at times...especially toward the coast.
Outlook...IFR ceilings are likely to persist through Monday with
periods of rain possible into Tuesday. Conditions improve by Tuesday
night with VFR/dry weather 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 anz633.
Small Craft Advisory until 7 am EST this morning for anz630-