Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
745 PM EST Wednesday Dec 4 2013
high pressure will linger off the middle Atlantic coast through
Thursday. Meanwhile...a warm front lifts north through the region
tonight. A slow moving cold front is expected to move into the
area by midday Friday...followed by a period of unsettled weather
through the weekend.
Near term /through Thursday/...
a warm front is currently draped along the NC/SC border. Not much
precipitation is seen on the regional radar mosaic except a couple of
showers moving NE through the Outer Banks. Light S-southeast winds are
providing plenty of low-level moisture this afternoon...with
clouds plentiful across the area.
Warm air advection really kicks into gear tonight as the warm front lifts north
and puts the area within the warm sector. The best moisture
associated with the warm frontal boundary will move away from the
forecast area overnight and this should allow for a a dry forecast. Given the
abundant low-level moisture in place...expect overcast conditions
for most areas overnight and even patchy fog. A mild night is on
tap with lows in the low-middle 50s (upper 40s for interior Maryland
Short term /Thursday night through Saturday/...
Thursday through Friday night...
a cold front crosses the Ohio Valley on Thursday and gets hung up along
The Spine of the Appalachians Thursday night into Friday morning. This is
due to a blocking pattern developing...where a strong Arctic high
is digging into the nctrl U.S. And another high in the western
Atlantic is preventing the cold front from progressing eastward.
Because the progression of the front remains slow on Thursday...have
continued with a dry forecast during the day. Have maintained a
schc/chance for precipitation along a line north of generally Farmville-
Richmond-Salisbury for late Thursday night but suspect that this may
not happen until closer to Friday morning. S-SW winds will help
bring even milder air into the area...resulting in high temperatures
in the upper 60s to around 70 north...and low/middle 70s south...despite
mostly cloudy skies.
As the cold Arctic airmass finally intrudes on the warmer air to
its south...the front will finally start to push across the area
from the northwest by Friday afternoon. Sharp temperature and pressure
contrasts between the warmer airmass over the region versus the
cold Arctic airmass to the northwest will cause SW winds to become
breezy with gusts up to 25 miles per hour during the afternoon south of the cold
front. Continued warm air advection advection south of the front and favorable mixing
will once again help to boost high temperatures well above normal on
Friday...especially over southeastern areas where temperatures should reach the middle-
upper 70s. For northwest areas...temperatures may only be in the low-middle 60s due
to where low clouds and precipitation occur. The cold front crosses the
rest of the forecast area Friday night and moves just off the coast by Sat
morning. Precipitation is expected to become more widespread and
steady overnight Friday. Low temperatures Friday night will be tricky
depending on how fast the Post-frontal Arctic air can move into
the region and when winds turn to the northwest/north. Am
currently anticipating a contrast with lows in the upper 30s/lower
40s northwest to lower 50s far southeast. As far as probability of precipitation are concerned on
Friday...will carry likely probability of precipitation 55-65% across far northern
areas...with likely/categorical probability of precipitation (70-80%) spreading south across
much of the area Friday night.
the aforementioned cold front stalls out across the southeastern U.S. As
Arctic high pressure expands eastward from the Ohio Valley into
the northeast. North-NE surface winds will continue to funnel colder air
into the middle-Atlantic region through the day with highs during the
day either holding steady or only rising a couple of degrees from
their morning lows. Highs around 40 northwest to the low/middle 50s southeast. The
question that still remains is just how much precipitation lingers across
the local area on Saturday. At this time...the European model (ecmwf) and GFS models still
favor light rain lingering along and south of a avc-ric-sby line
through the day. The NAM/sref drives the surface cold front a little
farther south which supports less precipitation on Saturday...especially
after noon. Tend to favor the precipitation getting hung up and being
slower to exit given the position/strength of the western Atlantic
ridge. Therefore...will keep chance probability of precipitation across the southeastern half of the
forecast area through the day.
Long term /Saturday night through Wednesday/...
rather challenging forecast Saturday night and Sunday as both the
12z GFS and European model (ecmwf) are a bit colder at the surface due to the apparent
ridge being a bit slower to move out of eastern New York. This will be
critical as to where surface temperatures fall to or stay below 32 leading to a
fz rain versus a cold rain scenario as the next in a series of S/w's
rides NE with overrunning moisture. Leaned toward the European model (ecmwf) solution
as it seems to handle the cold wedge better than the GFS. The GFS
has the strongest ridging east of the Piedmont while the Euro has
the strongest ridging along and just east of the mts (which is key
to holding the colder air in longer). In addition...BUFKIT soundings
shows the potential for several hours of ice (along and northwest of a
fvx-ric-xsa line). So with this in mind have come further south &
east with the fz rain late Saturday night...have also added a few
hours of sleet at the onset mainly northwest of ric giving the initial dry
air. Lows 30 northwest to 40 southeast.
Sunday will have its challenges as the cold air gets locked in
across the Piedmont with steady or slowly rising temperatures to just above
freezing in the afternoon while east-southeast winds brings milder air in from
the ocean with coastal temperatures rising well into the 50s...possibly
near 60. Have extended the fz rain into the early afternoon across
Louisa / Fluvanna / western Goochland / Cumberland countys where the
best chances for accumulating ice will be. Otw...likely probability of precipitation for rain
into Sunday night with steady or slowly rising temperatures Sunday night.
Dryer and cooler conditions return by middle week behind a cold frontal
passage Tuesday. Highs Tuesday in the 40s/50s (falling temperatures in the afternoon).
Lows Tuesday night in the 20s. Cold Wednesday with highs in the m30s-l40s.
Aviation /01z Thursday through Monday/...
as of 00z...surface warm front has lifted north of the area. Slowly
rising temperatures/dewpoints into southern/central Virginia will create IFR/LIFR
conditions at all sites. Warmer south-southwest flow will increases to 10-15 knots
or so and should scatter out the low clouds Thursday.
A cold front will be slow to progress into the area Friday/Friday
night...highest chances for significant reductions in ceilings/visibilities
looks to arrive later Friday night through Sat/sun. Generally appears to
be a rain event for korf/kphf/kecg/ksby...with some potential for
mixed precipitation at kric 2nd part of the weekend.
no headlines in short term as a light south flow follows a warm
front as it lift north of the area. Flow becomes SW Thursday but expect
winds over the land to be a bit higher than over water. Prs gradient
increases Thursday night/Friday ahead of a slow moving cold front. Mixing
will be limited..so no Small Craft Advisory expected due to winds. Wna continues to
advertise marginal Small Craft Advisory conditions (5ft seas) over the northern
Models continue to forecast potent cold frontal passage early Sat
morning. Small Craft Advisory conditions appear likely for all zones by Sat morning
as strong high pressure builds to the north of the area and much
colder air aloft begins to mix down over the waters. Boundary stalls
to the south as strong high pressure builds from the Great Lakes to
New England on Sunday...with Small Craft Advisory conditions still possible.