Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
709 am EST sun Nov 29 2015
a cold front slowly drops south through the middle Atlantic region
today...stalling across the Carolinas Sunday night into early next
week. The next cold front is expected to cross the region on
Near term /until 6 PM this evening/...
high pressure in Canada skirts by the northern Great Lakes region
today...effectively pushing a cold front southward through the area. As
of 630 am...the front stretches from Melfa to Tappahannock and
nwwd into central WV. Composite radar echo returns appear to be
widespread in central and eastern Virginia...however actual ground
observations show light rain and drizzle occurring in far northern
counties of the forecast area. Rainfall north of the front will become more
defined for most of the region throughout today as it tracks southward
and an 80-90kt jet streak enhances lift during peak heating this
afternoon. Light quantitative precipitation forecast trends continue with generally 0.10 inches or
less expected in the next 12 hours. Temperatures across the north
are close to reaching their highs (54-60 degrees) and will then
remain steady the rest of today in steady light rain. Farther
south...temperatures should warm nicely ahead of the front with highs in
the 60s despite cloudy skies.
Short term /6 PM this evening through Tuesday night/...
the cold front exits the area this evening and stalls across the
Carolinas on Monday/Monday night. Meanwhile...high pressure slides
across southeast Canada into northern New England tonight and moves just off
the northern New England coast Monday night. The high gradually extends
down into the Middle Atlantic States tonight and becomes wedged down
the Lee of the Appalachians...resulting in a cold air damming
setup. In regard to precipitation...the cold front actually
extends across to the arklatex region with a surface low developing
over the Tennessee Valley tonight. Shortwave energy from this feature
crosses NC and southern Virginia and effectively overruns the developing cad
wedge. This will enhance precipitation across the southern half of the
County Warning Area overnight tonight. Shortwave continues to track from west to
east along the Virginia/NC border on Monday...weakening as the day
progresses and thus precipitation is expected to gradually diminish.
Models vary greatly with quantitative precipitation forecast amounts and placement...therefore
forecast is a short range model blend with the main focus across
southern Virginia/NE NC tonight/Monday morning. Overall totals range from
0.25-0.50 inches across the south with lesser amts the farther
north you go. Temperatures may be a bit tricky tonight depending
on evaporative cooling effects of ongoing precipitation and timing of not
only the cad wedge development but also the arrival of cooler air
from the north. Low temperatures tonight generally in the 40s most
areas...except in the lower 50s far southeast Virginia/coastal NE NC. Monday highs
also tricky due to aforementioned reasons. Highs should be in the
middle-upper 40s northwest and low-middle 50s southeast (upper 50s coastal areas of
far southeast Virginia/NE nc).
Low pressure along the stalled frontal boundary is expected to
deepen off the Carolina coast Monday night and move up the middle
Atlantic coast on Tuesday. This should erode the cad wedge by Tuesday as
the Tennessee Valley low gets absorbed into a larger low pressure system
crossing the Midwest. Both low pressure features will bring
another round of rainfall to the region late Monday night into Tuesday. A
brief dry period across the south may be possible as the coastal
low exits the north of the area and a more substantial Midwest low
pushes a cold front toward the middle Atlantic region late Tuesday night.
Models in slightly better agreement with quantitative precipitation forecast placement during this
timeframe...however amounts still vary. Once again went with a
short range model blend with totals averaging 0.50-0.75 inches northwest
to 0.20 inches southeast for Monday night through Tuesday night. Temperatures likely to
hold nearly steady Monday night as more rainfall moves into the
region. Lows in the 40s inland/lower 50s along the coast. Highs
Tuesday in the middle-upper 50s inland (lower 50s far northwest counties)...
lower 60s closer to the coast. Lows Tuesday night in the lower 50s
(upper 40s possible far northwest counties).
Long term /Wednesday through Saturday/...
going with a blend of the 12z GFS/European model (ecmwf) for the extended period.
Cold front will approach from the west Tuesday night...then cross the region
and move off the CST Wednesday into Wednesday night. Will have hi chance to likely
probability of precipitation for rain Tuesday night into early Wednesday afternoon...then decreasing probability of precipitation
from west to east later Wednesday afternoon into Wednesday eveng. Both the latest GFS and
European model (ecmwf) now indicate dry weather for later Wednesday night through Sat...as a large
area of hi pressure builds eastward and eventually over the area from the
plains and Midwest. Lows in the upper 40s to middle 50s Wednesday morng...in
the middle 30s to middle 40s Thursday morng...and in the lower 30s to lower 40s
Friday and Sat morngs. Highs in the upper 50s to middle 60s Wednesday...and
mainly in the lower to middle 50s Thursday...Friday and Sat.
Aviation /12z Sunday through Thursday/...
a cold front is sagging southward through the middle-Atlantic
tonight and will slide through the area by Sunday evening. At
12z...the front has dropped more quickly donw the Delaware-Maryland-Virginia with
the front south of Melfa and then extends west-northwest through the middle
peninsula and just north of lku/cho. The front will continue to
sag south today with ceilings dropping to IFR levels. The bulk of
the rain on radar is still north of the area and sby would be the
first site impacted. The models show the lift enhancing during
the day on Sunday so have added more precipitation and visibility
restrictions from middle afternoon on Sunday into the evening hours.
The best forcing slides off the coast by around 21z and as the
high to the north builds southward with some drier air at the low
levels...expect to see ceilings lift some after 00z so have shown
a return to MVFR condition tonight.
Outlook...periods of rain and IFR conditions can be expected
Monday through Wednesday with onshore NE winds at the surface and a
moist west to southwest flow aloft. As high pressure builds south
into the Middle Atlantic States...a cold air wedge will develop along
the east side of the Appalachians...promoting deterioration of
aviation conditions...especially at ric.
A cold front sweeps off the coast Wednesday bringing in drier air
and VFR conditions to the area beginning Wednesday night and
the cold front is making its way into the northern coastal waters
this morning and is continuing to push south as the surface high
pressure system that has been over the region has drifted south
into Georgia. The winds are still light SW in advance of the
front...but behind the front the winds are our of the north and
initially around 10 - 15 knots. This front will continue to sink
south today and move through the waters by early Sunday evening.
As the surface high builds southward today...it will help tighten
the gradient along the coast and the winds are expected to
increase to 20 to 25 knots and the seas will build back to 5 to 7 feet.
So will raise Small Craft Advisory for the northern 3 coastal zones beginning at 3z
and the 2 southern zones and the mouth of the Bay at 6z. The rest
of the Bay should remain around 15 kts with the nearly flow.
The combination of the surface high and weak low pressure forming off
the coast will keep the Small Craft Advisory conditions in place through Monday
night with a strong east-northeast flow. As the surface high begins to retreat on
Tuesday...the winds will expect begin to relax and turn more to
the southeast and then SW on Tuesday afternoon as a warm front lift back
north of the area. The Small Craft Advisory is only in effect through Monday at
this time but will probably need to be extended into Tuesday...
until the warm front passes.
The next cold front will cross the area on Wednesday. Expect the
SW winds to turn out of the northwest and with the strong cold air that
is expected to move in behind the front...winds should again be
strong enough for Small Craft Advisory conditions.
Marine...Small Craft Advisory from 1 am to 5 PM EST Monday for anz634-
Small Craft Advisory from 10 PM this evening to 5 PM EST
Monday for anz650-652-654.