Scientific Forecaster Discussion
fxus61 kakq 220016
Area forecast discussion
National Weather Service Wakefield Virginia
716 PM EST Thu Nov 21 2019
high pressure centered along the Carolina coast moves offshore
tonight. A cold front enters the region late Friday and lingers
through Saturday before a strong low pressure system pulls the
front off the coast by Sunday. High pressure returns late Sunday
Near term /until 6 am Friday morning/...
as of 630 PM EST Thursday...
Only minor tweaks to the near term forecast. Adjusted sky cover
up a bit as high clouds continue to move across the area.
Unfortunately for those hoping for clearer skies later tonight
to catch a glimpse of the meteor showers, viewing conditions will
not be optimal across our area, although some of the hi-res
guidance is optimistic that there could be some breaks over southeast
portions of the area. Rest of the forecast remains on track. Dew
points will be on the increase overnight as southerly flow
brings in moisture ahead of an approaching cold front from the
west. Combination of cloud cover and rising dew points should
hold overnight temps in the 40s.
Short term /6 am Friday morning through Sunday night/...
as of 330 PM EST Thursday...
By Fri, the potent northern stream upper shortwave/sfc low will
be tracking ewd from Ontario to Quebec. As it does so, the
trailing cold front will be approaching the region from the NW,
reaching nrn portions of the County Warning Area by late aftn-early evening.
Deeper moisture (along with a series of weak disturbances) moves
in from the west-west-southwest during the day on Fri. 12z/21 deterministic
models (as well as the href/eps/gefs) continue to show the
deepest moisture/lift tracking ewd across the nrn two-thirds of
the County Warning Area from 15-21z Fri. Models do show the potential for
scattered showers across southeast Virginia/NE NC. Given increasing
confidence, have raised pops to ~70% from the northwest Piedmont to the
Virginia nrn neck to the lower Maryland ern shore for a 3-6 hr period, with
likely pops now over the entire ric Metro. Have pops of 30-50%
across far srn Virginia and most of Hampton Roads, with only 20-30%
pops for NE NC (mainly from 18z Fri-00z sat). Quantitative precipitation forecast amounts on
Fri look light (mainly 0.10-0.20"). Given the rain (and mostly
cloudy skies), have lowered highs a bit (especially across the
n). Forecast highs are mainly in the mid-upper 50s over the nrn
two-thirds of the cwa, with low-mid 60s across srn Virginia/NE NC.
Rain chances diminish and shift S from 21-00z Fri.
The front crosses most of the region Fri night, before
stalling just S of the Virginia-NC border in response to developing
sfc low pressure hanging back over the lower MS valley. This
happens at the same time the closed upper low now over the SW
Continental U.S. Becomes centered over the plains and continues to slowly
move eastward. Expect some drying (with very little chc for
pcpn) behind the front Fri night, but will keep slight chc pops
for light rain across srn Virginia/NE NC through 06z Fri. Mostly
cloudy although there will likely be some clearing over the far
north/NE late. Lows range from the low-mid 30s across north/NE zones to
the mid 40s across coastal southeast Virginia/NE NC.
The aforementioned surface low is progged to move eastward
towards the Ohio Valley on Sat. The stalled boundary will move
back north as a warm front and will try to cross our region during
the day on Saturday, but model consensus continues to show the
front not making it much past srn Virginia (becoming centered from the
srn Virginia Piedmont to the Virginia ern shore by Sat evening). Not a
whole lot of changes to the forecast, as the 12z/21 GFS/ECMWF/Gem
continue to be slightly slower W/ the arrival of the pcpn
during the day on Sat (nam/NAM nest are slightly faster).
Regardless, most areas will be dry Sat morning, but still mostly
cloudy except over the Eastern Shore and NE zones where some
sunshine is expected until midday. Expect a quick overspreading
of rain due to deep isentropic lift by early-mid aftn across the
wrn two-thirds of the County Warning Area (with at least a chc of rain in all
zones after 18z sat). Rain is expected to overspread all areas
by the early evening hours on Sat. Expect a cool/cold day
(especially in areas north of the warm front). Forecast highs are in
the low 40s across the northwest Piedmont, mid-upper 40s across the
central third of the County Warning Area (oriented SW-ne), and low-mid 50s
across coastal southeast Virginia/NE NC. Latest 12z/21 eps/gefs continue to
depict highest chance for widespread moderate rainfall to be Sat
night so have ~80 to 90% pops in all zones during this period
as the trailing cold front pushes through as the sfc low tracks
to our north. In addition, models are showing some elevated
instability (mucape of 100-300 j/kg) moving across much of our
area during the Sat evening-early sun am timeframe. Cannot rule
out a rumble of thunder or two during this time (best chc
across the sern two- thirds of the cwa), but left any mention of
thunder out of the forecast for now. The warm front continues
to slowly move north through the first part of Sat night (as the sfc
low tracks to our n). As a result, expect a non-diurnal
temperature trend starting Sat evening, tending to warm several
degrees during the first part of Sat night. Temperatures then
fall during the latter half of Sat night as the cold front
crosses the region from northwest to southeast. Lows sun am range from the
upper 30s northwest to the upper 40s/lower 50s across far southeast Virginia/NE NC.
Rain chances end in all areas (except along the immediate coast)
by 12z sun as the low quickly moves offshore. Skies eventually
become partly-mostly sunny by sun aftn as weak high pressure
builds toward the region. Highs mainly in the 50s on sun.
Long term /Monday through Thursday/...
as of 330 PM EST Thursday...
The beginning of the week starts off dry as high pressure will be in
control. On Monday the high will be centered over the Florida Panhandle
and by Tuesday the high will drift NE off the mid-Atlantic coast.
This will result in a west/SW flow for Monday and a S/SW flow for
Tuesday. Temps on Monday will remain several degrees below normal
with low temps ranging from the low 30s northwest to upper 30s se, and high
temps in the mid to upper 50s. The southerly flow on Tuesday will
bring temps up to seasonal norms with high temps in the upper 50s to
A cold front associated with a low pressure system that will drift
from the Great Lakes region to northern New England will cross the
area on Wednesday into Wednesday night. There won't be much moisture
at all out ahead of the front, so just chance pops in for Wednesday.
Rainfall amounts will be minimal, with most guidance suggesting less
than a tenth of an inch. Since the front likely won't cross the area
until later in the day, temps on Wednesday will remain warm, with
low temps Wednesday morning in the 40s and high temps in the lower
60s. After the frontal passage, high pressure builds in for Thursday
resulting in dry and slightly cooler conditions.
Aviation /00z Friday through Tuesday/...
as of 715 PM EST Thursday...
VFR conditions prevail through the 00z taf period. Mainly scattered to broken
high clouds (20-25k feet) prevailing over the area tonight. Light
and variable winds right now will become west/SW through the day
Fri and will slowly increase to 10-15 kt with gusts to 22 kt
between 17z-22z before decreasing to 10 kt afterwards. Still
looking like a good (70%) chc of shras at ric/sby mainly between
17z-21z Fri. The chc of shras is lower across the southeastern
terminals (20-40%) with the greatest chance from 18z-21z Fri
over orf and phf). There will be a chc for brief MVFR conditions
Fri aftn at ric/sby. Brief MVFR conditions are also possible
across southeast Virginia/NE NC by Fri evening, although confidence is low
for this region.
Outlook...VFR conditions late Fri night into mid-afternoon
Sat with winds shifting to north/NE after the cold frontal passage by
Sat morning. Low pressure approaches from the SW on Sat before
tracking across the region Sat night. Rain is likely, as well as
flight restrictions during the Sat aftn-Sat night timeframe
(due to both cigs/vsbys). VFR/drying out for sun with a breezy
as of 315 PM EST Thursday...
This afternoon, high pressure is gradually shifting offshore as the
next low pressure system begins to approach from the northwest.
Winds are generally light and variable to west or northwest. Winds
become southwesterly later this evening and tonight as high pressure
moves offshore and south of the region. Winds pick up to Small Craft
Advisory levels after midnight as the pressure gradient tightens
between the departing high pressure and approaching low pressure
system to the north. Expect SW winds of 15 to 20 knots with gusts to
25 knots over the Chesapeake Bay and near 20 knots with gusts to as
high as 30 knots over the ocean zones. Winds remain elevated into
late Friday morning/early afternoon, before a weak front crosses the
waters turning winds towards the northwest. As a result, have sca's
going into effect later tonight and lasting through the day Friday
for all coastal zones minus the rivers (the lower James may also
need a sca, but for the time being have capped sustained winds at 15
knots). Seas will once again increase to 3 to 5 feet during this
time period (perhaps up to 6 feet out 20 nm), and waves in the Bay
to 2 to 3 feet. Seas may remain elevated to 5 feet into Friday
night, especially across the north/out 20 nm.
Winds may briefly pick up again Friday night/Saturday morning as
cooler air filters into the region from the northwest. North to northwest may approach
Small Craft Advisory criteria across the Bay for a brief period late Friday
night/early Saturday morning, before diminishing closer to sunrise
Saturday. Calmer conditions (regarding the winds), during the day
Saturday with a light east to southeast flow ahead of the next system.
A low pressure system will track east of the Appalachian Mountains
and across the Carolinas Saturday afternoon-evening, then across our
area Saturday night into early Sunday morning. Winds become
southerly late Saturday as the low tracks across Virginia and Maryland. The area
of low pressure tracks off the mid Atlantic coast Saturday night-
Sunday turning winds to the west-northwest and increasing wind speeds to 15 to
25 knots by Sunday morning. Another round of scas will likely be
needed for this period across the Bay and coastal zones. Seas
increase again to 4 to 6 feet, and waves in the Bay around 2 to 3
feet. Calmer conditions take hold late Sunday into early next
Marine...Small Craft Advisory from 1 am to 4 PM EST Friday for anz632-
Small Craft Advisory from 7 am to 4 PM EST Friday for anz633-
Small Craft Advisory from 1 am to 1 PM EST Friday for anz630-
Small Craft Advisory from 1 am to 7 PM EST Friday for anz650-