Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 232140
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
540 PM EDT Mon Oct 23 2017

.SYNOPSIS...
A weakening cold front slowly push through the local area late
tonight into early Tuesday. A second cold front crosses the area
Tuesday night. High pressure builds across the Gulf of Mexico
Wednesday and Thursday...as low pressure lingers from the Great
Lakes to New England.

&&

.NEAR TERM /THROUGH TUESDAY/...
Current analysis indicates sfc high pressure well off the coast,
with low pressure deepening along the central Appalachians (this
out ahead of parent sfc low over NW OH/northern IN). Area of
showers overspreading much of the western Piedmont continues to
be very slow to progress eastward, while some scattered showers
have developed over interior NE NC. Little overall change in
thinking with the scenario tonight, with a high shear/low CAPE
event expected. The best lift/forcing for likely to categorical
PoPs (60-90%) looks to reach to areas west of I-95 prior to
midnight, then pushing E to the I-95 corridor from 03-06Z, and
to the coast from 06-12Z. Strong low level jet and effective
shear values to 50-60 KT (and some directional shear through 06Z
as SSE sfc winds interact with SSW winds in the H85 to H7 layer.
SPC has SLGT risk SVR for SW parts of the local area (shifting
to the ern shore Tue morning). If it all comes together, an
isolated severe tstm with damaging winds and even an isolated
tornado can`t be ruled out. However, more likely it will be
just a narrow line of showers with embedded convection with wind
gusts staying below severe limits (to 40-45 mph). Will continue
the mention of locally heavy rain and strong/gusty winds in the
HWO.

Expect skies to turn partly to mostly sunny by late morning W
and by late aftn E...and have continued w/ lowering PoP trend
W-E. Still rather warm as winds remain from the SW, with highs
Tues in the mid 70s W to the lower 80s SE as cold air lags well
behind off to the NW of the local area.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
Latest 12Z/23 GFS/NAM/ECMWF remain in good agreement Tue night
into Wed, but then show some fairly significant differences
with respect to the strength of the upper low over the eastern
CONUS by late Wed/Thu. The ECMWF the deepest/farthest south and
the GFS the weakest/most progressive and the NAM somewhere in
between but genly a little more like the ECMWF.

Will side a little more to the NAM/ECMWF consensus, but not
quite to the extent of how deep the upper low digs south. Thus,
the sfc cold front reaches the coast early Tue night and is
expected to exit the coast by daybreak Wed morning. Any RA
tapers/ends at the coast Tue evening. Lows will range from the
upper 40s west of I-95 to the mid/upper 50s closer to the coast
by Wed morning. Dewpoints also fall from the lower 50s NW to
lower 60s SE in the evening to 40-45F inland and 45F to around
50F by morning. On Wed...local area looks to remain in between
the sfc cold front well offshore and deeper moisture/cold pool
aloft to our WNW. Some SCT/BKN cu will tend to linger due to
some shortwave energy aloft, but should be dry with highs
mainly in the m-u60s (staying a little below MAV numbers as
they are based off the warmer GFS). For Wed night/Thu, siding to
the NAM/ECMWF allows for some digging SE of the upper level
shortwave energy from the Great Lakes through the Carolinas by
thu morning. Will keep it dry for now, with partly cloudy
conditions. Lows Wed night mainly in the 40s and highs Thu 60-65
F under partly to mostly sunny skies.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Long term period starts off dry Thu night/Fri with sfc high pressure
over the immediate area and W/SW flow aloft. With light sfc winds
under a clear sky, expect low temps Thu night in the low/mid 40s
most of the area, and highs in the mid/upr 60s Fri. Attention then
turns to an approaching deep upper-level trough Sat. Although any
pcpn will likely hold off until after daytime Sat, included a 20%
chance of a shower in case the faster ensemble member solutions pan
out. Better chance of rain (40-50%) arrives Sat night/Sun as strong
sfc low pressure forms out ahead of the upper-level trough. There is
still plenty of uncertainty over the track of this low, but the
possibility is there for moderate to heavy rain Sun. High temps in
the mid/upper 60s Sat drop to the upr 50s to mid 60s Sun.

&&

.AVIATION /22Z MONDAY THROUGH SATURDAY/...
Low pressure and an associated cold front will approach fm the
west this evening, then the actual cold front will gradually
cross the region and move offshore later tonight into Tue
evening. Increasing SE then S winds expected this evening thru
Tue morning ahead of the front, with showers and possible tstms
moving thru the CWA later this evening into Tue morning. SE or S
winds 10-15 kt, with gusts up to 25 kt possible during this time
period, with higher gusts possible in stronger showers or tstms.
This front will bring the potential for MVFR/IFR conditions in
showers and lower CIGS. Mainly VFR conditions expected later Tue
aftn/evening through Fri.

&&

.MARINE...
Previous marine headlines remain in place ahead of an approaching
cold front. Decided to put all headlines in effect with this package
with SCA conditions expected to commence over all wtrs within 12 hr.
The SCA is for 15-20 kt southerly winds over the rivers/Sound and 15-
25 kt winds with gusts up to 30 kt over the Bay and ocean. Waves up
to 4 ft over the Bay with seas over the ocean up to 7-8 ft. A trough
of low pressure ahead of the cold front slides through the area
early Tue, with the pressure gradient relaxing a bit into the day
Tue and winds decreasing to below SCA thresholds. Main cold front
crosses the area Tue night with sub-SCA NW winds expected behind the
front into Wed. Will maintain the SCA over the ocean through the day
Wed due to a prolonged period of 5 ft seas. Lighter winds and sub-
SCA conditions into Thu and Fri with sfc high pressure over the
area.

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...None.
NC...None.
VA...None.
MARINE...Small Craft Advisory until 10 AM EDT Tuesday for ANZ635>638.
     Small Craft Advisory until 4 PM EDT Tuesday for ANZ630>632-634.
     Small Craft Advisory until 7 PM EDT Tuesday for ANZ633.
     Small Craft Advisory until 7 PM EDT Wednesday for ANZ650-652-
     654-656-658.

&&

$$
SYNOPSIS...LKB
NEAR TERM...LKB
SHORT TERM...ALB/LKB
LONG TERM...MAS
AVIATION...LKB/TMG
MARINE...AJB/MAS


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