Area Forecast Discussion
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FXUS61 KAKQ 301812
Area Forecast Discussion
National Weather Service Wakefield VA
212 PM EDT Fri Sep 30 2016
An upper level low lingers over the Ohio Valley today. Meanwhile,
high pressure builds well north of the region and steers a
moisture rich airmass into the region through today. Slowly
improving conditions are expected into the weekend as the upper
low lifts back to the north.
.NEAR TERM /THROUGH TONIGHT/...
The Delmarva is presently getting a much need break from heavy
rain, which has totaled up to 6-12" across DE/Lwr MD Ern Shore
over the past 48 hours. This water will result in rising main
stem rivers through the afternoon and potentially into tonight.
Follow the latest flood warnings for more details.
Current GOES WV imagery continues to depict a stubborn anomalous
upper low over central KY. A plume of deep moisture extends from
off the SC/GA coast nwd into central NC/s-central VA, and nw
across the central Appalachians. Another plume to the east has
pushed offshore brining the need break in rain to the Delmarva.
Showers and embedded tstms are developing across central NC and
streaming nwd into the Piedmont. This activity is being triggered
by the combination of the aforementioned moist plume/mid-level
theta-e ridge, a push of mid-level dry air on the wrn flank of the
moisture stream, a spoke of shortwave energy rotating around the
upper low. The interaction of the push of dry air into the moist
airmass will create some convective instability aloft. Strong
mid-level flow (55-65kt at 500mb) will result in strong deep layer
shear. This combination could trigger some strong to marginally
severe tstms this afternoon and evening, which is reflected in the
marginal outlook from SPC. The main threats are hail and locally
strong wind gusts. The main limiting factor will be the lack of
SB/BL CAPE with an in situ wedge airmass in place. The best
coverage will be west of Richmond initially through early
afternoon, before shifting ewd later this afternoon and evening.
Locally heavy rainfall will produce an isolated flood threat for
the more sensitive areas.
Otherwise, mostly cloudy to overcast. Strong high pressure to the
n will maintain the in situ wedge airmass over the piedmont with
highs around 70/low 70s, gradually ranging/rising to the low 80s
se where some breaks in cloud cover are expected.
Area of showers lifts northeastward this evening toward the
northeast zones as the front begins to lift. Deepest moisture flux
and convergence pushes offshore, which will limit overall rainfall
amounts. However, additional localized flooding is possible in the
areas sensitive from the previous days rain. Drying inland this
evening through the overnight with some breaks in the clouds
possible over the southern Piedmont. Mild again with lows in the
mid to upper 60s.
.SHORT TERM /SATURDAY/...
Dry air continues to entrain into the system Saturday as the
upper low fills and lifts northward. The result will be gradually
improving conditions. Addition energy lifts over the region in
southwest flow aloft, so can`t rule out isolated to scattered
showers east of interstate 95. Sky conditions also improve with a
partly cloudy sky inland, but remaining moistly cloudy near the
coast. Highs Saturday range from the upper 70`s to low 80`s, but
less humid as dewpoints drop into the upper 50`s to low 60`s
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Anomalous upper low over the Ohio Valley during the short term will
make its way slowly north and northeast early next week...allowing
for high pressure to build into the Mid Atlantic States. A chance
for showers remains Sunday over the Chesapeake Bay and portions of
Hampton Roads and east and end all areas by Monday morning. A strong
surface high will remain over southeast Canada which will increase
its influence across the Eastern Seaboard early next week with its
associated easterly flow. A chance for showers returns to the
forecast Tuesday and Wednesday. Tropical Cyclone Matthew may have an
influence late in the week...especially in the marine area.
Uncertainty remains in terms of the timing and track. Refer to
guidance from the National Hurricane Center and extended forecasts
from the Weather Prediction Center for details.
High temperatures from 75 to 80 Sunday and Monday lower to around 70
in the northern Piedmont to the upper 70s northeast North Carolina
by Thursday. Lows will range through the 60s.
.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
The combination of low pressure over the Ohio Valley and a
stationary front from North Carolina to off the Virginia coast was
producing a moist onshore flow over the Mid Atlantic States.
Satellite showed clearing over the coastal waters and portions of
the Bay and mostly cloudy sky over the TAF sites. Occasionally where
the sky clears over southeast portions...the clouds fill back in
with a broken MVFR layer. IFR cigs were over SBY and may continue
through nearly all of the TAF period.
Thunderstorm activity was beginning to develop over far southern
Virginia and south into eastern North Carolina and was spreading
northward. With the unstable airmass in place...put VCTS for
portions of the afternoon at all the TAF sites except SBY.
IFR (and possibly LIFR) redevelops late this evening and overnight
at RIC and SBY. It may need to be added to PHF but is unlikely at
ORF and ECG. Conditions improve during the mid to late morning
Update...SCA for mouth of Ches Bay extended through 400 PM this
aftn. Waves will average 3-4ft during this time before subsiding.
Strong/anomalous sfc high pressure (1035 mb+) still centered over
eastern Canada with a weak trough of low pressure along the VA
coast. The stronger pressure gradient is shifting N and winds have
diminished significantly except across the northern coastal zones
where 20-25 KT winds persist for a few more hrs. SCA`s for the
mouth of the Bay have been extended through 1 pm (for 4 ft waves)
Elsewhere, SCA`s will remain in effect through today/tonight for
southern coastal waters (and into Sat farther N as seas are slow
to subside with residual 9-10 sec period swell).
Calmer marine conditions expected Sat ngt thru Mon.
Allowed coastal flood advisory for Virginia Beach to expire at
noon. Tide levels for this area as well as Eastern Currituck will
be within 0.3ft of minor flooding thresholds through high tide
this evening and nuisance flooding may be possible in the
persistent onshore flow. Also extended flood advisory for Maryland
Beaches through Saturday morning as water levels near Ocean City
remain just above 4ft during high tide.
The synoptic pattern with strong High pressure centered over
eastern Canada with a slow moving boundary/sfc low pressure inland
over the Carolinas/Mid-Atlantic will continue to bring persistent
ENE flow to the area this evening/Fri. As of 11Z, Departures avg
1.5 to 2.0 feet for the most part.
Have updated CFW to expand the Coastal Flood Warning to include
all of the VA Northern Neck zones through the upcoming high tide
cycle that occurs late this morning into the aftn and the MD
eastern shore counties along the Bay (both for moderate flooding
expected). Elsewhere, have continued coastal flood Advisories
(and expanded to include VA Beach) to include both the upcoming
morning/early aftn High tide cycle and the following late
evening/early Sat am cycle. Looking at latest currents data in the
lower Bay suggests outgoing tides are slowly strengthening but
water will remain piled up in the Bay for at least 2 more cycles.
In addition, high rip risk for all beaches as seas are remaining
elevated at 5-7 ft with 9-10 second dominant periods.
MD...Coastal Flood Advisory until 11 AM EDT Saturday for MDZ024-025.
Coastal Flood Warning until 9 PM EDT this evening for
VA...Coastal Flood Advisory until 4 AM EDT Saturday for VAZ089-090-
Coastal Flood Advisory until 2 AM EDT Saturday for VAZ084>086-
Coastal Flood Advisory until 11 AM EDT Saturday for VAZ099-100.
Coastal Flood Warning until 5 PM EDT this afternoon for
MARINE...Small Craft Advisory until 10 PM EDT Saturday for ANZ650-652-
Small Craft Advisory until midnight EDT tonight for ANZ656-658.
Small Craft Advisory until 4 PM EDT this afternoon for ANZ634.