Area Forecast Discussion
Issued by NWS Wakefield, VA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KAKQ 220315
Area Forecast Discussion
National Weather Service Wakefield VA
1115 PM EDT WED SEP 21 2016
A frontal boundary remains stalled along or just off the Southeast
or Mid Atlantic coast into Friday morning, with low pressure
lingering near the Southeast or Mid Atlantic coast tonight into
Friday morning. High pressure builds over the local area Friday
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
-- Changed Discussion --Update...
Flash Flood Watch extended through 400 AM and areal flood warnings
also extended for another 6 hours across SE VA/NE NC. Shortwave
energy rotating around the stacked low near the SC coast is
becoming enhanced as it interacts with a deformation axis situated
across south central VA. Rainfall is effectively training over
these same areas with locally moderate to heavy rainfall at times.
This trend will continue overnight, thus the reasoning to continue
flood headlines since many areas within the flood warnings are
still experiencing flooding and road closures with nowhere for the
additional rainfall to go.
Added a hydrology section to forecast discussion for the Cashie
River near Windsor. See below for details.
Previous discussion (616 PM)...
Meanwhile, a dry slot seen in water vapor imagery is moving up the
coast from the Outer Banks to as far north as Ches Bay attm. This
is allowing precip rates/1 hr totals to diminish closer to the
coastal areas of far SE VA/NE NC despite the continuous moisture
feed coming off the ocean in onshore flow. Expect this trend to
continue near the coast overnight...with moderate showers within
a deformation axis located n-nw of the stacked low (best seen
utilizing infrared imagery). Have adjusted POPs to account for
the aforementioned precip trends this evening with light to
moderate rain showers becoming focused closer to southeast
coastal areas late tonight into Thursday morning.
Previous discussion (424 PM)...
Late this aftn, remnant lo pres that was tropical cyclone Julia
was cntrd ovr ern SC. This lo pres area continues to pull bands of
showers into the srn two thirds of the CWA, with moderate to
heavy showers affecting much of the srn half of the region. Due to
continued areal flooding going on acrs most of SE VA and NE NC,
and additional rainfall between .50 inch and 2 inches possible in
these areas thru this evening, have extended or expanded the Flash
Flood Watch until midngt. Coverage and intensity of the pcpn will
decrease overnight, and Pops will decrease rapidly as you go N of
a Farmville to Petersburg to Wallops Island line. Lows tngt will
range fm the mid 60s to lower 70s.
-- End Changed Discussion --
.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
A frontal boundary and lingering lo pres near the SE or Mid Atlc
coast, will continue to result in at least hi chc pops (40-50%)
acrs the Srn/SE portions of the region Thu into Thu evening.
The combination of nrn stream energy and the upr lo/associated
upr trough weakening, will finally result in Pops shifting offshr
later Fri/Fri evening. Surface hi pres will bld over the region
Fri evening into Sat morning. A backdoor front will then drops
acrs the area during Sat. Expecting dry conditions Fri evening
thru Sat. Highs in the mid 70s to lower 80s Thu, and in the upr
70s to mid 80s Fri and Sat. Lows in the 60s to arnd 70 Thu ngt,
and in the mid 60s to near 70 Fri ngt.
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
A trough digs over the Northeast US Saturday night into Sunday as
an upper level ridge builds over the Mississippi Valley. That
ridge then slowly amplifies and pushes eastward Mon-Wed. Models
have trended weaker with respect to pushing the associated cold
front completely through the area on Sunday. Surface high pressure
is progged to become centered over eastern Canada with a piece of
the High ridging down into the northern mid-Atlantic states Sunday
night into Tue (rather than actually building over the local
area). While deep moisture will be pushed south of the local area,
this pattern suggests that the sensible weather will still feature
a persistent easterly low level flow with skies to avg partly to
mostly cloudy Sunday (and perhaps Mon/Tue as well). Have also
lingered 20% POPS for much of the area Sunday, shifting to the Sw
zones Sun night/Mon. Highs will average in the 70s with lows in
the upper 50s to mid 60s.
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
A stalled frontal boundary remains near the coast this evening
with weak low pressure continuing to slowly move across eastern
NC. Weak high pressure is currently situated to the north of the
area. Showers continue to move across portions of SE Virginia and
NE North Carolina with a slight decreasing trend in
coverage/intensity. Showers have also developed across central
Virginia and continue to propagate west of RIC.
Similar to the past few nights, tricky forecast is in store for IFR
versus MVFR. Expecting stratus to develop in this moist airmass,
thus have IFR conditions in the forecast for RIC/SBY/ECG with cloud
decks hovering between 500-800 feet at these locations later
tonight. Also cannot rule out the chance for showers at
PHF/ORF/ECG, especially during the first half of the overnight
period. Am expecting a gradual improvement in cigs to MVFR
conditions during morning with cloud decks rising above 1000 feet
across the region after 12Z. Winds across the area are generally
onshore around 10-15 knots with occasional gusts.
Outlook: Gradual improving conditions are expected Thursday into
Friday as high pressure continues to build just north of the area.
VFR conditions can be expected by Saturday. Another frontal
boundary approaches the area Sunday into Monday.
SCA headlines are in effect for all coastal waters (through Thu
night), for the lower/mid Bay (through tonight/Thu morning, and
lower James/Currituck Sound through this evening.
The wind slowly diminishes late tonight/Thursday, but seas remain
4-6 ft for Ocean waters. The latest data suggests low pressure
emerges back over the ocean Thursday night into Friday, which
suggests a modest 10-15kt nne wind continues. This will allow seas
to remain 3-5ft, with 2-3ft waves in the mouth of the Bay. A cold
front approaching from the N Friday night and pushing into the
area Saturday is now looking to stall over the Carolinas by
Sunday. Marginal SCA conditions are possible but appear less
likely now that the cool surge behind the front may stay mainly
N of the local area.
-- Changed Discussion --The Cashie River near Windsor is expected to reach major flood
stage (which is 13.0 ft or above) around midnight tonight and
crest near 14.6 ft around 200 AM tonight. The ongoing rainfall
tonight into Thursday morning will keep river levels elevated
within major flooding Thursday morning and within moderate levels
(10-12.99 ft) through Thursday afternoon before slowly subsiding.
The Cashie River is not expected to fall below flood stage until
early Friday afternoon.
-- End Changed Discussion --
As of 22Z, tidal departures avg +0.5 to 1.0 ft over the marine
area, so despite significant flooding from heavy rainfall across
portions of Hampton Roads and northeast NC, actual coastal/tidal
flooding has been minimal from this event with most sites falling
short of Minor Flood thresholds by around 0.5 ft. Have allowed the
Coastal Flood Advisory for the mid/upper James River zones to
expire as High Tide has passed. Additional tidal flooding does
not look likely for Thu but some areas (especially the upper James
River may reach minor flooding again). Feel it is too marginal at
this point for an advisory so will allow next shift to determine
need for a statement or possible an advisory if departures were
to increase more than is currently expected. For now, departures
expected to continue at +0.5 to +1.0 ft through Thu/Fri. One
explanation for the rather low departures may be due to water that
has been able to exit the Bay into the Ocean fairly efficiently
despite the persistent onshore flow. Will continue to monitor
however, as tidal anomalies may build nwd through the Bay by Thu
aftn which could lead to some marginal tidal flooding by that
time farther up into the Bay.
The beach hazard statement has been discontinued, with a moderate
risk for Rips expected for Thu.
-- Changed Discussion --MD...None.
NC...Flash Flood Watch until 4 AM EDT Thursday for NCZ012>014-030-
VA...Flash Flood Watch until 4 AM EDT Thursday for VAZ092-093-
MARINE...Small Craft Advisory until midnight EDT Thursday night for
Small Craft Advisory until 10 AM EDT Thursday for ANZ631-632.
Small Craft Advisory until 4 AM EDT Thursday for ANZ638.
Small Craft Advisory until 10 AM EDT Friday for ANZ652-654.
Small Craft Advisory from 4 AM Thursday to 10 AM EDT Friday
-- End Changed Discussion --