Area Forecast Discussion
Issued by NWS Wakefield, VA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KAKQ 202038
Area Forecast Discussion
National Weather Service Wakefield VA
438 PM EDT Thu Apr 20 2017
A cold front will approach from the northwest tonight, then
push across the area late Friday and Friday night. The front
will stall across North Carolina and offshore Saturday through
Sunday. Low pressure will track eastward along the frontal
boundary across Tennessee and into the Carolinas Saturday
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
A warmer/more humid airmass was prevailing acrs the region late
this aftn, under a partly to mostly sunny sky. Temps were
ranging fm the mid 70s to mid 80s. Latest rdr showed sctd
showers and a few tstms moving ewrd thru W.VA and into wrn/nrn
VA. This activity will hold together, as it runs into the lee
side trof, and moves acrs the CWA this evening into early
tonight. So, will have 20-40% Pops during this time period.
Otherwise, becoming partly cloudy tonight with lows only in the
lower to mid 60s.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
Warmer and slightly more humid on Fri, due to SW winds and at
least a partly sunny sky in advance of a cold front. Highs in
the lower to mid 80s. Sctd showers and tstms will develop right
in advance of the front Fri aftn/evening, as the front slowly
drops into/thru the area. Have maintained 30-50% PoPs over the
region. At this time, SPC has the entire fcst area in a
marginal risk for severe storms.
The frontal boundary will sink into NC by 12Z Sat. Then, fm Sat
thru Sun, will go with the latest GFS model fcst. The front
will remain nearly stationary acrs NC and offshore Sat thru Sun.
Low pressure will track ewrd along the frontal boundary acrs TN
and into the Carolinas Sat thru Sun. This will result in an
overrunning scenario over the CWA, with a mainly cloudy sky and
high chc to likely Pops for rain/showers and chc of tstms acrs
srn portions of the area. There is the potential for heavy rain
over much of the region (1 to 2 inches), esply later Sat thru
Lows Fri night will range fm the mid 50 to mid 60s, and range fm
the upper 40s to upper 50s Sat night. Highs on Sat will range fm
the lower 60s N, to arnd 70/lower 70s S. Highs on Sun will range
fm the upper 50s to arnd 70.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
-- Changed Discussion --Latest 20/12z models continue to depict unsettled conditions
for at least the first portion of the long term/Sun night
through Tue. Deep/anomalous upper trough progged to be centered
along the southern Appalachians by 00z/Mon, with sfc low along
the SC coast and weakening sfc high pressure along the southern
New England coast. GFS/ECMWF now in very good agreement with
the upper low continuing to dive SE through GA/SC on Mon, while
remaining as a closed low. The ECMWF is still somewhat stronger
with the strength of the upper low and also farther NW with the
widespread precip shield through the day Mon than the GFS. Will
blend these solutions/slightly favoring the GFS as the ECMWF has
been somewhat of an outlier for several runs. Overall though,
the forecast has trended wetter and cooler for Mon, after the
potential for some locally heavy rain lingers all areas Sun
night, and mainly over southern and eastern sections for Mon.
Low pressure slowly pulls offshore by Tuesday as high pressure
builds in from the NNW with drier conditions returning, but
still likely enough moisture for continued 30-40% chance PoPs E
and 20% PoPs west. Highs Mon to avg 60-65 F with mid-upper 60s
on Tue. Warmer/dry for Wed and likely turning much warmer by
Thu as the low finally will be far removed from the region and
ridging aloft begins to center off the SE coast. Lows mainly in
the 50s with highs mid 70s inland to 65-70 F near the coast Wed,
and highs 80-85 F Thu (70s near the coast).
-- End Changed Discussion --
.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
Shwr exiting SBY attm with only SCT clouds expected behind it.
Otw, VFR conditions expected to start forecast period with only
SCT clouds. High res models are showing a line of convection
developing across the Piedmont then moving east following I64
towards 00Z. Medium confidence that this will actually occur,
so went ahead and indicated a BKN cloud group generally between
21Z-01Z. Best area that would see any convection would be at
RIC so went ahead with VCTS there toward sunset. Kept thunder
out of all other TAF sites. VFR conditions expected all areas
by mid evening. SW winds aob 10 KTS.
OUTLOOK... Scattered showers and thunderstorms are expected
Friday afternoon and evening as a cold front tries to cross the
area Friday. As the front stalls around or just south of the
local area...low pressure will move out of the southern Great
Plains and eastward along the front. This will bring widespread
precipitation late Saturday through Sunday night with periods of
degraded aviation conditions.
Relatively benign conditions over the marine area this aftn with
pressure gradient weak enough allowing winds to turn onshore/SSE
at around 10 kt on avg. SSE winds this evening become SW
overnight and on Fri as a cold front approaches from the W.
Winds to avg 10-15 kt during this period with seas mainly 2-3 ft
and waves in the Bay/Rivers 1-2 ft. The front crosses the area
late Friday with high pressure building N of the region
Saturday. A SW wind will continue Friday and then shift to N
Saturday behind the front. Low- end/brief SCA conditions are
possible Saturday with CAA surge, though models show some timing
differences. Overall best chance is the lower Bay/southern
Low pressure approaches from the SW Saturday and tracks across the
region Sunday into Sunday night. Still some uncertainty as to exact
location of the boundary on Sun (the NAM now actually shifting the
boundary well south with weak high pressure trying to build in from
the N). The GFS/ECMWF is favored over the NAM solution and will
therefore continue to forecast an extended period of NNE winds...and
marginal SCA conditions at least for southern areas on Sunday, with
more significant winds/strong SCA conditions likely Mon-Tue
(potential for low-end Gales mouth of the Bay/southern coastal
waters on Mon). This as the system moves off the coast with
sfc high to the NE. This setup lingers into Tue. Winds should
gradually diminish Tuesday as the low slowly pushes farther
offshore. Seas to build to 6-8 ft and waves to 4-5 ft in the Bay