Area Forecast Discussion
Issued by NWS Wakefield, VA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KAKQ 080843
Area Forecast Discussion
National Weather Service Wakefield VA
343 AM EST Thu Dec 8 2016
-- Changed Discussion --Weak low pressure tracks along the Virginia North Carolina border
Thursday morning through early afternoon...followed by a cold
front later Thursday afternoon. Canadian high pressure builds into
the area Friday and Saturday. The high slides offshore Sunday,
ahead of the next cold front on Monday. Another strong cold front
impacts the region during the middle of next week.
-- End Changed Discussion --
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --Latest GOES water vapor imagery depicts a broad cyclonic flow over
the western and central US, with an anomalous upper low over
eastern Canada. An embedded potent shortwave is currently tracking
across the Midwest, with another shearing wave stretching from the
Southern Plains into the Tennessee Valley. At the surface, weak
high pressure resides along the coast with a trough of low
pressure/lingering frontal boundary located over the Piedmont. Mid
and upper level clouds continue to stream into the area in fast
southwest flow aloft. Expect a mostly cloudy to cloudy sky by
daybreak as the shearing southern wave lifts along the
Virginia/North Carolina border. The northern stream wave tracks
into the Ohio Valley, reinvigorating the surface boundary over the
Piedmont and pushing it across the local area. Subtle forcing for
ascent provided by increasing winds aloft and the shearing wave
will combine with modest moisture (precipitable waters of 0.5 to
0.9 inches) across the southeast half of the forecast area for
isolated to widely scattered showers along the advancing frontal
boundary. Best chances will generally be along and east of
Interstate 95. Some local convergence near the Bay could enhance
showers briefly, but overall expect only a few hundredths of an
inch of rain. The front pushes offshore mid to late afternoon.
Cold air advection and dry northwest flow will result in a
clearing sky behind the front, but the strongest cold air
advection will be delayed until tonight. Cloud cover should hold
highs in the upper 40`s to low 50`s.
-- End Changed Discussion --
.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
-- Changed Discussion --Low level thicknesses plummet tonight as Arctic high pressure
builds into the central US and nudges eastward into the Southeast.
850Mb temperatures drop to -8 to -10C (-1 to -2 st dev) late
Thursday night. Lows drop into the mid/upper 20`s under a clear
sky. A cold/brisk day is anticipated Friday as the Arctic high
builds from the Central Plains toward the southern Appalachians.
850mb temps drop to around -10C (-2 st dev) Friday afternoon.
Strong CAA will prevent temperatures from reaching their full
potential Friday afternoon, even with a sunny sky. MOS guidance
continues to show highs generally in the low/mid 40s, but will
trend toward cooler thickness regressions. Some Piedmont locales
may struggle to get out of the 30s, with around 40/low 40s
elsewhere. A brisk northwest wind of 10-15 mph inland and 15 to 20
mph near the coast is expected to keep wind chill values in the
low to mid 30s.
The high builds into the region Friday night into Saturday as the
upper trough axis pushes offshore. By this point the air mass will
have modified enough to lose its arctic characteristics. Still
cold and well below normal nonetheless, with lows Friday night in
the upper teens to low 20s inland, to the low/mid 20s for se
coastal locations. Limited mixing Saturday will keep highs in the
upper 30s to low 40s despite some warming at 850mb. Sunny with a
light west to northwest wind.
-- End Changed Discussion --
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Sfc high pressure slides overhead Sat night and offshore by Sun
morning. Winds become more southerly and breezy...especially as a
weak coastal trough begins to develop along the Carolina and Mid
Atlantic coasts Sun night. Meanwhile, another upper level trough
digs across the Midwest and Ohio Valley Sun/Sun night...followed
by a strong cold front pushing through the area Mon and a more
progressive, westerly flow pattern aloft for Tue/Wed.
A brief warm-up should be anticipated with the coastal trough Sun
night into early Mon...along with increasing chances of
precipitation Sun evening through Mon evening with the passage of
a cold front. The Piedmont may remain wedged and keep cooler air
in place prior to the initial onset of precip. This could result
in precip starting as light snow showers Sun evening before
quickly transitioning to all rain overnight. Precip should remain
as rain through Monday, however if any precipitation lingers into
Mon night, it could easily transition back to light snow showers
as another round of cooler, modified arctic air and sfc high
pressure return to the region Mon night through mid week.
Temperatures generally at to slightly below normal throughout the
.AVIATION /09Z THURSDAY THROUGH MONDAY/...
A weak area of high pressure remains over the region early this
morning, resulting in VFR conditions and light winds. Expect some
patchy fog over the Piedmont through daybreak, with patchy ground
fog closer to the coast. Increasing mid level clouds over the
southern forecast area will limit any further fog development, so
have only tempoed a few hours of IFR ground fog at the usual
culprits of KPHF and KECG. A cold front pushes across the region
late morning into the afternoon, with increasing low to mid clouds
along the boundary. Broken to overcast ceilings will lower to MVFR
for a brief period along the front, with clearing skies post
frontal. Isolated to widely scattered showers are possible, but
rainfall amounts will be light. VFR conditions return all sites
this afternoon as Canadian high pressure builds into the region.
Surface winds become west to southwest around 10 knots this
High pressure builds into the area Thursday night through Saturday.
High pressure slides offshore Sunday as another cold front
approaches from the west. This cold front crosses the region Sunday
night into Monday. with a chance for rain.
A weak cold front crosses the waters late this aftn into this
evening...with cooler air filtering down over the waters the rest
of tonight into Thu. Winds generally nw-n aob 15kt during this
timeframe. Seas have been slow to subside through today, and have
therefore extended SCA flags for ocean through 500 AM Thu morning
when seas finally drop below 5ft. Meanwhile, an upper level trough
sits just north of the region on Thu...slowly sagging swd Thu
night and then sliding across the area on Fri. Winds become more
wnw as the day progresses with speeds remaining aob 15kt. Wind
speeds increase to 15-20kt Thu evening for Bay/Ocean/Sound/Mouth
of James River as a strong 125-150kt jet sags south over the
waters in advance of the upper trough.
A much colder arctic airmass arrives after midnight Thu night as
the sfc pressure gradient tightens and speeds increase to 20-30kt
(aforementioned areas) and 15-20kt (Rivers); still w-nw direction.
SCA flags will likely be issued beginning with this initial surge
in winds. Gale force gusts may still be possible (especially as
skies clear with the strong jet streak overhead), however
confidence is low at this time. The cold air begins to equalize
and the sfc pressure gradient starts to relax late Fri night into
early Sat as sfc high pressure axis shifts ewd and closer to the
waters. Winds remain within solid SCA speeds through Sat morning
before diminishing below 15kt all waters by Sat aftn. Seas build
to 5-7ft north (possibly up to 8ft near 20nm Fri evening)/5-6ft
south by Fri morning and are expected remain steadfast through
early Sat morning before subsiding below 5ft by Sat aftn. The high
slides overhead Sat night (light/variable winds) and offshore by
Sun morning. Winds become more sly on Sun with a possible surge in
speeds to 10-15kt into Sun night as a weak coastal trough starts
to develop off the Carolina and Mid Atlantic coasts. The trough
axis is expected to stall just offshore on Mon with winds becoming
more sw-w aob 15kt. Seas average 2-3ft Sat night through Sun Night
and may build to 4ft near 20nm on Mon. Waves 1-2ft.
MARINE...Small Craft Advisory until 5 AM EST early this morning for