Area Forecast Discussion
Issued by NWS Wakefield, VA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KAKQ 211757
Area Forecast Discussion
National Weather Service Wakefield VA
157 PM EDT THU JUL 21 2016
High pressure prevails through the weekend, with heat returning
Friday into early next week. Heat indices will climb to 100 to 108
degrees Saturday and Sunday. The next cold front approaches the
region late Monday.
.NEAR TERM /THROUGH TONIGHT/...
High pressure prevails over the region this morning, resulting
in quiet conditions. An anomalous upper ridge over the Midwest
builds eastward today, but the heat remains suppressed west of the
mountains for one more day. The surface high center slides off the
coast this afternoon, with winds remaining light and onshore.
Light flow will result in afternoon seabreeze boundaries, but BUFR
soundings indicate very little available moisture. However, cannot
rule out an isolated to widely scattered thunderstorm along the
seabreeze boundary due to instability and favorable mid level
lapse rates. Best chances over the Eastern Shore, but also
possible southeast VA and northeast NC. Otherwise, dry conditions
expected. 850mb temps warm slightly compared to yesterday, but
similar low level thicknesses place highs in the upper 80`s.
.SHORT TERM /FRIDAY THROUGH SUNDAY/...
Anomalous upper ridge over the nation`s mid section dampens and
builds eastward through the short term. 850mb temps warm to +20 to
+22 C (+2 standard deviation) Friday afternoon. Thicknesses and dry
adiabatic lapse rates place highs solidly in the low to mid 90`s
Friday. A southwest wind around 10 mph will help mix dewpoints into
the mid to upper 60`s, resulting in heat indices in the upper 90`s.
High pressure remains over the western Atlantic as pressure falls on
the lee side of the mountains induce lee/thermal troughing over the
Piedmont. Lack of appreciable forcing, limited moisture, and warm
temperatures aloft expected to keep the local area dry Friday.
Expect some afternoon cumulus. Mostly clear Friday night with lows
in the low to mid 70`s. Few degrees warmer Saturday as the ridge
builds eastward. Highs solidly in the mid 90`s area wide. Mixed
layer dewpoints cool back into the mid to upper 60`s, with heat
indices of 100 to 105. Retained silent POP`s due to warm air aloft
(cap) but can`t rule out an isolated thunderstorm over the Piedmont
as better moisture arrives ahead of a weak cold front in northwest
flow aloft. The weak frontal boundary is expected to reach the
northern Mid Atlantic region Saturday night into Sunday morning as a
shortwave drops over New England. Models indicate some elevated
instability, but moisture and forcing remain weak resulting in
silent POPs. Lows back into the mid 70`s.
Upper trough drops off the Canadian Maritimes/Northeast coast Sunday
as flow aloft becomes more zonal. Hot again with temperatures back
into the mid 90`s. Heat indices 100 to 109. Will carry slight
chance POPs with the thermal trough and increasing moisture ahead of
the next northern stream shortwave tracking across the upper
.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
A thermal trough is expected to remain in place Mon-Wed for
continued very warm to hot conditions. 595dm upper ridge also
remains situated off the SE coast. A slight buckle in the ridge
across the Northeast/Mid- Atlantic due to a weak upper trough
passage will knock a few degrees off max temps but still remain
above normal. Highs in the mid/upr 90s Monday and low to mid 90s
Tue/Wed. Thunderstorm chances will mainly be tied to the aftn/eve
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --Surface high pressure settles over the western Atlantic and
Southeast Coast through the weekend...resulting in primarily
Weatherwise, isolated seabreeze thunderstorms are possible near
the coast this aftn/early evening. A brief period of shallow fog
development is possible at KRIC and KSBY between 22/1000-1200Z.
KECG may also experience shallow fog within this timeframe,
however confidence is much lower and can be added as a tempo group
if needed. Otherwise, conditions are dry on Saturday with another
round of isolated to scattered storms possible across the area on
Sunday. A cold front approaches the region on Monday and then
crosses the area on Tuesday. There is enough incoming moisture to
interact with a thermal trough on Monday and with the cold front
on Tuesday to trigger a higher chance for scattered thunderstorms
both days...primarily during the afternoon/evening hours. Locally
heavy downpours, strong gusty winds, and brief reductions in
flight conditions to MVFR/IFR ceilings and visibilities will be
the primary impacts with thunderstorms early next week.
-- End Changed Discussion --
Headlines are not anticipated over the next several days, though
conditions may come close to reaching SCA thresholds Fri night. High
pressure over the area today will slide offshore and become
centered off the mid- Atlantic/SE coast Thu- Fri as a weak front
approaches from the NW Fri night into Sat. This front looks to
remain N of the CWA, with a pre-frontal trough in place over the
region on Sat. Winds today will be light from the E-NE (<10kt) and
transition to the S to avg around 10 KT tonight into Fri morning.
Bay waves avg 1-2 ft with coastal seas 2-3 ft. The pressure
gradient will increase a bit by late Fri, especially by fri night
so S/SW winds will ramp up and avg around 15 KT during this
period. A few gusts may reach SCA thresholds across the Bay (20
KT) and northern coastal waters (25 KT) Fri night as warm water
temperatures will be conducive to mixing the low level nocturnal
Jet. Still would be marginal at best, with waves over the Bay
building to 2-3 ft, and coastal seas to around 4 ft N and 3 ft S.
The sfc trough/boundary drops into the area on Sat with lighter
W/SW flow turning back to the S Sat night. The front then washes
out/dissipates on Sun.