Area Forecast Discussion
Issued by NWS Wakefield, VA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KAKQ 290033
Area Forecast Discussion
National Weather Service Wakefield VA
833 PM EDT Wed Sep 28 2016
An upper level low slowly drops south from the Great
Lakes tonight through Friday. Meanwhile, high pressure builds well
north of the region and steers a moisture rich airmass into the
region tonight Through Thursday night.
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Current wv imagery depicts an anomalous upper low
dropping s across the lower Great Lakes, with deep sw flow aloft
over the Mid-Atlantic region ahead of the upper low. At the surface,
1034mb high pressure is situated over se QB, which is ridging s
through the ne US. Weak surface low pressure is depicted beneath the
upper low, with an attendant boundary extending across the central
Appalachians and central/se VA. Effective shear values of 30-40kt
are co-located with 1000-1500 J/kg of MLCAPE across central/s-
central VA down into central NC. This will interact with increasing
forcing aloft and trigger sct-numerous showers/tstms through the
late afternoon and evening hours. Some tstms could be severe, mainly
producing hail and damaging wind gusts, with an isolated tornado
possible in vicinity of the surface boundary.
The deep layer flow will become more southerly through the night,
which will allow a higher pw airmass to advect into the region. The
primary threat associated with showers/tstms should transition to
heavy rainfall by later this evening. Initially the heavy rainfall
threat should be across the nw piedmont counties, and then gradually
shift toward central VA (generally around and n of RIC metro) and
toward the Nrn Neck and Ern Shore overnight. Mild and humid tonight
with lows in the mid 60s nw, to around 70 se.
.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
The upper low continues to digs swd through the Ohio
and Tennessee Valleys Thursday into Thursday night. Meanwhile, upper
ridging builds n of the Great Lakes across se Canada. At the
surface, high pressure builds to around 1036mb per 28/12z GEFS over
the same region. This will result in a strengthening easterly LLJ
over the nrn Mid-Atlantic, potentially reaching -3 to -4 st dev at
925mb Thursday aftn, before gradually slackening Thursday night.
This will continue to push a high pw airmass into the region and
will result in a continued heavy rainfall threat across the nrn half
of the area into Thursday night. Rainfall amounts could reach 3-5"
across the far nrn tier counties bordered by 2-4". Locally higher
amounts are possible.
Unsettled conditions continue into Friday as the upper low lingers w
of the area, but overall moisture transport should diminish, with
the heavy rain threat diminishing. The upper low begins to fill and
lift n by Saturday resulting in gradually improving conditions.
The sky remains mostly cloudy to overcast through the period. High
temperatures range from the upper 70s to low 80s, with lows
generally in the 60s.
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Anomalous upper low will make its way through the eastern Great
Lakes Sat night/Sunday and into New England by Monday where it
becomes more of an open wave/trough. This feature then moves off the
Northeast coast early next week. Based on the latest model
guidance...have slowed the timing of pcpn exiting the FA with chc
pops (30-50%) lingering across eastern areas Sat night...diminishing
to slight chc pops across eastern areas by Sun eve. Will maintain
dry wx Monday, then a lot of uncertainty develops by Monday night
into the middle of next week. There`s the potential for the remnants
of the upper low/trough to linger offshore (providing moist
onshore/easterly flow locally) and also uncertainty with regards to
the eventual track of TS Matthew. Will carry low end pops for now
Tue-Wed. Highs through the period mainly in the 70s. Lows in the
.AVIATION /01Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --An east-west stationary front will continue to remain
across Virginia through the period, serving as the focus for
showers and thunderstorms.
Heavy rain and thunder are still ongoing at RIC, added TEMPO
group to account for this. Expecting the rain/thunder to mainly
impact central Virginia and portions of eastern Maryland through
the first half of the night. Introduced IFR conditions for later
tonight at RIC and SBY which will remain closer to the stationary
front. Lower chances for MVFR across the VA tidewater and NE NC
as this region will remain further away from the front. Slowly
improving conditions are expected across all sites later into the
day on Thursday.
Outlook: Unsettled weather persists into Friday with
continued chances for showers and thunderstorms due to the
frontal boundary remaining nearby. Improving weather conditions
are expected this weekend.
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Late this aftn, upr/sfc low pressure was spinning ovr the OH
valley with weak sfc low pressure well off the Mid Atlc/nrn Mid
Atlc coast. Also, strong high pressure was cntrd ovr ern Canada.
The pattern over the next few days will feature this high
strengthening ovr ern Canada, ridging into New England. This will
make for a persistent and rather strong E/NE flow over northern
portions of the marine area. Have kept Bay zones N of New Pt
Comfort in a SCA, as well as the coastal waters fm Cape Charles
Lgt nwrd to Fenwick Island (beginning this evening/late tonight
or Thu morning). Seas are expected to build to 6-8 ft over
northern waters, while remaining around 4 ft across the south). It
is possible that marginal SCA conditions could make it to NC
border for 5 ft seas by Thu aftn, and that the lower Bay could
also get to marginal SCA levels, (but confidence is rather low at
Seas will slowly subside later Fri thru Sat. A lighter SSE flow
expected Sat leading to sub-SCA conditions with 1-2 ft waves over
the Bay and 2-4 ft seas over coastal waters.
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 bring persistent ENE flow to
the area Thu-Fri. Strongest winds expected for the northern areas,
with minor tidal/coastal flooding becoming a concern for Ocean
City/Chincoteague/Wachapreague by Thu evening and Fri morning high
tide cycles. Also, some potential for flooding into the Bay (both
lower and mid-upper Bay) by Fri-Sat, as seas remain elevated and
water is expected to struggle to exit the bay for several days.
No coastal flood watches have been issued as chance for moderate-
severe flooding is low, but we may eventually need to issue
Coastal Flood Advisories.
-- Changed Discussion --MD...Flash Flood Watch from midnight EDT tonight through late
Thursday night for MDZ021>023.
VA...Flash Flood Watch through Thursday evening for VAZ048-060>062-
Flash Flood Watch from midnight EDT tonight through late
Thursday night for VAZ075>078-083-085-517>522.
MARINE...Small Craft Advisory from 7 AM Thursday to 6 AM EDT Friday for
Small Craft Advisory until 6 PM EDT Friday for ANZ650-652.
Small Craft Advisory from 7 AM Thursday to 1 AM EDT Friday for
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