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000
FXUS61 KAKQ 181004
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
604 AM EDT Fri Aug 18 2017

.SYNOPSIS...
A warm and humid air mass remains in place across the Mid-
Atlantic states today on continued south flow. The next cold
front will arrive late tonight and exit the region by Saturday
morning. High pressure builds in for Saturday night through
early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A warm/muggy start to the day across the local area. Some
SCT/BKN low stratus developing across the area attm, but little
bit of mixing we do have has precluded more widespread fog
development.

Aloft, shortwave ridging remains in place over the local area.
However, this will be short-lived...as an upper trough, and
associated mid-level shortwave drops from the Great Lakes toward
the northeast today into tonight. The associated surface cold
front will drop across the Ohio Valley/interior northeast this
afternoon, reaching our area tonight into early Saturday
morning.

For today, expect some pre-frontal showers to develop by late
morning/early afternoon...however areal coverage should be quite
low with these showers. More widespread showers and storms
should occur along and just ahead of the front. PW values in the
2-2.5" range, increasing lift and increasingly diffluent flow
aloft with time as the upper trough and sfc front approaches
will allow for a period of moderate to heavy rainfall. Area of
greatest concern is once again over the Northern Neck of Easter
VA into the Lower MD Eastern Shore, where dynamics are most
favorable for a period of heavy rainfall late this afternoon
into this evening. Have held off with any flash flood headlines
at this time, as Corfidi vectors do indicate decent storm
movement with sct to numerous storms that develop this
afternoon. However, this will obviously bear watching through
the day. Have added heavy rain mention into grids and will
highlight in HWO. Also, given strong heating and high PWs, a
marginal risk for severe is in place across the local area, with
the NE CWA also highlighted in a slight risk for severe. Once
again, as noted above the best dynamics are along and NE of the
local area into the northeast, with lesser deep layer shear
likely portending to more of a pulse storm threat over much of
the area. Also, timing of frontal passage in the
evening/overnight will allow for a gradual but steady weakening
trend with any storms. That said, Sig TOR/EHI values do indicate
potential for isolated tornadoes across the Eastern Shore
during the evening hours just ahead of the frontal passage.
These parameters have been useful in previous events earlier
this summer, and will therefore add a mention into the HWO for
tonight.

Lastly, temperatures will creep up slightly after stratus
dissipates this morning. It will remain humid, with dewpoints
creeping up slightly from the past few days into the low to mid
70s. In tandem with highs in the u80s/l90s, this will bring heat
index values back into the low 100s. Have held off on heat
headlines for now, as any exceedance of criteria would be quite
brief.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
The front slowly pushes southeast early Saturday, and models
have once again trended a bit faster with the frontal passage,
allowing for a quicker end to showers Sat morning.

A strong shortwave trough sweeps across the Mid-Atlantic States
Saturday night, but it remains north of the area and with the
low level moisture gone, not anticipating much except some mid
level clouds. By Sunday, high pressure will be over the region
with dry and seasonable weather in place.

For temperatures, will continue to see near normal weather with
highs in the upper 80s to around 90 each day and lows in the low
to mid 70s each night except for Saturday night when the drier
air will allow temps to drop into the upper 60s to low 70s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Sfc high pressure builds north of the area with stacked high
pressure residing off the Southeast Coast through Mon night.
A thermal trough develops in the lee of the Appalachians for
Tue/Tue night, and then a cold front is expected to track
through the area on Wed...exiting the coast late Wed night.
Conditions will become increasingly more humid with each
passing day. Sfc features rather diffuse for Mon, however
seabreeze boundaries with the presence of ample moisture will
keep a slight chance for showers/storms in the forecast...
primarily for the aftn/early evening. Thunderstorm activity
expected to become widely scattered Tue as convection develops
invof lee trough. The frontal passage Wed/Wed night will
provide a better focus for more organized thunderstorms to
occur. Highs Mon-Wed generally upper 80s to lower 90s;
low-mid 80s beaches. Lows Sun-Tue nights generally 70-75F.
Lows Wed night mid-upper 60s NW to 70-75F SE.

&&

.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
VFR conditions across the terminals this morning. A weak
boundary will move north of the area later tonight into Friday
morning. High-res models hint that a few showers are possible
around daybreak along the coast near ORF, PHF and ECG, areal
coverage should be low and as such will continue to keep out of
TAF for now. Main story will be MVFR/IFR cigs and possible VSBY
restrictions (mainly at RIC) after 09z. With the wind staying
around 5 kt, still anticipate more of a lower stratus event vs.
a low VSBY event at RIC. Elsewhere, it should remain VFR or
MVFR with low probability of IFR expected.

A cold front approaches the region today, with showers and
thunderstorms developing and becoming more widespread Fri
evening into Saturday. This will bring another chance for sub-
VFR conditions in heavier showers. Confident enough to throw
showers in at RIC/SBY, but will keep thunder mention out for
now.

Outlook: VFR conditions returns later Sat through the weekend as
High pressure builds back into the region. Some early morning
fog possible both Sunday and Monday mornings.

&&

.MARINE...
Latest sfc analysis shows weak high pressure offshore with a cold
front over the OH Valley. This front will track east towards the Mid
Atlc today, with southerly flow increasing ahead of the front as the
pressure gradient increases. By this aftn/eveng before the fropa
conditions will be close to SCA criteria over Bay due to ~15 kt
sustained winds and northern cstl wtrs due to 4 ft seas. Not
confident enough that SCA conditions will occur to issue headlines
attm. The cold front drops into the wtrs tonight, with shras/tstms
psbl and winds/waves/seas decreasing thereafter. For Sat, with the
front weakening in the vicinity, expect winds aob 10 kt by the aftn
with 1-2 ft waves over the Bay and 2-3 ft seas over cstl wtrs.
Similar conditions into Sun with little change in the overall
pattern. Sub-SCA conditions will continue into early next week with
weak sfc high pressure in the area.

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...None.
NC...None.
VA...None.
MARINE...None.

&&

$$
SYNOPSIS...MAM
NEAR TERM...MAM
SHORT TERM...ESS/MAM
LONG TERM...BMD
AVIATION...MAM/JAO
MARINE...MAS