Area Forecast Discussion
Issued by NWS Wakefield, VA-- Remove Highlighting --
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FXUS61 KAKQ 270133
Area Forecast Discussion
National Weather Service Wakefield VA
933 PM EDT MON SEP 26 2016
A warm front will weaken as it snakes its way across the mountains
tonight. A cold front will move southeast across the region Tuesday
morning, then stall along the coast Tuesday afternoon and night
before moving farther offshore late Wednesday. An upper level low
will track across the area later in the week.
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Latest MSAS showing the old frontal boundary that cooled the region
off a few days ago is snaking it way across the mts late this
afternoon. This boundary will weaken as it continues to drift back
north as a warm front this evening. Shwrs will accompany this
boundary with low chc pops over the piedmont through midnite.
Cold front to slowly cross the mts overnight with its position just
entering NWRN most zones by 12Z. Good moisture surge out ahead of it
for a band of likely/categorical pops across NWRN half of fa, chc
pops SERN half. Instability is marginal but will keep slght chc
thunder across the north ahead of the approaching boundary. Enuf
lift and moisture influx seen for some moderate to possibly heavy
downpours north of I64 and VA ST RT 360. Lows in the low-mid 60s.
.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Still a rather complex forecast for Tuesday. Latest data supports
the front sagging SE across the fa during the morning but stalling
across the SE after 18Z. The reason for this is twofold, first is a
weak wave progged to ride NE along the boundary and second is an
area of tropical moisture off the Carolina coast that causes to
boundary to slow its SE movement. Am a bit concerned about this
offshore moisture as to whether any of it gets entrained into the
stalled frontal system along the coast. This could enhance rainfall
across the SE in areas that got drenched a few days ago. Something
to watch over the next 12-24 hours. Upshot here is for a wet day
with likely pops most areas, categorical across the SE after 18Z.
Thunder will shift towards the SE after 18Z closer to the boundary.
Somewhat drier air is progged to filter in behind the front across
NWRN zones. Despite the dry air aloft, enuf moisture noted to
continue chc pops back through the piedmont. Again. some moderate to
lclly heavy downpours possible across the SE. Highs in the low 70s
north to mid-upr 70s south.
Boundary gets hung up along the coast Tues nite then shifts a bit
farther east Wed. Likely pops continue along the coast Tue evening
with chc pops all areas after midnite through Wed as moisture from
the approaching upr level low crosses the mts. Lows upr 50s NW to
near 70 SE. Highs Wed in the mid-upr 70s. Thunder possible across
the SE Wed afternoon.
Models differ a bit with the actual cut off low position by mid
week, but anyway you look at it it appears unsettled with sct shwrs.
NAM slower and further west than GFS/SREF but can`t rule out aftrn
tstrms once the cold pool aloft crosses the mts. Lows Wed nite in
the 60s. Highs Thurs in the 70s.
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Long term forecast is complicated by the presence of an upper-level
cutoff low over the E/NE CONUS for the duration of the period. This
will lead to below normal temps and frequent chances for rain.
Difficult to time the precip this far out in time but at this
point the best chances will be Thu night/Fri (30-50% pops). As the
cutoff low slides NE through the period, the chances of rain will
slightly decrease through the end of the week. As for temps, highs
will avg in the mid 70s each day with lows ranging from the mid
50s over the Piedmont to the mid 60s near the coast.
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
VFR conditions continue at start of TAF period forecast (this
evening). Area of lower cigs and SCT shras/isolated tstms
approaching from the W (exiting the higher terrain). Lower level
moisture to continue a gradual increase through the night/into
Tue. Nudge timing of arrival to pcpn in RIC/SBY by an hour or two
overnight. Expecting gradual arrival of MVFR cigs by late
tonight/Tue morning w/ shras (possible isolated tstm but not
included in forecast attm). Brief/Locally lower vsbys (< 2 mi)
possible in heavier shras.
Pcpn not expected to get into the SE VA/NE NC taf sites until
after 12-15Z/27. Shras will linger through much of the work week
ahead as an upper level low tracks across the region.
-- Changed Discussion --...930 PM Update...Have dropped SCA on the Lower Bay, as current
observations and latest high resolution model forecasts suggest
strongest winds will be across the northern 2 Bay zones. The lower
2 bay zones will remain AOB 15 knots overnight and Tuesday
...Late afternoon discussion...Latest sfc analysis shows high
pressure centered offshore with a frontal boundary approaching
from the west. Southerly flow increases tonight ahead of the frnt
as the pressure gradient increases. Maintained the SCA hazards in
place for the entire Bay and Rappahannock River for winds up to
15-20 kt. Conditions will be marginal and winds do not appear to
be high enough to warrant a SCA over the ocean and other rivers.
The front drops into the area Tue with winds decreasing through
the day as the front stalls and weakens in the vicinity. Waves of
low pressure then form along the front through the end of the work
week as an upper-level cutoff low persists over the E/NE CONUS.
Expect mainly 1-2 ft waves over the Bay and 2-4 ft seas over
coastal waters through this period.
-- End Changed Discussion --
-- Changed Discussion --MD...None.
MARINE...Small Craft Advisory until 7 AM EDT Tuesday for ANZ630-631.
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