Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
1000 PM EDT Tuesday Jul 28 2015
high pressure remains offshore through midweek...with the next
cold front crossing the area by Thursday night.
Near term /until 6 am Wednesday morning/...
latest regional radar mosaic depicts area of showers persisting
over the eastern Virginia Piedmont late this evening...remaining generally
west of the local area. Otherwise...earlier showers/thunderstorms
have dissipated over the local area. Shortwave visible on GOES WV
prognosticated to drop over eastern Virginia tonight in concert with increasing
winds aloft. A warm/moist air mass remains in place over the
local area with dewpoints in the 70s and precipitable waters around 2 inches.
Will maintain slight chance-chance probability of precipitation over the Piedmont into
central Virginia as rap depicts an axis of deep moisture convergence
over that region. Sky averages partly cloudy/mostly cloudy inland
and mostly clear NE counties. Lows in the low 70s.
Short term /6 am Wednesday morning through Friday/...
upper level ridging continues to expand eastward from the
Southern Plains. This will help to limit afternoon convection while maximum
temperatures warm a couple of degrees. Have chance probability of precipitation (25-30%) along and
west of I-95. Partly sunny west/ high temperatures in the upper 80s to low
90s...with low/middle 80s at the beaches. Mild Wednesday night west/ low temperatures
in the low/middle 70s.
upper ridging retrogrades a bit Thursday as a trough moves across
the Great Lakes and pushes a cold front into the middle-Atlantic
region by late in the day. Due to the late arrival of the
front...chance probability of precipitation (30-50%) will remain across western areas during
the afternoon...lowering to ~20% at the coast. Maximum temperatures will reach
into the upper 80s to low 90s...except low/middle 80s at the immediate
Thursday night and Friday...
the cold front moves across the forecast area Thursday night before stalling
across far southeast Virginia and the eastern Carolinas on Friday. Have solid
chance probability of precipitation (30-50%) most areas with the passage of the front
through midday Friday...then focus chance probability of precipitation across southeast Virginia and NE NC
Friday afternoon. Dry weather should return to northwest areas by late morning or
afternoon. Lows Thursday night in the 70s. Highs Friday in the 80s to
Long term /Friday night through Tuesday/...
pattern begins with a middle/upper level ridge centered
over the SW Continental U.S. And an upper level low persisting across Hudson Bay
Canada. GFS/European model (ecmwf) into better decent agreement that an upper trough
axis will extend south into the Great Lakes Sat...then flatten out
sun with a shortwave pushing across the middle Atlantic by Monday.
Front stalls and weakens over far southern Virginia/NC late Friday into the
weekend. Best chance for precipitation looks to be across the far south/mainly
NE NC through the weekend but even here will only go with a 20-30%
probability of precipitation/primarily for the afternoon/evening timeframe (tapered to 20% far
southern Virginia and dry elsewhere). Did raise probability of precipitation a bit for Monday due to the
shortwave moving through but not a lot of confidence as this is 5-6
days out so will generally keep probability of precipitation only at 30-40% south to 20% north.
Keeping probability of precipitation around 20% all areas Tuesday. Typical summertime
temperatures can be expected with highs mainly ranging from the
middle/upper 80s along the coast to the upper 80s to lower 90s inland.
Lows generally ranging from the middle 60s northwest to the lower 70s southeast through
Aviation /02z Wednesday through Sunday/...
thunderstorms have come to an end this evening with scattered
light to moderate showers left in areas along and west of
Interstate 95. Showers will continue to taper off and should end
by 29/0400z. Due to recent rainfall today at kric and ksby...
shallow ground fog and few-scattered clouds around 400ft are expected to
develop after 29/0900z and persist through 29/1200-1300z before
Upper level ridging continues to expand eastward from the Southern Plains on
Wednesday. This will help to limit afternoon thunderstorms for the eastern
half of the area (including taf sites ksby/kphf/korf/kecg)...
however there is just enough moisture and energy wrapping around
the upper ridge to keep vcsh at kric (including areas along and
west of Interstate 95). Overall shear remains very weak...
therefore the main threat with afternoon/evening thunderstorms will be
heavy rainfall causing quick reductions to ceilings (mvfr) and
visibilities (lifr to ifr). A trough crosses the Great Lakes on
Thursday and pushes a cold front into the middle Atlantic region late
in the day into Thursday night...then it stalls across far southeast Virginia
and the eastern Carolinas on Friday. More organized thunderstorms
should be anticipated in vicinity of this frontal boundary both aftns/evenings.
weak surface high pressure is centered off the coast with
weak surface troughing inland across the Piedmont and coastal plain. S/southeast
winds average 10-15 knots this evening/overnight...and will drop off to
S/SW 5-10 knots Wednesday morning. Models suggest that winds may be a little
stronger late Wednesday afternoon/Wednesday night as surface/Lee trough over Virginia deepens
slightly and helps S/southeast winds average around 15 knots in the Bay. Could be
a few hours Worth of 20 knots gusts in the Bay but too marginal to
consider any Small Craft Advisory headlines for now. Waves generally 1-2 feet in the
Bay but will probably build to 2-3 feet Wednesday evening. Seas 2-3 feet.
A weak cold front approaches the waters late Thursday...then stalls south
of the area by late in the week. S/southeast winds average 10-15 knots...turning
south-southwest Thursday night. Not a strong cool surge on Friday as winds shift to the
north with the front dissipating over southern Virginia/eastern NC so will keep
winds in the 10-15 knots range. Flow gradually shifts to east/southeast into the
weekend with waves 1-2 feet/seas 2-4 feet.