Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
1005 am EDT Wednesday Aug 20 2014
a warm front slowly pulls north into the area today...then remains
nearly stationary across the area into the upcoming weekend.
Near term /until 6 PM this evening/...
weak surface low pressure offshore continues to slowly move east and away from the
mdatlc CST today. Lingering frontal boundary S of the forecast area this morning...W/
surface hi pressure to the north-northeast...resulting in continued surface flow from the east-northeast
across the forecast area (in the wake of departing surface low pres). Remnant boundary
to the S pulls slowly north into the forecast area today as weak surface low pressure in vicinity of
lakes/upper Ohio Valley approaches from the west-northwest. Isolated/scattered convection along
weak cold front and associated west/ middle/upper level short wave moving through eastern Ohio
Valley at this time. During today...expecting vrb clouds to pcldy weather across forecast area after
morning St erodes over the Piedmont and far southeast Virginia/NE NC. Otherwise...from
midday through afternoon/evening hours...scattered convection possible...especially northern
portion of forecast area...as system passes by just to the north of the forecast area. Hi temperatures
from the l/m80s at the CST...to M/u80s inland.
Short term /6 PM this evening through Friday/...
the overall pattern is agreed upon in the Middle Range part of the
forecast as the upper low over the Great Lakes slides into the
east and the upper ridge over the MS valley builds
northward...setting up northwest flow aloft over of the middle Atlantic
region. However...beyond the that...the timing of individual waves
and the potential for convective complexes makes the timing of
precipitation very uncertain for Thursday and Friday. At the
surface...a weak frontal boundary that will be in the vicinity should
be some stationary and nearly parallel to the flow aloft and could
also be a focus for convection. At this point...with the
uncertainty...will continue to lean more toward climatology with best
chances in the Piedmont early in the afternoon and then area wide
in late afternoon through about midnight.
Low temperatures tonight from the m60s to around 70f. Hi temperatures Thursday from the m80s at
the CST to l90s inland. Hi temperatures Friday in the l/m80s.
Long term /Friday night through Tuesday/...
unsettled weather pattern continues into the extended period in northwesterly
flow aloft...but drier conditions expected by early next week. Temperatures
will be slightly below seasonable...late Summer norms to begin the
extended before returning to near normal early next week.
Upper level flow during the extended is highlighted by split/blocky
flow off the eastern Canada and northestern US coast and amplifying high
pressure over the southern Continental U.S.. this places the middle-Atlantic region in
northwesterly flow aloft. Associated back door front will push south of the
local area Saturday morning. Surface high pressure prognosticated over the NE
will ridge southwestward along the coast and into central Virginia. Northerly low-level
flow indicated in medium range guidance will drive dewpoints
downward into the middle 60s. However...model derived precipitable waters remain
around 1.8 to 2.0 inches. Combined with perturbations in the northwesterly
flow...will have mainly cloudy weather and maintain chance probability of precipitation for
diurnally driven showers/thunderstorms. Will also need to watch
for possible mesoscale convective system development upstream...rounding the ridge and
dropping into the region overnight through the weekend. By early next
week the ridge axis will begin to build into the region as surface
high pressure is prognosticated to locate off the coast. Block will
remain off the NE coast...but moisture feed will be cut off.
Decreasing moisture and increasing subsidence will likely result
in dry conditions. However...confidence is not high at this time...so will
leave probability of precipitation silent.
North of the boundary...thicknesses and guidance yield temperatures in the
low to middle 80s through Monday (around -1 Standard dev). Overnight lows
generally in the upper 60s to low 70s near the water. Warming back
up to near seasonable norms toward the middle of next week.
Aviation /14z Wednesday through Sunday/...
weak surface hi pressure over the region along with decent low-level
moisture has led to another morng with reduced cigs/vsbys. IFR
that was previously expected has not materialized but is still
possible through middle morng. Main expectation is MVFR ceilings...eventually
transitioning to VFR everywhere. Improvements may not occur until
middle to late morng near the CST (orf/phf). Otws...scattered to broken
cloudiness today with 5-10 knots NE winds on average transitioning to east/southeast
by this afternoon.
Outlook...chance for afternoon thunderstorms Thursday through Saturday. Some
MVFR/IFR possible around sunrise each morning.
no headlines necessary with this forecast package. Hi pressure persists just north
of the area today as low pressure and an associated frntal boundary slowly
slide southeast of the waters. The result will be NE flow mainly 5-10 knots over
the Bay/sound/rivers and 10-15 knots over coastal waters. Expect 2-3 feet seas
over the ocean and 1-2 feet waves over the Bay for today into tonight.
Sub-Small Craft Advisory conditions continue as the aforementioned boundary lifts north as a
warm front Thursday into Friday...then slides offshore over the weekend.
During the weekend...the pressure gradient tightens with northeasterly winds
increasing to 10-20 knots. This will push seas in the northern waters to 3-4
feet...with 5 feet possible 20nm out.