Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
946 PM EDT Thursday Aug 28 2014
a weak cold front settles south into North Carolina overnight
into Friday...before lifting north as a warm front Friday night
and Saturday. A weak trough develops on Sunday and should result
in increasing precipitation chances later in the day.
Near term /until 6 am Friday morning/...
weak surface boundary remains draped from along the Virginia/NC border in southern/southeast Virginia...to
west-central Virginia. Isolated/scattered convection continues to track slowly southeast through
areas of the Piedmont west of I 95. Dewpoints remain from the u60s to l70s S
along/S of that boundary...and mainly in the l60s north (along north-northeast wnds).
00z/29 RUC continue to push that convection to the southeast into NE NC after
midnight as the boundary sinks S. Will keep probability of precipitation for those areas
until after mdngt...elsewhere just clr-pc. May need to add fog over southern
areas of the forecast area...though expecting a gradual lowering of dewpoints from the north-northeast
as the boundary sinks to the S. Low temperatures from the l60s north to the
u60s/around 70f S.
Short term /6 am Friday morning through Sunday/...
a weak frontal boundary remains stalled across northern NC Friday as a
surface high pressure over New England extends southward into the middle Atlantic
region. Once again...the weak frontal boundary should provide just
enough forcing/instability for isolated to scattered showers and
thunderstorms in vicinity of the stalled front (still primarily south of
Interstate 64 with best precipitation chances along the Virginia/NC border into
NE nc). The axis of the surface high sits over central New York to central Virginia
Friday morning and then pivots eastward along the coast from NC to New
England by Friday evening. This will bring a slightly cooler airmass
across the northern half of the County Warning Area while temperatures stay on the cooler side
in vicinity of the front due to partly to mostly cloudy skies. It is
difficult to say exactly where the dividing line will set-up between
highs in the middle-upper 80s SW to low-middle 80s NE. Current forecast
thinking generally keeps the cooler highs across the Northern Neck/Maryland
lower Eastern Shore/Accomack County Virginia...despite mostly sunny skies
across these areas.
The stalled boundary lifts northward as a warm front Friday night into
Saturday as the surface high over New England slides off the New
England coast late Friday night into Saturday. As it does so...
will need to carry slight chance probability of precipitation across much of the forecast area Friday
night...with the best chances for precipitation (still in the
20 percent range) along and north-NE of Interstate 64 during most of
Saturday. Return flow also develops on Saturday as the ridge axis
moves offshore...bringing warmer temperatures and a more humid airmass
into the region. Lows Friday night in the low-middle 60s north and
upper 60s to lower 70s south. Highs Saturday around 90/mid-upper
80s immediate coast. A generally dry forecast for Saturday night
into the first half of Sunday as high pressure dominates at the
surface and aloft. Lows Saturday night around 70 under partly cloudy
skies. A weak trough develops along the Lee of the Appalachians on
Sunday and may be just enough of a focusing mechanism for showers
and thunderstorms during the afternoon/evening as weak shortwave energy
streams along the periphery of an upper level ridge...which should
be centered over the western Atlantic as a Bermuda high. Middle-Range
model solutions vary regarding overall precipitation placement...
but the general trend has higher probability of precipitation of 30-40 percent along and
northwest of a line from avc-ric-sby and lower probability of precipitation around 20 percent
across NE NC/far southeast Virginia. Temperatures remain warm in the persistent
return flow with highs once again around 90/mid-upper 80s immediate
Long term /Sunday night through Thursday/...
Summer-like pattern will tend to prevail through the medium range period
as middle/upper level ridging centered along/off the southeast US coast...gradually
shifts to the west-southwest and becomes anchored over the deep south/Gulf
Coast region. Temperatures will generally run about 5 f above average with
highs into the upper 80s to lower 90s and lows in the upper 60s to
Lower/Middle 70s. A couple of weak middle level shortwaves will bring
somewhat higher probability of precipitation to the area for Labor Day...will carry 40%
probability of precipitation throughout...followed by probability of precipitation only ~20% on Tuesday in between the
departing wave and a cold front approaching from the northwest. Tuesday
likely the hottest day..with most locations getting above 90 f and
perhaps into the middle 90s over the interior. Another round of
somewhat high probability of precipitation is slated for Tuesday evening/Tuesday night as the cold
front moves closer to the local area and heights aloft drop as the
ridge breaks down.
By late Wed-Thu...a general consensus of the GFS/ECMWF/wpc
forecast does push a surface cold front south of the area with high
pressure building across the NE Continental U.S.. this should allow slightly
cooler/drier air to move into the region...but the front does not
looks very strong so highs will still average in the middle-upper 80s on
Thursday. Will focus highest probability of precipitation Wednesday-Thursday across the south (20-30%) with
generally a dry forecast across the Eastern Shore.
Aviation /02z Friday through Tuesday/...
cold front will stall along and just south of the local area late
tonight and Friday, with guidance indicating potential for some
low stratus early Friday morning, as low level moisture gets
trapped beneath the nocturnal inversion. Have gone with mention
for scattered-broken ceilings ~ 4-5 kft over southern terminals (phf/orf/ecg),
with potential for some light fog/mist at/in vicinity of ecg Friday morning.
Outlook...mainly dry weather with continued VFR conditions expected
Friday and through much of the upcoming Holiday weekend. Slight to
low chance probability of precipitation for afternoon/evening thunderstorms Sunday evening increase to
30 to 40 percent Monday ahead of the next frontal passage.
Otherwise, some potential for fog or low clouds will exist each
day within a few hours of sunrise.
Cristobal now >500 nm east-northeast of the local area...with a weak surface
boundary have pushed south of the waters. North/NE winds average around 10
knots...will likely increase a bit later tonight as modest push of
cooler air moves over the waters with surface high pressure moving east-southeast
from Michigan into the NE and northern middle Atlantic region.
As for headlines...will maintain schs headline for coastal waters north
of Parramore Island through 10pm...with no headlines elsewhere even
though there will be some increase in winds over the Bay overnight
into early Friday. (Much like what occurred earlier today). North/NE
winds will slowly veer to the east/NE in the afternoon and average 10-15 knots
across the Lower Bay and southern coastal waters to 5-10 knots farther
north. Seas will generally only be around 3 feet...but will generally still
have a moderate risk for rip currents along area beaches as energy
from Cristobal is slow to diminish.
Winds then gradually veer and become southeast and gradually increase by
Saturday aftn/evening. Winds then become S/SW Sunday. Seas will
generally run 3 feet or less but may increase to 4 feet in the outer
portion of 20nm late Saturday and Sunday...with a period of 2-3 feet
waves in the Bay Sat night. Fairly quiet (outside of convection) into
early next week with seas 2-3 feet and waves 1-2 feet or less as surface
high remains anchored offshore and no significant fronts move into
the area until late Tue/Wed.
Maryland...moderate rip current risk through Friday evening for mdz025.
NC...moderate rip current risk through Friday evening for ncz102.
Virginia...moderate rip current risk through Friday evening for
Marine...Small Craft Advisory for hazardous seas until 10 PM EDT this
evening for anz650-652.