Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
918 PM EDT Friday Aug 22 2014
a frontal boundary across the Middle Atlantic States will move to the
southwest of the area Saturday. High pressure from New England slowly
builds into the area Saturday night into Sunday...before settling
over the Piedmont early next week.
Near term /until 6 am Saturday morning/...
as of 01z...precipitation has moved out of County Warning Area. Widely scattered showers
persist just west of County Warning Area...and may move into portions of the Piedmont
later this evening. Otherwise...think risk for showers/thunderstorms has
decreased cwa-wide...and have thus lowered probability of precipitation everywhere. Was
tempted to keep NE half of County Warning Area dry overnight...but 18z NAM would
suggest the potential for at least isolated showers persists. So
have maintained slight chance NE half...with no higher than 40 percent probability of precipitation
extreme SW. Skies should remain mostly cloudy overnight...and this
should inhibit fog formation across the Delaware-Maryland-Virginia...where some
significant rainfall occurred this afternoon. In addition...trend
has been for dew points to fall over the last couple of hours across
the lower Maryland Eastern Shore...which also argues for less fog
potential. Min temperatures in the upper 60s/around 70 look good.
Short term /6 am Saturday morning through Monday/...
chance probability of precipitation along with considerable cloud cover will be maintained for
Saturday as the remnant boundary remains near the local area. The
potential for thunder will be confined away from the coasts due to
east-northeast flow with high pressure building over New England. The high
surges south-southwest over the area Saturday night into Sunday with the surface
ridge axis settling over the Piedmont by Monday. This will produce a
drying trend along with a NE wind that should be rather breezy along
the coast. Partly to mostly sunny conditions are expected by
Sunday...with mostly clear/sunny conditions by Sunday night and
Highs will be below seasonal averages Saturday through Monday
(around -1 St dev). Saturday highs will range from 80-85 (upper 70s
along the Atlantic coast)...with upper 70s to low 80s Sunday and
Monday. Lows should be in the middle/upper 60s Sunday morning...with
low/middle 60s expected Monday morning.
Long term /Monday night through Friday/...
surface high pressure and upper level ridging along the eastern Seaboard
is expected to keep tropical cyclone activity well off the coast by
about 500-600 miles. This pattern will maintain a cooler airmass
over the area through Wednesday before the ridge axes at the surface and aloft
aloft begin to shift just east of the forecast area...and moving offshore by
Thursday. The forecast is generally dry through the extended forecast
periods due to well-established subsidence through the atmospheric
profile...however a few showers cannot be ruled out near the far southeast
Virginia/NE NC coast on Wednesday due to the potential for wraparound moisture
from the tropical system passing well to the east. High and low
temperatures will run below normal from Monday night through Wednesday night
(lows in the 60s...upper 50s far western counties/highs in the low-middle
80s...mid-upper 70s beaches) and then rebound toward seasonal normals
Thursday/Thursday night (highs in the middle-upper 80s...upper 70s-lower 80s
beaches/lows in the middle-upper 60s...around 70 beaches).
Aviation /01z Saturday through Wednesday/...
a frontal boundary across the middle Atlantic region will move to the
southwest on Saturday. High pressure builds over the area from the
northeast following the frontal passage. Several days of northeast
flow can be expected.
MVFR ceilings will be possible at some of the taf sites and included IFR
conds at sby after 07z where the ground is fairly wet and the boundary
layer is moist. VFR conds should take over by late morning. Chance for
precipitation through the taf period is no higher than 30 percent and left
precipitation out of the forecast.
Outlook...MVFR/IFR due to stratus or fog will be a potential a few
hours around sunrise Sunday morning. Dry weather is forecast for
several days beginning Sunday.
Small Craft Advisory headlines issued for coastal waters and southern ches Bay Sat afternoon
A stationary frontal boundary will slowly drift southward across the southern
waters tonight as low pressure deepens off the coast. Meanwhile...a
weak backdoor cold front will drop into the area late tonight into
Sat. Northerly winds around 10-15 knots will be common ahead of the
front...then they will turn to the north-NE behind it as high pressure
ridges down over the waters. A period of persistent onshore winds
will result in prolonged Small Craft Advisory conditions for the coastal waters and
southern ches Bay...mainly due to elevated seas/waves (4-5ft/3-4ft
respectively). Winds will average 15-20kt ocean and 10-15kt
Bay/rivers/sound. Gusts may reach 25 knots at times over coastal
waters but main focus of Small Craft Advisory will be on seas of 5 feet. Given the
persistent onshore fetch...it is possible for seas to reach 6 feet
near buoy 44009 Sat evening during a weak push of cold air advection. Currituck
Sound and the mouth of the James River may be experience a brief
period of low-end Small Craft Advisory winds (15-20kt) on sun from daybreak until
sunset but decided to hold off on headlines for these areas for
now. Although current headlines end at 8pm Sun night...there is a
very good chance that Small Craft Advisory flags will be extended through Monday. High
pressure builds into the region Monday/Tuesday but a tropical system is
expected to pass about 500-600 miles east-southeast of the middle Atlantic
coast during this time. Swell from this system...in addition to
continued onshore winds...could keep seas elevated through Monday
before seas begin to subside.
Marine...Small Craft Advisory from 5 PM Saturday to 8 PM EDT Sunday for
Small Craft Advisory from 8 PM Saturday to 8 PM EDT Sunday for
Small Craft Advisory from 2 am to 8 PM EDT Sunday for anz656-
Small Craft Advisory from 2 PM Saturday to 8 PM EDT Sunday for