Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
431 PM EDT Wednesday Sep 17 2014
high pressure builds over the northern middle Atlantic region
tonight. A weak cold front crosses the local area late Thursday.
High pressure returns Thursday night into the upcoming weekend.
Near term /until 6 am Thursday morning/...
latest regional radar mosaic depicts isolated showers...some
producing brief heavy rainfall...generally south of the Albemarle
Sound. Isolated small showers have also briefly popped up on radar
in NE NC...but dissipate quickly. Skies average partly cloudy with
mostly cloudy in NE NC...but visible Sat trends depict some added
sunshine breaking through in the southeast. These isolated showers are in
response to a weak wave/vorticity lobe tracking through NC at this time. This wave
will push offshore as another vorticity lobe tracks in its wake over
southern Virginia/northern NC. However...moisture remains rather limited...with
precipitable waters at or below 1.25 inches and very little moisture above 700mb. High
pressure and dewpoints in the 50s will also limit precipitation chances.
Will keep slight chance probability of precipitation in the far southeast tonight as models
continue to depict light showers over that area. Otherwise...skies
remain generally partly cloudy thanks to the wave and remnant middle-
level moisture. Some patchy fog possible across the Piedmont north
of Richmond and to the Maryland Eastern Shore.
Trended toward warmer met guidance overnight based on
clouds/thicknesses...with lows generally in the middle-upper 50s
inland to low 60s in the southeast. A few rural areas may drop into the
low 50s in the Piedmont and Maryland Eastern Shore.
Short term /6 am Thursday morning through Saturday/...
upper low over eastern Canada begins to fill and eject eastward Thursday as
the trough axis aligns along the eastern Seaboard. An associated weak
reinforcing cold front will drop into the region Thursday as Canadian
high pressure builds over the Great Lakes region. While moisture
remains rather unimpressive (pwats ~1.25 inches)...moist low-level
onshore flow...weak shortwave energy aloft and Theta-E advection
will result in a slight chance of light showers along the front
during the middle-late afternoon. The best chances for any measurable
precipitation...albeit still a slight chance...will be across the
Piedmont into central Virginia and the Maryland Eastern Shore. High pressure builds
over New England into Friday...ridging southwestward over the local area.
Onshore flow will persist. Heights begin to rise Friday...but the southern
portion of the trough will remain over the southeast coastal plain as the
frontal boundary stalls along the southeast coast. This remnant trough
will result in cyclogenesis along the frontal boundary off the southeast
coast Friday night-Sat. Local area will remain generally precipitation free
Friday and Sat...but middle level clouds will linger with generally
partly cloudy skies. Few light showers will be possible inland Friday
and along the coast Sat...but will leave silent to slight chance
at this time...generally due to relatively little moisture and low
Onshore flow and cloud cover will keep temperatures slightly below
normal through the short term. Highs generally in the middle-upper 70s.
Overnight lows generally in the upper 50s to low 60s.
Long term /Saturday night through Wednesday/...
mainly going with a blend of the 12z GFS and 12z European model (ecmwf) for the
extended period. The center of hi pressure will move into the northern Atlantic
Sat night. Weak low pressure will lift NE off the southeast and middle Atlantic CST Sat
night into Monday morng. Will maintain a dry forecast during this period
with a mostly clear or partly cloudy sky. Lows Sat night in the upper
50s to middle 60s. Highs on sun in the upper 70s to lower 80s. A cold
front will cross the area late Sun night and Monday...bringing a slight
chance of showers. Hi pressure will then build from the lower Great Lakes ewrd into
southern New England Tuesday through Wednesday. Lows will range through the 60s Sun
night...range from the upper 50s to middle 60s Monday night...and range through the
50s into the lower 60s Tuesday night. Highs in the upper 70s to lower 80s
Monday...and mainly in the lower to middle 70s Tuesday and Wednesday.
Aviation /20z Wednesday through Monday/...
a weak surface low is slowly developing across the southeast states as a middle
level trough lingers off the Carolina coast late this afternoon.
Showers are just starting to redevelop in NC S-SW of Albemarle
Sound at this hour...and are expected to spread north in vicinity of the
Virginia/NC border. Any showers that occur should stay south of a line
from kfvx-kptb-kmfv. Expect mostly cloudy to cloudy skies south
of this line through tonight and variable partly to mostly cloudy
skies north of it. Ceilings should remain above 3 kft above ground level during this
time with the exception of kecg...which may experience ceilings around
2 kft above ground level after 18/0800z. Ksby may experience foggy/hazy
conditions with visibilities down to around 2sm also after
18/0800z. NE flow persists at speeds at or below 10 knots the rest of today
High pressure slowly builds across the Great Lakes into New England
Thu-Sat...with a somewhat breezy 10-20 knots of NE flow continuing at
korf/kecg. Overall...still expect a fair amount of cloud cover in
this pattern but likely too much mixing and overnight cloudiness
for any significant fog development.
NE or east winds will dominate the waters through Sat...due to one area of
hi pressure sliding off the northern middle Atlantic CST tonight...followed by a
larger area of hi pressure bldng from the Great Lakes eastward and off the New
England CST Thursday through Sat. Wind speeds will likely remain around 15
knots or less through the period. Waves will be 1 to 3 feet and seas
generally 2 to 4 feet tonight through Thursday night. Some longer period swells
(12-15 sec) will continue into Thursday...due to distant tc Edouard.
A little stronger NE or east winds expected Friday and Friday night due to
strong hi pressure to the north-northeast. This will result in waves 2 to 3 feet
(possibly reaching near 4 feet mouth of the bay)...and seas bldng to
4 to 5 feet.
Maryland...moderate rip current risk until 8 PM EDT this evening for
NC...moderate rip current risk until 8 PM EDT this evening for
Virginia...moderate rip current risk until 8 PM EDT this evening for