Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
412 am EDT Tuesday Sep 2 2014
high pressure builds over the southeastern states today. A weak
front drops into the area tonight and settles near the Virginia
North Carolina border Wednesday. High pressure returns Wednesday
night and Thursday.
Near term /until 6 PM this evening/...
per latest water vapor imagery...high pressure remains over the
southern Continental U.S. With ridging over the western Atlantic. At the surface...high
pressure remains over the western Atlantic into the southeast states with a
weak surface trough over eastern Virginia. A shortwave trough over the upper
Midwest is producing a broad area of showers/thunderstorms from
the lower MO valley into the Ohio Valley. This shortwave and an
associated cold front will approach the local area today.
Meanwhile...latest regional radar mosaic depicts echo free local
area with only a few showers lingering well offshore. Dry
conditions will prevail through the morning with mild morning temperatures.
For today...shortwave will Delaware-amplify and lift into the NE states
as the weak cold front reaches the central Appalachians late. Warm air advection in
SW low level flow will push 850 mb temperatures to around 20c (~+1 Standard dev).
Combined with deep mixing and SW wind of 10-15 miles per hour...high temperatures
expected to warm into the middle-upper 90s inland with low 90s along
the coastlines. Afternoon dewpoints forecast to mix back into the
middle 60s...which should once again serve to keep heat indices at or below
100. Forecast highs average around +1.5 to +2 St dev above seasonal
means...and approach but fall just short of records (please see
climate section below). Model soundings show much of the area to
be well-capped above cumulus bases...and thus have kept a silent pop
through much of the day. The exception is over NE NC along
possible sea breeze. The best chances for precipitation (albeit low-end
chance) hold off until the short term as the front drops through the
Short term /6 PM this evening through Thursday/...
cold front drops into the region tonight as a weak wave pushes
over the central Appalachians. Warm/moist and marginally unstable
airmass in place in advance of the weakening front will result in
only isolated to widely scattered showers/thunderstorms. While
precipitable waters prognosticated around 1.8 inches...lack of upper level
support/forcing for ascent and westerly flow will limit overall
coverage. Front washes out over the area/just south of the area
Wednesday as westerly flow aloft prevails. Surface high pressure builds over the
region Wednesday as weak surface trough remains over the southeastern portion of
the local area. Given continued warm/moist and marginally unstable
air mass...will maintain slight chance-low end chance probability of precipitation Wednesday
and Thursday...centered mainly along the trough axis and Theta-E
ridge over the southern local area.
Highs remain nearly +1 Standard dev through the short term...generally
around 90 degree inland and slightly cooler along the immediate
coast. Mild overnight lows generally in the upper 60s to lower
Long term /Thursday night through Monday/...
long term period will start off with above normal temperatures and
occasional chances for rain. For Thursday ngt/Fri...surface hi pressure centers
offshore with a broad upper-level ridge across the eastern Continental U.S.. did
include a slight chance-chance for a rain showers/thunderstorm (especially over western
areas) closest to the greatest moisture axis and surface Lee trough...but
nothing widespread expected. Temperatures Friday will rise into the upper 80s to
lower 90s under a mostly/partly sky and light southerly winds.
For the remainder of the period...cold front approaches from the west
as an upper-level trough digs across the eastern Continental U.S.. chances for rain
will increase into the weekend as the front drops into the middle
Atlantic. Tough to exactly time the precipitation this far out in
time...but for now will go with a 30-40% chance for rain showers/thunderstorms both
Sat and sun. Hi temperatures ahead of the front Sat will be near
90...dropping into the low to middle 80s on sun with increased cloud
cover and the front in the vicinity.
Aviation /08z Tuesday through Saturday/...
VFR conditions prevail early this morning through today in warm SW
flow. SW winds will average around 10 knots this aftn/evening...and will
slowly shift to the northwest overnight into Wednesday morning. Could see
isolated showers/thunderstorms late this afternoon...but expect the greatest chance
will be from 00-06z/Wednesday as the front pushes into the region.
Coverage will tend to be scattered so still too much uncertainty
to include rain showers or thunderstorms and rain in tafs at this point.
Mainly dry/VFR conditions Wednesday-Friday as surface front washes out across
NC...although an isolated late afternoon/evening shower or thunderstorm still
possible for far southern Virginia/NE NC. Does appear to be a higher
probability for showers/thunderstorms and reduced visibilities and ceilings by Sat as
next front moves into the area and stalls.
conditions look to remain sub-Small Craft Advisory through the next several
days...S/SW flow averages 10-15 knots or less today as surface high stays anchored
over the western Atlantic with a weak trough over the interior. 1-2 feet
waves over the Bay and 2-3 feet seas over coastal waters for the most part.
A frontal boundary drops into the area and weakens later tonight/early
Wednesday. While there will probably be an hour or two of increased winds
as they shift to the north/northwest as the front passes...not anticipating
any headlines. This due to an overall lack of cold air in the wake
of the front. Pressure gradient is rather weak as well as surface high
pressure builds to the north of the area on Wednesday. Winds shift from
north/northwest Wednesday morning to the east/southeast late Wednesday afternoon/Wednesday night. Winds generally
should be east-southeast to S Thursday into Friday at 10-15 knots or less...eventually
shifting to the south-southwest Friday night/Sat as next cold front approaches.
record high temperatures for Tuesday 9/2: