Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
915 PM EDT Tuesday Sep 23 2014
high pressure remains across the northern middle Atlantic tonight as
low pressure develops off the southeast coast. This area of low
pressure will slowly move up the coast Wednesday and Thursday.
Meanwhile...high pressure will remain anchored across New England.
Near term /until 6 am Wednesday morning/...
update to increase pop/sky cover the rest of tonight...
increased precipitation coverage across NE NC the rest of this evening
and expanded coverage/wording into far southern Virginia late this evening.
Initially...probability of precipitation start out as slight chance to chance pop with low
quantitative precipitation forecast. Showers so far this evening have been very light in a fairly
dry lower atmosphere and also due to cloud bases averaging
8-12 kft. After midnight...isentropic lift begins to push into
NE NC from the east thus providing enough upglide to enhance
precipitation generation across NE NC and far southeast Virginia.
latest surface analysis reveals ~1029 mb hi pressure centered over western PA
with a stationary frontal boundary located off the Carolina CST. The hi
will spread east into the northern middle Atlantic region and NE states tonight
as an area of low pressure develops along the front. Aloft...a weak
cutoff low will continue to spin over the southeast states...drawing
moisture northward up the eastern Seaboard. Think for the most part the
entire forecast area will remain dry this eveng with hi ceilings...however as
moistening occurs did increase probability of precipitation from S to north through the overnight hours.
Probability of precipitation are capped at 50% through 6am for now with any precipitation expected
to start off light. Otws...expect a mostly cloudy sky on average with
north/NE winds. Low temperatures will range from the low/middle 50s over the Piedmont
to the low 60s near the CST.
Short term /6 am Wednesday morning through Friday/...
short term period will see a return to wet weather as the aforementioned
surface low moves up the middle Atlantic CST. Despite the middle-level cutoff
low weakening on Wednesday...continued pivoting shortwave troughs and the
coastal trough/surface low in conjunction with moist Erly flow aloft will
lead to the potential for moderate to heavy rain especially Wednesday
aftn/eveng. Did increase probability of precipitation to 60-70% western areas and 80-90% eastern
areas. Highest precipitation amounts are expected near the CST where 2-3
inches is possible. Will maintain mention in the severe weather potential statement for the
potential of flooding in low lying...poor drainage...and other
flood prone areas. The precipitation will end from west to east Thursday/Thursday night. Dry
weather returns for Friday aside from a slight chance of rain over far eastern
As for temperatures...readings will continue to be below normal...with highs
avgg in the upper 60s to middle 70s and lows in the upper 50s to upper 60s.
Long term /Friday night through Tuesday/...
models now pull low pressure out near 70w then stall it there for a
while Friday night and Erly Sat before lifting it farther away from the
area by Saturday night. This keeps lingering moisture along the southeastern
coastal areas Friday night into Erly Sat. Otw..high prs builds into the
area Sat afternoon through Monday resulting in dry conditions with seasonable
temperatures. Highs 75-80. Lows in the m50s-m60s.
Next system approaches from the west Monday night and Tuesday. This is
much slower than ystrdys runs so will intro low chance probability of precipitation at this time given
a day 7 forecast. Lows Monday 60-65. Highs Tuesday in the M-u70s.
Aviation /01z Wednesday through Sunday/...
low pressure developing along a stalled frontal boundary off the
southeast coast will make its way NE...spreading moisture into NE NC and
southeast Virginia by Wednesday morning. With high pressure to the north...the
pressure gradient will increase overnight with NE-east winds gusting to
~25kt along the coast by early morning.
MVFR ceilings and reduced visible will likely develop through the
day on Wednesday...with IFR visible possible during the afternoon/evening as
rain increases and overspreads the area. The low moves off the
coast Thursday evening ending the chances for precipitation and helping to
improve flight conditions.
low pressure prognosticated to lift northward over the waters by Wednesday & Wednesday night.
Pressure gradient strengthens as NE winds increase to Small Craft Advisory conditions.
Will go ahead and start the sca's with this package for conditions
that begin tonight. Held off on starting time for rivers & Bay since
Small Craft Advisory winds not expeceted to begin until after 12z Wednesday.
The persistent NE winds will push seas to 4-5 feet in the southern water
beginning late tonight. Speeds/seas/waves increase across the rest
of the waters through the day Wednesday. Combination of strong low level
gradient winds...NE flow and warm waters will result in solid Small Craft Advisory
conditions Wednesday into Wednesday night. 20-25 knots...gusts to 30 knots for the
coastal waters and Lower Bay...15-20 knots with gusts to 25 knots
elsewhere. Waves expected to build to 4-5 feet with 3-4 feet in the
lower James and 2 feet in the sound. While a few gusts to near gale
force are possible across the northern coastal waters Wednesday night...
confidence not high enough to hoist gale flags so have capped gusts
at 32 kts at this time.
Seas quickly build upwards of 8-10 feet out near 20 nm. Flow and wave
direction will result in nearshore waves of 5-7 feet. Not quite high
enough to issue a high surf advisory at this time.
Models bring the surface low over the Bay Wednesday night the move it NE of
region Thursday. Have opted to push Small Craft Advisory headlines in the coastal
waters and Bay through Thursday...mainly for seas at or above 5 feet.
Will issue a beach hazard statement for high rip current risk Thursday.
persistent NE flow will strengthen by Thursday as high pressure
remains anchored over New England...and low pressure develops moves
NE along the coast. Current guidance suggests tidal departures rise
to between 1-1.5 feet above normal Wednesday night and Thursday. While
astronomical tides are relatively low around the new moon...some
locations in the Bay (including sewells point) will approach minor
flooding thresholds. Maryland beaches may also approach minor flooding
thresholds. No headlines in effect at this time.
Maryland...Beach hazards statement from 8 am EDT Wednesday through
Wednesday evening for mdz025.
NC...beach hazards statement from 8 am EDT Wednesday through
Wednesday evening for ncz102.
Virginia...Beach hazards statement from 8 am EDT Wednesday through
Wednesday evening for vaz098>100.
Marine...Small Craft Advisory from 6 am Wednesday to midnight EDT
Wednesday night for anz635>638.
Small Craft Advisory until 4 PM EDT Thursday for anz634-650-
Small Craft Advisory from 6 am Wednesday to 6 am EDT Thursday
Small Craft Advisory until midnight EDT Wednesday night for