Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
414 PM EDT Friday Mar 14 2014
high pressure over the southeast states will slide off the
Carolina coast today. A weak cold front drops through the area
Saturday night. Low pressure will track from the lower
Mississippi Valley northeast and off the Carolina coast Sunday
Near term /until 6 am Saturday morning/...
a Special Weather Statement remains in effect through 6 PM EDT for
increased fire danger across the entire forecast area due to min relative humidity values of
generally 15 to 20 percent and sustained winds of 15 to 20 miles per hour.
Please refer to the fire weather section below for more details.
A broad surface high pressure is located off the southeast coast late this
afternoon. The placement of the high will allow S-SW flow to continue
overnight. A clipper system passes across southern Ontario tonight and
drags a cold front toward the area...tightening the pressure gradient
and keeping winds breezy overnight. The front will primarily be
precip-free...however there is a very remote chance for a sprinkle
or two across the Maryland lower Eastern Shore and off the NE NC coast
after midnight (no higher than 10 percent). Overall...the best
lift/instability is elevated and any falling precipitation should
evaporate before reaching the dry surface conditions left in the wake
of the southeast coast surface high. Temperatures should generally fall into the
lower 40s in the well-mixed environment (upper 30s far western areas
of the fa).
Short term /6 am Saturday morning through Monday/...
the dry front stalls across the forecast area by Sat morning and then slowly
sags southward during the day. Saturday will start out mostly cloudy
with skies breaking up by the afternoon. The combination of sunshine
and breezy west winds will bump temperatures to readings about 10
degrees above normal. Expect highs in the middle to upper 60s north
to upper 60s to lower 70s south.
A colder airmass gets drawn into the NE Continental U.S. As high pressure
builds down from Canada Sat night. Meanwhile...a surface low develops
over the arklatex region Sat night and moves into the southeast states on
Sunday. This low will start to move along the stalled boundary
just south of the area and move toward the Carolina coast Sun night
into Monday. The aforementioned stalled boundary is expected to take
on more warm frontal characteristics Sat night. As isentropic lift
ahead of the ctrl pressure lifts over this boundary...steady rain
will begin spreading into the middle Atlantic region from the
southwest by Sun morning. 12z model data indicates that a cold air
wedge may build down the Lee side of the Appalachians Sun night
into Monday...which could lead to a wintry mix of precipitation for
northwest and northern areas of the forecast area. However...the Canadian high is prognosticated
to weaken on Monday...which may cause the cold air to retreat northward and
allow the surface low to shift northward across the southern half of the forecast area before
precipitation-type has a chance to become wintry Sun night into Monday.
Additionally...model soundings indicate a warm nose developing roughly
between 850-750 mb late Sun night into Monday morning. There are enough
discrepancies between NAM/GFS/sref solutions to make for a tricky
forecast regarding precip-type. Taking the current model data into
consideration...will tentatively lean toward the colder wedge
solution and confine sleet or a rain/sleet mix to the northwest half of
the County Warning Area for now.
Highs sun in the upper 40s northwest to lower 50s southeast. Highs Monday in the
low-middle 30s northwest to middle-upper 40s southeast. Lows Sat night in the
middle-upper 30s most areas/low-mid 40s far southeast Virginia/NE NC. Lows Sun
night in the middle-upper 20s northwest to near 40 southeast.
Long term /Monday night through Friday/...
low pressure steadily pulls off the coast Monday night with
precipitation potential diminishing from NW-se. Generally expecting
rain over southeast portions...with the potential for central portions ending
as a mix of -sn/ip...and a slight chance of -sn for northern portions. High
pressure remains over New England Tuesday as low pressure lingers
off the coast. NE flow should keep high temperatures below normal
(mid 40s north...to around 50 s) along with only partial clearing.
Wednesday has the potential to be the mildest day as low pressure
pulls through the Great Lakes producing south-southwest flow across the region.
However...there is some moisture embedded within the flow. This
should keep the sky partly to mostly cloudy...with a slight chance pop
along the coast. Forecast highs are above guidance (due to south-southwest
low-level flow) with readings ranging from the upper 50s north...to middle
60s S. A cold front crosses the area Wednesday night/Thursday with
limited moisture. Deep layer northwest flow prevails thereafter for the
remainder of the extended period.
Aviation /20z Friday through Wednesday/...
VFR conditions in place at this moment and these conditions should
prevail through the forecast period. With high pressure in
place...just off the southeast US coast...strong southwest flow is
keeping dry air in place...leading to clear sky. The surface high will
continue to slide east tonight in Saturday morning...before a cold
front...now over the Central Plains...slides through the region.
This front lacks significant low level moisture...and should just
produce some middle to high level cloudiness upon its passage early
Sat morning. Behind the front the moisture again clears and with
westerly flow...expect clear sky into Sunday.
Outlook: dry/VFR weather prevails through Sunday...with a chance of rain
by late Sun night/Monday with MVFR to IFR conditions possible Monday
high pressure continues to shift offshore this evening and overnight
as low pressure tracks through the Saint Lawrence valley. The
presence of a modest pressure gradient...along with increased mixing
within the nocturnal marine boundary layer will result in a period
of marginal Small Craft Advisory conditions...mainly over the Bay/northern ocean zones. A
south-southwest wind of 15-20kt is expected in the Bay...with a 20-25kt south-southwest wind
north of Cape Charles. Seas north of Parramore Island will build to 4-5ft
out near 20 nm. Expect a 15-20kt south-southwest wind over the S of Cape Charles
with ~3ft seas. The sound/rivers should experience a 15kt south-southwest wind
The gradient relaxes Saturday ahead of a cold front along with a
wind shift to the west with speeds at or below 15kt. This front sags through
the region north-S Saturday night into Sunday. Low pressure develops
along the boundary Sunday into Sunday night...before pulling
offshore Monday. A NE wind will increase Sunday and especially
Sunday night/early Monday as low pressure deepens. Wind speeds
potentially reach 25-30kt over the ocean/mouth of Bay/sound...with
20-25kt for the remainder of the Bay and rivers. Seas should build
to 6-10ft Sunday night into Monday. Low pressure lingers off the
coast through Tuesday...as high pressure remains north of the region.
This will result in continued onshore flow and slowly subsiding seas.
a Special Weather Statement remains in effect through 6 PM EDT
this evening for increased fire danger. A markedly warmer day is
expected today...with temperatures warming into the upper 50s to
lower 60s and a relatively dry S-SW wind developing by this afternoon.
Min relative humidity values will generally range from 15 to 20 percent across
the area. 10 hour fuels will also continue to dry through today.
The Maryland lower Eastern Shore may be close to reaching wind criteria...
however min relative humidity values are only expected to fall into the 20 to 25
percent range (too high to consider a red flag warning).
Marine...Small Craft Advisory from 7 PM this evening to 4 am EDT
Saturday for anz631-632-634-654.
Small Craft Advisory until 4 am EDT Saturday for anz630.
Small Craft Advisory from 7 PM this evening to noon EDT
Saturday for anz650-652.