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Area forecast discussion 
National Weather Service Wakefield Virginia
638 am EST Wed Dec 7 2016

Synopsis...
low pressure pushes offshore this morning as a weak cold front
pushes across the region. Weak high pressure builds into the area
this afternoon. A reinforcing cold front crosses the region
Thursday. Canadian high pressure builds into the area for the
weekend.

&&

Near term /through tonight/...
latest GOES water vapor imagery depicts broad mid to upper level
troughiness over the central US, with a deep northern stream low
over southern/southeast Canada. West to southwest flow is observed
over the mid-Atlantic region. At the surface, ~1001mb low pressure
has centered offshore of the Eastern Shore with high pressure over
the northeast. A weak secondary boundary is located over the
central Appalachians. Light rain still lingers along the coast of
the Maryland Eastern Shore, so will keep chance pops for that
region through daybreak.

Weak, secondary cold front pushes across the region this morning,
stalling/washing out offshore this afternoon. The front will help
kick the surface low farther offshore, with any chance of light
rain ending for the Maryland Eastern Shore after sunrise.
Northerly low level winds will be slow to scour out the lingering
wedge air mass this morning, but expect dry air advection to erode
the low clouds over the Piedmont by mid-morning. Clearing will
spread eastward toward the coast through early-mid afternoon.
Little change expected in low level thicknesses compared to 24
hours ago, but still expect temperatures to warm into the mid 50's
across the region.

Cloud cover will be on the increase again tonight ahead of the
approaching central US trough and associated strong cold front.
Lows forecast in the low to mid 30's inland to upper 30's
southeast.

&&

Short term /Thursday through Friday/...
strong cold front quickly pushes across the forecast area
Thursday morning into the afternoon. Associated anomalous upper
trough digs into the northeast. While the best height falls and
dynamics lag behind the front, a shear axis and increasing winds
aloft will provide subtle forcing for ascent along the front. The
main limitations for precipitation will be downslope/westerly flow
and marginal moisture return. Precipitable waters progged between
0.5 and 0.9 inches across the eastern half of the forecast area.
Will continue the trend of a line of isolated to widely scattered
showers along the convergence boundary Thursday morning into the
afternoon. Will drop pops to silent for the Piedmont due to the
aforementioned downslope flow. Model quantitative precipitation forecast remains only a few
hundredths of an inch at best. Clouds increase Thursday morning
ahead of the front, with a mostly sunny to partly cloudy sky
expected behind the front as mid/upper level moisture remains. The
front pushes offshore mid-late afternoon as low level thicknesses
plummet inland. Highs warm into the upper 40's to low 50's thanks
to westerly flow inland and into the mid 50's southeast. An Arctic
air mass surges into the region Thursday night as the Arctic high
builds southward into the Midwest, nudging eastward into the
southeast. 850mb temperatures begin to level off around -8 and
-10c (-1 to -2 Standard deviations) late Thursday night. Lows
forecast generally in the mid to upper 20's Thursday night under a
quickly clearing sky.

A cold/brisk day is in store Friday as the Arctic high builds from
the Central Plains toward the southern Appalachians. 850mb temps
drop to around -10c (-2 Standard deviations) Friday afternoon.
Strong cold air advection will prevent temperatures from reaching
their full potential Friday afternoon, even with a sunny sky. Have
undercut MOS guidance with highs generally in the low 40's. Some
Piedmont locales may struggle to get out of the 30's. A brisk
northwest wind of 10-15 mph inland and 15 to 20 mph near the coast
is expected to keep wind chill values in the low to mid 30's.

&&

Long term /Friday night through Tuesday/...
long term period starts off Fri night/Sat with dry weather as sfc
high pressure builds directly over the mid Atlc. Main story in the
extended will be cold temps, with lows in the low/mid 20s Fri night
and Sat night. High temps Fri and Sat avg in the low 40s both days.
Next chance of pcpn arrives Sun night/Mon with an approaching cold
front, with the best chance of rain being during the day Mon based
on the 12z GFS/European model (ecmwf) (40% pops). High temps Mon in the mid/upr 50s.

&&

Aviation /12z Wednesday through Sunday/...
widespread IFR conditions persist early this morning, but latest
infrared satellite trends indicate clearing over the Piedmont. However,
the low ceilings have been replaced with patchy fog. Patchy fog
will quickly burn off after sunrise, but the low ceilings/IFR
conditions will be slow to improve from central Virginia to the
coast. Ceilings slowly lift/erode mid to late morning, but expect
low to mid clouds to persist along the coast into the afternoon
thanks to a moist northerly flow. North to northwest winds
generally around 10 knots with a few gusts around 20 knots near
the coast this afternoon.

Outlook...a strong cold front impacts the area on Thursday, with
only a quick chance for showers Thursday afternoon. High pressure
returns Friday through Sunday.

&&

Marine...
the coastal low that brought strong sca winds with some gale force
gust is quickly moving to the east this morning nearing 70w
longitude. On the back side of the low still seeing sca level
winds over the waters out of the north and northwest. But as the
low continues to exit the region, expect to see the pressure
gradient continue to weaken and the winds should gradually weaken
below sca levels later this morning. Have already seen then drop
across the area rivers and northern portions of the Chesapeake Bay
so have dropped sca flags there with this forecast package.

Weak high pressure will nose into the area later this afternoon and
evening allowing the winds to relax across the region, but the seas
over the coastal sections will be slow to diminish so will keep sca
flags up for seas through tonight. But should see the 7 to 10 ft
seas drop to 5 to 7 ft this evening and eventually below 5 ft by
Thursday morning.

A surge of cold Canadian air will arrive in the area on Thursday and
will reinvigorate a cold front that is dissipating over the central
Appalachians today. This front will then push through the waters by
Thursday afternoon. While there could be some showers with this
front, expect strong northwest winds to develop again with strong sca
conditions. This cold air will allow mixing of the winds aloft to
the surface and could keep sca conditions in place into Friday night
or Saturday. The models are struggling some with the wave heights
generated by these winds as the wnawave guidance quickly reduces the
seas on Friday while the nwps guidance keeps seas in the coast areas
up 7 to 9 ft. For now have gone in the 5 - 7 feet range for now with
the sca conditions.

Finally by Saturday afternoon...with high pressure centered over the
area, will see the winds relax and benign conditions returning
through Sunday.

&&

Equipment...
kakq radar is offline due to a pedestal dynamic fault. Techs will
evaluate the radar first thing this morning. No return to service
time is available.

&&

Akq watches/warnings/advisories...
Maryland...none.
NC...none.
Virginia...none.
Marine...Small Craft Advisory until 10 am EST this morning for
anz631>634.
Small Craft Advisory until 10 PM EST this evening for anz650-
652-654-656-658.

&&

$$
Synopsis...Sam
near term...Sam
short term...Sam
long term...mas
aviation...Sam/lsa
marine...ess
equipment...

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