Area Forecast Discussion
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FXUS62 KRAH 031123
Area Forecast Discussion
National Weather Service Raleigh NC
625 AM EST Sat Dec 3 2016
High pressure will build into the Carolinas from the northwest
through Saturday night. A storm system will move from northern
Mexico across Texas and the Gulf Coast states into the Southeast
states Sunday through Tuesday, bringing unsettled weather for North
.NEAR TERM /today through tonight/...
As of 345 AM Saturday...
Deep low pressure continues to dig over NW Mexico early this
morning, and this low along with the preceding deep plume of
moisture spreading into the TX/Gulf States and Southeast over the
next couple of days will be the primary driver for our weather into
early next week. The latest surface analysis shows a weak mesohigh
over Central NC loosely connected to a larger high centered over the
Mid Miss Valley. This general surface configuration will hold
through today and tonight as the core of the larger high shifts NE
through the Ohio Valley. Fast WNW mid level flow acting on a slug of
high level moisture within a stable column have led to enhancement
of cirrus in the lee of the southern Appalachians early this
morning, which should linger at least into mid morning. Irrespective
of this phenomenon, high clouds will gradually increase and become
more opaque later today into tonight as minor mid level
perturbations ride NE atop the flat ridge extending over the Gulf
and Southeast states toward NC. But the persistence of dry low level
air today will mean a dry forecast today. The decreased insolation
compared to yesterday and lower thicknesses will result in highs
today around a category lower than yesterday, in the lower to mid
50s. Cloud bases will continue to lower tonight with thickening
broken to overcast decks overspreading the area, and while moist
isentropic upglide does deepen, it remains rather weak and confined
above 5000 ft AGL, which would seem to favor just patchy very light
rain at most moving into the western Piedmont late tonight. Will
keep very low chance pops in the far west only. Lows from 35 NE to
near 40 SW. -GIH
.SHORT TERM /Sunday through Sunday night/...
As of 405 AM Saturday...
The deep low will wobble slowly across N Mexico toward TX Sun
through Sun night, as surface frontogenesis ramps up over the Gulf
Coast to the northeast, across GA/SC to the southern coast of NC.
The east-northeastward expansion of what should be widespread rain
from TX into the Southeast will initially be stymied by the surface
ridge, which will extend from Ontario/Quebec southward into the area
through much of Sunday, as well as by the effects of the broad mid
level ridge, the axis of which will be passing over the Carolinas,
limiting overall ascent. Will bring low chance pops into Central NC
Sunday, ~30% chance west ranging to slight or no pops in the east
where the relatively dry subcloud layer will be deeper. Thick clouds
will further hold temps down, and expect highs from the mid 40s NW
(beneath the most pronounced combination of thick clouds and
cool/stable low levels) to the lower 50s SE. The arrival of a 40+ kt
low level jetlet across GA/SC/NC Sun evening along with
strengthening IVT will result in a ramping up of moist upglide and
overall forcing for ascent, in tandem with the departure of the
surface ridge, making the low levels vulnerable to saturation.
Expect rain coverage to increase to likely in the NW CWA and
categorical south/southeast Sun evening, followed by a slow exit
later Sun night as the low level jetlet shifts to our east and deep
moist upglide shuts down. Rainfall from late Sun through Sun night
could approach 0.25-0.50", higher in the south. Expect lows from
around 40 NW to mid 40s SE. -GIH
.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 325 AM Saturday...
Monday will be a transitional day with high pressure moving off the
coast, a weak wave along the coast and new high pressure moving into
the mid-Atlantic region from the Ohio Valley. The upshot of this is
that we will move from more of an in-situ damming situation to more
of a hybrid scenario but northeasterly winds across the area and
chances for precipitation early in the day with a lull later on. The
cold air damming should keep temperatures down around 50 degrees in
the Triad with middle 50s across the southeast.
Tuesday the Miller B scenario takes full effect a pair of lows on
either side of the wedge parked over the Piedmont. Precipitation
should begin early Tuesday morning and continue all the way through
Tuesday night before the system starts to move off to the northeast.
Accumulations for this event should be over an inch and possibly up
to two inches. Temperatures will be tricky and dependent highly upon
the track of the coastal low. With fairly high confidence, the Triad
should stay cold throughout the day under the wedge with highs
possibly only in the upper 40s. The bigger uncertainties in the
temperature forecast lay in the south and east where highs could be
as much as 60 degrees.
Wednesday and Thursday will be dry and a little warmer on the front
side of a longwave trough bisecting the continent. Highs in the 60s.
By Thursday night, models begin to diverge on timing and available
moisture leading to two very different possible scenarios for
Thursday night into Friday. The GFS solution has a very progressive
trough and a drier solution which brings very cold temperatures into
the area on Thursday night. The ECMWF solution is slower and wetter
which means warmer temperatures hanging around longer Thursday
night. For now we are taking the dry, colder forecast so expect
temperatures below freezing both Thursday and Friday nights with
Friday being the coldest as very anomalous thickness values move
into the area and bring low temperatures down into the 20-25 degree
.AVIATION /12Z Saturday through Wednesday/...
-- Changed Discussion --As of 625 AM Saturday...
High confidence in VFR conditions for the next 24 hours. Surface
high pressure will continue to build into the region today, with
deep dry air as mid level ridging shifts over the Southeast states.
Only a thin veil of high clouds is expected across the area today,
although clouds will become more opaque with lowering bases to
12,000-18,000 ft AGL late today through midnight tonight as upper
level perturbations emanating from the developing storm system over
N Mexico track ENE toward the Carolinas. Mid clouds will continue to
thicken and lower late tonight, dropping to 5,000-6,000 ft AGL by
early Sunday. Surface winds will be light from the NW through
daybreak, then from the NW around 8-10 kts through sundown, becoming
light/variable once again tonight.
Looking beyond 12z Sun: Patchy light rain will start to spread in
during the day Sunday from the SW as the upper level disturbances
break down the mid level ridge, although VFR conditions should hold
for much of the day. Confidence is high that conditions will
deteriorate further to IFR Sunday evening/night and remain poor at
IFR or LIFR into early Monday with periods of rain, particularly
south. Some improvement to MVFR or even briefly VFR on Monday, but
should quickly drop again to IFR/LIFR Monday night into Tuesday
evening with rain areawide. Rain should taper off Tuesday night but
IFR/LIFR conditions may hold through daybreak Wednesday, followed by
improvement to VFR by midday Wednesday. The potential for low level
wind shear will remain a concern, especially Sunday night and again
on Tuesday. -GIH
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