Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KRAH 140620
Area Forecast Discussion
National Weather Service Raleigh NC
120 AM EST Sat Jan 14 2017
-- Changed Discussion --Cool high pressure will briefly build in from the northeast on
today, followed by a secondary cold front on Sunday, and then
another reinforcing high pressure Sunday night.
-- End Changed Discussion --
.NEAR TERM /THROUGH TONIGHT/...
As of 905 PM Friday...
KRAX reflectivity shows surface cold front making it`s way into the
southern portions of the forecast, with some notable 20 to 25 kt
wind gusts at KGSB and KGWW immediately behind the fropa. The front
should be exiting south of the area in the next couple of hours with
cold dry air advection commencing from NE to SW as a transitory
+1040 mb surface high over the the Eastern Great Lakes begins to
wedge south down the Central and Southern Appalachians. Min temps
are expected to range from near 40 north to mid/upper 40s south.
Thus far, both low ceilings and precip has been overdone by the
models. However, by 06z expect to see an increase in both cloud
cover and patchy rain owing to the onset of weak 925-850 isentropic
ascent, especially across far the western zones where easterly
upslope will aide in lift. Rain will be very light, with only a few
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
AS OF 300 PM Friday...
Strong arctic high centered over New England will nose southward
into central NC Saturday and Saturday night. Circulation around this
narrow ridge will keep our near sfc air mass rather chilly.
Meanwhile 925-850mb will veer Saturday morning to a west-sw
direction, initiating a cold air damming episode (classical by
classification). The widespread cloudiness with the low level
northeast flow will result in a small diurnal range in temperatures.
Some places may only see temps recover 3-5 degrees from the morning
lows. While cloud cover will be extensive, threat for rain will
decrease to less than 20 percent by late morning as forcing
available to generate precip absent. Rather dramatic shift in temps
compared to the current spring-like conditions. Highs Saturday
expected to vary from the low-mid 40s north to near 50 far south.
Little change in sensible weather Saturday night as widespread
cloudiness and cool conditions will persist. A weak perturbation
expected to cross overhead which may trigger some patchy drizzle or
light rain, mainly north of highway 64. Also, expect to see patches
or areas of fog develop. Overnight temps near 40 to the lower 40s.
.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 300 PM Friday...
The overall pattern for Sunday and Monday hasn`t changed much since
the previous forecast. A 1032-1034 mb high will move from the Great
Lakes through NY/PA and over the New England coast Sunday and
Monday. The High will ridge southward, setting up a CAD wedge over
NC. Meanwhile, an upper level low over the Baja will swing northeast
into the Midwest through Monday Night.
There is still a question of if/when the wedge will erode early
Sunday morning and re-establish itself late Sunday, or whether it
will hold all the way through Tuesday night. The west-northwest flow
aloft on Sunday would normally result in some subsidence and drying,
however there is enough moisture in the mid-upper levels that weak
disturbances may generate some light rain/drizzle into the wedge
airmass, thus reinforcing it. Regardless, expect overcast skies
Sunday onward, which despite any clearing in the boundary layer,
will help limit temperatures. Given the uncertainty, confidence is
not terribly high, but current forecast highs range from upper 40s
NE to around 60 degrees SW. Chances for light rain/drizzle will
linger over the west through Sunday night with lows in the low 40s.
Cooler but dry weather expected in the NE Sunday night.
The wedge will remain in place on Monday and may slowly start to
erode on Tuesday as the surface flow becomes more southerly between
the high over the Atlantic and the approaching front to the west of
the Appalachians. Also expect moderating temps Tuesday through
Friday. The strong southerly flow ahead of the front will result in
good moisture feed off the Gulf and thus high chances for rain ahead
of the front. However, the medium range models are significantly
different with respect to the strength/character of the low/trough
as it approaches, as well as the timing of the pre-frontal rain and
subsequent cold frontal passage. Will lean more toward the slower
ECMWF solution which currently brings the rain in on Wednesday
through Wednesday night. Uncertainty is still high at this time and
thus confidence is low, however do expect a good chance of rain and
possibly thunder ahead of the front, regardless of when it
progresses through Central NC.
.AVIATION /06Z FRIDAY THROUGH WEDNESDAY/...
-- Changed Discussion --AS OF 120 AM Saturday...
An 8-12kt northeast wind has developed in the wake of a cold front
that has pushed south of the NC/SC as of 06Z. MVFR cigs have been
slow to develop but have started to expands from RDU to GSO/INT and
northward, as an area of rain also expands near the NC/VA border.
MVFR cigs should continue to develop southward overnight as the low-
level flow turns to southerly and strengthens. The aforementioned
rain may aid in lowering ceilings at GSO and INT this morning,
possibly to IFR, but confidence is relatively low. Otherwise, MVFR
cigs may not move very much today without more widespread precip,
and the low clouds may even mix out at FAY where the moisture and
lift are not as pronounced.
Outlook: Cold air damming and associated widespread MVFR to
diurnally IFR conditions will persist Sunday through most of
Tuesday. Warm air scours out the colder air Tuesday with a return to
VFR conditions briefly as a cold front and its associated adverse
conditions approaches on Wednesday.
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