Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Remove Highlighting --
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FXUS62 KRAH 301952
Area Forecast Discussion
National Weather Service Raleigh NC
252 PM EST Wed Nov 30 2016
A cold front will approach the area this afternoon and then move
across central NC this evening. High pressure will build into the
region on Thursday and persist through Saturday.
.NEAR TERM /THROUGH TONIGHT/...
As of 1055 AM Wednesday...
The morning upper air analysis shows a large long wave trough over
the central U.S. with a potent short wave ejecting from the
Arkansas area northeastward into Illinois and Indiana associated
with a 110kt jet at 500 hPa. Ahead of the trough, a deep and
vigorous southwesterly flow is present across the Southeast
transporting Gulf and even some Pacific moisture into the region
with precipitable water values ranging from 1.3 to 1.5 inches. The
latest surface analysis shows an eastward advancing cold front
approaching the southern Appalachians.
A band of showers and with embedded thunderstorms stretches from
western PA southwest across WV into eastern KY and TN and then
into AL from this morning. Thunderstorms as noted by total
lightning data, stretch from southwestern VA into TN, and AL with
a ongoing prefrontal QLCS from eastern TN into AL.
Given the limited forcing for ascent across central NC, the
latest regional radar shows virtually no precipitation across
most of the state with a limited area of showers across the
Carolina coast with the more significant band of showers just
reaching the NC mountains. The vigorous flow aloft as noted by the
42kts observed at 2kft and 50kts at 2800ft on the 12Z KGSO
sounding, will be mixed down to the surface at times today with
routine surface gusts of 20 to 25kts. As the low stratus melts
away and some breaks in the mid and high cloud deck develop,
temperatures will warm into the 72-80 range by afternoon.
The band of convection to our west will push east reaching the
western Piedmont and Triad area between 22 and 02Z then spread east
reaching the eastern Piedmont, Triangle, and Coastal Plain between
02 and 09Z. The SPC has our region outlooked in the a marginal
risk for severe weather, largely driven by the vigorous wind field
in a high shear/low CAPE environment. The primary limiting factor
for severe convection remains the limited instability. Peak MLCAPE
values generally range around 500 J/Kg although a pocket of
higher instability, ranging from 500-1000 J/Kg may develop across
the central and northern Coastal Plain in an area of higher dew
points. In addition, the modest synoptic scale forcing with weak
height falls and FGEN will not compensate for the limited
instability. Finally, these parameters will become less favorable
during the evening as the convective band approaches outside of
peak heating and as the modest upper air features weaken with
time. SHERBE values approach 1 near the frontal zone. Convection
allowing models generally weaken the convection with time and
eastward progress suggesting a more limited event that will still
need to be monitored for locally damaging wind gusts.
The weakening band of convection will slowly progress east this
evening, slower than previously expected. All of the
precipitation should clear central NC by daybreak. Slow clearing
will arrive behind the front overnight. NAM and GFS BUFR
soundings show a strengthening low level jet during the evening
which could result in a local wind gust of 35+ MPH, even outside
of convection. Temperatures will fall behind the front with lows
by daybreak ranging from the upper 40s in the Triad to around 60
in the Coastal Plain where the front will just have cleared the
.SHORT TERM /THURSDAY THROUGH SATURDAY/...
As of 230 PM Wednesday...
The synoptic cold front will have moved to the coast by 12Z tomorrow
morning, with perhaps some early morning clouds giving way to sunny
skies and cold air advection throughout the day. Models indicate low
level thicknesses during mid afternoon about 50 meters down from
Wednesday afternoon...which translates to 10-15 degrees cooler. As
such, highs will edge above normal one final day...reaching around
60 northwest ranging to upper 60s in the southeast.
Seasonable high pressure over the central plains will build eastward
and the pressure gradient will relax Thursday night. Under clear
skies with the cool dry airmass in place, mins will tumble into the
30s over the area, with some locations in the north and
west potentially falling slightly below freezing near sunrise.
Near zonal flow aloft and reinforcement of the surface high with
modestly cooler air from the northern plains will maintain the
status quo with mostly sunny skies Friday and increasing high
cloudiness Saturday. Highs will be in the mid to upper 50s
Friday cooling to the low and mid 50s Saturday.
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
-- Changed Discussion --As of 252 PM Wednesday...
In the Sunday time frame...moisture advection out of the Gulf will
stream east along a frontal zone setting up across the Gulf States.
With a cool dry airmass in place, we should see a thickening
cloudiness Saturday night with light rain breaking out due to
isentropic lift in the west by mid day Sunday, and will maintain
ongoing chance PoPs in the west during the morning spreading over
the east during the afternoon. Highs will be subsequently suppressed
by clouds and evaporative cooling, ranging from mid 40s in the
northwest to lower 50s in the southeast.
The forecast from Sunday night onward remains low confidence pending
consensus as to the progression of a cutoff low over northern Mexico
which will be lifting ENE across the plains early next week.
Initially, the high pressure over the area is reinforced by the
arrival of a second surge of cool dry air from a transitory surface
high oriented more classically from New England south down the east
coast, which would suppress moisture southward on Monday. This would
set the stage for another isentropically induced rain regime on
Tuesday/Wednesday as the moisture associated with the aforementioned
cutoff low and associated surface reflection ride up the cooler
denser air. Will keep PoPs on the low chance side for now, with
highs in the 50s Monday through Wednesday as we wait to see how
the scenario plays out.
-- End Changed Discussion --
.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
As of 205 PM Wednesday...
MVFR ceilings in a low overcast across the Piedmont have largely
lifted with mainly scattered clouds at around 3kft and various BKN
clouds layers above. Further east and south, the low overcast has
been more stubborn with a predominance of BKN clouds at around
2.5kft. Mainly dry conditions with only isolated showers are
expected this afternoon before an eastward advancing cold front
pushes a band of showers and perhaps an embedded thunderstorm east
across central NC during the evening and especially the overnight
The front`s eastward progress has slowed today. The best chances
of showers along with ceiling and visibility restrictions range
from 22Z to 03Z at the KINT and KGSO terminals and from 02Z to 08Z
at the RDU/KRWI/KFAY terminals. Improving conditions with breaks
in the overcast and clearing skies will arrive behind the front
for the daybreak hours with VFR conditions in scattered cumulus
clouds expected on Thursday. Gusty south winds today will become
south-southwest this evening at 10-15kts with gusts of 20-30kts,
even stronger in any thunderstorm. The winds will become westerly
behind the front at 10kts and northwest at 10-15kts on Thursday.
Looking beyond the 24 hour TAF period... High pressure will build
into the region on Thursday and persist into Saturday resulting
in fair weather. A storm system will approach the area from the
southwest on Sunday with a chance of adverse aviation conditions
late sunday into Monday. -Blaes
Record highs for 11/30
RDU 77 2006
FAY 80 1927
GSO 74 1991
Record high minimums for 11/30
RDU 62 1934
FAY 62 2001
GSO 62 1934