Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 222115

National Weather Service Raleigh NC
515 PM EDT Tue Oct 22 2019

A warm front, triple point surface frontal wave, and following
cold/occluded front(s) will cross the Carolinas and southeastern VA
through this evening. High pressure will then build east across the
region Tuesday night through Thursday.


As of 435 PM Tuesday...

A broad 1008-1009 mb surface low across n-cntl NC and s-cntl VA
(centered near FVX at 20Z) will track into the Chesapeake Bay
vicinity through 00Z. A warm front was analyzed from the frontal
wave sewd across Wake, Johnston, and Sampson Co.

This boundary, and warm sector characterized by 500-1500 J/kg
MLCAPE, will retreat briefly nwd across the ern half of cntl NC
through early this evening. The surface flow behind the retreating
warm front has veered to swly and consequently limited low lvl
shear/hodograph curvature, and thereby minimized tornado potential
in this most buoyant airmass. Relatively long and straight
hodographs there will instead provide a favorably sheared
environment for cell splits, with a low end risk for damaging wind
gusts and perhaps even some small hail. To the north/across the ne
Piedmont and nrn Coastal Plain, the surface flow has remained
slightly more backed (to sly or ssely) immediately preceding the
aforementioned elongated frontal wave and broken convective line;
and that environment has proven conducive for the development of
several LEWP and mesovortices across the nrn Piedmont, including
most notably in TRDU data across Person Co. and more recently in ern
Durham Co. Episodic strong to marginally damaging wind gusts or even
an isolated tornado will be possible in this regime, across nrn Wake
and Franklin, and adjacent ne Piedmont and nrn Coastal Plain
counties during the next few hours.

While the ongoing broken line of convection currently over cntl NC
should serve as the wrn bound of any severe threat, shallow,
isolated showers may yet develop along the nrn portion of a cold
front fractured by the srn Appalachians, analyzed from near
(formerly) IGX to CLT, as it encounters a residually moist and
weakly unstable environment behind the foregoing main convective
line prior to sunset.

Skies will otherwise continue to clear from west to east this
evening, amidst CAA and as downslope wly flow noted on upstream VWPs
from FCX to MRX and JKL, spread ewd. Much cooler lows are expected to
range from low-mid 40s over the rural wrn Piedmont to lwr 50s in the
Coastal Plain.


As of 445 PM Tuesday...

A vertically stacked low pressure will be located over Ontario
Wednesday morning with surface high pressure settling over MS/
AL. Across central NC northwest flow will continue with weak CAA
occurring over the region. 1000/850 mb thicknesses fall towards
1355 m Wednesday afternoon with 850 mb temperatures near 8
degrees C. This will support highs in the upper 60s to near 70
degrees. Downslope flow across the northwest will again support
an over achievement in highs over the Triad, with area wide
highs in the upper 60s to near 70 degrees. Mostly clear skies
with no precipitation is expected.


As of 525 PM Tuesday...

Models continue to struggle in the long term with the evolution
of a wave that is forecast to dive south over the Mountain West
Thursday morning. The latest runs of the ECMWF and CMC continue
to show this energy breaking off into a closed low while the GFS
keeps the energy embedded in the main flow. The latest run of
the GEFS has trended towards the ECMWF and CMC.

Thursday morning surface high pressure will center overhead with
low level thicknesses (1000/850 mb) falling towards 1350 m.
Given the ideal radiational cooling setup have kept lows towards
the tail of the model spread. Dry and seasonal weather will then
persist through the day with highs near 70 degrees.

Thursday night into Friday models quickly diverge as noted
above. Have continued to trend the forecast towards the ECMWF,
CMC, GEPS, and EPS means and kept Friday dry. By Saturday the
GFS shows widespread precipitation moving over the area with
surface low pressure heading northeast across central NC. This
would favor a CAD type regime. The ECMWF and CMC solutions on
the other hand show the mid-level wave exiting the east coast
Saturday morning with another weak cold front sagging south
through the region. Sunday the front quickly washes out and
heads north with surface low pressure pulling northeast towards
IL/IN. Either camp provides precipitation for Sunday (for very
different reasons). For now have kept broad brushed PoPs
Saturday into Sunday until further clarity materializes.

By the end of the long term another potent shortwave will dive
south out of Saskatchewan and slowly translate east. Overall am
expecting this to only slowly translate east. Due to this have
trended temperatures up Monday/ Tuesday.


As of 300 PM Tuesday...

Earlier LIFR-MVFR ceilings continue to retreat nwd and scatter to VFR
with the nwd retreat of a warm front into e-cntl NC. A quickly-
following cold front and line of convection with gusty surface wind
gusts will move east and affect RDU, FAY, and RWI during the next
several hours, with following clearing/VFR and light wnwly surface
winds - just as has already occurred at INT/GSO as of 19Z.

Outlook: High pressure will result in mainly VFR conditions for at
least the next several days, with the primary exception being
radiation fog at RWI due to local effects. The next storm system and
chance for sub-VFR conditions will be late Sat-Sun.




LONG TERM...Haines
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