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Area forecast discussion 
National Weather Service Raleigh NC
643 am EDT Friday Sep 30 2016

an upper level low stalled over the Tennessee Valley will retrograde
northward through the Ohio Valley and lower Great Lakes this weekend.


Near term /today and tonight/...
as of 200 am Friday...

Strong low-level warm advection in advance of a cold front extending
southward along the I-77 corridor and upper level forcing in the
form of a jet entrance/exit and small amplitude waves /weak DPVA/
rotating around the eastern periphery of a stalled upper level low
in Kentucky have allowed deep convection to develop within the dry
mid/upper level airmass in place over central/western NC since 00z.
Nocturnal destabilization assoc/W low-level warm advection will
yield 1000-2000 j/kg of MUCAPE through sunrise. Low-level fgen and
upper level forcing on the eastern periphery of the stalled upper
low may further enhance thermodynamics via the release of potential
instability, in the presence of vertical wind shear sufficient for
supercells (scp values 2-6). Any isolated convection in central NC
this morning should remain elevated in nature, with parcels
launching from ~925 mb (atop a ~2500 ft stable layer). With the
above in mind, isolated convection will remain possible overnight,
primarily in the northwest Piedmont where low-level forcing will be
juxtaposed with marginal upper level forcing on the eastern
periphery of the stalled upper low. If layer-lifting is sufficient
for deep convection to survive entrainment of dry air aloft in the
northwest Piedmont, updrafts could acquire mid-level rotation and exhibit
deviant motion. Given the elevated nature of any convection and the
lack of such characteristics thus far, severe weather appears
unlikely. Should a robust elevated updraft acquire rotation, small
to marginally severe hail could not be ruled out.

Instability will decrease from west-east today as a drier low-level
airmass advects into portions of the area (western Piedmont for
sure) attendant a slow moving cold front and temps aloft (h5) begin
to warm. The front is expected to further slow down this afternoon,
stalling in a northwest-southeast orientation along/near a line from int-tta-ctz.
As a result, expect dry conditions in the SW Piedmont with isold/sct
convection possible elsewhere and the relative best chances from in
the NE coastal plain. Expect highs ranging from near 80f in the north/northwest
Piedmont to ~85f in the sandhills and southeast coastal plain. Lows tonight
ranging from the mid 50s west to mid 60s east.

If convection can survive entrainment of dry air in the mid/upper
levels this afternoon, instability/shear would support supercellular
organization along with a potential for damaging winds/large hail.
Though diurnal destabilization will be greatest across portions of
the the sandhills/southeast coastal plain, the potential for an isolated
severe storm may be confined to the north/northwest Piedmont in closer vicinity
to the stalled upper low where upper level forcing /layer-lifting/
(and release of potential instability) is more likely. -Vincent


Short term /Saturday and Saturday night/...
as of 200 am Friday...

Dry/stable conditions will prevail Sat/Sat night as a dry low-level
airmass advects into the region beneath an increasingly warm/dry mid-
level airmass as the upper level low retrogrades northward away from
the region (toward the great lakes). Expect highs in the upper 70s
to lower 80s and lows mid/upper 50s to lower 60s. -Vincent


Long term /Saturday through Thursday/...
as of 350 PM Thursday...

He upper low over the Great Lakes will finally open up and weaken as
it finally ejects eastward off the New England coast late Monday and
into Tuesday. Warm dry air aloft will cap central NC off from any
convection Sunday and Monday with daytime highs continuing to run a
good 3 to 5 degrees above normal. Highs in the upper 70s north to
lower 80s south. Lows 60 to 65.

In the wake of the low lingering off the New England coast, Canadian
high pressure will wedge south down the Atlantic Seaboard, bringing
cooler, more seasonable temperatures Tuesday through Thursday.
The NHC forecasts has Matthew moving northward through the Bahamas
on Tuesday, with large model spread thereafter in both the track
and speed of Matthew for the latter half of next week. Refer to the
National Hurricane Center for the latest information on tc Matthew.


Aviation /12z Friday through Tuesday/...
as of 645 am Friday...

24-hr taf period: IFR/LIFR ceilings and fog will begin to lift to
MVFR everywhere late morning, possibly scattering out to VFR at the
int/gso terminals by mid afternoon, perhaps earlier if shower
activity shifts east of The Triad by that time. MVFR ceilings may
prevail through the afternoon at eastern terminals, where isolated
convection is more likely to persist. VFR conditions are expected at
eastern terminals by or shortly after the end of the taf period as a
dry low-level airmass gradually advects eastward through central NC.

Looking ahead: expect an extended period of dry/VFR conditions this
weekend through early next week as a dry airmass prevails over the
Carolinas. -Vincent


Rah watches/warnings/advisories...



near term...Vincent
short term...Vincent
long term...cbl

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