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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 300602
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
202 AM EDT FRI SEP 30 2016

.SYNOPSIS...
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An upper level low stalled over the Tennessee valley will retrograde
northward through the Ohio valley and lower Great Lakes this weekend.
-- End Changed Discussion --

&&

.NEAR TERM /TODAY AND TONIGHT/...
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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 NW 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
NW 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 NW-SE 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 N/NW
Piedmont to ~85F in the Sandhills and SE 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/SE Coastal Plain, the potential for an isolated
severe storm may be confined to the N/NW Piedmont in closer vicinity
to the stalled upper low where upper level forcing /layer-lifting/
(and release of potential instability) is more likely. -Vincent
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&&

.SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
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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
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&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
As of 350 PM Thursday...

The persistent upper low over the Tenn Valley will finally lift
north into the Great Lakes and weaken, as a trough deepens over the
Pacific Northwest.  This will lead to a general trend toward higher
heights over the eastern U.S, a surface high pressure ridge down the
East Coast and temps near at or just slightly above.  Before the low
fully departs the region, some diurnal convection is possible across
the far south/east Saturday and Sunday given the continued presence
of the front that sinks over the area this weekend, but with
diminishing in coverage with each day.

Most of the long term focus is with the uncertainty in the track of
what is currently Hurricane Matthew over in the Central Carribean.
The official NHC track brings Matthew north across the Bahamas early
next week in response to an upper trough cross the Gulf Coast
region.  This is still rather uncertain at day 7, however, and quite
likely to change in the coming backs.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
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As of 1245 AM Friday...

24-hr TAF period: IFR ceilings (500-1000 ft AGL) are expected to
deteriorate to LIFR/VLIFR (100-500 ft AGL) between 06-09Z and
persist through sunrise in association with low-level warm advection
in advance of a cold front approaching from the west. Isolated
convection could potentially affect all terminals through 12Z this
morning, though probabilities are too low to warrant mention at most
terminals (aside from perhaps INT/GSO). IFR/LIFR ceilings will begin
to lift to MVFR everywhere late morning to early afternoon, then
scatter out to VFR at the INT/GSO terminals by mid afternoon. MVFR
ceilings will likely persist through the afternoon at eastern
terminals, where isolated convection will also be possible. 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
-- End Changed Discussion --

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Vincent
NEAR TERM...Vincent
SHORT TERM...Vincent
LONG TERM...BS
AVIATION...Vincent