Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 241912

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
312 PM EDT Mon Apr 24 2017

A deep and vigorous low pressure system will slowly move from
the South Carolina coast to near Cape Hatteras by late Tuesday.
Expect drier and warmer weather Tuesday and Wednesday.  A
dissipating cold front crosses our region Thursday and Friday.


The Cwfa remains well entrenched in an unseasonably cool wedge, well
removed from the sfc based unstable air which is coastward of I-95.
Atop of the sfc ridging, broad forcing is still progged to translate
slowly NE acrs the ftlhs/piedmont...mainly along and NE of I-26.
Coincident with the moderately robust llvl flow...widespread showers
will translate and/or least until the llvl flow veers
to northerly and weakens.

The first order of business will be to trim a few more counties out
the going flood watch. Based on the QPF from here on out and limited
routed flow, feel confident in removing the Tuckasegee, Pigeon and
Lower French Broad Valleys from the watch. Based on the convection
allowing model consensus and the NAMNest panels, the greatest chance
for the redevelopment of heavy showers and the  aggravation and/or
maintenance of existing flooding will be along and east of I-77 in
NC, where the flood watch will be extended into the overnight hours.

A much improved day is on tap for Tuesday with the flow through a
deep layer backing to the NW as the sfc/upper flow wobbles toward
the mid-atlantic. Maximum temperatures are expected to be 12-15 deg
f milder than today/s chilly readings.


As of 100 PM Mon: Heights rise Tue night and Wed as a shortwave
upper ridge moves overhead. A strong subsidence inversion accordingly
will develop. With weak warm/moist advection occurring in the low
levels, as well as saturated soils across the area, there is
potential for low stratus and perhaps some dense fog to develop early
Wed morning, particularly over the Upstate and NE GA. That afternoon,
the same inversion should be strong enough to stifle convection
across the whole CWFA, so PoPs will be kept below slight chance. Max
temps are expected to be 6 to 9 degrees above normal.

Wed night into Thu, the upper ridge axis will be just to our east. A
full-latitude trough will be hot on its heels, centered near the
Mississippi River at 12z Thu. This trough will be associated with a
low over the western Great Lakes, and a frontal zone that will
impinge on the western CWFA by 00z Fri. A plume of midlevel moisture
preceding the trough suggests increasing clouds/PoPs. Elevated tstms
will be possible in the aftn, but sfc-based convection continues to
be suppressed by poor lapse rates resulting from either the ridge or
from the moisture aloft. The best-verifying blend of guidance
suggests max temps will top out 5 to 8 degrees above normal, held
down a bit more by the cloud cover.


As of 200 PM Mon: Friday and Saturday will see the resurgence of a
late-spring pattern over the Carolinas and Georgia, as the upper
pattern amplifies. Temps will trend upward under continued
southwesterly flow; the warmest day looks to be Saturday, when a few
spots may hit 90. Convection will be limited by a weak capping
inversion on Friday, but the warming temps overcome that Saturday.
By Sunday the ridge will have drifted east slightly, allowing
slightly better lapse rates and still greater instability. Given the
pattern, we`ll maintain diurnally driven PoPs, with chances trending
up from day to day. As one might expect, weak wind profiles result in
little shear, and sfc-to-midlevel theta-E differences are high.
Together these findings suggest pulse storm threats from the stronger


At KCLT: Flight restrictions could briefly/occasionally bounce
upward this afternoon in conjunction with gusty nely winds. Shower
activity should also remain light until more robust activity
overspreads the southern NC piedmont at some point after 20z. The
pattern remains favorable for renewed showers this evening into some
part of the overnight hours as winds gradually back to north and IFR
cigs lock in through daybreak.  Improving flight conditions are on
tap Tuesday, especially heading into the afternoon.

Elsewhere: Similar conditions to KCLT except generally better
conditions at KAND and KAVL. Winds will not be as gusty at KAVL as

Outlook: An area of low pressure will move slowly up the Carolina
Coast on Tuesday. Conditions should gradually improve later Tuesday
through Wednesday morning as dry air works in behind the departing
low. Return flow moisture ahead of the next system will develop late
in the week.

Confidence Table...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       Low   57%     High  82%     High  82%     High  88%
KGSP       Med   66%     Low   49%     Med   67%     Med   77%
KAVL       Med   74%     Med   73%     Med   70%     High  83%
KHKY       Med   72%     Med   75%     Med   75%     Med   72%
KGMU       Med   65%     Med   66%     Med   71%     High  82%
KAND       High  93%     High  89%     High  89%     High  85%

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:


NC...Flood Watch until 8 PM EDT this evening for NCZ033-049-050-053-
     Flood Watch through Tuesday morning for NCZ035>037-056-057-071-
SC...Flood Watch until 8 PM EDT this evening for SCZ002-003-005>014-


SHORT TERM...Wimberley
LONG TERM...Wimberley
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