Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 261120

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
720 AM EDT Thu Apr 26 2018

An area of low pressure will cross the region today through early
Friday, bringing rain chances back to the area. High pressure will
build across our area this weekend and persist into early next week.


As of 715 AM: The forecast remains on track with water vapor imagery
showing a closed low pressure system moving rapidly southeast over
the lower Mississippi River Valley this morning. This compact system
should bring a narrow window of fairly intense deep-layer forcing to
much of the Deep South and the southeast over the next 24 hours.
Ahead of this system, IR imagery and surface observations indicate
stratocumulus at 5000 to 7000 feet over the forecast area due to an
inversion layer around 750 mb in thermal profiles. The combination
of early morning clouds and then increasing clouds ahead of the
approaching system will limit heating and the associated temperature
rise somewhat today. This will have implications for instability
later in the day. The convection-allowing models generally bring the
leading edge of the rain shield ahead of this system across our
forecast area from late morning west through the afternoon hours
east. The best convection may be associated with the surface wave
and the deeper-layer DPVA just ahead of the upper low. Although
consensus instability is for only a few hundred J/kg of sbCAPE
(limited by the increasing clouds), a brief window of 50 to 60 kt
sfc to 6 km bulk shear may pass over areas southeast of I-85 this
evening. The current Day 1 Marginal Risk for these areas appears
well-placed, and a severe mention will be added to the HWO for the
late day and evening hours.

The main potential for any hydro concerns, given the wet ground,
will be for training of cells over the Charlotte metro area this
evening. This appears too uncertain to entertain any Flash Flood
Watches, but an HWO mention of the heavy rainfall will be added as
well. Weak deformation zone forcing behind the departing low may
keep showers going through late tonight, especially along I-77.


As of 350 AM Thursday: Expect scattered, light precipitation (all
rain) to be falling across much of the FA on Friday morning,
continuing into the early afternoon hours (becoming isolated in
nature) as the storm system across the eastern Carolinas continues
to exit off to the north. As it`s accompanying upper (now open) wave
joins the upper longwave trough across the Northeast, at the same
time, another 500 mb wave is progged to dive out of the southern
plains, into the GOM and across FL within split flow, where it is
suggested that it`ll then join the upper flow as it rides northward
and just off the Carolina coast late Saturday night. With the quick
return to NW flow Friday night, expect conditions through the rest
of the forecast period to remain dry, setting the stage for the
medium range forecast period. Temperatures will remain slightly
below normal on Friday and Saturday.


As of 330 AM Thursday: The medium range forecast period begins
Sunday morning where, per latest guidance, upper trough across the
northeast will continue to swirl and slowly propagate eastward
throughout the day, eventually making it`s way offshore late Monday.
At the same time, behind the exiting system, sfc high pressure is
progged to build down from the Great Lakes and into the Southeast,
where it`ll meander and slowly shift off the Carolina coast by
midweek. This along with upper ridging back to the west, which will
gradually weaken and move overhead into Wednesday, do expect
conditions to remain dry through the forecast period. Will note that
the coverage of passing clouds will gradually increase Tuesday into
Wednesday as the shifting of sfc high pressure offshore allows for
the return of SW flow and GOM moisture. Temperatures will remain
below normal Sunday into Monday and then climb above normal, with
high temperatures on Wednesday in the upper 70s/around 80 degrees
across most of the area, slightly cooler across the mountains.


At KCLT and Elsewhere: VFR bases at 5000 to 7000 feet will continue
this morning as moisture persists below a 750 to 700 mb inversion in
the thermodynamic profiles. These clouds will give way to lowering
VFR and then MVFR clouds through the day as isentropic lift develops
ahead of the approaching low pressure system. Anticipate rain
showers spreading into the region from the west from 16Z to 18Z,
with thunder chances ramping up mainly from KAND to KCLT toward
evening. Light winds will generally adjust between NE and SE through
the day before becoming northerly tonight behind the departing low
pressure. IFR visibility will certainly be possible under any heavy
showers and thunderstorms.

Outlook: Restrictions should end Friday morning as dry air moves
in from the west behind the departing low. A dry cold front will
approach from the northwest early in the weekend, with much drier
and solidly VFR conditions likely persisting well into early next

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       High 100%     High 100%     High 100%     Low   46%
KGSP       High 100%     High 100%     Med   72%     High 100%
KAVL       High  94%     High  94%     High  83%     Med   64%
KHKY       High 100%     High 100%     Med   78%     Med   78%
KGMU       High 100%     High 100%     Med   72%     High 100%
KAND       High 100%     High 100%     Med   72%     High  93%

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:




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