Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 280826

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
326 AM EST Tue Feb 28 2017

A warm front will lift north across our area today warming
temperatures further and then a cold front crosses the area
Wednesday night preceded by showers and thunderstorms.  Cool high
pressure will drop temperatures to near normal for the second half
of the week. As the high moves off the Carolina coast, a warm
southerly flow brings temperatures above normal again Sunday and


As of 300 AM: Large scale moist isentropic lift acting upon elevated
instability is expected to result in continued expansion of
convection across the lower Miss Valley and eventually the TN Valley
this morning. This activity is expected to progress east throughout
the day, possibly reaching the southern Appalachians by late
afternoon, as indicated by most operational guidance as well as a
consensus of mesoscale model output. Even so, even most unstable
CAPE as indicated in the latest model guidance is meager across the
region this afternoon, so we feel that showers and embedded storms
will be doing well just to make it to our forecast area, much less
make significant inroads into it. 50-60 pops will be advertised
across much of the NC mtns by late afternoon, with 20-40 percent
across the Piedmont by evening. Despite having great difficulty to
do so thus far, low clouds should expand across the forecast area
this morning, but the rather shallow depth of the moisture should
make it susceptible to thinning and perhaps scattering in some areas
later today, allowing temps to warm well above normal, esp across
the SC Piedmont and southern NC Piedmont, where maxes in the
mid/upper 70s appear likely.

Precip chances will wind down this evening, with typical warm sector
conditions (anomalously high dewpoints, persistent surface flow,
clouds) resulting in Wed morning min temps pretty close to where out
highs should be this time of year.


As of 230 AM EST Tuesday:  The short range fcst period kicks
off on Wednesday morning amidst falling heights aloft as a deep
upper trough slides east out of the Plains.  At the surface, a
subtropical high will be anchored over the Western Atlantic while
a cold front pushes into the MS/OH River Valleys.  Llv flow around
the aforementioned high, combined with improving swly H85 flow ahead
of the front will work to enhance waa across the region through the
day leading to modest destabilization as guidance has trended toward
steeper lapse rates.  With that, profiles will exhibit uncapped pos
CAPE fairly early in the afternoon, however lack of any triggering
is expected to keep any convection at bay until later as the front
approaches, therefore pops will remain rather low.

Guidance seems to have converged a bit better with latest runs
regarding any prefrontal late day precipitation, as well as any
frontal forced convection into the evening as the front itself looks
to move into the high terrain by around 8-9PM.  Instability fields
have improved somewhat with ample pooling of nearly 1-1.5k j/kg
sbcape westward across Middle TN, upwards of 5-7 hundred joules
east into Northeast GA and the Western Carolinas, all mainly due
to the slightly increased speed of the system negating a mostly
nocturnal fropa.  Overall, given that shear fields continue to
look impressive, think chances for strong/severe convection have
improved a bit.  Still to early to tell some of the details, but
given the overall synoptic pattern and the placement of features,
think convection will likely fire to the west across MS/AL ahead
of the front in the moist/unstable warm sector before sliding
east into North Georgia, possibly moving into the Upper Savannah
River Valley by late afternoon, all while frontal convection gets
going to the west.  Evolution of diurnally favored instability
fields would suggest some weakening of the earlier convection
after dark before the primary frontal MCS arrives.  The front
will slide across the region into early morning Thursday, likely
at a fast pace, especially if any cold pooling gets established.
Given relatively veered llv flow, and no backing of surface flow
at all, think the tornado threat is rather low, thus the primary
threats will be damaging winds and possibly some large hail.

Beyond the fropa into Thursday, high pressure will build across
the region from the west leading to drier and cooler conditions yet
again.  Winds could be a bit gusty early on Thursday across the mtns
as the pressure gradient remains enhanced, however should weaken
through the day.  Skies are expected to clear out in response to
the drying conditions and ample downslope flow across the Piedmont.
Temperatures on Wednesday will be well above normal, likely topping
out in the mid/upper 70s across the Piedmont, generally 5-7 degrees
cooler in the mtns.  Expecting temperatures to fall behind the front
for Thursday, however likely hovering at or just above normal for
highs, but cooling substantially into Friday morning as the cool
high settles in.


As of 145 AM EST Tuesday:  On Friday a shortwave passes through the
trough north of our area with the ECMWF having all energy
sufficiently north of our region with no precip for our northern
mountains. The GFS on the other hand has a deeper shortwave
resulting in NW Flow precip reaching the northern NC mountains
around 18Z Friday. Since this shortwave passage would be up in the
daytime, precip would be less snow and more rain than if it were
nighttime. Not a significant event either way.  The shortwave moves
quickly off the East Coast with the center of surface high pressure
centered over NC at 12Z Saturday.  As the high moves offshore late
in the weekend, a southerly flow will result increasing clouds ahead
of the next cold front.

The wind field models are not showing any upslope low level flow
ahead of this front as wind shifts quickly SW early Sunday and stays
that way until frontal passage on Tuesday. Little if any instability
with the front before our forecast ends at 12Z Tuesday. Chances of
precip begin in the mountains late Monday then the bulk of the
frontal precip arrives late Monday night.

Temperatures slightly below normal Friday and Saturday then several
degrees above normal again by Monday.


At KCLT and elsewhere, low level moisture is still set to increase
through the morning hours, but guidance continues to back off of the
timing and magnitude of any restrictions. In fact, some of our more
reliable guidance have removed the potential for any restrictions at
KCLT through the TAF period (which does NOT mean that the potential
is not there). Considering the trends in guidance and observational
data (surface dewpoints just aren`t increasing as quickly as
guidance wants them to) we have backed off of any restrictions at
the NC terminals until at least Tue evening. MVFR cigs have been
retained at the SC terminals, but not until sunrise or thereafter,
and they are generally maintained in the 020-030 range. With the
exception of the valleys of far SW NC (i.e., west of KAVL), chances
for visby restrictions appear to be quite low until at least Tue
evening. Chances for showers will increase this afternoon across the
mtns, extending into the foothills by this evening. Also can`t rule
out a stray thunderstorm. However, only PROB30s for SHRA appear
warranted attm.

Outlook: With low level moisture remaining in place, flt
restrictions could develop Tue night and continue into early Wed,
although uncertainty in this is quite high. A cold front will
approach from the west late Wednesday and bring additional chances
of showers and restrictions, as well as some thunderstorms. Drier
conditions end the week following the fropa.

Confidence Table...

            08-14Z        14-20Z        20-02Z        02-06Z
KCLT       High 100%     High  98%     High 100%     High 100%
KGSP       High  91%     High  82%     High  93%     High 100%
KAVL       High 100%     High 100%     High  86%     High  84%
KHKY       High 100%     High  90%     High  95%     High  81%
KGMU       High  95%     High  82%     High  86%     High 100%
KAND       Med   79%     High  95%     High  82%     High 100%

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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