Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 201124

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
624 AM EST Mon Feb 20 2017

Warm high pressure will move over the area through the early part of
the week, bringing temperatures close to record highs. MA cold front
will bring a chance for some modest rainfall over the area by mid
week, followed by brief drying, before a frontal system arrives next
weekend with rain and thunder chances.


600 AM EST Update...Only minor tweaks made to hr/ly temps and td/s
as localized areas are running below the fcst curve in calm and
decoupled conds.

430 AM EST sigfnt changes need to the fcst. Made some
minor tweaks upward to hr/ly temps. The morning fg/br potential
looks pretty low...expect perhaps across the srn zones where tdd/s
are currently running arnd 3 degrees F. Not expecting dense fg

A strong upper level ridge has developed to the west of the FA and
streaks of thin Ci are rounding axis and dissipating in the
downstream subs zone. Expect this Ci to increase in coverage slowly
this afternoon...and become more overcast thru the overnight period.
Soundings are showing a pronounced subs inversion lowering to h9
today and winds weakening sigfnt/ly thru 12 Kft. Meanwhile a cP sfc
high will ridge in from the NE...however no lowering sfc temp adv
will occur according to llvl sigma winds. So...will count on very
good insol and compressional warming to allow max temps to reach
about 20 degrees above normal. This will likely reach or break the
record of 75 F at GSP by a degree or two. CLT and AVL will also come
close to record highs for this date. The increasing cloud cover
overnight will aide in holding mins about 10 degrees above normal.
Basically...another very nice Feb day is in store feeling more like
late Apr.


As of 2 AM EST Monday: The dominant ridge over the southeast will
move off the eastern seaboard Tuesday as the southern stream closed
low pressure system wobbles near the Louisiana Gulf coast and
northern stream waves create more zonal flow across the western
Carolinas. Low level southerly winds developing ahead of the Gulf
coast system may provide some afternoon upslope triggering for
isolated showers in and near the southern Appalachians Tuesday
afternoon. Deeper moisture between the northern tier frontal system
and the Gulf coast low will then likely pool over the region Tuesday
night to warrant briefly enhanced PoPs for rain showers throughout.
Temperatures will exhibit the smallest diurnal range of the week
Tuesday-Tuesday night given the increased clouds and precip chances,
but with Tuesday afternoon maxes still reaching around 70 in some
lower piedmont areas.

The closed system over the Gulf of Mexico should continue to move
southeast toward the FL Keys Wednesday through Wednesday night. 850
mb flow over the southeast is expected to become more westerly with
time, with deeper moisture likely moving off to the east. This will
allow PoPs to steadily dwindle across our forecast area with mainly
continued shower chances over the mountains by Wednesday night.
Wednesday afternoon maxes should rebound to some 15 degrees above


As of 230 AM EST Monday: The medium range picks up at 12Z Thursday
morning with rising heights aloft, indicating the potential is there
once again for near record highs across much of the area. Later on
Thursday, guidance is showing some signs of possible warm front
development near the southern Appalachians as the surface low
ejecting from the Southern Plains undergoes rapid surface
cyclogenesis over the Midwest. With our area under the influence of
moist southerly flow at the surface and weak low level Q-vector
convergence, some QPF response Thursday later in the afternoon looks
favorable. Though not the most favorable setup as far as dynamics or
instability , we will likely have the opportunity for a small amount
of destabilization Thursday afternoon and evening, so thunder
remains on the table as a possibility Thursday evening. Temperatures
will be at least 20 degrees above average Thursday and Friday.

By Friday, the surface cyclone will have lifted towards the NE after
deepening considerably as its progressive cold front crosses over
the southern Appalachians. Upper support for this system on Friday
is more substantial with an upper trough positioned just to the
north of our area. Though it is clear that the best instability and
dynamics are well to our north with this cyclone in the OH river
Valley, right now it appears that CAPE and most shear/SRH values are
non-zero on Friday. The best forcing will arrive Friday night and
early Saturday morning, basically at an unfavorable time for dirunal
heating to contribute too much to instability. The pattern for
Thursday through Friday remains interesting even if not overly
threatening, and will be watched as this time period comes into
better range of higher-resolution models.

The forecast becomes quite easy by the time the front has the
cleared the area on Saturday, with dry high pressure building in at
the surface and briefly in in the upper levels. A longwave trough
approached by the end of the medium range, indicating a possible
return to cooler weather, though this "cool down" will only drop
temperatures to about 10 degrees above average.

As of 220 PM Sunday: A quasi-zonal/fairly progressive flow pattern
will be in place across much of the eastern 2/3 of the conus through
the period. SW low level flow will support plenty of warmth early in
the period, as temps are expected to remain around 20 degrees above
climo through the end of the work week. The southerly flow will also
bring about increasing low level moisture, which combined with very
strong insolation could yield positive surface-based buoyancy by Thu
afternoon. Also by this time, global model guidance hints at warm
frontal activation across the central/southern Appalachians and
vicinity, as cyclogenesis commences across the southern Great
Plains. Therefore, isolated-to-widely scattered convection,
including thunderstorms is not out of the question Thu afternoon and

Although the warm front will be long gone by Friday, additional
convection is possible Fri afternoon, particularly in response to
terrain effects, and chance pops will be carried in most locations
by the end of the day. Model guidance is gradually coming into
better agreement regarding the advance into our area of a frontal
boundary associated with aforementioned deepening cyclone early in
the weekend, with late Fri night/early Saturday appearing to be the
most likely time for fropa in our forecast area. Likely pops will be
carried across much of the area during this time. The convective
potential remains the most interesting aspect of this event, and
while it does not appear that the time of day will be conducive to
robust buoyancy, it appears fairly likely that some degree of sbCAPE
will be in place. Meanwhile, shear will likely be adequate for
organized convection, although the latest guidance depicts fairly
unidirectional profiles with a strong-but-not-scary low level jet.
This would certainly makes sense with the better deep layer forcing
passing west and north of the area, but it all honesty it`s still a
bit early to get too far in the weeds with severe wx parameters.

Cooler and much drier air will push into the area for the last
couple of days of the period, although temps are expected to remain
a good 10 degrees above normal through the weekend.


At KCLT and elsewhere: Mainly VFR conds thru the period at all sites
except for some MVFR CIGS/VSBY at KAVL and KHKY arnd daybreak due to
increasing llvl Atl moist flux. Other than that...increasing Ci and
winds remaining weak with a strong ridge axis traversing the area
and a broad sfc high building in from the NE.

Outlook: Expect VFR conditions to continue through early in the
week before another low pressure system gradually brings moisture
back to the area from Tuesday through late week. Precipitation and
associated restrictions remain highly uncertain from mid week on.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     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:



  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      75 1939     26 1908     50 1951      4 2015
   KCLT      77 2014     31 2015     59 1939      7 2015
   KGSP      75 2014     33 2015     57 1939      9 2015




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