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fxus62 kgsp 172343 
afdgsp

Area forecast discussion
National Weather Service Greenville-Spartanburg SC
743 PM EDT sun may 17 2020

Synopsis...
an unsettled and cooler weather pattern will commence on Monday as a
large low pressure system moves over our region and lingers through
much of the week. Expecting this low to weaken later in the week
with temperatures slowly warming and returning to a near Summer type
weather pattern next weekend.

&&

Near term /through Monday/...
as of 730 PM sunday: the cumulus field has started to dissipate with
the loss of daytime heating across the region, but deeper layer
moisture in area profiles continues to fill in on low-level east to
southeast flow, and more southerly flow encroaching from the west
aloft. Regional radars are depicting better coverage in the deeper
moisture sliding slowly east across Georgia toward the region. With
the lack of any upslope triggering thus far, the band arriving from
Georgia late this evening and overnight may Herald the arrival of
the first real shower chances of the night. Pops have been increased
for the overnight hours, especially in the southern mountains.

Otherwise, the upper level circulation currently over the lower
Mississippi River valley will move across the deep south through the
near term, while a more substantial upper low will wobble southeast
from the corn belt...with phased flow evolving between these two
features by the end of the period. Resultant height falls to our
west will allow for backing low level flow tonight into tomorrow,
with southeast flow into the Blue Ridge gradually strengthening. With
moisture increasing as well, pops will increase to likely or better
across the western half of the area by sunrise Monday. This will
also cover any convection originating from the more robust forcing
to our west sneaking into our western areas after midnight. Overall
qpf should be light through 12z, as upslope will remain quite weak
through that time.

The convective potential will steadily improve through the daytime
hours Monday, as deep-layer forcing, improving upslope flow and
moisture, along with a destabilizing air mass should yield numerous,
if not widespread coverage of convection from afternoon through the
end of the period. Short term guidance depicts SBCAPE in the
neighborhood of 2000 j/kg across much of the forecast area during
the afternoon. Since widespread low cloud cover is expected in
association with the upslope flow...and mid-level lapse rates are
forecast to be quite poor...this level of instability will be hard
to come by, except perhaps in locations around the periphery of the
County Warning Area. Nevertheless, modest levels of instability combined with
improving shear profiles will yield an isolated severe storm threat,
especially across the Piedmont.

&&

Short term /Monday night through Wednesday/...
as of 130 PM EDT sunday: numerous, if not widespread shower activity
is still expected for Monday night into Tuesday as energy pivoting
around Ohio/Mississippi Valley closed low lifts northward atop the
cwfa. Broad and persistent llvl upslope/upglide flow above weak
damming hipres should also aid in focusing locally heavy showers
along and east of the Blue Ridge. The short range model/ensemble
quantitative precipitation forecast accumulates the heaviest rainfall acrs the NC Blue Ridge and
foothills by Tuesday. Based on this, there is increasing risk of
excessive rainfall leading to flooding beginning perhaps as early as
Tuesday morning. Later forecast shifts will continue to monitor this
trend and possibly for Flash Flood Watch issuance. During the latter
half of the period, the broad waa pattern within the east side of
the encroaching closed upper low will continue to promote widespread
locally heavy rainfall through Wednesday.

&&

Long term /Wednesday night through Sunday/...
as of 1235 PM EDT sunday: unsettled conditions will likely be
ongoing to start off the period given the proximity of lingering
closed upper low, progged to be centered just off to our west. I
would expect energy pinwheeling around said system to be able to
regenerate at least another round or two of numerous showers. It is
also probable that damming hipres will be lingering, effectively
resulting in a low diurnal temperature and maximums svrl categories
below climo. The pesky upper low should be able to open up as it
translates downstream of the region next weekend with the cyclonic
flow giving way to some degree of ridging by Sunday. Expect a return
to climo temperatures on Friday followed by above normal maximums
Saturday and Sunday.

&&

Aviation /00z Monday through Friday/...
at kclt and elsewhere: the VFR cumulus field from daytime heating
has generally thinned to few to scattered early this evening. However, VFR
ceilings should fill back in quickly as low-level moisture increases
from the east and southerly flow moisture arrives from the west
ahead of the next upstream system. A deteriorating trend through
MVFR cigs is expected in the easterly flow overnight, with a period
of IFR cigs likely during the morning hours as the light
rain/showers begin arriving from the west. Anticipate a steady
uptick in shower coverage through the day as upslope improves, with
thunder chances mainly during the afternoon hours. Cannot really
rule out a thunderstorm anytime from mid morning through tomorrow
evening, but will focus prob30 and thunderstorms in the vicinity chances during the most
unstable afternoon hours. Easterly flow will become more east-northeast to NE
through the night at all but kavl, where southeast flow will persist.
Anticipate winds toggling back toward southeast through the day throughout
as mixing improves and cigs gradually lift back into the MVFR range
from late morning through the afternoon. Winds should remain less
than 10 kt through the period at all taf sites.

Outlook: numerous to widespread coverage of showers and
thunderstorms may continue through Monday night and into Tuesday
morning. Flight restrictions should be expected. Some brief
improvement may arrive from the west on Tuesday afternoon, but
additional waves of moisture will then fill back in through much of
the week.

Confidence table...

23-05z 05-11z 11-17z 17-18z
kclt high 100% high 100% Med 68% high 85%
kgsp high 100% high 100% Med 77% high 95%
kavl high 100% Med 68% high 83% high 100%
khky high 100% low 59% high 95% high 100%
kgmu high 100% high 100% Med 77% high 95%
kand high 100% high 100% high 86% high 90%

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

Www.Weather.Gov/gsp/aviation

&&

Gsp watches/warnings/advisories...
Georgia...none.
NC...none.
SC...none.

&&

$$

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