Severe Thunderstorm Warning 258, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
431 PM EDT Sun Jul 22 2018

.SYNOPSIS...
A broad upper low will settle across the Deep South through
Wednesday. This low will remain nearly stationary and support moist
unsettled weather across the region through mid-week, before
weakening ahead of an approaching cold front.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 420 PM: A 500 mb trough axis will sharpen up just west of
the area tonight through Monday as the associated H5 low center
slides southward west of the Appalachians. Weak upper-level DPVA
lobes east of the trough, along with lower-level terrain forcing in
southerly flow, will generate the best shower/thunderstorm coverage
across the mountains through evening, with a secondary maximum out
along the I- 40 corridor. Additional scattered coverage is likely
farther south into the Upstate and NE GA on outflows. Profiles are
fairly moist, instability will be less than yesterday, DCAPE is low,
and wind shear will be much less so anticipate a much lower risk of
severe thunderstorms overall. Rainfall rates will need to be closely
monitored for any training of heavy showers, though. Based on the
lingering forcing aloft, and projected slow decline in MLCAPE,
the previous forecast appears to be on track: expect a diurnal
waning of coverage, although scattered showers will likely persist
across western NC through the nighttime hours. Minor adjustments
to PoP distribution were made based on CAM consensus. Temp trends
this aftn have been wrecked by outflow cooling in some spots;
these were touched up based on HRRR, which captures some of that.

Surface to 850 mb flow will steadily back toward southeasterly
through the day on Monday. This will increase the upslope forcing
into the east side of the southern Appalachians, with precipitable
water values steadily increasing as well. Anticipate fairly high
(likely to categorical) POPs for showers and embedded thunderstorms
through Monday afternoon. This will keep max temperatures about
two categories below climo.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 215 PM EDT Sunday: The short-term fcst picks up at 00z on
Tuesday with a large and persistent upper low centered over the
Southeast CONUS and upper ridging to the east and west of the low.
Over the next couple of days, the low will gradually open back up
to the mean flow and lift northward. A large sfc low will be
co-located with the upper low over the Southeast to start the
period. This low is expected to persist over the region thru most
of the short-term period. By the end of the period late Wed, the
low does begin to fill in and lift northward as a cold front
approaches the fcst area from the NW. This synoptic pattern will
keep the fcst area under persistent, moist, SLY to SELY low-lvl
flow thru the period. This coincides with an area of weak, though
persistent, deep-layer Q-vector convergence. Although the guidance
keeps the highest QPF to our north and east, we should still have
periods of numerous showers with embedded tstms, capable of producing
torrential downpours. Isolated flooding concerns will exist thru
at least Tuesday night, with a greater overall threat across the
eastern half of the CWFA. Under ample cloud cover, high temperatures
are expected to remain below climatology each day while lows remain
near climo.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 1230 PM EDT Sunday: An ulvl trof will continue to get sheared
out and engulfed in the mean w/ly flow during the beginning of the
period. The anomalous sfc low will weaken during this time as well
which will reduce the amt of Atl moist flux. This will reduce the
upslope hydro threat somewhat...yet PWATs will remain relatively
high thru the period with no good airmass change/mix anticipated
except for the wrn mtns on Thu as a weak sfc front pushes in.
Afternoon pulse tstms will generate fairly easily within the moist
airmass...yet instability will remain conditional with no sigfnt
triggers or conducive thermal layers available. The avg cloud cover
will continue to fairly high and this will help hold max temps arnd
or just below climo while keeping mins abv normal by a few degrees.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
     AMD NOT SKED CONTINUES FOR MISSING KAND ASOS DATA...

At KCLT and Elsewhere: Moistening profiles will produce increasing
chances of several rounds of showers and thunderstorms through the
TAF period, especially across western NC but also near KGSP and
KGMU. The better coverage across western NC, along with a developing
moist SSE upslope, may also contribute to morning MVFR or IFR
clouds, particularly at KAVL and KHKY. Some recovery to VFR is
expected throughout tomorrow, but frequent showers and afternoon
thunderstorms will be accompanied by MVFR to possibly IFR
restrictions at times throughout. Anticipate SW winds early becoming
SE or light overnight and then SE to ENE through the day on Monday.

Outlook: An active/wet period is expected to continue through at
least mid-week as a slow moving low pressure system impacts much of
the East. Numerous coverage of showers and thunderstorms is expected
during this period with associated lower restrictions. While there
will likely be an afternoon/evening peak in the coverage on most
days, higher-than-normal chances will also exist during the
overnight and morning hours.

Confidence Table...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High  87%     High 100%
KAVL       High 100%     High  91%     Med   70%     High  95%
KHKY       High 100%     High 100%     Med   60%     High 100%
KGMU       High 100%     High 100%     High  89%     High 100%
KAND       High 100%     High 100%     Med   61%     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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

SYNOPSIS...SBK
NEAR TERM...HG/Wimberley
SHORT TERM...JPT
LONG TERM...SBK
AVIATION...HG

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
424 PM EDT Sun Jul 22 2018

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-232030-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Avery-Alexander-
Iredell-Davie-Madison-Yancey-Mitchell-Swain-Haywood-Buncombe-Catawba-
Rowan-Graham-Northern Jackson-Macon-Southern Jackson-Transylvania-
Henderson-Cleveland-Lincoln-Gaston-Mecklenburg-Cabarrus-Union-
Caldwell Mountains-Greater Caldwell-Burke Mountains-Greater Burke-
McDowell Mountains-Eastern McDowell-Rutherford Mountains-
Greater Rutherford-Polk Mountains-Eastern Polk-Oconee Mountains-
Pickens Mountains-Greenville Mountains-Greater Oconee-
Greater Pickens-Greater Greenville-Spartanburg-Cherokee-York-
Anderson-Abbeville-Laurens-Chester-Greenwood-
424 PM EDT Sun Jul 22 2018

This Hazardous Weather Outlook is for northeast Georgia, piedmont
North Carolina, western North Carolina and upstate South Carolina.

.DAY ONE...Tonight.

Scattered to numerous showers and thunderstorms will continue to
develop across the region through the evening and into the overnight.
The main threats will be cloud-to-ground lightning and locally heavy
rainfall. However, isolated severe storms will be possible, capable
of producing damaging winds and large hail.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

..Monday...Heavy rain possible. A persistent moist southeasterly
flow will increase the risk for heavy rainfall and flooding across
the area beginning late Monday and continuing through Wednesday.
..Tuesday...Heavy rain and flooding possible.
..Wednesday...Heavy rain and flooding possible.
..Thursday...No hazardous weather is expected at this time.
..Friday...No hazardous weather is expected at this time.
..Saturday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

JPT

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