Severe Thunderstorm Warning 348, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
328 PM EDT Tue Aug 29 2023

.SYNOPSIS...
A stationary front stalled over the Carolinas and Georgia will
continue the chance of heavy rain showers with embedded
thunderstorms at times through tonight. Hurricane Idalia is forecast
to strengthen further before making landfall along the Florida Gulf
Coast on Wednesday then become weaker as it passes over land
reaching the South Carolina coast Wednesday night. Idalia will move
east from the Carolina coast on Thursday and Friday. All interests
should pay close attention to the Idalia forecast track this week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 325 pm EDT: Our lull is coming to an end as of mid-afternoon,
with new development seen on radar over the southwest mtns of NC and
the western Piedmont of NC over the last hour. More development is
likely through the late afternoon on the edges of the cloudy area
left over from the morning activity, so precip chances should ramp
back up into the early evening.

For tonight...we have a continuation of the same environment that
remains in place across the western Carolinas and northeast Georgia
that we have had the last day or two, so a somewhat persistent
chain of events is expected. Mid-level forcing is not as favorable
compared to last night, but another round of upper divergence is
expected to move overhead, with sufficient buoyancy retained into
the evening hours. The upshot is that another round of convection
is a decent bet, especially over the area east of the mtns through
late this evening. The main concern once again is the potential for
excessive rain and flash flooding. Precipitable water remains high,
with values up around the climatological max, and fcst soundings
show tall CAPE profiles with modest amounts of buoyancy, and a
deep warm cloud layer. Fcst soundings show this maximizing thru
the late evening/early morning hours, which is typical for such
a sub-tropical air mass. Several of the ingredients for flash
flooding should be in place, but the location of where excessive
rain is uncertain enough such that a Watch is not warranted...yet.

That changes on Wednesday as the outer fringe of Idalia makes
northward progress into the southeastern edge of the fcst area after
noon. Of note is the fcst trend of the axis of heavy rain, which has
shifted westward enough to suggest an increased heavy rain threat
creeping into the southeastern fringe of the fcst area Wednesday
night/Thursday morning. Based on what neighboring offices have
planned, think it the course of least regret is to include the area
from Greenwood County SC to Mecklenburg County NC and points east
into a Flash Flood Watch beginning at 18Z Wednesday, as a starting
point. Note that the track of Idalia would remain far enough to
the east to negate the threat of high wind, even over the higher
terrain. So, precip chances ramp up in the afternoon on Wednesday,
with ultimately a NW-to-SE gradient of probability by the end of the
day. Temps will remain below normal under thickening cloud cover.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 215 PM EDT Tuesday: Rainbands associated with Idalia are
expected to be ongoing Wednesday evening, with the southeast corner
of the forecast area getting the heaviest QPF. Models have trended
slightly northwest/inland with the track, so the axis of the heavy
QPF now pushes into the southern Upstate to the southern Charlotte
metro area. Given that trend, a Flood Watch will be issued for these
areas roughly from Greenwood, SC to Cabarrus, NC. The rain should
begin to shift east Thursday morning, with PoPs tapering off from
NW to SE thru the day. Breezy conditions expected Wed night thru
Thu as the pressure gradient will remain tight between a 1020 mb
high over the Great Lakes and Idalia tracking thru Carolina coastal
plain. Wind gusts may approach 30 mph, but at this time are not
expected to reach advisory criteria. Wind should start to slacken
Thu aftn, as Idalia pushes off the Carolina coast. Obviously if
the storm track trends a little north and west of the latest NHC
forecast, more of the forecast area may see heavy rain and winds
may be a little stronger. Temps will feature a small diurnal range,
with lows near normal, but highs a deg below normal under plenty
of clouds.

Drying conditions behind Idalia Thu night into Fri. Pleasant
continental air will filter in from the north, allowing temps to
fall below normal with relatively low humidity.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 200 PM Tuesday...The entire medium range fcst looks quiet,
as mild high pressure settles over the Southeast under a building
upper ridge. The air mass will gradually moderate thru the end of
the week, with continued dry conditions. Highs and lows expected
to be a few deg below normal Fri night and Saturday, then return
to normal Sunday, and a category or so above normal Monday.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: More or less a persistent forecast over the
next 24 hours. We have entered something of a convective lull in the
action through mid-afternoon, whereby only the mtns may still get
a passing shower/thunderstorm, thus the TEMPO at KAVL. Meanwhile,
we are gradually scattering out the MVFR level clouds across the
area east of the mtns and should continue to do so. Winds are light,
but kind of all over the place. Expect new convective development
moving up from the S and aided by differential heating left over
from the morning activity. The consensus of the CAMs is to hit
another round of thunderstorms at all terminals developing in
the middle evening and continuing into the early morning hours,
and this could linger into the overnight. This will be handled
with TEMPOs. Expect brief restrictions to LIFR and VLIFR in
the heavier storms. In the wake of this activity, with light
upslope flow, widespread IFR stratus/fog will develop again before
daybreak. Again...will broad brush what will probably be somewhat
variable ceiling/vis. Precip should be suppressed in the general
subsidence on the NW periphery of the tropical cyclone. Thru the
middle part of the day, the N/NW edge of the light rain should
spread into the region. This will generally not be accounted for
with any detail on this issuance.

Outlook: Shower and thunderstorm chances, with associated
restrictions, continue through Wednesday night as the circulation
of Tropical System Idalia moves off the South Carolina coast. Much
drier weather will arrive from the west Thursday through Saturday.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...Flood Watch from Wednesday afternoon through Thursday evening
     for NCZ071-072-082.
SC...Flood Watch from Wednesday afternoon through Thursday evening
     for SCZ009-012>014-019.

&&

SYNOPSIS...DEO
NEAR TERM...PM
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...PM

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
404 PM EDT Tue Aug 29 2023

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>070-501>510-SCZ008-010-011-101>109-302015-
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-Caldwell Mountains-
Greater Caldwell-Burke Mountains-Greater Burke-McDowell Mountains-
Eastern McDowell-Rutherford Mountains-Greater Rutherford-
Polk Mountains-Eastern Polk-Cherokee-Anderson-Abbeville-
Oconee Mountains-Pickens Mountains-Greenville Mountains-
Greater Oconee-Greater Pickens-Central Greenville-
Southern Greenville-Northern Spartanburg-Southern Spartanburg-
404 PM EDT Tue Aug 29 2023

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

.DAY ONE...This afternoon and tonight.

Rounds of heavy-rain producing showers and thunderstorms are
expected today and tonight. The threat of localized flash flooding
along streams and nuisance flooding of poor drainage areas will
continue. Any thunderstorm will be capable of producing cloud-to-
ground lightning and gusty winds.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Tropical System Idalia is forecast to make landfall on the Florida
Gulf Coast Wednesday morning and cross the coastal waters of South
Carolina Wednesday night. Winds will become gusty, especially across
the lower Piedmont. Heavier rain bands would mainly impact the lower
Piedmont areas. Be aware that any westward shifts in the forecast
track would increase the potential for wind and rain impacts in our
area from Idalia.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to forward any reports of large hail,
damaging winds, tornadoes, or flash flooding to our office.

NCZ071-072-082-SCZ009-012>014-019-302015-
Mecklenburg-Cabarrus-Union NC-York-Laurens-Union SC-Chester-
Greenwood-
404 PM EDT Tue Aug 29 2023

...FLOOD WATCH IN EFFECT FROM WEDNESDAY AFTERNOON THROUGH THURSDAY
EVENING...

This Hazardous Weather Outlook is for Piedmont North Carolina and
Upstate South Carolina.

.DAY ONE...This afternoon and tonight.

Rounds of heavy-rain producing showers and thunderstorms are
expected today and tonight. The threat of localized flash flooding
along streams and nuisance flooding of poor drainage areas will
continue. Any thunderstorm will be capable of producing cloud-to-
ground lightning and gusty winds.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Flood Watch.

In addition to flood threat, Tropical System Idalia is forecast to
cause gusty winds, especially across the lower Carolina Piedmont. Any
westward shifts in the forecast would increase the potential for wind
impacts in our area from Idalia.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to forward any reports of large hail,
damaging winds, tornadoes, or flash flooding to our office.

MPR