311
FXUS62 KGSP 231800
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
200 PM EDT Mon Sep 23 2024

.SYNOPSIS...
A moist airmass will spread over the area today and linger
through mid-week. A tropical system is expected to strengthen
over the Gulf of Mexico on Thursday and will likely impact our
area by the end of the week.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 150 PM: Low level stratocu is eroding along the edges but
won`t fully be out of the NC Piedmont until late afternoon.
Instability is building in areas where insolation is taking place.
The atmos should rapidly destabilize when the clouds erode. This
will lead to a moderately unstable air mass with 20 to 35 kts of
effective bulk shear. The shear will help with storm organization
helping create the potential for a few severe storms with damaging
winds. Storms should diminish through the evening with isolated
showers possible into the early overnight. Expect low stratus and
patchy fog to redevelop from NE to SW across the area overnight.
Lows will be around 10 degrees above normal.

Tuesday should see a similar scenario as today with morning stratus
slowly eroding and lifting from SW to NE through the day. Moderate
instability with up to 35 kts of effective bulk shear expected as
well. There may be better DCAPE Tuesday afternoon though. Expect
good diurnal convective coverage during the afternoon with a few
severe thunderstorms. Highs will see a similar pattern as well with
cooler temps where the stratus burns off latest. Highs will be
around 5 degrees above normal.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 3:15 AM EDT Monday: The short-term fcst picks up at 12z on
Tuesday with upper ridging still in place over the Southeast. Over
the next 24 hrs or so, the upper pattern amplifies as broad upper
trofing digs down over the central CONUS. By the end of the period
early Thursday, a fairly large upper low is expected to spin off
from the main trof as the trof itself lifts back northward. This
upper low is progged to be centered to our west and over Arkansas by
the end of the period. At the sfc, another low will spin up over the
Ohio River Valley on Tuesday and bring another weak cold front to
our doorstep by early Wednesday. This front is now expected to stall
out just to our west late Wednesday into Thursday with the broad
area of high pressure behind it remaining to our NW. At the same
time, a tropical low will strengthen over the Gulf of Mexico and
track northward as the period is ending early Thursday. As for the
sensible fcst, no major changes were needed for Tuesday or Wed-
nesday with likely PoPs carried over the northern half of our CWA
for both days. Temperatures will cool somewhat thru the period, yet
highs will still likely top-out just above climatology on Wednesday,
especially over our southern zones.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 3 AM EDT Monday: The extended forecast picks up at 12z
on Thursday with upper ridging still in place just to our east
and a fairly large upper low centered to our west over Arkansas.
At the same time, the upper low associated with a tropical sys-
tem in the Gulf of Mexico will lift northward on Thursday and
then rotate around the other low in response to the Fujiwhara
effect late Thursday into Friday. Another upper low is still
expected to develop over New England on Friday, but most of
the long-range guidance now has it moving offshore as we go
into the weekend. Over the weekend, the tropical low is expec-
ted to get absorbed by the larger upper low over Arkansas. By
the end of the period early next week, the upper low is expec-
ted to gradually drift north and open back up to the northern
stream flow. At the sfc, a weak but moist cold front will stall
out over our area just before the period begins, while broad
high pressure remains well to our NW. At the same time,  a
robust tropical low will strengthen over the Gulf of Mexico
and track north. Most of the current model guidance has it
moving onshore over the Florida Panhandle late Thurs and then
over our area early Fri. Based on the current guidance, the
center of the low is likely to pass over the western extent
of our fcst area (or just west of it) on Fri and then quickly
lift NW of our area and dissipate as we go into the weekend.
At this time, it`s looking like the main impacts to our fcst
area from this tropical system will be heavy rainfall and some
gusty winds on Thursday and Friday. Confidence should increase
wrt to these impacts over the next few days.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
At KCLT and elsewhere: MVFR to IFR stratocu is eroding around the
edges and will scatter out at the SC sites shortly, then KHKY and
KCLT about 22Z. Convection ongoing across the mountains and should
move out across the area through the afternoon and early evening.
Have included TEMPO TSRA at all sites but timing may need to be
adjusted later. TSRA ends this evening but isolated SHRA could
continue into the early overnight. Guidance is in good agreement
that MVFR stratus redevelops from NE to SW overnight, drops to LIFR,
then lingers through the morning Tuesday as it rises back to MVFR.
Have gone with this in the TAFs. There will be some MVFR to possibly
IFR vsby as well. Expect mainly diurnal convection again on Tuesday.
E to SE wind this afternoon becomes light and variable overnight
then S to SE on Tuesday.

Outlook: A slowly approaching weak cold front stalls to our
northwest Wednesday. This will keep the chance for diurnal showers
and thunderstorms over the area. Fog/low stratus may develop each
morning, especially in the mountain valleys. Confidence is
increasing that a tropical cyclone, with attendant heavy rain and
possible strong winds will approach the area Thursday, move over or
near the area Friday, then move out of the area for Saturday.

&&

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

&&

$$

SYNOPSIS...JPT
NEAR TERM...RWH
SHORT TERM...JPT
LONG TERM...JPT
AVIATION...RWH