National Weather Service Raw Text Product

233 
FXUS62 KGSP 230736
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
336 AM 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 TONIGHT/...
As of 250 am: A narrow inverted surface ridge/associated E/NE flow 
is nosing into the area this morning, and an area of stratus is 
amassing across the NC Piedmont associated with an Atlantic moisture 
surge. This cloud cover is expected to ooze SW through the morning, 
likely reaching roughly the U.S. Highway 25 corridor before slowing/ 
stalling around sunrise. As an upper ridge axis shifts east of the 
forecast area later this morning, so will the surface ridge shift to 
near the East Coast, and clouds are expected t steadily scatter from 
the SW throughout the late morning into the afternoon. This will 
allow for good heating and destabilization, with afternoon sbCAPE 
expected to range from 1500-2000 J/kg. The temp forecast will be a 
bit tricky today due to the varying cloud cover, but max temps are 
forecast to range from around 10 degrees above climo again across 
the western third of the area, to close to normal in the cloudier 
locations across the northeast corner of the CWA. 

With the synoptic pattern becoming broadly more favorable for 
convective development, especially as a short wave trough approaches 
from the TN Valley this evening, scattered diurnal convection is 
expected to develop across the high terrain during mid-late 
afternoon, with coverage enhancing and moving off the escarpment 
into the foothills and Piedmont this evening as the short wave 
approaches. Mountain PoPs generally peak in the 50-60% range this 
afternoon, while the highest Piedmont chances (40-50%) are withheld 
until after 00Z. A combination of moderate instability and improving 
deep layer shear (~35 kts by the end of the day) may be just enough 
to support a brief severe storm or two. Convective coverage and 
intensity will steadily wane beginning around late evening, but 
slight chance PoPs linger for at least part of the area through 12Z 
Tuesday. Min temps will again by 5-10 degrees above normal.

&&

.SHORT TERM /TUESDAY 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 /08Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: Low clouds are already filling in across 
western NC, particularly at KHKY and KCLT, which are already 
reporting low MVFR cigs. These low clouds will spread steadily SW 
through the morning, reaching KAVL/KGSP/KGMU by daybreak. Cigs will 
eventually lower to IFR, likely bottoming out at LIFR around sunrise 
before improvement begins during late morning. Some MVFR 
restrictions are also possible, but low cigs will be by far the 
bigger concern. As skies begin to clear from the SW throughout the 
morning and afternoon, instability is expected to develop, fueling 
the potential for scattered diurnal convection. Convection should 
initially develop over the high terrain, but will likely spread 
across the remainder of the Terminal Forecast Area during the 
evening, as an upper level disturbance approaches. Prob30s for TSRA 
are featured at all sites, favoring the afternoon and early evening 
at KAVL, and primarily the evening hours at the other sites. Winds 
will remain light through the period, with directions generally 
being E/NE this morning, turning toward the E/SE during the daylight 
hours.   

Outlook: A weak cold front will slowly approach from the west this 
week before tracking over the area on Thursday. This will allow the 
chance for diurnal showers and thunderstorms to remain elevated 
through at least Thursday. Mountain valley fog/low stratus may 
develop each morning around daybreak. Confidence is increasing that 
a tropical cyclone, with attendant heavy rain and possible strong 
winds will pass over or near the area late in the week.

&&

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

&&

$$

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