textproduct: Greenville-Spartanburg

SYNOPSIS

Above normal temperatures expected through Saturday, with near- record highs possible. Rain chances increase Friday night through Saturday, ahead of a cold front. Temperatures return to near-normal Sunday into early next week behind the cold front.

NEAR TERM /THROUGH WEDNESDAY/

As of 1235 PM Tuesday:

Key Message #1: A weak frontal boundary brings spotty showers to the mountains this evening but near record highs expected Wednesday.

A weak frontal boundary drops south across the area tonight. There will be enough low level moisture and weak upslope flow for some spotty rain showers across the mountains this evening, but any rainfall would be very light. Gusty winds continue into the evening then diminish overnight. Low clouds return by evening and linger into the overnight but look to scatter out from north to south across the area before daybreak as drier air and a northwest low level flow develops. This should also keep fog formation at a minimum as well. That said, there is potential for low clouds to linger through daybreak into mid morning Wednesday if the drier air or northwesterly flow is delayed. Lows will be 5 to 10 degrees above normal.

No cooling is expected on Wednesday behind the boundary. In fact, highs will be warmer with near record highs at GSP. Relatively high records at AVL and CLT appear to be safe for now. Winds will be lighter as well with sunny skies by late morning or early afternoon.

SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/

As of 1208 PM EST Tuesday:

Key Message: Well above-normal temperatures Thursday and Friday, with increasing rain chances to end the workweek.

A weak cold front will be situated south of the CWFA Wednesday night as a weak surface high sets up shop over the southern/central Appalachians. Weak CAA will filter in behind the front as increasing clouds move in from the southwest. As a result, overnight lows will end up 5-10 degrees above normal. The increase in clouds will be in association with a potent shortwave that quickly ejects from the Southern High Plains into the Upper Great Lakes region and Ontario/Quebec by Friday, inducing a strong surface low via surface cyclogenesis. The aforementioned front to south is expected to encounter warm frontal activation as a result and lift north of the CWFA Thursday night into Friday morning, leading to deeper moisture transport from the Gulf and advecting warmer air from the southwest, while the surface high gets pushed offshore the Mid-Atlantic Coast in response. Guidance continues to pick up on some form of upslope showers in the southwest mountains and parts of the Blue Ridge Escarpment Thursday night into Friday as well with WAA showers not being ruled out either for the mountains and foothills, with some of the western Piedmont zones as the CWFA becomes socked in with extensive cloud cover. Afternoon highs on Thursday will run 10-15 degrees above normal despite the increase in cloud cover, while overnight lows end up 15-20 degrees above normal.

A digging positively-tilted longwave trough will replace the aforementioned shortwave over the west-central CONUS on Friday. Deep layer southwesterly flow will result from this on Friday as a conveyor belt of deep moisture will be pulled from the Lower MS Valley through the Deep South and TN Valley on Friday. Model guidance are having a hard time with the timing and how far east the conveyor belt of convection shifts into the CWFA. Some of the guidance pulls the better QPF response into the NC/TN border by 00Z Friday, while others keep the heavier precip just to the west. The better dynamics should remain west of the CWFA through the short term forecast period, however, PWAT values surge above an inch and provides an environment conducive for heavier precip with potential convective elements if the dynamics are in place when the main line moves across the CWFA during the beginning portions of the extended forecast period. With deep low-level WAA in place behind the warm front, expect afternoon highs on Friday to run 15-20 degrees above normal with dewpoints in the upper 50s, leading to a muggy airmass for early January.

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

As of 1252 PM EST Tuesday:

Key Message #1: Above-normal temperatures continue through Saturday, before a cold front moves across the area during the latter of the upcoming weekend. Rain chances remain elevated through Saturday night, with the potential of a few thunderstorms.

Continued southwesterly WAA flow ahead of the encroaching cold front will help keep extensive cloud cover in place with pockets of light precip, ahead of the main moisture plume associated with the better dynamics of the system as the aforementioned upper trough deepens and latest model guidance even has it evolving into a closed upper low. In this case, the advancement of the attendant cold front would be slowed down even further as the trough would only gradually move across the north-central CONUS into the Great Lakes region late Friday through Saturday night. Model guidance suggest that the better moisture plume and enhancement from the right entrance region of the jet streak moves across the CWFA Friday night (mainly across the mountains) through Saturday across the rest of the CWFA and lingering outside of the mountains into Saturday night. The QPF response is best over the higher terrain as the front weakens as it shifts east of the mountains. Not really seeing a good signal for a flash flood threat as ongoing drought conditions and latest QPF probs of 2" or greater remains below 50% in the southwest mountains, basically 0% outside of the mountains. A severe threat still can't be ruled out as deep layer shear of 55-65 kts and low SBCAPE (<200 J/kg) may overlap with the main conveyor belt of convection during the daytime period Saturday. Better severe threat looks to remain south and west of the CWFA, but the highest CAPE Values are located over the Upper Savannah River Valley in our CWFA. Will be something to monitor, but the line of QPF response should shift east of the CWFA by Sunday morning at the latest.

Key Message #2: Temperatures return to near normal Sunday and Monday behind the front. Light northwest flow snow is possible in the mountains Saturday night and Sunday.

A post-frontal regime will be in store for the CWFA Sunday into Monday as the cold front completes a full fropa by Sunday and CAA filters in behind the front. Gusty winds of 30-40 mph will accompany the front and behind across the higher elevations, but should remain below Advisory criteria at this time outside of the highest peaks. Cooling temperatures and enough moisture within the northwest flow behind the front should promote light northwest flow snow showers, especially along the immediate Tennessee border Saturday night through Sunday. Light accumulation is expected, mainly above 3500'. Otherwise, the pattern remains dry through the early part of the next week, but guidance shows a relatively active southern stream jet getting its act together by the very end of the forecast period, which could set the area up for more precip beyond D7. Temperatures will be at or slightly below normal Sunday into early next week.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: Fcst remains tricky as low level moisture increases this evening ahead of a weak frontal bndy. Intermittent MVFR cigs have been impacting KAND over the past few hrs and will likely spread to KGSP/KGMU during the next hour or two. I expect these clouds will remain sct more than bkn, but my confidence is not very high wrt either scenario. KCLT (and to a lesser extent, KHKY) are more likely to see MVFR cigs overnight. I limit restric- tions at KHKY to a TEMPO group with some lower visby included as well. I expect these cigs to sct by roughly 12z, with VFR for the rest of the taf period. With the frontal bndy dropping south across the area overnight, the fog potential appears fairly low for most terminals. Otherwise, gusts diminish tonight with winds remaining SW to WSW (outside the mtns) into the morning. KCLT and KHKY will go NW during the aftn tomorrow, while KGSP, KGMU, and KAND will likely remain south of west tomorrow aftn. At KAVL, winds should toggle to NW around midnight, although they may be light and VRB at times thru the overnight/morning. They will remain NWLY thru the day tomorrow, with speeds around 5 kts.

Outlook: Expect dry, VFR conditions thru Thursday. A cold front brings increased rain chances and associated restrictions Friday and Saturday. Clearing skies with gusty winds expected Sunday.

CLIMATE

RECORDS FOR 01-07

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 70 1913 20 2014 58 1913 -1 2014 KCLT 77 1890 24 1988 62 1998 6 2014 KGSP 71 2012 27 2014 59 1998 5 2014 1988 1912

RECORDS FOR 01-08

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 68 2019 13 1970 55 1937 -1 1970 1946 KCLT 74 1946 21 1970 61 1998 8 2015 1907 1970 1890 KGSP 72 1907 24 1970 56 1998 5 1970 1946

RECORDS FOR 01-09

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 71 1937 13 1970 55 1937 -4 1970 1930 KCLT 72 2008 25 1970 60 1946 4 1970 KGSP 74 1949 28 1970 57 1946 1 1970

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...None. SC...None.