995
FXUS62 KGSP 231949
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
249 PM EST SUN FEB 23 2020
SYNOPSIS
A VIGOROUS LOW PRESSURE SYSTEM WILL MOVE FROM THE PLAINS ON MONDAY
TO THE OHIO RIVER VALLEY TUESDAY SPREADING MOISTURE BACK ACROSS THE
SOUTHEAST. CONDITIONS WILL REMAIN UNSETTLED THROUGH THE MIDDLE OF
THE WEEK. EXPECT BREEZY CONDITIONS WEDNESDAY INTO THURSDAY WITH
BELOW NORMAL TEMPERATURES THROUGH THE END OF THE WEEK.
NEAR TERM /THROUGH MONDAY/
AS OF 230 PM...A LOW PRESSURE SYSTEM WILL CONTINUE TO STRENGTHEN AS
IT CROSSES THE SOUTHERN PLAINS TONIGHT, SPREADING MOISTURE ACROSS
THE SOUTHEAST. PROFILES SHOW A MOISTENING FROM THE TOP DOWN WITHIN
DEEP-LAYER WESTERLY TO WEST-SOUTHWESTERLY FLOW. THE EVENING SHOULD
BE SEASONABLY MILD UNDER THICKENING MID CLOUDS. PRECIP ISN'T
EXPECTED TO START ENTERING THE WESTERN NC MOUNTAINS UNTIL AFTER
MIDNIGHT, AND SHOULD BE LIGHT. FCST SOUNDINGS IN THE MOUNTAINS DO
SHOW AN INITIAL LACK OF WARM NOSE, AS DRY SUB-CLOUD AIR WILL HELP
WET-BULB TEMPS DOWN. SO A MIX OF SLEET AND SNOW WILL BE POSSIBLE
ABOVE ABOUT 4000 FT AT THE ONSET, BUT STRONG WAA SHOULD TURN
EVERYTHING TO RAIN EXCEPT ABOVE 5500-6000 FT, WHERE AN INCH OR SO OF
SNOW ACCUM WILL BE POSSIBLE BEFORE CHANGING TO RAIN LATE MONDAY
MORNING. MIN TEMPS TONIGHT WILL BE HELD ABOVE NORMAL (MAINLY UPPER
30S TO LOWER 40S) THANKS TO THE CLOUD COVER AND WAA.
MONDAY, GUIDANCE IS IN GOOD AGREEMENT ON A FAIRLY LARGE RAIN SHIELD
SPREADING ACROSS THE ENTIRE AREA BY MIDDAY, AS LOW PRESSURE OCCLUDES
AND ENTERS THE MID-MS VALLEY. DEEP-LAYER ISENT LIFT AND UPPER
DIVERGENCE WITHIN THE LEFT EXIT REGION OF THE 300 MB JET SHOULD
PROVIDE PLENTY OF FORCING FOR PRECIP ACROSS THE REGION. BUT RAIN
RATES SHOULD BE LIMITED SOMEWHAT BY LACK OF INSTABILITY. A WEAK IN-
SITU WEDGE MAY DEVELOP, AND HOLD TEMPS IN THE MID TO UPPER 40S, WITH
LOWER 50S ALONG THE SOUTHEAST EDGE OF THE FCST AREA.
SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/
AS OF 200 PM SUN: SURFACE LOW WILL MOVE INTO THE LOWER OHIO VALLEY
MONDAY EVENING, WITH CAD ENTRENCHED ACROSS OUR CWA. LIFT ATOP THE
WEDGE WILL PEAK OVERNIGHT WITH LLJ, AND WEDGE BOUNDARY IS DEPICTED AS
RETREATING. A NONDIURNAL TEMP TREND IS THEREFORE FCST WITH CONTINUED
WARMING THRU THE DAY TUESDAY. AFTER HAVING TRENDED DOWNWARD, FCST QPF
HAS TICKED UPWARD ONCE AGAIN, THOUGH USING PWAT AS A METRIC, THE
EVENT DOES NOT LOOK ESPECIALLY REMARKABLE, WITH VALUES REMAINING LESS
THAN 2 SD ABOVE CLIMO, SO FLOOD RISK APPEARS LOCALIZED TO THE
NUISANCE SPOTS, AT WORST. ONE TREND TO MONITOR IS THE INSTABILITY NOW
BEING DEPICTED BY BOTH NAM AND GFS TUESDAY AFTERNOON SOUTH OF THE
WEDGE BOUNDARY, AS THE LOW APPROACHES LAKE ERIE, STILL MAINTAINING
0-3KM SHEAR AS HIGH AS 30-35 KT DURING PEAK HEATING. THIS INSTABILITY
LIKELY WILL TAPER OFF BEFORE COLD FRONT ARRIVES TUESDAY NIGHT, SO AT
THE PRESENT TIME THE SEVERE THREAT IS NOT APPRECIABLE--NOT ENOUGH FOR
SPC DAY 3 OUTLOOK TO HIGHLIGHT, AT LEAST. ABOVE-NORMAL TEMPS WILL
PREVAIL DURING THE WEDGE, BUT WILL FALL BACK BELOW NORMAL BEHIND THE
FRONT AS SKIES CLEAR. UPSLOPE FORCING WITHIN THE COLDER AIRMASS WILL
ALLOW POPS TO LINGER NEAR THE TENN BORDER INTO EARLY THURSDAY;
FALLING TEMPS SHOULD PERMIT A CHANGE TO SNOW, THOUGH THE MOISTURE IS
RELATIVELY SHALLOW AND IS NOT EXPECTED TO PRODUCE ADVISORY-LEVEL
ACCUMULATION AT THIS TIME.
LONG TERM /THURSDAY THROUGH SUNDAY/
AS OF 220 PM SUN: EASTERN CONUS TROUGH WILL LINGER FOR THE REMAINDER
OF THE FCST PERIOD, THRU SATURDAY NIGHT. THE AIRMASS THAT ARRIVES
BEHIND THE MIDWEEK FRONT WILL BRIEFLY MODIFY TO END THE WORK WEEK,
BUT A REINFORCING FRONT LATE FRIDAY WILL TEMPER THE REBOUND. A PAIR
OF EMBEDDED SHORTWAVES WILL BRING A SMALL PRECIP CHANCE TO PARTS OF
THE AREA FRIDAY NIGHT AND SATURDAY, BUT IT IS QUESTIONABLE HOW MUCH
PRECIP WILL MAKE IT EAST OF THE MOUNTAINS. IN LIGHT OF RECENT
EXPERIENCE, THOUGH, WILL GO AHEAD AND INCLUDE A SLIGHT-CHANCE POP AS
SUGGESTED BY MODEL BLEND. EXPECT TEMPS TO REMAIN WELL BELOW NORMAL
OVERALL, WITH THE WARMEST PART OF THE PERIOD BEING THURSDAY NIGHT AND
FRIDAY WHEN MINS/MAXES ARE "ONLY" 5 TO 10 DEGREES BELOW NORMAL.
AVIATION /20Z SUNDAY THROUGH FRIDAY/
AT KCLT AND ELSEWHERE: THE 18Z TAFS START OUT VFR WITH MAINLY THIN
CIRRUS CIGS, THICKENING AS THE DAY WEARS ON. A MID-LEVEL CLOUD DECK
SHOULD EXPAND ACROSS THE AREA THIS EVENING, FOLLOWED BY LOW VFR
CIGS AFTER DAYBREAK MONDAY. GUIDANCE IN GOOD AGREEMENT ON LEADING
EDGE OF PRECIP SHIELD ENTERING THE NC MOUNTAINS BETWEEN 06-12Z,
WITH SN/PL POSSIBLE ON THE HIGHEST PEAKS (BUT SHOULD BE ALL RA AT
KAVL). FROM THERE, THE -RA WILL EXPAND FROM WEST TO EAST ACROSS
REST OF THE AREA, WITH CIGS AND VSBY FALLING INTO THE MVFR (AND
POSSIBLY IFR RANGE) FROM LATE MORNING THRU THE AFTN HOURS. WINDS
WILL BE OUT OF THE SW GENERALLY 7-10 KTS ACROSS THE PIEDMONT,
BECOMING VERY LIGHT AFTER SUNSET. SOME WEAK WEDGE MAY DEVELOP AS
THE RAIN MOVES IN MONDAY MORNING, WHICH COULD RESULT IN VRB OR
NE WINDS ON MONDAY, ESPECIALLY ACROSS THE UPSTATE SITES. KCLT IS
EXPECTED TO STAY SW TO SE.
OUTLOOK: WIDESPREAD LOW CLOUDS AND RAIN WILL AFFECT THE AREA
THRU MONDAY NIGHT, THEN SOME IMPROVEMENT IS EXPECTED ON TUESDAY,
AS PRECIP EXITS TO THE EAST. VFR CONDITIONS SHOULD RETURN ON
WEDNESDAY AND PERSIST THRU THE END OF THE WORKWEEK.
CONFIDENCE TABLE...
19-01Z 01-07Z 07-13Z 13-18Z
KCLT HIGH 100% HIGH 100% HIGH 100% HIGH 96%
KGSP HIGH 100% HIGH 100% HIGH 100% HIGH 82%
KAVL HIGH 100% HIGH 100% HIGH 100% HIGH 92%
KHKY HIGH 100% HIGH 100% HIGH 100% HIGH 98%
KGMU HIGH 100% HIGH 100% HIGH 100% HIGH 83%
KAND HIGH 100% HIGH 100% HIGH 100% HIGH 83%
THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES ARE AVAILABLE AT
THE FOLLOWING LINK:
WWW.WEATHER.GOV/GSP/AVIATION
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...DEO
NEAR TERM...ARK
SHORT TERM...08
LONG TERM...08
AVIATION...ARK
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