237
FXUS62 KGSP 191909
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
309 PM EDT FRI APR 19 2019
SYNOPSIS
A STRONG COLD FRONT WILL MOVE ACROSS THE FORECAST AREA THROUGH THIS
EVENING BRINGING SHOWERS AND THUNDERSTORMS TO THE REGION. COOLER
TEMPERATURES AND LINGERING SHOWERS ARE EXPECTED BEHIND THE FRONT.
TEMPERATURES WILL WARM AGAIN BY EARLY NEXT WEEK.
NEAR TERM /THROUGH SATURDAY/
AS OF 240 PM: A DEEP TROUGH EXTENDS ACROSS THE MISSISSIPPI VALLEY,
WITH AN EMBEDDED UPPER LOW CENTERED OVER NORTHERN MISSISSIPPI. THIS
FEATURE WILL DRIVE A COLD FRONT INTO THE AREA FROM THE WEST AND
SOUTHWEST THIS EVENING. WITHIN A MOIST AND MODERATELY UNSTABLE
AIRMASS OVER OUR AREA, AND THE STRONGLY DIVERGENT FLOW ALOFT
DOWNSTREAM OF THE TROUGH, WIDESPREAD CONVECTION WILL AFFECT THE
CWFA THIS AFTERNOON. WITH STRONG GRADIENT FLOW ALOFT, EXCEPTIONALLY
STRONG LOW-LEVEL SHEAR WILL CONTINUE TO SUPPORT A DAMAGING WIND AND
TORNADO THREAT. A TORNADO WATCH REMAINS IN EFFECT FOR MOST OF THE
PIEDMONT. CURRENTLY THE MOST SIGNIFICANT CIRCULATIONS ARE PRESENT
IN DISCRETE CELLS MOVING THRU THE SOUTHEASTERN CWFA, WHERE SBCAPE
EXCEEDS 1000 J/KG, SCP EXCEEDS 8, AND STP IS AS HIGH AS 3. FURTHER
WEST, AHEAD OF THE COLD FRONT, A SQUALL LINE HAS FORMED. WHILE
NOT CURRENTLY SEVERE, THE LINE IS BEING MONITORED CLOSELY FOR
QLCS CHARACTERISTICS, ON ACCOUNT OF THE STRONG SHEAR. SUFFICIENT
INSTABILITY EXISTS UPSTREAM OF THAT LINE, BENEATH THE COLDER AIR
ALOFT, THAT A SECOND LINE HAS FORMED ACROSS GA. EARLIER HRRR RUNS
INDICATED THAT SUCH A SECONDARY POCKET OF ACTIVITY COULD SWING
THROUGH OUR AREA LATE IN THE DAY IF NOT DURING THE EVENING, AND
WHILE THE LATEST RUN DOESN'T SHOW ANYTHING PARTICULARLY ORGANIZED
AT THAT TIME, POPS HAVE BEEN KEPT FAIRLY HIGH UNTIL AFTER THE LOSS
OF DIURNAL HEATING. THE TORNADO WATCH CURRENTLY RUNS UNTIL 5 PM,
BUT WE MAY BE ABLE TO CLEAR SOME COUNTIES FROM THE WATCH FOLLOWING
THE WELL-DEFINED SQUALL LINE.
FORCING AND TO SOME EXTENT MOISTURE TAPER OFF OVERNIGHT, BUT FALLING
HEIGHTS OVER THE MOUNTAINS SUGGEST PRECIP MAY REDEVELOP THERE. THE
LOW WILL BEGIN TO MOVE NORTHEAST AND ACROSS THE APPALACHIANS. AS
TEMPS DROP BEHIND THE COLD FRONT, THERE IS POTENTIAL FOR THE COLDEST
SPOTS (HIGH ELEVATIONS) TO SEE THIS PRECIP CHANGE FROM RAIN TO
SNOW. SLRS WILL NOT BE PARTICULARLY GOOD OWING TO SHALLOW MOISTURE
PRESENT AT THAT TIME, AND LOW-LEVEL FLOW REMAINS SOUTHWESTERLY,
THUS BEING LESS FAVORABLE FOR UPSLOPE FORCING ON THE MAJORITY OF
THE RIDGES. CONDITIONS LOOK MUCH MORE FAVORABLE AFTER DAYBREAK,
WHEN THE COLUMN SATURATES OVER A DEEP LAYER BENEATH THE CORE OF
THE UPPER LOW. MOST OF THE AREA WILL BE SUBJECT TO SCATTERED LIGHT
RAIN SHOWERS DURING THE DAY AS A RESULT. HOWEVER, IN VERY HIGH
ELEVATIONS (ALMOST ENTIRELY ABOVE 5000 FT) WILL COOL EARLY ENOUGH,
AND REMAIN COLD LONG ENOUGH, THAT ACCUMULATING SNOW OF SEVERAL
INCHES IS POSSIBLE. THESE AREAS CURRENTLY APPEAR TOO SMALL/ISOLATED
TO WARRANT A WINTER WEATHER ADVISORY. CAN'T ABSOLUTELY RULE OUT
SOME EVAPORATIVE COOLING THAT WILL ALLOW A FEW FLURRIES TO BE
EXPERIENCED IN POPULATED AREAS OF THE MOUNTAINS AND FOOTHILLS
DURING THE MORNING.
SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/
AS OF 230 PM EDT FRIDAY: THE MID LEVEL LOW PRESSURE SYSTEM WILL
PIVOT JUST NORTH OF THE AREA ON SATURDAY NIGHT BEFORE PULLING AWAY
TO THE NORTHEAST ON SUNDAY. LINGERING WRAP AROUND SHOWERS WILL
MAINLY IMPACT THE MOUNTAINS ON SATURDAY NIGHT. SOME SNOW IS EXPECTED
AT THE HIGHER ELEVATIONS ON SATURDAY NIGHT WITH AROUND 1
ACCUMULATIONS EXPECTED AT THE HIGHEST ELEVATIONS.
A DRYING AND WARMING TREND WILL OCCUR SUNDAY NIGHT AND MONDAY AS
HIGH PRESSURE BUILDS INTO THE AREA.
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
AS OF 200 PM EDT FRIDAY: MID LEVEL RIDGING AND SURFACE HIGH PRESSURE
WILL BE IN PLACE ACROSS THE REGION FOR TUESDAY AND WEDNESDAY.
CONDITIONS SHOULD BE DRY AND WARM WITH HIGHS REACHING INTO THE LOWER
80S IN THE PIEDMONT BY WEDNESDAY. A MID LEVEL TROF AND ASSOCIATED
COLD FRONT WILL APPREACH THE AREA FROM THE NORTHWEST LATE IN THE
WEEK WITH AN INCREASING CHANCE OF SHOWERS.
AVIATION /19Z FRIDAY THROUGH WEDNESDAY/
AT KCLT AND ELSEWHERE: MULTIPLE ROUNDS OF CONVECTION WILL AFFECT
AVIATION ACROSS THE REGION THIS AFTN AND EARLY EVENING. FOR KCLT
AND KHKY IMPACTS MOST LIKELY WILL COME FROM A BAND OF MOSTLY
STRATIFORM RA WITH EMBEDDED TSRA. KGSP AND KGMU WILL START OFF
DRY AND VFR, BUT A WELL DEVELOPED QLCS WILL PUSH THRU EARLY IN
THE PERIOD, POSSIBLY SURVIVING TO KHKY/KCLT. THE SHRA/TSRA ARE
LIKELY TO BRING BRIEF GUSTS ABOVE 30 KT, MAINLY OUT OF THE W OR
SW. THE QLCS POSES A RISK OF DAMAGING WIND AND A TORNADO CANNOT BE
RULED OUT ALONG IT. EVEN FOLLOWING THE DEPARTURE OF THESE EVENTS,
AN UPPER LOW PASSING NEAR THE AREA THIS EVENING MAY ACCESS ENOUGH
REMNANT INSTABILITY TO DRIVE A FEW SHOWERS AND POSSIBLY TSRA,
WHICH WOULD STILL BE CAPABLE OF AT LEAST GUSTY WINDS. MAINLY
MVFR CIGS ARE EXPECTED THRU TONIGHT, WITH IFR TO LIFR VSBY LIKELY
WITH THE STRONGER TSRA. A CONTINUING CHANCE FOR SHRA (EVEN SHSN
IN VERY HIGH ELEVATIONS) EXISTS OVERNIGHT ACROSS THE MTNS, WITH
WINDS REMAINING BREEZY ACROSS THE REGION. THE UPPER LOW WILL DRIFT
ACROSS THE AREA DURING THE DAY AND ISO/SCT SHRA SHOULD REDEVELOP
ACROSS THE PIEDMONT, PERHAPS BRINGING MVFR CIGS/VSBY.
OUTLOOK: MAINLY VFR CONDITIONS ARE EXPECTED SUNDAY AND EARLY
NEXT WEEK.
CONFIDENCE TABLE...
19-01Z 01-07Z 07-13Z 13-18Z
KCLT MED 76% MED 75% MED 71% LOW 59%
KGSP HIGH 85% HIGH 80% MED 68% HIGH 84%
KAVL HIGH 84% HIGH 90% MED 71% HIGH 83%
KHKY MED 71% HIGH 89% MED 72% HIGH 85%
KGMU HIGH 80% HIGH 82% MED 68% HIGH 86%
KAND HIGH 82% HIGH 84% MED 76% HIGH 94%
THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK:
WWW.WEATHER.GOV/GSP/AVIATION
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
SYNOPSIS...SW
NEAR TERM...WIMBERLEY
SHORT TERM...SW
LONG TERM...SW
AVIATION...WIMBERLEY
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