594
FXUS62 KGSP 211818
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
118 PM EST THU FEB 21 2019
SYNOPSIS
CHILLY HIGH PRESSURE ATOP THE REGION WILL WEAKEN TODAY AS A SERIES
OF LOW PRESSURE SYSTEMS MOVES UP FROM THE GULF. THE MOIST PATTERN
WILL CONTINUE WELL INTO THE WEEKEND UNTIL A COLD FRONT FINALLY MOVES
THROUGH THE REGION SUNDAY. AFTER A BRIEF BREAK EARLY NEXT WEEK,
ANOTHER SYSTEM WILL APPROACH BY MID-WEEK.
NEAR TERM /THROUGH TONIGHT/
AS OF 115 PM: MAIN UPDATE FOR THE 18Z TAF ISSUANCE, ALONG WITH
MINOR ADJUSTMENTS TO TEMPS/POPS/WINDS TO COINCIDE WITH LATEST
TRENDS, AS THE REST OF THE NEAR TERM FORECAST REMAINS ON TRACK.
CONDITIONS HAVE QUIETED DOWN OVER THE PAST FEW HOURS WITH
OVERALL BREAKS IN THE CLOUDS. DO EXPECT THIS LULL IN
PRECIPITATION WILL BE BRIEF, WITH CLOUDS FILLING BACK IN THIS
EVENING, AND PRECIP CHANCES RETURNING TONIGHT.
OTHERWISE, RAINFALL FROM OVERNIGHT HAS CAUSED NUMEROUS STREAM GAUGES
TO RISE INTO ADVISORY-LEVEL LEVELS, WITH SOME MINOR FLOODING IN
SPOTS. THUS, A FLOOD WATCH REMAINS IN EFFECT FOR PORTIONS OF THE
AREA. WITH A LULL IN PRECIP ALONG WITH A LACK OF ANY PARENT HIGH,
EXPECT AN EROSION OF THE CAD. HOWEVER, THE COLD POOL DOESN'T
COMPLETELY SCOUR (AS THE INVERSION IS VERY STRONG), AND WITH LITTLE
BREAK IN THE LOW OVERCAST, TEMPS SHOULD ONLY WARM INTO THE 50S TO
AROUND 60 (DESPITE WHAT OTHER GUIDANCE LIKE THE GFS SUGGESTING MID
TO UPPER 60S).
TONIGHT, THE RIGHT ENTRANCE REGION OF THE 300 MB JET PIVOTS BACK
OVER OUR AREA AGAIN AND WILL BE COUPLED WITH INCREASED 850 MB WAA
AND STRONG 850-700 MB FRONTOGENESIS. THIS FORCING WILL ALSO BE ATOP
A NEW COLD AIR DAMMING WEDGE, AS A 1032 MB SFC HIGH BUILDS OVER THE
GREAT LAKES AND PUSHES A BACKDOOR COLD FRONT THRU THE AREA. POPS
RAMP BACK UP TO LIKELY TO CATEGORICAL. THERE WILL BE SOME MUCAPE
ATOP THE WEDGE, BUT NOT AS MUCH AS THIS MORNING. STILL COULD SEE
ISOLATED ELEVATED THUNDER IN THE SOUTHERN ZONES OVERNIGHT. PRECIP
RATES WILL PICK UP, AND EVEN MODEST 0.5-1.0" TOTALS MAY CAUSE SOME
RAPID STREAM RISES. IN ANY CASE, HYDRO CONCERNS WILL CONTINUE TO
INCREASE WITH EACH ADDITIONAL ROUND OF RAIN. TEMPS WILL COOL A
LITTLE WITH CAD AND PRECIP, BUT REMAIN ABOVE NORMAL (MAINLY IN THE
40S TO LOWER 50S).
SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/
AS OF 245 AM EST THURSDAY: THE SHORT TERM PERIOD BEGINS FRIDAY
MORNING WITH THE RECURRING PATTERN OF DAMMING-ISENTROPIC UPGLIDE-
RAIN-YUCK. SURFACE HIGH OVER THE GREAT LAKES WILL BE DAMMING DOWN AT
THE BEGINNING OF THE PERIOD WITH A SLUG OF MOISTURE LIFTING UP OVER
THE WESTERN ATLANTIC RIDGE. RECENT GUIDANCE TRENDS HAVE INCREASED
THE STRENGTH OF THE DAMMING AND THIS REMAINS THE CASE, THOUGH THE
LOW-LEVEL CAA WON'T BE COLD ENOUGH FOR ANY P-TYPE ISSUES. INSTEAD,
THE PRIMARY CONCERN WILL BE THE CONTINUED RAINFALL. AT LEAST
INITIALLY, THE HEAVIEST RAIN WILL BE OVER THE MOUNTAINS ALONG THE
MOISTURE AXIS, BUT THE UPPER RIDGE AXIS WILL BEGIN TO MOVE EAST
THROUGH THE DAY IN RESPONSE TO A DEEP LOW EJECTING OUT OF THE
ROCKIES, ALLOWING ISENTROPIC UPGLIDE TO RESULT IN A PROLONGED PERIOD
OF LIGHT RAIN, POSSIBLY DRIZZLE, OFF AND ON DURING THE DAY (AS IF WE
HAVEN'T HAD ENOUGH CLOUDY COLD RAINY MISERABLE YUCKY DAYS LATELY).
QPF IS NOT PARTICULARLY IMPRESSIVE ON FRIDAY, GENERALLY 1/2" OR SO,
BUT SOILS ARE VERY SATURATED AND WITH NEAR-TERM RAIN, FELT IT
PRUDENT TO GO AHEAD AND TAKE THE FLOOD WATCH THROUGH THE DAY FRIDAY,
AND WILL REEVALUATE IN LATER SHIFTS WHETHER OR NOT IT NEEDS TO BE
EXTENDED (OR EXPANDED) FURTHER.
LITTLE DIURNAL RANGE INTO FRIDAY NIGHT, AND VERY LITTLE CHANGE INTO
SATURDAY FOR TEMPERATURES. HOWEVER, AS THE WAVE AMPLITUDE INCREASES
IN RESPONSE TO THE NOW-PLAINS UPPER LOW, THE MOISTURE AXIS WILL BE
SHUNTED NORTH, RESULTING IN A LITTLE BIT OF A LULL SATURDAY
AFTERNOON.
AS THE APPROACHING SURFACE LOW OCCLUDES AND THE UPPER SYSTEM FILLS
AND LIFTS RAPIDLY NORTHEAST, THE ATTENDANT FRONT WILL APPROACH
SATURDAY NIGHT. RESIDUAL COOL POOL WILL TRY ITS HARDEST TO REMAIN
ENTRENCHED UP AGAINST THE BLUE RIDGE, BUT THE STRONG FRONT WILL
RAPIDLY SCOUR THE DAMMING OUT OVERNIGHT SATURDAY NIGHT INTO EARLY
SUNDAY, WITH THE FRONT BASICALLY CLEARING THE AREA BY MIDDAY SUNDAY
(WITH THE THUNDERSTORM THREAT BASICALLY NIL FOR OUR AREA DUE TO THE
TIMING). HUGE DIFFERENCE WITH THE ERODED DAMMING AND JUST BEFORE THE
FRONTAL PASSAGE, AS SOUTHWESTERLY LOW-LEVEL FLOW WILL BRING SOME
STRONG AIRMASS RECOVERY TO THE AREA BEFORE THE POST-FRONTAL CAA
PICKS UP. PRESSURE GRADIENT WILL RESULT IN A BIT OF A BREEZE SUNDAY,
BUT HIGHS NEAR 70 IN THE PIEDMONT (50S TO NEAR 60 IN THE MOUNTAINS -
ALL A GOOD 10-20 DEGREES WARMER THAN FRI AND SAT) WILL RESULT IN A
REALLY REALLY BEAUTIFUL DAY. OF COURSE, THE DIURNAL RANGE RETURNS
WITH LOWS SUNDAY NIGHT PRETTY CLOSE TO SEASONAL NORMALS.
LONG TERM /MONDAY THROUGH WEDNESDAY/
AS OF 300 AM EST THURSDAY: POST-FRONTAL CONDITIONS EARLY IN THE WORK
WEEK WILL BE PLEASANT, THOUGH WITH A COOLING TREND BACK TO SEASONAL
NORMALS FOR HIGHS AND LOWS EARLY-ON. EXPECT A NICE DAY ON MONDAY,
ANOTHER GREAT OPPORTUNITY TO SOAK UP SOME SUNSHINE AFTER THE WEEK OF
GLOOM. TOWARD THE LATTER PART OF THE WEEK, MODEL DIFFERENCES
INCREASE, BUT THE OVERALL PICTURE IS THAT ANOTHER SYSTEM IN THE
NORTHERN STREAM WILL APPROACH TUESDAY INTO WEDNESDAY, POSSIBLY
PHASING WITH A SOUTHERN STREAM WAVE. THE ECMWF KEEPS THE TWO SYSTEMS
SEPARATE, LEAVING US IN MUCH DRIER CONDITIONS, WHEREAS THE GFS
PHASES THE TWO AND BRINGS MOISTURE BACK INTO THE AREA TUESDAY NIGHT.
HAVE KEPT A BLEND WITH SOME LOW-END POPS.
AVIATION /18Z THURSDAY THROUGH TUESDAY/
AT KCLT AND ELSEWHERE: A MIXTURE OF VFR/MVFR/IFR PREVAILS ACROSS THE
AREA THIS AFTERNOON, WITH SOME BREAKS IN THE CLOUDS, THOUGH THE CAD/
LOW-LEVEL INVERSION HAS YET TO DISSIPATE COMPLETELY. DESPITE THE
IMPROVED CONDITIONS IN SOME LOCATIONS, DO ANTICIPATE LOWERING CIGS
AND INCREASING PRECIPITATION CHANCES TO RETURN WITH IFR TONIGHT WITH
A BACKDOOR COLD FRONT. GIVEN LOWER CONFIDENCE ON EXACT TIMING OF
EXPECTED CONDITIONS, HAVE KEPT WITH A GENERAL TREND OF SLOWLY
DETERIORATING CONDITIONS TONIGHT, CONTINUING THROUGH THE END OF THE
VALID TAF PERIOD. EXPECT SW WINDS 5 TO 7 KTS THIS AFTERNOON TO
BECOME NE LATE TONIGHT, AOB 5 KTS, WITH THE EXCEPTION OF KAVL, WHERE
CURRENT NW WINDS WILL BECOME NE.
OUTLOOK: A SERIES OF LOW PRESSURE SYSTEMS WILL CONTINUE TO MOVE
THROUGH THE REGION THROUGH THE END OF THE WEEK. THIS WILL PRODUCE
PRECIPITATION AND ASSOCIATED RESTRICTIONS FOR LONG PERIODS OF TIME
WITH EACH SYSTEM. A COLD FRONT IS EXPECTED TO DRY OUT THE REGION
SUNDAY.
CONFIDENCE TABLE...
18-24Z 00-06Z 06-12Z 12-18Z
KCLT HIGH 85% MED 69% MED 75% MED 71%
KGSP HIGH 88% HIGH 87% HIGH 88% HIGH 86%
KAVL MED 79% HIGH 85% HIGH 94% HIGH 89%
KHKY MED 78% HIGH 83% MED 75% MED 74%
KGMU HIGH 89% HIGH 88% HIGH 85% MED 79%
KAND HIGH 90% HIGH 82% MED 75% HIGH 81%
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...FLOOD WATCH THROUGH FRIDAY EVENING FOR GAZ010-017-018-026-028.
NC...FLOOD WATCH THROUGH FRIDAY EVENING FOR NCZ048-051>053-058-059-
062>065-509-510.
SC...FLOOD WATCH THROUGH FRIDAY EVENING FOR SCZ001>007-010.
SYNOPSIS...TDP
NEAR TERM...ARK/SGL
SHORT TERM...TDP
LONG TERM...TDP
AVIATION...SGL
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