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Area Forecast Discussion

776
FXUS62 KGSP 080848
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
348 AM EST MON FEB 8 2016

.SYNOPSIS...
A COLD FRONT WILL CROSS THE REGION TODAY...WITH A BROAD AND MOIST
AREA OF LOW PRESSURE LINGERING INTO WEDNESDAY NIGHT. CANADIAN HIGH
PRESSURE WILL THEN BUILD IN THURSDAY AND REMAIN THROUGH THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 300 AM...WATER VAPOR IMAGERY SHOWS DEEP UPPER TROUGH WITH
EMBEDDED CYCLONE ORIENTED ALONG THE UPPER MISSISSIPPI RIVER
VALLEY. THE TROUGH WILL EXPAND SOUTH AND EAST THROUGH TUESDAY
MORNING...BRINGING A COLD FRONT WITH IT. A BROAD AREA OF LIGHT RADAR
RETURNS IS PRESENT OVER KY IN RESPONSE TO A CHANNELED POCKET OF VORT
AT THE LEADING EDGE OF THE TROUGH. THE VORT MAX WILL PUSH EASTWARD
ACRS THE CWFA LATER TODAY...AND STRONG QG FORCING WILL ACCOMPANY
IT THROUGH THE AREA. MOISTURE DOES NOT APPEAR TO BE MUCH OF A
LIMITING FACTOR EVEN EAST OF THE MTNS. FALLING HEIGHTS WILL ALLOW
LAPSE RATES TO INCREASE DURING THE DAY AS WELL. A BULLSEYE OF CAPE
VALUES UP TO NEAR 200 J/KG IS SHOWN ON BOTH NAM AND GFS...THE GFS
HAVING TRENDED TOWARD THE NAM WHICH HAS BEEN CONSISTENTLY UNSTABLE
FOR MONDAY OVER THE PAST FEW RUNS. THIS INSTABILITY...ESPECIALLY
GIVEN THE UPPER FORCING...LENDS CONFIDENCE TO SHOWERS DEVELOPING
AND SPREADING ACROSS THE AREA TODAY. CONVECTION ALLOWING MODELS
ARE SURPRISINGLY UNRESPONSIVE...THE HI-RES WRF WINDOWS BASICALLY
SUPPORTING ONLY ISOLATED/SCHC POPS DURING THE DAY. I STILL FEEL
POPS SIMILAR TO THOSE FROM THE PREV FCST ARE WARRANTED. INCLUDED
A LOW THUNDER CHANCE OVER WRN NC BASED ON PEAK CAPES.

COLDER AIR FILTERS IN STEADILY AT 850MB THRU THE DAY. BASED ON
FAVORED BLEND /MOSTLY SREF/...TEMPS IN THE HIGHER ELEVATIONS
ARE EXPECTED TO REMAIN NEARLY STEADY...WITH VALLEYS AND THE
PIEDMONT MANAGING TO WARM ENOUGH THAT ANY PRECIP WILL INITIALLY
BE RAIN. STILL LOOKS LIKE SNOW LEVELS WILL FALL AS THE DAY
PROGRESSES. SNOW LEVELS REACH THE VALLEY FLOOR AROUND SUNSET. WITH
THE LEADING SHOT OF UPPER FORCING DEPARTING THIS EVENING...PRECIP
CHANCES TAPER OFF IN THE PIEDMONT...AND WITH TEMPS REMAINING SO WARM
THIS ROUND SHOULD END AS RAIN. HOWEVER...WHILE MODEL QPF RESPONSE
IS AGAIN QUITE LOW...A SECOND VORT LOBE ROTATING AROUND THE UPPER
CYCLONE WILL DIVE THRU THE TENN VALLEY THIS EVENING BEFORE SWINGING
ACROSS WESTERN NC IN THE WEE HOURS TUE. I FELT THIS DEPICTED WAVE
APPEARED STRONG ENOUGH TO BE ABLE TO GENERATE A FEW PIEDMONT SHOWERS
FROM THE STILL-MOIST LOW LEVELS. BY THE TIME THIS MOVES THRU...TEMPS
SHOULD BE COLD ENOUGH FOR SNOW. HOWEVER ACCUMULATION IS NOT LIKELY.

WESTERLY UPSLOPE FLOW WILL BE AN ADDITIONAL FACTOR FOR THE
TENN BORDER AREAS. THIS WILL GET UNDERWAY THIS MORNING AND
REMAIN STEADY...BUT THE LOW LEVEL WINDS VEER AND STRENGTHEN THIS
EVENING. FURTHERMORE THE SECOND PERIOD OF UPPER FORCING MAY ENHANCE
PRECIP RATES EVEN MORE. I BLENDED IN MORE OF THE CAM/HI-RES GUIDANCE
IN ORDER TO BETTER CAPTURE THE NW FLOW ENHANCEMENT. NEW SNOW TOTALS
MEET WARNING CRITERIA IN THE UPSLOPE AREAS DURING THE FIRST 24
HOURS OF THE FCST. THUS...A WINTER STORM WARNING IS BEING RAISED
FOR THE TENN BORDER ZONES. AVERY IS OMITTED SINCE THE CAM GUIDANCE
PLACED MORE OF THE SNOW WEST AND SOUTH OF THE COUNTY. ADVISORY
HAS BEEN EXTENDED THRU 12Z TUE FOR AREAS THAT WERE PREVIOUSLY IN
THE ADVISORY...BUT THAT DO NOT MEET WARNING CRITERIA. THE WARNING
COULD BE EXTENDED TO HIGHLIGHT THE CONTINUING THREAT OF NW FLOW
THRU MIDWEEK.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 315 AM MONDAY...DEEP UPPER TROF REMAINS OVER THE AREA TUE AND
SLOWLY SLIDES EAST ON WED. A SERIES OF SHORT WAVES WILL MOVE THRU
THE TROF AND ACROSS THE AREA BOTH DAYS. SURGES OF CAA AND STRONG NW
FLOW WILL ACCOMPANY THE SHORT WAVES. THIS WILL LEAD TO PERIODS OF NW
FLOW SNOW SHOWERS ACROSS THE NC MTNS BOTH DAYS. EXPECT CLOUDS TO
BREAK CONTAINMENT AND SPREAD ACROSS THE FOOTHILL AND PIEDMONT...AND
POSSIBLY SNOW SHOWERS AS WELL WITH THE RELATIVELY DEEP STEEP LOW
LEVEL LAPSE RATES THAT DEVELOP. DO NOT EXPECT ANY ACCUMS FROM ANY
SNOW SHOWERS THAT DO DEVELOP OUTSIDE OF THE MTNS. HOWEVER...WITH THE
LONG DURATION OF SNOW SHOWERS ACROSS THE MTNS...AMOUNTS WILL BE UP
TO 4 INCHES IN THE USUAL LOCATIONS OF THE NRN MTNS...WITH 1 TO 2
INCHES SOUTHWARD ALONG THE TN BORDER BY THE TIME THE SNOW TAPERS OFF
WED NITE. COULD SEE SOME CLOUDS OUTSIDE OF THE MTNS ON WED BUT NO
SNOW SHOWERS EXPECTED THAT DAY. HIGHS TUE WILL BE 10 TO 20 DEGREES
BELOW NORMAL THEN FALL TO 15 TO 25 DEGREES BELOW NORMAL ON WED AS
THE COLDEST PART OF THE AIR MASS MOVES INTO THE AREA. LOWS 5 TO 10
DEGREES BELOW NORMAL TUE NITE FALL TO 10 TO 20 DEGREES BELOW NORMAL
WED NITE. WITH THE STRONG AND GUSTY WINDS CONTINUING THRU THE
PERIOD...WIND CHILL VALUES FALL INTO THE ADVISORY RANGE ACROSS THE
HIGHER ELEVATIONS TUE NITE...AND DOWN INTO THE VALLEYS ON WED
NITE...WITH WARNING LEVEL WIND CHILLS POSSIBLE IN THE HIGHER
ELEVATIONS.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 340 AM MONDAY...ALTHOUGH THE GUIDANCE SHOWS THE OVERALL
PATTERN IN THE MEDIUM RANGE IS IN DECENT AGREEMENT...THERE IS QUITE
A SPREAD IN THE DETAILS. A LONG WAVE TROF REMAINS OVER THE ERN CONUS
THRU THE PERIOD. THE FLOW FLATTENS SLIGHTLY ON THU AS THE SHORT WAVE
FROM THE SHORT RANGE MOVES EAST...THEN DEEPENS AGAIN FRI AND SAT AS
ANOTHER SERIES OF SHORT WAVES DIG INTO THE TROF. THE ECMWF IS DEEPER
AND STRONGER WITH THE TROF AS A CLOSED UPPER LOW DIVES INTO THE MID
ATLANTIC...WHILE THE GFS KEEPS THE UPPER LOW OVER QUEBEC. HEIGHTS
THEN RISE ON SUN IN THE GFS AS THE TROF AXIS MOVES EAST...WHILE THE
ECMWF KEEPS HEIGHTS LOW AS THE TROF ONLY SLOWLY MOVES EAST.

AT THE SFC...THE GUIDANCE AGREES ON A CLIPPER SYSTEM AFFECTING THE
AREA...BUT THE GFS IS FASTER AND WEAKER WITH THE SYSTEM WHILE THE
ECMWF IS STRONGER AND SLOWER. BOTH ALSO HAVE A REINFORCING VERY COLD
AIR MASS MOVING IN BEHIND THE SYSTEM...BUT THE GFS BRINGS IT IN
SOONER AND MODERATES IT FASTER. GIVEN THESE DIFFERENCES....HAVE GONE
WITH A GUIDANCE BLEND. THIS MEANS A DRY FCST FOR THU...WITH CHANCE
POP FOR THE TN BORDER COUNTIES FRI AND FRI NITE...WITH SLIGHT CHANCE
POP ELSEWHERE...THEN DRY FCST AGAIN FOR SAT AND SUN. EVEN THOUGH
TEMPS REMAIN NORMAL THRU THE PERIOD...DO HAVE A WARMING TREND THRU
SAT WITH COOLING AGAIN FOR SUN. WIND CHILL VALUES WILL AGAIN
APPROACH ADVISORY LEVELS ACROSS THE HIGHER ELEVATIONS SAT NITE. THAT
SAID...THIS IS A LOW CONFIDENCE FORECAST GIVEN THE WIDE RANGE IN THE
GUIDANCE.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
AT KCLT AND EAST OF THE BLUE RIDGE...INITIALLY VARIABLE WINDS
EARLY THIS MORNING WILL BACK TO SOUTHERLY AFTER DAYBREAK IN
ADVANCE OF APPROACHING COLD FRONT ASSOCIATED WITH A DEEP UPPER
TROUGH. INCREASING MIDLEVEL CLOUDS WILL BE SEEN THRU MIDDAY...WHEN
A VORT LOBE EMBEDDED WITHIN THE TROUGH BEGINS TO PASS OVER THE
REGION. A PERIOD OF LOWER CLOUD BASES ASSOCIATED WITH DEEP CU WILL
DEVELOP OVER THE FIELD IN RESPONSE TO THE UPPER LIFT AND STRONG
MID-UPPER LEVEL LAPSE RATES. THERE IS ALSO A CHANCE OF LOW VFR
SHRA...AND A NONZERO CHANCE OF A TS AND MVFR CIG CHANCE IS AT THE
HIGH END OF THE PROB30 RANGE...BUT AT THIS TIME IT IS DIFFICULT TO
PIN DOWN A SPECIFIC TIME OF PEAK CHANCE...SO WILL KEEP THE PROB30
FOR SEVERAL HOURS /BRIEFLY PREVAILING SHRA ONLY AT KHKY/. CHANCES
TAPER OFF IN THE EVENING IN THE WAKE OF THE VORT LOBE...BUT WITH
FALLING TEMPS IN THE WAKE OF THE FRONT...ANY REMNANT SHOWERS COULD
MIX WITH SN BEFORE ENDING. THAT CHANCE IS LOW ENOUGH TO OMIT AT
THIS POINT.

AT KAVL AND IN THE MOUNTAINS...CONVECTIVE POTENTIAL WITH PASSING
UPPER DISTURBANCE IS A BIT EARLIER IN THE DAY. COOLER TEMPS WILL
SUPPORT ALL SN ON RIDGETOPS AND A RASN MIX IN THE VALLEYS /AND
KAVL/. LATER IN THE AFTERNOON THE BIGGER STORY WILL BE THE ONSET OF
WHAT LOOKS TO BE A PROLONGED NW FLOW SNOW EVENT AS WINDS BACK IN
THE WAKE OF THE DISTURBANCE...AND COLD ADVECTION STRENGTHENS. THE
BETTER CHANCES WILL BE IN THE HIGH ELEVATIONS...BUT A LOW CHANCE
OF -SHSN EXISTS AT KAVL AFTER SUNSET. HANDLING THIS WITH VCSH
FOR NOW. BRISK FLOW ACRS THE MTNS IS PROGGED TO RESULT IN A RARE
CROSSWIND AT KAVL...WITH A FEW GUSTS NOT OUT OF THE QUESTION.

OUTLOOK...SEVERAL ROUNDS OF STRONG UPPER DISTURBANCES WILL CONTINUE
TO SWING ACROSS THE AREA MONDAY NIGHT THRU WEDNESDAY. MOISTURE
AND REINFORCING COLDER AIR ARRIVE FROM THE NORTHWEST DURING
THIS TIME. RESTRICTIONS WILL BE POSSIBLE...ESPECIALLY IN THE
MOUNTAINS...WHERE SNOW SHOWERS ARE MOST LIKELY.

CONFIDENCE TABLE...

            08-14Z        14-20Z        20-02Z        02-06Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULE TAF ISSUANCE FLIGHT RULE CATEGORY.  COMPLET 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...WINTER WEATHER ADVISORY UNTIL 7 AM EST TUESDAY FOR NCZ033-053-
     062-063.
     WINTER STORM WATCH FROM TUESDAY MORNING THROUGH THURSDAY
     MORNING FOR NCZ033-048>052-058-059-062.
     WINTER STORM WARNING UNTIL 7 AM EST TUESDAY FOR NCZ048>052-058-
     059.
SC...NONE.

&&

$$
SYNOPSIS...RWH
NEAR TERM...ARK/WIMBERLEY
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...WIMBERLEY



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