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Area Forecast Discussion

145
FXUS62 KGSP 310550
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
150 AM EDT FRI OCT 31 2014

.SYNOPSIS...
MOISTURE WILL INCREASE ON FRIDAY OUT AHEAD OF AN APPROACHING COLD
FRONT. THIS FRONT...AND A STRONG MID LEVEL AREA OF LOW PRESSURE IS
FORECAST TO TRACK ACROSS THE REGION FRIDAY NIGHT INTO SATURDAY. A
STRONG SURFACE LOW PRESSURE SYSTEM WILL DEVELOP OFFSHORE ON
SATURDAY...THEN TRACK QUICKLY NORTH BY SATURDAY NIGHT. CIRCULATION
AROUND THE COASTAL LOW WILL BRING A CANADIAN AIR MASS TO THE REGION
INTO MONDAY.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 130 AM...FCST REMAINS ON TRACK WITH ONLY SOME HIGH CLOUDINESS.
TEMP/RH TRENDS LOOK GOOD. MIN TEMPS ALSO ON TRACK. NO CHANGES FOR
THE REST OF THE OVERNIGHT PERIOD. THEN THINGS START TO GET
INTERESTING...

REMAINDER OF PREVIOUS DISCUSSION...

AS OF 1025 PM...GOING FCST STILL ON TRACK WITH MAINLY LIGHT WINDS
AND MOSTLY CLEAR SKIES. HAVE SLOWED THE INCREASE IN CLOUDS...BUT
STILL HAVE PARTLY CLOUDY SKIES ACROSS THE MTNS BY MORNING GIVEN THE
CLOUDS UPSTREAM HEADING THIS WAY. OTHERWISE...UPDATES MAINLY FOR
CURRENT CONDITIONS.

AN UPPER TROUGH WILL AMPLIFY OVER THE EASTERN USA THROUGH
FRIDAY...WHILE A RIDGE UPSTREAM PROGRESSES FROM THE ROCKY MOUNTAINS
TO THE PLAINS. A SHORTWAVE ROUNDING THE BASE OF THIS TROUGH WILL
CROSS THE SOUTHERN APPALACHIANS BY DAYBREAK...WHILE AN UPPER LOW
CLOSES OFF OVER THE GREAT LAKES. THIS DEEPENING LOW WILL MOVE INTO
THE OH RIVER VALLEY BY LATE FRIDAY.

A NEARLY STATIONARY FRONT WILL REMAIN NEAR THE CAROLINA AND GA
COASTS TONIGHT...THEN BEGINS MOVING SLOWLY EAST ON FRIDAY AS A
SURFACE WAVE MOVES NE UP THE BOUNDARY. MEANWHILE...A SURFACE LOW
WILL FILL AS IT MOVES FROM THE SOUTHERN PLAINS TO THE TN VALLEY.
MOISTURE AHEAD OF THIS LOW WILL REACH THE SOUTHERN APPALACHIANS BY
DAYBREAK...BUT PRECIPITATION ASSOCIATED WITH THE SYSTEM WILL LIKELY
NOT ARRIVE UNTIL MIDDAY...WHEN A COLD FRONT REACHES THE MOUNTAINS
FROM THE NW. THE FRONT MOVES ACROSS OUR AREA DURING THE AFTERNOON...
ACCOMPANIED BY MODEST PRECIPITATION WITH LIMITED LIFT ALONG THE
BOUNDARY. VERY LIMITED INSTABILITY WILL BE PRESENT IN THE
PIEDMONT...AND CONVECTION CANNOT BE TOTALLY RULED OUT...BUT
THUNDERSTORMS WILL NOT BE MENTIONED AT THIS TIME.

THE BETTER PRECIPITATION WILL FOLLOW THE FRONT IN THE MOUNTAINS...
WHERE ROBUST MOST UPSLOPE FLOW WILL SETUP FROM THE NW. WITH
SUFFICIENT COLD ADVECTION BEHIND THE FRONT...PRECIPITATION WILL
CHANGE OVER TO A MIX OF RAIN AND SNOW AT HIGHER ELEVATIONS DURING
AFTERNOON...AND ALL SNOW ON THE VERY HIGHEST PEAKS TOWARD EVENING...
BUT DURATION APPEARS TOO SHORT FOR ACCUMULATIONS BEFORE DUSK.

MINIMUM TEMPERATURES WILL RUN A FEW DEGREES BELOW NORMAL TONIGHT IN
A COOL NW FLOW BEHIND THE COASTAL FRONT. HIGH TEMPERATURES ON FRIDAY
WILL RUN AROUND FIVE DEGREES BELOW NORMAL DUE TO CLOUD COVER AND
PRECIPITATION.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...
DDHHMM
WRKSHT

AS OF 230 PM THURSDAY...12Z GUIDANCE PACKAGE REMAINS CONSISTENT IN
MOVING AN ANOMALOUS UPPER LOW RAPIDLY SE FROM THE GREAT LAKES INTO
THE CAROLINAS ON SAT. THIS LOW IS IN THE NEIGHBORHOOD OF 5 SD`S
BELOW NORMAL. SO WE DO NOT SEE THIS TYPE OF SYSTEM VERY OFTEN.
THUS...WE WILL BE ONGUARD IN REGARD TO THE UNEXPECTED. WITH THE VERY
GOOD RUN TO RUN MODEL CONSISTENCY...WE ARE CONFIDENT ENOUGH TO GO
AHEAD A UPGRADE THE WINTER STORM WATCH IN THE NC MOUNTAINS TO A
WARNING FOR FRIDAY NIGHT AND SAT...EXCEPT FOR BUNCOMBE...NORTHERN
JACKSON AND GRAHAM COUNTIES WHERE A WINTER WEATHER ADVISORY WILL BE
ISSUED.

THE VERY POTENT COMPACT VORTMAX/CLOSED 500 MB LOW WILL INDUCE
CYCLOGENESIS EAST OF THE OUTER BANKS DURING THE DAY ON SAT... WITH A
DEFORMATION ZONE SETTING UP FROM CENTRAL VA/NC EXTENDING AS FAR WEST
AS THE I-77 CORRIDOR ON SAT. AN ASSOCIATED COLD FRONT MOVING ACROSS
THE AREA FRIDAY NIGHT WILL BRING A SURGE OF VERY COLD AIR WITH 850
MB TEMPS PLUMMETING TO -6 TO -8C ALONG THE TN LINE AND GENERALLY 0
TO -4C ACRS THE PIEDMONT.  THE COLD TEMPS ALOFT ALONG ALONG WITH THE
RAPIDLY COOLING BOUNDARY LAYER WILL ALLOW RAIN TO CHANGE TO SNOW BY
MIDNIGHT FRIDAY NIGHT IN THE MOUTNAINS...WITH A RAIN/SNOW MIX
SPREADING EASTWARD ACROSS THE FOOTHILLS INTO THE I-85 CORRIDOR
TOWARD SR ON SAT. IN THE MOUNTAINS...UPSLOPE FLOW WILL CONTINUE TO
PRODUCE SNOW SHOWERS INTO SAT EVENING. STORM TOTAL SNOW AMOUNTS IN
THE TN BORDER COUNTIES WILL BE ON THE ORDER OF 4-8 INCHES WITH
POSSIBLY AS MUCH AS 10 INCHES IN THE HIGHER PEAKS OF THE SMOKIES.
OTHER MOUNTAINS LOCATIONS WILL SEE ANYWHERE FROM A DUSTING TO UP TO
3 INCHES.

ON SATURDAY THE BOMBING LOW ALONG THE COAST WILL GENERATE STRONG
LLVL WINDS ON THE ORDER OF 40-50 KTS OUT OF THE NW. OUR WIND GUST
ALGORITHM HITS THE UPSTATE AND NE GA WITH THE HIGHEST GUSTS ON THE
ORDER OF 35 TO 45 MPH...WHICH WOULD BE BELOW HIGH WIND WATCH
CRITERIA. PRECIP ENDS FOR THE MOST PART BY SAT EVENING...EXCEPT FOR
SOME LINGERING SNOW SHOWERS IN THE NC MOUTNAINS ADJACENT TO TN.
CLEARING CONDITIONS WILL OCCUR SAT NIGHT BUT ATMOSPHERE MAY STAY
MIXED ENOUGH TO PREVENT WIDESPREAD FREEZING TEMPS OUTSIDE THE
MOUNTAINS...SO NO FREEZE WATCH FOR NOW. TEMPS STAY WELL BELOW CLIMO
FOR SUN EVEN WITH FULL SUNSHINE.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 100 PM THURSDAY...MEDIUM RANGE MODELS ARE IN DECENT AGREEMENT
IN BUILDING DEEP LAYERED RIDGING ATOP THE SE CONUS ON MONDAY AND
TRANSLATING RIDGE CENTER OFFSHORE ON TUESDAY. IT NOW LOOKS LIKE MAX
TEMPERATURES WILL CREEP BACK TO WITHIN 5 DEG F OF CLIMO BY TUESDAY.
IT REMAINS TO BE SEEN JUST HOW MUCH IF ANY DEEPER CONVECTION DEVELOPS
WITHIN THE WARM SECTOR ON WEDNESDAY WITH THE BEST MODEL RESPONSE
STILL WEST OF THE MTNS BY THE EVENING HOURS. FOR NOW...WILL MAINTAIN
TOKEN SMALL OR SLIGHT SHOWER CHANCES AND CONTINUE TO MODERATE
TEMPERATURES.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
AT KCLT...EXPECT VFR CONDITIONS TO CONTINUE THROUGH THE
PERIOD...ALTHO THE SITUATION WILL BE GOING DOWNHILL AT THE END OF
THE FCST PERIOD. UNTIL THEN...MAINLY HIGH CLOUDS THROUGH THE EARLY
TO MID MORNING WITH A LIGHT NE WIND...FOLLOWED BY THICKENING MOSTLY
ALTOCU CEILINGS. BY MID/LATE AFTERNOON...THE WIND SHOULD BE LIGHT
AND VARIABLE AND MAY CHANGE BETWEEN NW AND SW OFTEN. AT THAT TIME...
A LOW CLOUD CEILING SHOULD MOVE IN FROM THE NW AHEAD OF THE
APPROACHING LOW...BUT STILL VFR. THE LATEST MODEL GUIDANCE IS IN
GOOD AGREEMENT WITH DEVELOPING LIGHT PRECIP INTO THE CLT METRO AREA
AROUND SUNSET. A CONSENSUS OF THE GUIDANCE SUGGESTS A PREVAILING
LIGHT RAIN...BUT WITH STILL A VFR CATEGORY VISIBILITY...AFTER 02Z.
WIND AT THAT TIME SHOULD SETTLE INTO A N COMPONENT. NO ISSUES WITH
PRECIP TYPE UNTIL AFTER 06Z SATURDAY.

ELSEWHERE...VFR THROUGH THE DAYLIGHT HOURS FRIDAY. LIGHT AND
VARIABLE WINDS AND INCREASING MID/HIGH CLOUDS EXPECTED THROUGH MID
MORNING. LOW VFR AND MID CLOUDS INCREASE THRU THE DAY FRI WITH LOW
VFR CIGS EXPECTED BY AFTERNOON AT KAVL. WINDS TURN WSW FRI AFTERNOON
AHEAD OF THE APPROACHING COLD FRONT. HOWEVER...WINDS REMAIN NLY AT
KAVL. KAVL ALSO HAS THE BEST CHC OF SEEING ANY SHRA BY LATE IN THE
AFTERNOON...WHICH WAS INCLUDED AS A VCSH AT THIS TIME. THE STEADIER
RAIN SHOULD MOVE INTO THE MTNS BY SUNSET. HAVE INCLUDED THE RAIN
PREVAILING AFTER 02Z AT KAVL...AT WHICH TIME THE CEILING SHOULD DROP
TO MVFR. PRELIMINARY INDICATION IS THAT PRECIP COULD CHANGE OVER TO
SNOW SHOWERS AT KAVL AS EARLY AS 05Z.  A SIMILAR PROGRESSION IS
NOTED AT KHKY...BUT PRECIP WAS KEPT LIQUID. OTHER TAF SITES ONLY
HAVE A VCSH AFTER 02Z OR 03Z...OWING TO LOW CONFIDENCE.

OUTLOOK...LIGHT PRECIP WILL DEVELOP ACROSS THE ENTIRE AREA LATE
FRIDAY NIGHT. SOME RESTRICTIONS ARE POSSIBLE...ESPECIALLY IN THE
MOUNTAINS WHERE EVEN SOME SNOW SHOWERS ARE EXPECTED LATE FRIDAY
NIGHT AND SATURDAY. VFR BEYOND SUNDAY.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...WINTER STORM WARNING FROM 8 PM THIS EVENING TO 8 PM EDT
     SATURDAY FOR NCZ033-048>052.
     WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 8 PM EDT
     SATURDAY FOR NCZ053-058-059.
SC...NONE.

&&

$$
SYNOPSIS...CSH
NEAR TERM...JAT/PM/RWH
SHORT TERM...ARK/LG
LONG TERM...CSH
AVIATION...PM



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