Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 180828
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
428 AM EDT MON AUG 18 2014

.SYNOPSIS...
A WEAK LOW PRESSURE SYSTEM WILL CROSS THE CENTRAL APPALACHIANS
TODAY...THEN ENTER THE MID ATLANTIC COASTAL WATERS ON TUESDAY. THIS
SYSTEM WILL BRING INCREASING MOISTURE TO THE REGION. THEN A LARGE
UPPER LEVEL RIDGE OF HIGH PRESSURE WILL BUILD ACROSS THE MISSISSIPPI
VALLEY FOR THE REST OF THE WEEK...RESULTING IN ABOVE NORMAL
TEMPERATURES AND DRIER WEATHER.

&&

.NEAR TERM /THROUGH TONIGHT/...
0830 UTC UPDATE...POPS HAVE BEEN ADJUSTED UP IN THE NC MOUNTAINS AND
INTERSTATE 40 CORRIDOR PER RADAR TRENDS. SKY COVER WAS UPDATED FROM
INFRARED SATELLITE IMAGERY...INTRODUCING A FEW BREAKS IN THE SC
PIEDMONT.

AT 230 AM EDT MONDAY...A WEAKENING SHORTWAVE WILL CROSS WESTERN
NORTH CAROLINA TODAY IN ZONAL FLOW ALOFT. INSTABILITY IN EXCESS OF
1000 J/KG AND THE LACK OF AN UPPER LEVEL CAP WILL SUPPORT CONVECTIVE
DEVELOPMENT. NEARLY UNIDIRECTIONAL SPEED SHEAR WILL BE PRESENT IN
THE LOWER LEVELS...BUT DRY AIR ALOFT FOR EVAPORATIVE COOLING WILL
GENERALLY BE LACKING...LIMITING DOWNBURST AND HAIL POTENTIAL. BY THE
TIME A LOW LEVEL DRY LAYER DEVELOPS LATE IN THE DAY...INSTABILITY
WILL BE WANING. THE BEST CHANCE FOR CONVECTION...AND PRECIPITATION
IN GENERAL...WILL BE ACROSS NC...CLOSEST TO THE TRACK OF THE
SHORTWAVE. MAXIMUM TEMPERATURES WILL RUN ABOVE NORMAL IN GA AND
SC...BUT NEAR OR SLIGHTLY BELOW NORMAL IN NC UNDER BETTER RAIN
COVERAGE.

A STRENGTHENING SHORTWAVE CROSSING THE GULF STATES TONIGHT WILL
APPROACH THE UPPER SAVANNAH RIVER VALLEY TOWARD DAWN TUESDAY.
ALTHOUGH SOME DRY AIR WILL HAVE MOVED IN ALOFT BEHIND THE DEPARTING
SHORTWAVE...LOW LEVEL WILL MOISTEN AGAIN AHEAD OF THE SECOND SYSTEM.
INSTABILITY WILL BE NEGLIGIBLE LATE AT NIGHT HOWEVER. THIS SECOND
ROUND OF RAINFALL WILL MAINLY AFFECT THE SW NC MOUNTAINS...NE
GA...AND THE WESTERN MOST PORTIONS OF UPSTATE SC. MINIMUM
TEMPERATURES WILL RUN SLIGHTLY ABOVE NORMAL DUE TO CLOUDS AND
MOISTURE.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 300 AM MONDAY...A WEAK UPPER LEVEL SHORTWAVE WILL CROSS THE
CWFA EARLY TUESDAY...BRINGING IN MAINLY CONVECTIVE DEBRIS CLOUDINESS
AND SOME LINGERING CONVECTION. THIS MAY KEEP TEMPS IN CHECK
SOMEWHAT...NEAR NORMAL. FCST SNDGS SHOW MODEST CAPE OF 1500 J/KG OR
SO...WITH WEAK SHEAR. SO NOT EXPECTING MUCH MORE THAN GARDEN VARIETY
TSTMS.

ON WEDNESDAY...UPPER RIDGE BEGINS TO BUILD ACRS THE LWR-MID MS
VALLEY...WHILE A TROF PROGRESSES ACRS THE GREAT LAKES TO THE EAST
COAST AND DIGS. THE NAM IS A LITTLE WEAKER ON THE RIDGE...AND HAS
MORE ENERGY DIVE SOUTHEAST THRU THE OHIO VALLEY...HINTING AT A
POSSIBLE MCS TRACK RIDING AROUND THE UPPER RIDGE. FOR NOW...I WILL
KEEP A DIURNAL CHC POP IN THE MTNS AND SLGT CHC POP ACRS THE PIEDMONT
FOR WEDNESDAY INTO WED NIGHT. TEMPS ARE EXPECTED TO BE A COUPLE
CATEGORIES WARMER THAN TUESDAY...AS HEIGHTS RISE ALOFT.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 315 AM MONDAY...THE UPPER LEVEL FLOW CONTINUES TO AMPLIFY INTO
A STRONG MS VALLEY RIDGE AND EAST COAST TROF FOR THURSDAY INTO THE
WEEKEND. THIS WILL KEEP THE CWFA WITHIN A PERSISTENT DEEP-LAYER NWLY
FLOW REGIME. SHORTWAVE ENERGY WILL CONTINUE TO DIVE SOUTHEAST ACRS
THE CWFA FROM THE RIDGE AXIS TO THE TROF. A WEAK SFC BNDRY WILL
LIKELY ALSO SET UP PARALLEL TO THE MID-UPR FLOW...WHICH MAY KEEP THE
AREA A LITTLE MORE UNSETTLED. THURSDAY AND FRIDAY LOOK LIKE THE
WARMEST DAYS...IN THE LWR-MID 90S EAST OF THE MTNS...WITH SLIGHTLY
COOLER TEMPS PERHAPS FOR SATURDAY AND SUNDAY. I BLENDED IN THE
LATEST WPC GRIDS WITH MODEL CONSENSUS AND THE OFFICIAL...RESULTING
IN ONLY CHC POP TO THE NW...TO MAINLY DRY CONDITIONS ACRS THE I-85
CORRIDOR AND SE THURSDAY AND FRIDAY...THEN MORE WIDESPREAD LOW-MID
CHC POPS FOR SATURDAY AND SUNDAY...AS THE STALLED FRONT INVOF THE
FORECAST AREA BECOMES MORE ACTIVE.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
AT KCLT...MODEL TIME HEIGHTS SHOW LOW VFR CLOUDS...WITH AN EVEN
LOWER LAYER AROUND DAYBREAK. WITH MODEL GUIDANCE DIFFERING ON JUST
HOW LOW DAYBREAK CIGS WILL BE...ONLY A VERY LOW VFR CIG WILL BE
CARRIED AT DAYBREAK. A GUIDANCE CONSENSUS ONLY LOWERS VSBY TO LOW
VFR BY DAYBREAK...BUT THE CONSENSUS DOES LOWER VSBY TO IFR TO THE
W...AND MVFR TO THE S AND N. CONVECTIVE CHANCES WILL WARRANT A
MENTION IN THE TAF ON TODAY...AS A MID LEVEL SYSTEM CROSSES THE
AREA. SW WINDS WILL PREVAIL...WITH SOME GUSTINESS DURING DAYLIGHT
HOURS.

ELSEWHERE...CONVECTION OVER E TN IS NOT EXPECTED TO SURVIVE THE LOSS
OF HEATING LONG ENOUGH TO REACH KAVL. MODEL TIME HEIGHTS ARE SHOWING
LOW CLOUDS...BUT NO FIRM CONSENSUS ON HOW LOW THEY WILL BE AT
DAYBREAK. FOR NOW A BLEND WILL BE USED...BRINGING CIGS TO LOW VFR BY
DAWN...EXCEPT MVFR AT KAVL. A BLEND OF GUIDANCE SUPPORTS MVFR VSBY
AT DAYBREAK. CONVECTIVE CHANCES WILL BE MUCH BETTER TODAY THAN
RECENTLY AS A MID LEVEL SYSTEM CROSSES THE AREA. SW WINDS WILL
PREVAIL...WITH GUSTINESS DURING DAYTIME HEATING...BUT WINDS SHOULD
CHANNEL UP VALLEY FORM THE NW AT KAVL.

OUTLOOK...UPPER LEVEL RIDGING WILL SET IN BY MIDWEEK WITH ENOUGH
MOISTURE IN THE PROFILE TO SUPPORT DIURNAL CONVECTION THROUGH WEEKS
END LEADING TO AFTERNOON TSRA RESTRICTIONS AND POSSIBLE EARLY
MORNING FOG.

CONFIDENCE TABLE...

            08-14Z        14-20Z        20-02Z        02-08Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       MED   70%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH  91%     HIGH  97%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH  95%     HIGH 100%     HIGH 100%     HIGH 100%

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: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...ARK
NEAR TERM...JAT
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...JAT






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