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Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 172123
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
523 PM EDT FRI MAY 17 2013

.SYNOPSIS...
-- Changed Discussion --A MID LEVEL DISTURBANCE WILL DRIFT ACROSS THE REGION THIS
WEEKEND... TRIGGEREING SHOWERS AND THUNDERSTORMS THROUGH THE
BEGINNING OF NEXT WEEK. SOUTHERLY FLOW WILL KEEP THE AIRMASS WARM
AND MOIST... AND THE PATTERN WILL REMAIN UNSETTLED UNTIL A FRONTAL
SYSTEM APPROACHES THE WESTERN CAROLINAS LATE NEXT WEEK.-- End Changed Discussion --

.NEAR TERM /THROUGH SATURDAY/...
-- Changed Discussion --AS OF 515 PM EDT FRIDAY...A FEW SHOWERS AND THUNDERSTORMS HAVE
DEVELOPED OVER THE WRN NC PIEDMONT...ESPECIALLY ACROSS ROWAN COUNTY.
THIS IS AN AREA OF WEAK MOISTURE AND SPEED CONVERGENCE. I/D EXPECT
CONVECTION TO CONTINUE ACROSS THIS AREA AND EXTENDING BACK INTO THE
SW NC FOOTHILLS FOR A FEW MORE HOURS. CONVECTION WILL ALSO PERSIST
OVER THE CENTRAL AND NRN MTNS. FARTHER SOUTH AND WEST LAPS ISN/T
SHOWING MUCH INSTABILITY AND MID AND HIGH LEVEL CLOUDS ARE SPREADING
IN WHICH SHOULD ALSO LIMIT CONVECTION. MUCH LATER
TONIGHT...HOWEVER...CONVECTION MAY SPREAD IN FROM THE SOUTHWEST AS
THE UPPER LOW APPROACHES. NOT SEEING A LOT OF ELEVATED INSTABILITY
BUT SHOWERS AND EVEN SOME STRATIFORM RAIN IS POSSIBLE. INTERESTINGLY
THERE IS SOME ELEVATED INSTABILITY OVER THE NC PIEDMONT. OUR
WORKSTATION WRF-ARW MODEL SHOWS CONVECTION DEVELOPING IN THAT AREA
AFTER MIDNIGHT. I WON/T BE THAT AGGRESSIVE...BUT IT/S SOMETHING TO
KEEP IN MIND.

AS OF 230 PM...LOOKING AT LATEST WV IMAGERY...WEAKENING UPPER
LEVEL TROF CONTINUES TO MOVE EASTWARD ACROSS THE TENNESSEE
VALLEY...THUS SPREADING MOISTURE THRU THE SOUTHEASTERN UNITED
STATES. WITH THIS...SOME SHOWER AND THUNDERSTORMS ACTIVITY IS
PRESENT ON RADAR ACROSS PORTIONS OF NORTHEAST MISSISSIPPI AND
NORTHWEST ALABAMA. LOCALLY...MID TO UPPER LEVEL CLOUD COVER
CONTINUES TO INCREASE ACROSS THE REGION AS A CONSEQUENCE OF DEEP
MOISTURE ADVECTION ALOFT. HEIGHTS WILL CONTINUE FALL ACROSS
NORTHEAST GEORGIA AND THE CAROLINAS THROUGH THE NEXT 24 HOURS AS
REMNANTS OF UPPER LEVEL TROF MOVE THROUGH. LATEST MESOANALYSIS
INDICATES A MODERATELY UNSTABLE AIRMASS ACROSS THE REGION THIS
AFTERNOON. STILL EXPECTING THE MAJORITY OF CONVECTIVE ACTIVITY TO
BE IN THE HIGHER TERRAINS AS UPSLOPE FLOW WILL PROVIDE ENOUGH LIFT
TO OVERCOME ANY CAPPING...THEREFORE KEPT LIKELY POPS ACROSS NORTHERN
MOST PORTIONS OF THE NC MOUNTAINS AND HIGHER END CHANCE POPS
ELSEWHERE IN THE HIGH TERRAIN. POPS DECREASE TO THE SOUTHEAST AS
LOCATIONS NEAR AND ALONG THE I85 CORRIDOR WILL HAVE THE MOST
DIFFICULT TIME OVERCOMING ANY INVERSION. THUS...WENT WITH SLIGHT
CHANCE POPS ACROSS THIS REGION.

TONIGHT AND TOMORROW...MODEL GUIDANCE REMAINS IN GOOD AGREEMENT WITH
REGARDS TO DECREASE IN CONVECTIVE ACTIVITY DURING THE OVERNIGHT
HOURS AS DAYTIME HEATING DISSIPATES. HOWEVER...AFTER SUNRISE
TOMORROW THE ABOVE MENTIONED UPPER LEVEL WAVE WILL BE CENTERED OVER
THE SOUTHERN APPALACHIANS. PRECIPITATION CHANCES WILL INCREASE ONCE
AGAIN DURING THE LATE MORNING HOURS ACROSS THE ENTIRE REGION. SOME
SHOWER AND THUNDERSTORM ACTIVITY COULD BE STRONG TOMORROW AFTERNOON
AND EVENING AS THERMAL PROFILES INDICATE SLIGHTLY DEEPER INSTABILITY
THAN PREVIOUS DAYS. LIKEWISE...SOME OF THESE SHOWERS AND
THUNDERSTORMS COULD PRODUCE LOCALLY HEAVY RAINFALL AS PRECIPITABLE
WATER VALUES EXCEED 1.5 INCHES THROUGHOUT THE PROFILE.-- End Changed Discussion --

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
AT 200 PM FRIDAY...A WEAKNESS WILL PERSIST IN THE UPPER HEIGHT FIELD
OVER THE SOUTHEAST THROUGH MUCH OF THE PERIOD...ALTHOUGH IT WILL
CONTINUE TO GRADUALLY FILL. MOISTURE WILL REMAIN DEEP AND ABUNDANT
ACROSS THE REGION THROUGH THE PERIOD...AS PWATS WILL RUN IN THE
NEIGHBORHOOD OF 1.5 INCHES THROUGH AT LEAST SUNDAY NIGHT. THIS
SHOULD PROMOTE DEVELOPMENT OF NUMEROUS SHOWERS AND THUNDERSTORMS
ACROSS THE AREA DURING THE AFTERNOONS AND EVENINGS. LOW LEVEL FOCI
FOR INITIATION SHOULD GENERALLY BE LIMITED TO DIFFERENTIAL
HEATING/TERRAIN EFFECTS AS WELL AS OUTFLOW BOUNDARIES. HOWEVER...IT
APPEARS A WEAK/QUASI-CAD BOUNDARY WILL BE DRAPED ACROSS THE
CAROLINAS DURING THIS TIME AS WELL. WITH RELATIVELY WEAK DEEP LAYER
FLOW EXPECTED TO PREDOMINATE...SLOW MOVING...TRAINING AND/OR
ANCHORING CELLS PRODUCING LOCALLY EXCESSIVE RAINFALL WILL BE THE
PRIMARY THREATS. ISOLATED PULSE SEVERE STORMS OR SMALL CLUSTERS WILL
BE POSSIBLE... BUT THE SEVERE WEATHER THREAT WILL HINGE LARGELY UPON
THE DEGREE OF INSTABILITY AND THEREFORE THE MAGNITUDE OF HEATING WE
SEE...WHICH WILL PROBABLY NOT AMOUNT TO MUCH CONSIDERING THE MOIST
ADIABATIC LAPSE RATES/PROBABLE WIDESPREAD AND PERSISTENT CLOUD
COVER. MIN TEMPS WILL AVERAGE WELL ABOVE NORMAL AND MAXES SLIGHTLY
BELOW CLIMO OWING TO THE VERY MOIST AIR MASS.

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AT 225 PM FRIDAY...AN UPPER LEVEL RIDGE WILL DOMINATE THE EASTERN
U.S INTO THE MIDDLE PART OF NEXT WEEK. AT THE SURFACE...THE WESTERN
EXTENSION OF THE BERMUDA HIGH WILL BE OVER THE SE STATES.
THEREFORE...EXPECT TEMPERATURES TO BE ABOVE CLIMO TUE AND WED.
DIURNALLY DRIVEN SCATTERED CONVECTION WILL OCCUR TUE AND WED WITH THE
GREATEST COVERAGE OVER THE MOUNTAINS. AN UPPER TROUGH WILL APPROACH
THE AREA FROM THE WEST LATE IN THE WEEK WITH THE ASSOCIATED COLD
FRONT MOVING THROUGH THE AREA LATE THU INTO FRI. THEREFORE...PRECIP
CHANCES WILL BE ON THE INCREASE THU...AND THEN DIMINISH ON FRI AS
THE FRONT MOVES TO THE EAST. TEMPERATURES WILL LOWER BACK TO
SEASONAL VALUES BY FRIDAY. STAYED CLOSE TO WPC GUIDANCE TEMPS/POPS.

.AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
-- Changed Discussion --AT KCLT...VFR CONDITIONS WILL PREVAIL THROUGH THE FIRST HALF OF THE
TAF PERIOD. SOME AFTERNOON CONVECTION IS EXPECTED OVER THE NC
MOUNTAINS...HOWEVER THIS ACTIVITY SHOULD STAY TO THE WEST OF KCLT.
WINDS FOR THE REMAINDER OF THE DAY WILL STAY LIGHT AND SOUTHERLY.
OTHERWISE...EXPECTING CLOUD COVER TO INCREASE THIS EVENING AS
EASTWARD MOVING UPPER TROUGH CONTINUE TO APPROACH. THUS...CARRIED
LOW END VFR CIGS THROUGH THE MORNING...THEN LOWERED TO MVFR BY 13Z
AS SHOWER AND THUNDERSTORM ACTIVITY WILL BEING TO INCREASE ACROSS
THE REGION.

ELSEWHERE...EXPECTING CONDITIONS TO STAY AT VFR LEVELS THROUGH THE
EVENING WITH THE ONLY EXCEPTION BEING AT KHKY AS CIGS LOOK TO DROP
JUST AT OR BELOW 3K FEET. BY DAYBREAK SATURDAY...EXPECTING FLIGHT
CONDITIONS TO LOWER FURTHER AT THE REMAINING SITES TO MVFR LEVELS AS
OVERALL COVERAGE OF SHOWERS AND OR THUNDERSTORMS INCREASES.

OUTLOOK...SHOWER AND THUNDERSTORM COVERAGE...AND ASSOCIATED
RESTRICTIONS...WILL GRADUALLY INCREASE SATURDAY THROUGH MONDAY. FAIR
WEATHER MAY RETURN BY TUESDAY.

CONFIDENCE TABLE...

21-03Z 03-09Z 09-15Z 15-21Z
KCLT HIGH 100% HIGH 100% MED 63% HIGH 81%
KGSP HIGH 85% HIGH 100% HIGH 82% HIGH 85%
KAVL LOW 57% LOW 56% MED 63% MED 63%
KHKY HIGH 100% HIGH 100% MED 77% MED 72%
KGMU HIGH 92% HIGH 100% MED 78% MED 77%
KAND HIGH 100% HIGH 100% MED 78% MED 72%

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-- End Changed Discussion --

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

$$
SYNOPSIS...LEV
NEAR TERM...CDG/MCAVOY
SHORT TERM...JDL
LONG TERM...LG
AVIATION...CDG

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