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-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --000 FXUS62 KGSP 220029 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 729 PM EST SAT NOV 21 2009 .SYNOPSIS... HIGH PRESSURE OVER THE REGION WILL SHIFT NORTH OVER THE WEEKEND. THIS WILL ALLOW A LOW PRESSURE SYSTEM TO MOVE EAST ALONG THE GULF COAST THEN NORTH ALONG THE CAROLINA COAST SUNDAY THROUGH MONDAY. THE LOW IS EXPECTED TO REACH THE NEW ENGLAND COAST BY TUESDAY AS WEAK HIGH PRESSURE REMAINS OVER THE SOUTHEAST STATES. ANOTHER COLD FRONT OR COASTAL LOW COULD MOVE INTO THE AREA BY THE MIDDLE OF NEXT WEEK. && .NEAR TERM /THROUGH SUNDAY/...-- Changed Discussion --SATELLITE IMAGERY SHOWS ONLY HIGH THIN CLOUDS ACROSS THE WESTERN CAROLINAS AT SUNSET. THIS HAS ALLOWED TEMPS TO DROP QUICKER THAN EXPECTED. WILL TAKE THIS OPPORTUNITY TO ADJUST TEMP TREND...BUT MIN TEMP STILL LOOKS OKAY. HAVE ALSO DELAYED THE CLOUD UP UNTIL LATER TONIGHT AS WELL. HAVE ALSO ADJUSTED POP FOR SUNDAY BASED ON THE 15Z SREF BECAUSE IT WAS PREFERRED BY THE PREVIOUS SHIFT. CONFLUENT FLOW OFF THE NEW ENGLAND COAST WILL GRADUALLY STRENGTHEN SFC HIGH PRESSURE OVER THE MID ATLANTIC STATES THROUGH SUNDAY. THE MORNING UPPER AIR SHOWED VERY DRY AIR DOWN ALONG THE GULF COAST. FOR EXAMPLE...THE TALLAHASSEE RAOB HAD A 40 DEGREE DEWPOINT DEPRESSION AT 850 MB. WITH THIS MUCH DRY AIR TO THE SOUTH...AND WITH A DEVELOPING CLASSICAL COLD AIR DAMMING EVENT...IT/S NOT SURPRISING THAT THE MODELS HAVE BEEN DELAYING THE ONSET OF PCPN OVER THE PAST SEVERAL RUNS. AT LEAST THE GFS HAS TONED DOWN THE POT VORT MAXES AND HEAVY PCPN THAT IT HAD BEEN DRIVING ACROSS THE HEART OF THE WEDGE RIDGE. THIS SEEMS MORE REALISTIC AS QPF SHOULD BE FAIRLY LIGHT WITH THE LLVL DRY AIR AND THE WEAKENING SRN STREAM SYSTEM. THE BEST CHANCES FOR HEAVY RAIN WILL BE ALONG THE COASTAL FRONT...WELL TO OUR SOUTH. OVERALL...THE SREF SEEMS TO HAVE DONE THE BEST JOB OF HANDLING THE EVOLUTION OF THE GULF COAST LOW AND PCPN DISTRIBUTION SO FAR. I/VE FOLLOWED IT FAIRLY CLOSELY FOR THE TIMING OF PCPN. THIS MEANS A DRY FORECAST TONIGHT. PCPN SHOULD OVERSPREAD THE REGION FROM THE SOUTHWEST ON SUNDAY...THOUGH I DON/T SEE ANYTHING FALLING NORTH OF GREENVILLE UNTIL THE AFTERNOON HOURS. I RAISED MAX TEMPS A COUPLE CATEGORIES OVER THE NE ZONES WHERE THINNER CLOUD COVER EARLY IN THE DAY WILL RESULT IN A LITTLE MORE WARMING THAN ORIGINALLY EXPECTED. I FOLLOWED A MET/MAV BLEND AND WE MATCH UP WELL WITH THE NEIGHBORS.-- End Changed Discussion --&& .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... AS OF 130 PM SATURDAY...NOT THAT THERE IS A GREAT DEAL OF CONFIDENCE WITH REGARDS TO THE SPECIFICS OF THE SUNDAY NIGHT FCST...BUT LIKELY SOME DEGREE OF DEEP RH AND ESE FLOW ABOVE LINGERING WEDGE WILL REMAIN ALL NIGHT. SENSIBLE WX IS STILL EXPECTED TO BE DAMP WITH RAINY AND DRIZZLY PERIODS...ALTHOUGH PCPN TOTALS WILL BE MODERATE AT WORST. CONFIDENCE INCREASING THAT DAMMING REGIME WILL REMAIN THRU MONDAY...ALTHOUGH FORCING FOR ADDITIONAL PCPN WILL WANE...EVENTUALLY JUST BEING FORCED BY SOME DEGREE OF WAA/EASTERLY FLOW JUST ABV SFC. EVEN THE MILDER 12 UTC MET NUMBERS...WHICH WILL PROBABLY BE TOO WARM ANYWAY...SUPPORT NOTABLE LOWERING OF GOING MAX TEMPS. GIVEN THE WEAKENING OF THE LLVL FLOW MONDAY NIGHT AND RESIDUAL WEAK SFC RIDGING...THERE SEEMS TO BE LITTLE HOPE OF SCOURING...SO WILL PLAN ON LEAVING OVC CONDS WITH SPOTTY AREAS OF LIGHT RAIN/DRIZZLE... ESPECIALLY ALONG AND EAST OF THE ESCARPMENT WHERE WEAK LLVL EASTERLY FLOW WILL CONTINUE TO LIFT SHALLOW MOISTURE. && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 145 PM SATURDAY...NOT MUCH AGREEMENT IS SEEN IN THE OP MODELS WITH RESPECT TO AMOUNT OF DEEPENING OF THE MID WEEK CUT OFF LOW AND THE LEVEL OF MOISTURE AVAILABLE FOR THE OCCLUDED FRONT TO WORK WITH ONCE IT REACHES THE CWFA WED MORNING. EVEN LESS AGREEMENT IS SEEN BETWEEN THE GFS AND THE ECMWF ON THU/FRI WITH THE POLAR VORTEX REINFORCING THE GLAKES LOW AND THE EVENTUAL TRACK AND SPEED OF THE LARGE SCALE PATTERN. THE GFS H5 ENS MEMBERS SHOW THE HIGHEST SPREAD EARLY FRI MORNING WITH ABOUT 8 DM OF UNCERTAINTY ASSOCIATED WITH THE HEIGHT FIELD...LENDING LOW CONFIDENCE TOWARD THE SETUP FOR A POSSIBLE MINIMAL NW FLOW EVENT. NOT MANY CHANGES HAVE BEN MADE TO THE GOING FORECAST WITH LITTLE CONFIDENCE HAD BOTH IN THE OP MODELS AND HPC GUIDANCE. SOME DECENT AGREEMENT IS SEEN TUE WITH THE SLOWER BREAKDOWN OF THE SFC WEDGE. MODEL SOUNDINGS INDICATE RATHER THICK STRATUS HANGING ON THROUGHOUT THE DAY AND VERY LOW WINDS IN THE BL. SO...MAX TEMP GUIDANCE HAS BEEN CUT BACK A CAT OR SO OUTSIDE THE MTNS TO ACCOUNT FOR THIS POSSIBLE SCENARIO. POPS STILL SEEM SUSPECT WITH LITTLE IN THE WAY OF ORGANIZED FLOW INTERACTING OVER THE WEDGE...SO THE LINGERING SLIGHT CHANCES WERE CHANGED LITTLE. THE GFS IS MORE AGGRESSIVE IN BRINGING A MOIST OCCLUDED FRONT TO THE MTNS BY 12Z WED THAN THE ECMWF. THE EC DOES EVENTUALLY BRING THE FRONT TO THE AREA LATE IN THE DAY...BUT BOTH MODELS CUT OFF THE GOM MOISTURE FLUX WITH LLVL RIDGING FROM THE WEST. WITH THE MAIN LARGE SCALE FORCING SHIFTED NORTH...WILL COUNT ON VERY LITTLE IMPACT AS FAR A PRECIP COVERAGE GOES. FOR NOW...SLIGHT CHANCES WILL REMAIN...BUT THIS COULD BE INCREASED ONCE BETTER DATA IS GLEANED ON THIS SYSTEM. THE NEXT SYSTEM TO THINK ABOUT WILL BE THU/FRI...AS THE GFS INSISTS ON A MOIST NW FLOW EVENT...YET THE EC REMAINS DRY AND LOW KEY ON THE KINEMATIC SETUP. THE GFS AS MENTIONED EARLIER IS BRINGING IN A MUCH STRONGER REINFORCING POLAR VORTEX INTO THE GLAKES LOW...ABOUT TWICE AS STRONG PVU/WISE THAN THE ECMWF. THIS SEEMS A LITTLE TOO STRONG FOR THIS TIME OF YEAR...AND FOR NOW WILL SIDE WITH THE MORE CONSERVATIVE ECMWF ON THIS ONE. THUS...MINIMAL POPS AND AN ALL RAIN P/TYPE ARE ADVERTISED FOR THAT PERIOD. OTHER THAN THE LOWER THAN NORMAL POPS EXPECTED TUE....MAX TEMPS SHOULD REBOUND RATHER NICELY WED THROUGH FRI. INCREASED INSOLATION AND A WAA FLOW WILL ENABLE MAXES AT OR PERHAPS A COUPLE DEGREES ABOVE NORMAL. THE NC MTNS WILL BE TRICKERY FRI...AS IT/S PROBABLE THAT CAA ASSOCIATED WITH THE PASSING VORTEX TO THE NORTH LOWERS TEMPS THROUGHOUT THE DAY. YET FOR NOW...WILL ONLY GO A COUPLE DEGREES BELOW NORMAL WITH SO MUCH UNCERTAINTY AND POOR CONTINUITY DISPLAYED BY THE GUIDANCE. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/...-- Changed Discussion --AT KCLT AND KHKY...EXPECT VFR CONDITIONS TO PREVAIL THROUGH MOST... IF NOT ALL...THE TAF PERIOD. MODEL GUIDANCE HAS BEEN SLOW TO DEVELOP THE LOW CLOUDS AND PRECIP ASSOCIATED WITH THE APPROACHING LOW. AT THIS POINT...IT APPEARS THAT MOISTURE WILL GRADUALLY DEEPEN FROM THE TOP DOWN ON SUNDAY...SUCH THAT A MID LEVEL CEILING SHOULD BE PRESENT SUNDAY MORNING...BUT THAT LOW CLOUDS WILL NOT ARRIVE UNTIL THE EARLY EVENING. ALTHOUGH IT IS CERTAINLY POSSIBLE THAT MVFR CONDITIONS WILL DEVELOP BEFORE THE END OF THE TAF PERIOD...IT REMAINS MORE LIKELY THAT THEY WILL HOLD OFF UNTIL RIGHT AROUND SUNSET SUNDAY...SO RATHER THAN INCLUDE ANOTHER FM GROUP I DECIDED TO LEAVE IT OUT FOR THIS ISSUANCE. WINDS SHOULD REMAIN NORTHEAST THROUGH THE PERIOD. ELSEWHERE...THIS WILL NOT BE THE CASE. ENOUGH LOW LEVEL UPGLIDE SHOULD DEVELOP IN THE AFTERNOON TO FORCE THE DEVELOPMENT OF LIGHT PRECIP. ONCE THAT HAPPENS...SOME TIME AFTER 18Z...THE PRECIP SHOULD BRING CLOUD BASES DOWN INTO THE MVFR RANGE. RAIN SHOULD BE LIGHT ENOUGH INITIALLY SO AS TO NOT REDUCE THE VISIBILITY IN MOST LOCATIONS...THE EXCEPTION BEING KAND WHERE MORE SIGNIFICANT PRECIP SHOULD ARRIVE FIRST. STILL THINK IFR CONDITIONS WILL HOLD OFF UNTIL AFTER THE END OF THE TAF PERIOD. OUTLOOK...CEILING AND VISIBILITY SHOULD COME CRASHING DOWN TO IFR AND LIFR SUNDAY NIGHT AS MAIN PRECIP AREA MOVES THROUGH. ONCE ESTABLISHED...THE COLD AIR DAMMING WEDGE WILL PERSIST THROUGH MONDAY NIGHT WITH WIDESPREAD IFR CONDITIONS. THE MODEL GUIDANCE SHOWS IMPROVEMENT TUESDAY BUT MOST LIKELY AT BEST MVFR SHOULD BE EXPECTED UNTIL WEDNESDAY.-- End Changed Discussion --&& .GSP WATCHES/WARNINGS/ADVISORIES... GA...NONE. NC...NONE. SC...NONE. && $$ SYNOPSIS...PAT NEAR TERM...MCAVOY/PM SHORT TERM...CSH LONG TERM...SBK AVIATION...PM
