FXUS62 KGSP 071121
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
621 AM EST MON DEC 7 2009
.SYNOPSIS...
HIGH PRESSURE WILL RIDGE DOWN THE EASTERN SEABOARD LATE TONIGHT AND
EARLY TUESDAY AS MOISTURE SPREADS ACROSS THE SOUTHEAST STATES FROM
THE WEST. A STRONG STORM SYSTEM WILL LIFT NORTH OF THE AREA TUESDAY
NIGHT...PUSHING A COLD FRONT ACROSS THE SOUTHERN APPALACHIANS ON
WEDNESDAY. THE FRONT WILL BE FOLLOWED BY COOL HIGH PRESSURE FOR THE
END OF THE WEEK.
&&
.NEAR TERM /THROUGH TONIGHT/...
RATHER SHALLOW FRONTAL ZONE MOISTURE STILL EXPECTED TO ENCROACH UPON
THE WESTERN CWFA THIS AFTERNOON...PERHAPS RESULTING IN A FEW SHOWERS
ACROSS THE NC MTNS. OTHERWISE...CLOUD COVER FCST FOR TODAY WILL
FEATURE A PERIOD OF PIEDMONT STRATOCU THIS MORNING...AND THEN AN
INCREASE IN MAINLY MID-LVL CLOUDS FROM THE WEST THIS AFTERNOON.
AS CHILLY AS SUNDAY/S MAXES TURNED OUT...EVEN THE COOLER MET
GUIDANCE WAS TOO WARM. WILL PLAN ON MAKING LITTLE MORE THAN TWEAKS
TO INHERITED MAXES FOR THIS AFTERNOON...A GENERAL UNDERCUT OF MOS.
A GRADUAL MOISTENING OF DEVELOPING WAA PATTERN ON TAP FOR TONIGHT.
USING A MODEL AVERAGE WITH RESPECT TO ANY LATE NIGHT RESPONSE...WILL
INTRODUCE MEASURABLE LATE NITE LIGHT PCPN CHANCES TO THE SW NC
MTNS.
&&
.SHORT TERM /TUESDAY THROUGH THURSDAY/...
AS OF 240 AM MONDAY...A POWERFUL UPPER LOW WILL DROP ACROSS NRN
CA AND NV TODAY. THE LOW WILL THEN QUICKLY EJECT TO THE ENE...TO A
POSITION OVER WRN NY STATE BY WED EVENING. THE ASSOCIATED SFC LOW
WILL DEEPEN RAPIDLY...TO ABOUT 975 MB BY THE TIME IT MOVES INTO THE
CENTRAL GREAT LAKES STATES BY THE END OF THE DAY ON WED. A STRONG
WIND FIELD WILL DEVELOP ON THE SOUTHERN QUADRANT OF THE
LOW...RESULTING IN THE RAPID DEVELOPMENT OF A LARGE AREA OF PCPN TUE
AND TUE NIGHT. THE NAM AND GFS GENERATE TWO AREAS OF HEAVIER PCPN.
ONE WILL FORM CLOSER TO THE SFC CYCLONE WHERE THERE WILL BE STRONG
LLVL CONVERGENCE. THIS WILL BE WELL WEST OF THE MTNS...OVER MIDDLE
TN...EXTENDING NORTHWARD INTO CENTRAL KY. THE SECOND AREA DEVELOPS
OVER NRN AL..GA..AND ACROSS THE SRN APPALACHIANS. THIS IS IN AN AREA
OF HIGHER PW/S AND CONVERGENCE INTO AN AREA OF WEAKENING COLD AIR
DAMMING.
THE LATEST DAY 2 HPC QPF FORECAST HAS THE AXIS OF HEAVIEST RAIN A
LITTLE SOUTH OF THE MTNS...OVER THE NRN UPSTATE AND NE GA. I HAVE
FOLLOWED THIS SOLUTION CLOSELY. THERE WILL CERTAINLY BE A LARGE AREA
OF RAIN THAT MOVES INTO THE MTNS LATE TUE. HOWEVER...I SUSPECT THAT
THE HEAVIEST RAIN WILL STAY WEST OF THE MTNS. THE LATEST ECMWF IS
SHOWING THIS RATHER DRAMATICALLY WITH IT/S HEAVIEST RAIN OVER MIDDLE
TN...AND QUITE A BIT LESS OVER THE WRN CAROLINAS. THE H5 TROUGH IS
STRONG BUT DOES NOT EXTEND VERY FAR TO THE SOUTH. WITH UNFAVORABLE
LAPSE RATES OVER THE DEEP SOUTH...I CAN SEE A LOT MORE PCPN
DEVELOPING CLOSER TO THE SFC LOW. AGAIN...I STAYED CLOSE TO
HPC...WHICH IS A LITTLE LIGHTER THAN OUR PREVIOUS FORECAST...BUT
THERE IS STILL UNCERTAINTY ON WHERE THE HEAVIEST RAIN WILL FALL.
ALSO...TOTALS FROM THIS EVENT LOOK TO BE MORE IN THE 1 TO 2 INCH
RANGE. THIS WILL STILL BE AN ISSUE OWING TO THE HIGH RIVER...STREAM
AND RESERVOIR LEVELS...BUT WE SHOULDN/T SEE AS MUCH PCPN AS WITH THE
EVENT A FEW DAYS AGO.
THERE IS AN AREA OF ELEVATED INSTABILITY THAT MOVES INTO THE REGION
TUE NIGHT...AND I/VE ADDED THUNDER TO MOST OF THE ZONES. THIS
INSTABILITY WEAKENS CONSIDERABLY AS IT TRANSLATES ACROSS THE
MTNS...ANOTHER SIGN THAT WE PROBABLY WON/T REALIZE VERY HIGH HOURLY
PCPN RATES TUE NIGHT...EVEN THOUGH THERE MAY BE A RUMBLE OR TWO OF
THUNDER. THE LLVL JET WILL BE ON THE ORDER OF 60 TO 65 KTS TUE
NIGHT. AS THIS WILL BE A WARM ADVECTION PATTERN...THE WINDS SHOULD
NOT MIX DOWN...THOUGH THE HIGHER ELEVATIONS OF THE MTNS WILL
EXPERIENCE A PERIOD OF VERY WINDY CONDITIONS. IN FACT...GUSTS OF 50
KTS ARE A GOOD BET ABOVE 3500 FEET. WITH THE WET GROUND...THIS
SHOULD KNOCK DOWN SEVERAL TREES...AND A WIND ADVISORY WILL ALMOST
CERTAINLY BE NEEDED...POSSIBLY EVEN A HIGH WIND WARNING.
PCPN WILL MOVE EAST OF THE REGION ON WED. WINDY CONDITIONS WILL
CONTINUE THROUGH THE DAY. WED NIGHT A FEW SHSN ARE POSSIBLE ALONG
THE TN LINE...BUT THE MOISTURE IS SHALLOW AND THE FLOW TOO
SOUTHWESTERLY TO AMOUNT TO MUCH. IT WILL BE FAIR BUT COOL ON THU.
&&
.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
AS OF 235 AM MONDAY...STARTING AT 00Z FRIDAY...THE MEDIUM RANGE
MODELS AGREE ON THE BEGINNING OF THIS PERIOD BEING DRY WITH HIGH
PRESSURE CENTERED OVER THE MISSISSIPPI VALLEY AND MOVING EAST. THE
GFS THEN MOVES THE NEXT SYSTEM MUCH FASTER FROM TEXAS THAN THE
ECMWF. CLOUDS WILL BE INCREASING FROM THE WEST ON FRIDAY. STILL
ASSUMING THAT THE BEST SOLUTION IS A BLEND OF THE GFS/ECMWF...I
BELIEVE THE WAY TO GO AT THIS POINT IS TO MAKE ONLY MARGINAL CHANGES
TO THE PREVIOUS FORECAST. AT 12Z FRIDAY...THE GFS NOW HAS LIGHT
PRECIP CROSSING PARTS OF ALABAMA WHILE THE ECMWF HAS HIGH PRESSURE
CENTERED OVER THE SMOKIES. BY 12Z SATURDAY...THE GFS HAS THE LOW
MOVING EAST OF THE SOUTH CAROLINA COAST WITH MOISTURE DECREASING
OVER OUR AREA WHILE THE ECMWF HAS THE LOW SOUTH OF LOUISIANA. THE
ONLY THING THEY AGREE ON IS THE TRACK BUT THE TIMING IS MAJOR
DIFFERENT. THE ECMWF ALSO HAS THE EXITING HIGH STUBBORNLY HANGING
ONTO THE MID ATLANTIC WHICH EXPLAINS THE TIMING DIFFERENCE WHILE THE
GFS HAS EXITING HIGH MOVING RAPIDLY OVER ATLANTIC WHILE PLAINS HIGH
RIDGES SOUTHEAST BRING COLDER AIR FROM NORTH. THE ECMWF SOLUTION
COULD BRING MIXED WINTRY PRECIP WITH SOME FREEZING RAIN...SLEET AND
SNOW. THE GFS WOULD BRING MOSTLY JUST SNOW AND RAIN. TEMPERATURES
WILL BE BELOW NORMAL. BOTH MODELS HAVE SOME DEGREE OF A CLASSIC
WEDGE PATTERN DEVELOPING SUNDAY INTO EARLY NEXT WEEK WITH THE GFS
BEING THE MOST AGGRESSIVE IN THIS SOLUTION. THE GFS ALSO HAS
MOISTURE WRAPPING IN FROM THE ATLANTIC NEXT MONDAY.
&&
.AVIATION /12Z MONDAY THROUGH FRIDAY/...
AT KCLT...FETCH OF ATLANTIC MOISTURE IS FCST TO WRAP BACK INTO
THE EASTERN CAROLINAS BY THIS AFTERNOON...ALLOWING LVFR CIGS
TO SCATTERED OUT. OTHERWISE...LIGHT NE WINDS THIS MORNING BECOMING
LIGHT SW BY THIS AFTERNOON...AS AC CIGS ENCROACHMENT FROM THE WEST
THIS EVENING. STRATOCU REDEVELOPMENT IS POSSIBLE DURING THE LATE
NIGHT HOURS.
ELSEWHERE...FLIGHT RESTRICTIONS LIMITED TO KHKY EARLY THIS MORNING
WILL QUICKLY IMPROVED AS STRATOCU ENCROACHES...OTHERWISE...
PIEDMONT LVFR STRATOCU CIGS WILL SCATTER OUT BY MIDDAY. INCREASING
ALTOCU THIS EVENING WILL BE FOLLOWED BY LOWER CLOUDS OVERNIGHT
ACRS THE WESTERN CWFA WITH LIGHT RAIN DURING THE PRE-DAWN HOURS
PSBL IN THE NC MTNS.
OUTLOOK...RAIN AND WIDESPREAD LOW CIGS AND VSBY ARE EXPECTED TUE
THROUGH EARLY WED AS A LOW PRESSURE SYSTEM FROM THE WEST BRINGS
ABUNDANT MOISTURE INTO THE AREA. DRYING IS EXPECTED MID TO LATE WEEK.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...DEO
NEAR TERM...CSH
SHORT TERM...MCAVOY
LONG TERM...DEO
AVIATION...CSH
