FXUS62 KGSP 261951
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
251 PM EST SAT DEC 26 2009
.SYNOPSIS...
A LARGE LOW PRESSURE SYSTEM SITTING OVER THE UPPER MIDWEST WILL
SLOWLY LIFT NORTHWARD THROUGH THE WEEKEND ALLOWING HIGH PRESSURE TO
BUILD INTO THE SOUTHEAST. HIGH PRESSURE WILL THEN BE THE DOMINANT
WEATHER FEATURE ACROSS THE EASTERN HALF OF THE COUNTRY THROUGH MID
WEEK.
&&
.NEAR TERM /THROUGH SUNDAY/...
STILL EXPECTING PLUME OF CONSIDERABLE HIGH CLOUDS TO TRANSLATE
DOWNSTREAM OF THE CWFA THIS EVENING...SETTING US UP FOR A CLEAR
AND SEASONABLY CHILLY NIGHT. LLVL RIDGING ATOP THE REGION SUNDAY
MORNING WILL GIVE WAY TO A PERIOD OF WEAK RETURN FLOW. MODEL
CROSSSECTIONS DEPICT SOME DEGREE OF LOW TO MID LVL CLOUD DEVELOPMENT
WITHIN THIS AFOREMENTIONED NEUTRAL TO WEAK UPGLIDE FLOW AS THE
DAY WEARS ON. A MOS BLEND STILL LOOKS GOOD FOR NEAR TO SLIGHTLY
ABOVE NORMAL MAXES.
&&
.SHORT TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
AS OF 205 PM SATURDAY...THE LARGE UPPER LOW AND OCCLUDED SFC LOW
ACROSS THE OH VALLEY WILL BEGIN TO SHIFT EAST AS DOWNSTREAM BLOCKING
WEAKENS SUN NIGHT. THIS WILL ALLOW A SPOKE OF VORT ENERGY TO SWING A
SHALLOW AND RELATIVELY WEAK SFC TROF ACROSS THE NC MTNS EARLY MON
AND CROSS EAST OF THE FA BY 00Z TUE. THE 12Z GFS IS A FASTER OUTLIER
FROM THE GGEM AND THE NAM...HOWEVER ONLY BY ABOUT 3 HRS AND NOT
ENOUGH TO GREATLY INFLUENCE THE TIMING OF THE SENSIBLE WX FCST.
GOOD AGREEMENT IS HAD IN AN OVERALL FLATTENING OF THE UPPER HEIGHTS
AND LITTLE IN THE WAY OF DEEP FORCING WITH THE ACUTELY NE/SW SLANTED
H5 TROF PRODUCING MODEST CHANNELED DPVA AT BEST. DROPPED SOUNDINGS
ACROSS THE NC/TN MTN BORDER SHOW SHALLOW MOISTURE WITHOUT A GOOD NW
COMPONENT SETTING UP UNTIL THE LLVL TROF AXIS SHIFTS EAST AFT 06Z.
UPSTREAM MOISTURE WILL BE MAINLY DYNAMICALLY MAINTAINED AND A BIT
SUSPECT AS NO GLAKES ENHANCEMENT WILL BE AVAILABLE. FROUDE NUMBERS
ACROSS SE/RN KY REMAIN GENERALLY UNDER 1.3 FOR THE EVENT AND TELL OF
WEAK LLVL INSTABILITY FOR UPSLOPE FLOW SNSH TO BE ENHANCED WITH.
SO...THE UPSHOT OF ALL THIS WILL BE TO LOWER POPS A BIT AND LOWER
QPF/SN AMOUNTS BY ABOUT A HALF INCH OR SO. STILL EXPECT THE NRN MTNS
AND SMOKIES TO RECEIVE AROUND 1.5 TO 2 INCHES...HOWEVER THE VALLEY
POPS HAVE BEEN REDUCED ENOUGH TO EXPECT ONLY A TRACE TO PERHAPS A
FEW TENTHS BY 15Z MON.
THE NEXT SMALL SCALE ARCTIC HIGH MOVES IN QUICKLY MON AND THE
AIRMASS MIX WILL KEEP MAX TEMPS A COUPLE CATS BELOW NORMAL. BELOW
FREEZING MINS FOR MON NIGHT ACROSS ALL ZONES AS THE SFC HIGH SETTLES
ACROSS THE MID ATL AND BEGINS TO WEDGE ACROSS THE AREA. TEMPS WILL
BE TRICKY FOR WED AS THE LLVL CAD WILL BE IN PLACE...HOWEVER IT WILL
BE WEAKLY SUPPORTED AND LITTLE AGEO CAA FLOW...ALL THE WHILE MAX
INSOLATION IS EXPECTED. FOR NOW WILL GO WITH NEAR NORMAL MAXES...BUT
AN EARLY ARRIVAL OF GOM CI/ACU COULD OFFSET THE HEATING POTENTIAL BY
SEVERAL DEGREES.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
AS OF 245 PM SATURDAY...THE SMALL SCALE RIDGE ACROSS THE SE REGION
WILL WEAKEN AS THE L/W UPPER FLOW BECOMES QUASI/ZONAL TO CYCLONIC
QUICKLY AFT 00Z THU. THE MODELS ARE COMING INTO SOMEWHAT OF AN
AGREEMENT WITH THE EVOLUTION OF THE UPPER CONFLUENT ZONE AND
ASSOCIATED SFC HIGH...BOTH THE GFS AND THE ECMWF CONTINUE TO MOVE
THIS ZONE OFF THE ATL...HOWEVER THE GFS IS MUCH FURTHER NORTH WITH
THE FORCING BY 12Z THU. THIS IS DUE TO THE VARYING IDEAS THESE
MODELS HAVE WITH THE HANDLING OF SPLIT FLOW PATTERN. THE ECMWF
PHASES THE POLAR VORTEX WITH THE SRN STREAM TROF BY 12Z THU AS IT IS
MUCH QUICKER EAST WITH THAT FEATURE. THE GFS...WHICH IS SUPPORTED
VERY WELL BY THE GGEM AND IT/S OWN ENS MEMBERS CLOSES OFF THE NRN
STREAM...WHILE MAINTAINING A RELATIVELY FLATTER SRN STREAM PATTERN.
FOR THIS FORECAST MORE WEIGHT WILL BE GIVEN TO THE GFS...AND THIS
WILL AFFECT THE AMOUNT CONFIDENCE OF QPF EXPECTED AND THE LLVL
THICKNESS SETUP. ALL THIS SAID...THE OVERALL CONFIDENCE IS A BIT
BELOW AVERAGE.
WITH THE RELATIVELY WEAKLY SUPPORTED SFC HIGH IN PLACE BEFORE THE
SRN STREAM LOW DEVELOPS AND MOVES ACROSS THE GOM COAST...THE LLVL
THICKNESS PATTERN SHOULD BE EASILY MODIFIED. WILL EXPECT A MIXED
P/TYPE SCENARIO ACROSS THE MTNS...PIEDMONT...AND THE ERN UPSTATE AFT
00Z THU WHEN THE MODERATE PRECIP INTERACTS WITH THE SOON TO BE
RETREATING WEDGE. NO SIGNIFICANT ICE/FROZEN ACCUMS OUTSIDE THE MTNS
ARE EXPECTED...WITH THE NC MTN VALLEYS HAVING THE BEST CHANCE OF
SEEING ANYTHING STICK. WILL COUNT ON THE MORE PROGRESSIVE SCENARIO
IN THE LATTER HALF OF THE FCST TO INSTIGATE CYCLOGENESIS OFF THE NC
COAST AND A CONTINUED NE TRACK OF THE LLVL SYSTEM. THERE COULD BE
SOME WRAP AROUND ISSUES...NOT DEPICTED BY THE GFS MASS FIELDS AND
ANOTHER BRIEF TASTE OF A WINTRY MIX IS POSSIBLE OUTSIDE THE MTNS
EARLY FRI. WITH THIS PATTERN...EXPECT MAX TEMPS ABOUT 5 DEGREES
BELOW NORMAL THU...AND A FEW DEGREES BELOW THAT FOR FRI AND SAT.
&&
.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
AT KCLT AND ELSEWHERE...HIGH CLOUD SHIELD WILL DIMINISH THIS EVENING
WITH CLEAR SKIES TONIGHT INTO SUNDAY MORNING. LIGHT WINDS ARE
EXPECTED ACRS THE REGION.
OUTLOOK...VFR CONDITIONS EXPECTED SUNDAY THRU THURSDAY. MOISTURE
AHEAD OF A WEAK COLD FRONT WILL RETURN TO THE AREA ON WEDNESDAY.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...PAT
NEAR TERM...CSH
SHORT TERM...SBK
LONG TERM...SBK
AVIATION...CSH
