FXUS62 KGSP 231136
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
636 AM EST WED DEC 23 2009

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN OVER THE AREA INTO THURSDAY. A STRONG LOW 
PRESSURE SYSTEM WILL TRACK THROUGH THE PLAINS STATES TO THE WESTERN 
GREAT LAKES...PUSHING A COLD FRONT THROUGH THE REGION ON FRIDAY. DRY 
HIGH PRESSURE WILL THEN RETURN OVER THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
OVERALL TODAY AND TONIGHT ARE EXPECTED TO BE QUIET AS THE MID AND 
UPPER LEVEL RIDGE SHARPENS UP AND TRANSLATES ACROSS THE FA. EXPECT 
CLOUDINESS CONSISTING OF GENERALLY HIGH LEVEL CIRRUS TO CONTINUE TO 
SPREAD EASTWARD OUT AHEAD OF THE APPROACHING COLD FRONT OVER THE MS 
VALLEY. AT THE SURFACE...LIGHT EASTERLY TO SOUTHEASTERLY FLOW WILL 
BECOME MORE NORTHEASTERLY OVERNIGHT AS THE SURFACE HIGH TO THE NORTH 
CONTINUES TO RIDGE DOWN THE EASTERN SEABOARD. ALL MODEL SOLUTIONS 
ARE IN GOOD AGREEMENT AND KEEP THE FA DRY THROUGH 12Z THURSDAY.

CONCERNING TEMPS...VALUES TODAY WILL BE TEMPERED A BIT BY THE 
CONSIDERABLE MID AND UPPER LEVEL CLOUDINESS. MODEL LOW LEVEL 
THICKNESSES SUPPORT LOW TO MID 50S OUTSIDE THE MOUNTAINS. CURRENTLY 
MET TEMPS ARE RUNNING A FEW DEGREES TOO WARM WHILE THE MAV IS MUCH 
MORE REFLECTIVE OF CURRENT CONDITIONS. THEREFORE...I BLENDED THE 
CURRENT FORECAST WITH THE MOST RECENT MAV GUIDANCE WHICH RESULTS IN 
MAX/S A COUPLE OF DEGREES BELOW FULL SUN THICKNESS VALUES. GENERALLY 
LOW 50S FOR THE NC PIEDMONT...MID 50S FOR NE GA AND THE 
UPSTATE...AND NEAR 50 IN THE MOUNTAIN VALLEYS.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
AS OF 300 AM WED...A VERY AMPLIFIED UPPER FLOW PATTERN WILL BE IN 
PLACE THU...WITH DEEP TROUGHING OVER THE PLAINS AND A STRONG RIDGE 
AXIS OVER THE ERN SEABOARD. THE SFC HIGH OVER THE NORTHEAST WILL BE 
IN A FAVORABLE POSITION FOR COLD AIR DAMMING TO DEVELOP THU...BUT 
PRECIPITATION WILL BE QUITE LIMITED AS DEEPER GULF MOISTURE IS SLOW 
TO REACH THE AREA FROM THE WEST. WILL THUS NOT SEVERELY CURTAIL MOS 
TEMPERATURES DESPITE THE SLOWLY DEVELOPING CAD. A SHARP WEST TO EAST 
POP GRADIENT WILL BE FEATURED LATE IN THE DAY.

AS LOW PRESSURE CONTINUES TO DEEPEN OVER THE MIDWEST...GOOD 
AGREEMENT IS INDICATED AMONG THE MODELS IN SENDING THE DEEPEST 
MOISTURE AND LIFT THROUGH THE FORECAST AREA THU NIGHT THROUGH FRI 
MORNING. THIS WILL RESULT IN MULTIPLE HAZARDS ARISING ACROSS THE 
FORECAST AREA...PROBABLY FOR A BRIEF PERIOD OF TIME.

FIRST...GOOD CONSENSUS IS DEVELOPING ON 850 MB FLOW OF 50 TO 60 KT 
DURING THE PEAK OF WARM ADVECTION THU NIGHT. A MOUNTAIN WIND 
ADVISORY COULD BE NEEDED. SECOND...THE DEVELOPING PRECIPITATION WILL 
ALLOW THE SURFACE BASED COLD LAYER TO DEEPEN THROUGH THU NIGHT TO 
PERMIT PRECIPITATION TYPES IN THE NRN MTNS AND FOOTHILLS TO CHANGE 
TO FREEZING RAIN. THE TROUBLING PART IS THAT THE HEAVIEST QPF 
CROSSING THE AREA EARLY FRI MORNING WILL COINCIDE WITH THE MOST 
FAVORABLE FREEZING RAIN PROFILES ALONG THE BLUE RIDGE. IT APPEARS 
MORE CERTAIN NOW THAT WE WILL SEE SOME ADVISORY CRITERIA ICING NORTH 
OF INTERSTATE 40 IN THE MTNS AND FOOTHILLS...WITH SOME DAMAGING ICE 
ACCUMULATIONS POSSIBLE NEAR THE NRN BLUE RIDGE. PER COORDINATION 
WITH OTHER FORECAST OFFICES...WILL MENTION THIS IN THE HWO FOR 
NOW...BUT WINTER STORM WATCH OR WINTER WEATHER ADVISORY PRODUCTS 
COULD BE NEEDED IN THE NEAR FUTURE FOR THU NIGHT AND FRI.

THIRD...LOW LEVEL CONVERGENCE WILL FOCUS IN THE SOUTHERN PIEDMONT 
CIRCA 12Z FRI. THE MODELS CONTINUE TO FEATURE LITTLE OR NO POSITIVE 
BUOYANCY AT THAT TIME...BUT LOW LEVEL HELICITY WILL BE TREMENDOUS. 
WITH GFS AND SREF MEAN SFC DEWPOINTS APPROACHING 50 DEGREES FROM SRN 
ELBERT TO GREENWOOD COUNTIES...THE POTENTIAL FOR SEVERE WEATHER 
ALONG A SHALLOW QUASI LINEAR CONVECTIVE SYSTEM EARLY FRI MORNING 
WILL HAVE TO BE CLOSELY MONITORED. WILL MENTION THIS THREAT IN THE 
HWO. WITH THIS SETUP...WE CAN SOMETIMES HAVE SEVERE WEATHER WITHOUT 
ANY ASSOCIATED THUNDER AND LIGHTNING. THE GREATER 
THREAT...HOWEVER...WILL BE TO THE SE EARLY FRI.

FINALLY...THE SYSTEM STILL LOOKS LIKE A VERY QUICK HIT ACROSS THE 
AREA. THIS WILL LIMIT QPF TO 1 TO 1.5 INCHES. HYDROLOGY CONCERNS 
WILL STILL NEED TO BE MONITORED...HOWEVER...GIVEN THE MELTING 
MOUNTAIN SNOWFALL.

RAPID DRYING IS INDICATED FROM THE SOUTHWEST AFTER 18Z FRIDAY...WITH 
THE DEEP LOW PRES SYSTEM TO THE NW BECOMING VERTICALLY STACKED ALONG 
THE SRN SHORES OF THE GREAT LAKES BY SAT. DRY WEATHER WILL RESULT 
WITH TEMPERATURES REBOUNDING TO NORMAL VALUES.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
AS OF 230 AM WEDNESDAY...THE MEDIUM RANGE IS STILL A RATHER LOW 
CONFIDENCE FCST AS MODELS ARE HAVING A TOUGH TIME WITH THE HANDLING 
OF A GREAT LAKES VORTEX...WHICH CONSENSUS HAS DRIFTING SLOWLY E/NEWD 
TOWARD THE CANADIAN MARITIMES BY LATE TUESDAY. THE LOW/S POSITION 
AND TRACK WILL KEEP THE FA UNDER CYCLONIC FLOW...WITH A SERIES OF 
WEAK-TO-MODERATE SURGES OF LLVL CAA (AS WELL AS PLENTY OF MOISTURE) 
IN GENERALLY WLY TO NWLY FLOW. MODELS SOMEWHAT AGREE ON LATE SUNDAY 
NIGHT THRU EARLY MON AFTN AS THE HIGHEST CHC OF SOME NW FLOW SNOW 
ACTIVITY. HOWEVER...EVEN AT ITS BEST...THE ORTHOGONAL COMPONENT OF 
THE H85 FLOW NEVER GETS MORE THAN 25 KTS...AND MOISTURE TRENDS 
SHALLOWER BY MON EVE IN PRETTY MUCH ALL THE GUIDANCE. SO I FEEL 
TIMING COULD PERHAPS BE NARROWED DOWN ENUF SUCH THAT I HAVE BUMPED 
POP UP TO LOW-END CHC ALONG THE TN/NC BORDER FROM 06Z-18Z MON. 
OTHERWISE...LTL TO NO CHANGE WAS MADE TO THE EXTENDED THIS MORNING. 
TEMPS WILL BE BELOW NORMAL...WITH VARYING AMOUNTS OF CLOUDINESS EAST 
OF THE MTNS.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...THERE IS NO SIGNIFICANT WEATHER EXPECTED FOR THE TAF 
PERIOD AND THE FORECAST PRIMARILY BOILS DOWN TO A WIND DIRECTION 
FORECAST. THIN CIRRUS WILL GRADUALLY THICKEN AND LOWER TO 
ALTOSTRATUS BKN/OVC BY THE AFTERNOON. WINDS WILL START OUT CALM OR 
LGT NLY OR NELY...AND THEN SOUTH OF EASTERLY DURING THE AFTERNOON. 
TAKING A BLEND OF THE NAM AND THE GFS YIELDS WINDS FROM AROUND 110 
AFTER 18Z BEFORE THEY BECOME SOLID NORTHEASTERLY BY THE EVENING.

ELSEWHERE...OTHER THAN SOME MVFR BR POSSIBLE AT KAVL AND 
KHKY...EXPECT VFR CONDITIONS. WINDS WILL BE LIGHT TODAY...MAINLY 
EASTERLY AND SOUTHEASTERLY DURING THE AFTERNOON. FLOW THEN TURNS 
MORE NORTHEASTERLY IN THE EVENING AS HIGH PRESSURE CONTINUES TO 
RIDGE DOWN THE EASTERN SEABOARD. EXPECT CIRRUS TO GRADUALLY LOWER TO 
A 12-15 KFT AS DECK IN THE AFTERNOON...BUT NO RESTRICTIONS EXPECTED. 
KAVL MAY HAVE SOME VSBY RESTRICTIONS LATE TONIGHT (BUT LESS LIKELY 
THAN PREVIOUS NIGHTS...AS MID LVL CLOUDINESS INCREASES...LIMITING 
RADIATIONAL COOLING). 

OUTLOOK...A STORM WILL APPROACH FROM THE WEST LATE THURSDAY 
PRODUCING WIDESPREAD MVFR/IFR RESTRICTIONS. A BRIEF PERIOD OF WINTRY 
WEATHER WILL BE POSSIBLE THURSDAY NIGHT INTO FRI BETWEEN KAVL AND 
KHKY...MAINLY AT THE ONSET OF PRECIP. CONDITIONS SHOULD IMPROVE FRI 
NIGHT-SAT AS DRY AIR COMES IN FROM THE W.

&&

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

&&

$$
SYNOPSIS...ARK
NEAR TERM...BSH
SHORT TERM...HG
LONG TERM...ARK/RWH
AVIATION...ARK/BSH