HAMweather.com Area Forecast Discussion for County Warning Area GSP

Thu, 16 Feb 2012 12:20:27 GMT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
645 AM EST THU FEB 16 2012

.SYNOPSIS...
A COLD FRONT WILL SWEEP ACROSS THE FORECAST AREA TODAY RESULTING IN 
UNSETTLED WEATHER WITH COOLER TEMPERATURES. HIGH PRESSURE WILL 
RETURN TO THE REGION ON FRIDAY AND LINGER THROUGH THE EARLY PART OF 
THE WEEKEND. LOW PRESSURE WILL THEN MOVE NORTHEAST FROM THE GULF TO 
ALONG THE CAROLINA COAST ON SUNDAY FOR ANOTHER ROUND OF UNSETTLED 
WEATHER AND COOLER TEMPERATURES.

.NEAR TERM /THROUGH TONIGHT/...
AT 630 AM...PRE FRONTAL BAND OF RAIN HAS PUSHED ACROSS THE MTNS AND 
UPPER SAVANNAH RIVER VALLEY. RAINFALL RATES HAS REMAINED 
LIGHT...WITH ONLY A FEW POCKETS OF MODERATE RAINFALL. ANOTHER BAND 
OF SHRA IS EXPECTED TO ARRIVE LATER THIS MORNING...ASSOCIATED WITH 
THE COLD FRONT PASSAGE. BASED ON RADAR TRENDS AND GUIDANCE I WILL 
REDUCE QPF...BUT WILL MAINTAIN HIGH POPS THIS MORNING. 

AT 245 AM...IR SATELLITE SHOWS AN EXPANSIVE AREA OF -45 TO -58C CLOUD 
TOP TEMPERATURES FROM THE NRN GULF COAST NORTH TO WEST VIRGINIA. 
RADAR COMPOSITE SHOWS A CONTINUOUS BAND OF LIGHT TO MODERATE 
PRECIPITATION UNDER THE COLD CLOUDS...WITH POCKETS OF HEAVY RAIN 
SOUTH OF I-20 IN AL. NEAR TERM MODELS INDICATE THAT H7 OMEGA AND 
VERTICAL VELOCITY ASSOCIATED WITH THE UPSTREAM PRECIPITATION WILL 
REACH THE NC MTNS AROUND 12Z. AT LOWER LEVELS...ISENTROPIC LIFT 
ALONG A WARM FRONT AND UPSLOPE FLOW WILL DEVELOP OVER THE UPPER 
SAVANNAH RIVER VALLEY AND MTNS BETWEEN 9Z TO 12Z. RAIN COVERAGE 
SHOULD PEAK ACROSS THE SOUTHERN APPALACHIAN AREA BETWEEN 12Z TO 18Z 
AS SFC COLD AND WARM FRONT INTERSECT WITH BROAD QG FORCING. POPS 
WILL PEAK AROUND 100 PERCENT. AFTERNOON POPS WILL BEGIN TO QUICKLY 
FALL FROM THE WEST IN THE WAKE OF THE COLD FRONT. BY 0Z 
FRIDAY...ONLY THE NRN MTNS WILL FEATURE CHC POPS FOR UPSLOPE 
SHRA...ELSEWHERE CONDITIONS ARE DRY. STORM TOTAL QPF MAY RANGE FROM 
THREE QUARTERS OF AN INCH ALONG THE I-85 CORRIDOR TO SLIGHTLY ABOVE 
A HALF INCH OVER THE NRN MTNS.

THICK CLOUD COVER AND WIDESPREAD MORNING RAIN WILL KEEP DAYTIME 
WARMING LIMITED TO AROUND 10 DEGREES. HOWEVER...HIGHS WILL REACH 
ABOVE NORMAL WITH MID TO UPPER 50S ACROSS MOST OF THE CWA...LATE DAY 
CLEARING MAY ALLOW LOW 60S NEAR THE GA STATE LINE.  

SFC HIGH PRESSURE WILL SLOWLY BUILD OVER THE FORECAST AREA 
OVERNIGHT...BUT CENTER WILL REMAIN OVER THE MID MISSISSIPPI RIVER 
VALLEY. SLOW CAA MAY ONLY COOL H85 TEMPS A COUPLE OF 
DEGREES...YIELDING 10C OVER ELBERT TO GREENWOOD TO 6C OVER THE NRN 
MTNS. MIN TEMPERATURES ARE FORECAST TO RANGE FROM MID 30S ACROSS THE 
NRN MTNS TO MID TO LOW 40S ACROSS THE I-85 CORRIDOR. CLEARING 
SKY...LIGHT WINDS...AND SATURATED SOIL WILL FAVOR THE DEVELOP OF FOG 
LATE TONIGHT. IF SFC WINDS BECOME CALM...THEN PATCHY TO AREAS OF 
DENSE FOG IS POSSIBLE.

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 240 AM THURSDAY...DRY SFC HIGH PRESSURE SLIDES INTO THE AREA 
FRIDAY AND FRIDAY NIGHT UNDER ZONAL FLOW. HIGHS FRIDAY WILL BE 
AROUND 10 DEGREES ABOVE NORMAL. CLOUDS DO INCREASE FRI NITE HELPING 
KEEP LOWS 5 TO 10 DEGREES ABOVE NORMAL.

MEANWHILE...A CLOSED LOW PRESSURE SYSTEM OVER THE BAJA REGION WILL 
BEGIN TO OPEN AND LIFT EWD ACROSS TX FRI NIGHT THROUGH SAT. THE GFS 
CONTINUES TO BE THE FASTEST IN BRINGING DEEP MOISTURE BACK INTO THE 
REGION SAT AHEAD OF THIS SYSTEM. THIS IS MAINLY DUE TO FASTER 
PHASING WITH THE RAPID NRN STREAM OVER THE CENTRAL CONUS FRI NIGHT. 
THE NAM IS ON THE SLOW END OF THE SPECTRUM...WITH THE LATEST ECMWF 
AND SREF IN THE MIDDLE. HAVE GONE WITH A MIDDLE OF THE ROAD BLEND 
FOR TIMING. THIS BRINGS MOIST UPGLIDE AND LIGHT PRECIP TO THE UPPER 
SAV RIVER VALLEY DURING THE MORNING...WITH SLIGHT CHC PRECIP UP THE 
LENGTH OF THE ESCARPMENT. LIKELY POP THEN DEVELOPS ACROSS MOST OF THE 
SRN AND WRN CWFA BY AFTERNOON. HAVE GONE ON THE COOL SIDE OF GUIDANCE 
AS COLD AIR DAMMING DEVELOPS AS PRECIP MOVES IN.

WIDESPREAD PRECIP SPREADS ACROSS THE ENTIRE CWFA SAT NITE AS GOOD 
FORCING AND THE MAIN SFC LOW MOVES IN. A DISCREPANCY STILL REMAINS 
IN PRECIP TIMING DURING THIS PERIOD...SO MIDDLE OF THE ROAD TIMING 
CONTINUES. THE GFS IS THE FARTHEST NORTH WITH THE SFC LOW TAKING IT 
ALONG AN I-85 TRACK. THE REST OF THE GUIDANCE IS NEAR I-20. EVEN 
WITH THE GFS FARTHER NORTH...IT IS SIMILAR TO THE REST OF THE 
GUIDANCE IN KEEPING THE CAD IN PLACE. THIS KEEPS INSTABILITY 
ESSENTIALLY ZERO EVEN WITH STRONG SHEAR DEVELOPING. THEREFORE...HAVE 
KEPT PRECIP AS STRATIFORM WITH NO TS MENTION. THERE IS POTENTIAL FOR 
THE PRECIP TO MIX WITH/CHANGE OVER TO SNOW/FREEZING RAIN. THE GFS IS 
THE WARMEST WITH ALL RAIN WHILE THE NAM SHOWS A DEEP NEAR FREEZING 
ISOTHERMAL LAYER DEVELOPING AT TNB BUT REMAINING WARM AT AVL. THE 
SREF PLUME DIAGRAMS SHOW ALL THREE P-TYPES AS BOTH SITES. 
THEREFORE...HAVE GONE WITH PTYPE DETERMINED BY SFC WET BULB AFTER 
MIDNIGHT WHICH ALLOWS A MIX/CHANGE OVER TO SNOW AT THE HIGHEST 
ELEVATIONS. NEEDLESS TO SAY...THIS SITUATION WILL NEED TO BE 
MONITORED AS THE EVEN APPROACHES. FOR NOW LOWS ARE 5 TO 10 DEGREES 
ABOVE NORMAL.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 200 AM THURSDAY...THE MEDIUM RANGE FORECAST PICKS UP AT 12Z 
SUNDAY WITH AN UPPER SHORTWAVE SWEEPING ACROSS THE CAROLINA SUNDAY 
FOLLOWED BY AN UPPER LVL RIDGING OVER THE EASTERN CONUS WITH 
INCREASING THICKNESS THROUGH NEXT TUESDAY. ANOTHER SHORTWAVE THROUGH 
WILL APPROACH FROM THE WEST BY NEXT WEDNESDAY.

THE LATEST 00Z MODELS ARE IN BETTER AGREEMENT WITH A SURFACE LOW 
OVER THE CAROLINAS EARLY SUNDAY MOVING OFF THE MID ATLANTIC SHORE BY 
18Z SUNDAY. HENCE...PRECIPITATION WILL TAPER OFF FROM WEST TO EAST 
TOWARD SUNDAY NOONTIME. HOWEVER...A MOIST NW FLOW BEHIND THE LOW 
WILL RESULT IN LINGERING PRECIP OVER THE NC MOUNTAINS THROUGH LATE 
SUNDAY. AS COLD SURFACE HIGH OVER THE GREAT LAKES AREA EXPANDS 
SOUTHEAST INTO THE CAROLINAS...TEMPERATURES WILL FALL TO NEAR...OR A 
LITTLE BELOW FREEZING LEVEL OVER THE APPALACHIANS BY LATE SUNDAY 
AFTERNOON. THIS WILL ALLOW SNOW LEVEL DECREASING TO LOWER VALLEY 
FLOORS. THEREFORE...RAIN OR MIXED RAIN SNOW SHOWERS WILL SWITCH TO 
ALL SNOW BY LATE SUN AFTERNOON OVER NORTHERN HALF OF OUR CWFA. 
HOWEVER...LITTLE TO NO ACCUMULATION IS EXPECTED DUE TO LIMITED 
MOISTURE. MONDAY...A BROAD SURFACE HIGH WILL BUILD OVER THE REGION 
THROUGH TUESDAY FOR DRY WEATHER AND MODERATING TEMPERATURES. ANOTHER 
SURFACE LOW WILL APPROACH FROM THE SOUTHWEST AND INFLUENCE OUR 
WEATHER IN THE MID WEEK. THE ECMWF IS A BIT FASTER SOLUTION TAKING 
THE LOW OVER OUR REGION BY 12Z WED WHILE THE GFS HAS THE LOW OVER 
THE LOWER MISSISSIPPI VALLEYS 12S WED AND ARRIVING OUR REGION BY 06Z 
THURSDAY. DUE TO UNCERTAINTY...I USED MODEL BLEND KEEPING AT LEAST 
SLIGHT CHANCE POPS IN THE GRIDS EARLY WED INTO LATE THURSDAY. 
TEMPERATURES WILL REMAIN WELL BELOW NORMALS SUNDAY INTO MONDAY 
BEFORE RETURNING BACK TO NORMALS TUESDAY.

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
AT KCLT...AT 1130Z...TCLT VWP INDICATES THAT CLOUD BASES WERE AROUND 12 
KFT. MVFR CEILINGS SHOULD SWEEP ACROSS THE MIDLANDS AND ARE EXPECTED 
TO REACH THE TERMINAL AROUND THE INITIAL HOUR OF THE 12Z TAF. 
CEILINGS ARE FORECAST TO FALL TO IFR AS A BROAD BAND OF PREFRONTAL 
SHRA ARRIVES DURING THE MID MORNING HOURS. CEILINGS MAY LIFT TO MVFR 
AROUND MID DAY. FROPA IS EXPECTED TO SWEEP ACROSS THE TERMINAL 
BETWEEN 18Z TO 21Z. IN THE WAKE OF THE FRONT...WINDS WILL VEER WEST 
TO NORTHWEST AND CEILINGS WILL REMAIN MVFR. VFR CONDITIONS SHOULD 
DEVELOP DURING THE EARLY EVENING AS DRY AIR INCREASES FROM THE WEST.

ELSEWHERE...AT 1130Z...AREA RADAR VWP AND OBS INDICATES THAT CLOUD 
BASES WERE WILL INTO IFR RANGE. CEILINGS AND POSSIBLY VIS ARE 
FORECAST TO REMAIN IFR AS A BROAD BAND OF PREFRONTAL SHRA PASSES 
DURING THE EARLY TO MID MORNING HOURS. CEILINGS MAY LIFT TO MVFR 
AROUND MID DAY. FROPA IS EXPECTED TO SWEEP ACROSS THE TERMINALS 
BETWEEN 18Z TO 21Z. IN THE WAKE OF THE FRONT...WINDS WILL VEER WEST 
TO NORTHWEST AND CEILINGS WILL REMAIN MVFR. VFR CONDITIONS SHOULD 
DEVELOP DURING THE LATE AFTERNOON TO EARLY EVENING AS DRY AIR 
INCREASES FROM THE WEST. KAND WILL HAVE A GOOD CHANCE OF THICK FOG 
LATE TONIGHT AS SKY CLEAR...WINDS DECREASE...AND GROUND REMAINS 
NEARLY SATURATED. 

AMD NOT SKED FOR KAVL DUE TO MISSING OBSERVATIONS.

OUTLOOK...VFR CONDITIONS EXPECTED FRIDAY. ANOTHER WEATHER SYSTEM ON 
SATURDAY AND SUNDAY WILL BRING ANOTHER ROUND OF RESTRICTIONS.

AN EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLE SHOWING THE
PERCENTAGE OF GUIDANCE MEMBERS AGREEING WITH THE SCHEDULED ISSUANCE
CATEGORY IS AVAILABLE AT FOLLOWING LINK (USE LOWER CASE)...

WWW.WEATHER.GOV/GSP/AVIATION/TABLES.HTM

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