000 FXUS62 KGSP 220835 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 335 AM EST SUN NOV 22 2009 .SYNOPSIS... HIGH PRESSURE WILL REMAIN WEDGED IN OVER THE REGION AS A LOW PRESSURE SYSTEM MOVES EAST ALONG THE GULF COAST...THEN NORTH ALONG THE CAROLINA COAST TODAY THROUGH MONDAY. THE LOW IS EXPECTED TO REACH THE NEW ENGLAND COAST BY TUESDAY AS WEAK HIGH PRESSURE REMAINS OVER THE SOUTHEAST STATES. A WEAK COLD FRONT WILL MOVE THROUGH THE THE AREA BY THE MIDDLE OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... REGIONAL RADAR TRENDS SHOW THE LEADING EDGE OF THE PRECIP SHIELD BEGINNING TO SPREAD NORTHWARD ACROSS CENTRAL GA...THOUGH A MODEL SOUNDING TAKEN FROM KAND SHOWS A VERY DRY ATMOSPHERE STRETCHING FROM THE SURFACE UP TO AROUND THE H6 LEVEL. THIS DRY LAYER SHOULD KEEP THE NORTHWARD EXTENT OF MEASURABLE PRECIP IN CHECK THROUGH DAYBREAK THOUGH HIGH CLOUDS WILL CONTINUE TO STREAM IN FROM THE SW. OVERALL...THE VARIOUS MODEL SOLUTIONS ARE IN PRETTY GOOD AGREEMENT WITH THE ONSET OF PRECIP ACROSS THE FA IN THE MID TO LATE MORNING TIME FRAME WITH A SW TO NE GRADIENT. ALOFT...THE MID AND UPPER LEVEL SHORTWAVE WILL DAMPEN OUT ALONG ITS NE TRACK TODAY. THE INITIAL BURST OF PRECIP...THAT IS SPREADING NORTHWARD NOW...IS LARGELY BEING FORCED BY AN AREA OF LOW LEVEL ISENTROPIC LIFT AND MID/UPPER LEVEL DIVERGENCE OUT AHEAD OF THE TROF AXIS. STILL EXPECT THE BULK OF PRECIP DURING THE TODAY PERIOD TO FAVOR AREAS TO THE SOUTH AND EAST ESPECIALLY AS A COASTAL FRONT TAKES SHAPE DURING THE AFTERNOON. THEN DURING THE OVERNIGHT...MODELS ALL INDICATE AN AREA OF WIDESPREAD LIGHT PRECIP DEVELOPING ACROSS THE HEART OF THE FA AS A SECONDARY AREA OF ISENTROPIC LIFT ON THE 295K SURFACE MOVES ACROSS THE REGION. THIS ALSO COINCIDES WITH WHEN THE DEEPEST MOISTURE SETTLES IN. WEDGE WILL FIRMLY REMAIN ENTRENCHED AS WAA SPREADS OVER TOP OF THE COOL DOME THROUGH 12Z MONDAY. CONCERNING TEMPS...I HAVE TRENDED HIGHS DOWNWARD ESPECIALLY ACROSS THE EAST WHERE SKIES HAVE REMAINED NEARLY CLEAR FOR MUCH OF THE EVENING AND EARLY MORNING. THIS HAS ALLOWED CURRENT TEMPS TO COOL TO A COUPLE OF DEGREES BELOW THE TREND INDICATED BY GUIDANCE. THEREFORE...I BLENDED TEMPS TOWARD THE COOLER MAV WHICH RESULTS IN LOW 50S ALONG THE I-77 CORRIDOR. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... AS OF 230 AM EST SUNDAY...SOUTHWEST UPPER FLOW IS EXPECTED OVER THE SOUTHEAST ON MONDAY...WITH SHORTWAVES CROSSING THE SOUTHERN APPALACHIANS EARLY AND LATE IN THE DAY. AN UPPER LOW CROSSES THE CENTRAL PLAINS FROM MONDAY NIGHT THROUGH WEDNESDAY NIGHT. A SURFACE RIDGE WILL REMAIN ALONG THE EAST COAST MONDAY AND TUESDAY...WITH ISENTROPIC UPGLIDE OVER IT THROUGH MONDAY... SUPPORTING EXTENSIVE CLOUD COVER AND HIGH POPS. BY MONDAY NIGHT THE MODELS DISAGREE ON THE AMOUNT AND LOCATION OF LINGERING UPGLIDE FLOW...BUT IN NO CASE IS ANYTHING MORE THAN WEAK DOWNGLIDE SHOWN. CLOUD COVER WILL BE INCREASED MONDAY NIGHT AND TUESDAY...AS THE CASE FOR SCOURING THE LOW LEVEL MOISTURE IS WEAK. SMALL POPS WILL BE MAINTAINED ALONG THE BLUE RIDGE ESCARPMENT MONDAY EVENING...UNTIL SURFACE WINDS BACK TO THE NORTH. SURFACE WINDS VEER TO NORTHEAST TUESDAY...AND WITH A LIGHT UPSLOPE COMPONENT...SMALL POPS WILL BE REINTRODUCED TO THE BLUE RIDGE. AS A SURFACE FRONT APPROACHES TUESDAY NIGHT...THE MODELS SHOW MOIST SOUTHERLY UPSLOPE FLOW DEVELOPING...SUPPORTING INCREASING CLOUD COVER AND POPS INCREASING FROM THE WEST. WITH COLD AIR DAMMING ONGOING MONDAY...A LOW DIURNAL TEMPERATURE RANGE WILL BE CARRIED. CLOUD COVER SHOULD KEEP MINIMUM TEMPERATURES UP MONDAY NIGHT. MAXIMUM TEMPERATURES TUESDAY WILL LEAN TOWARD LINGERING CLOUD COVER...ALTHOUGH THEY ARE SUBSTANTIALLY WARMER THAN MONDAY. MINIMUM TEMPERATURES TUESDAY NIGHT REMAIN ELEVATED AS SOUTHERLY FLOW AN MORE CLOUDS ARE EXPECTED. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... AS OF 330 AM SUNDAY...MDLS SHOWING BETTER AGREEMENT DURING THE MEDIUM RANGE THAN THE PAST COUPLE OF DAYS. THIS RESULTS IN INCREASED FORECAST CONFIDENCE. HOWEVER...GIVEN THE POSSIBLE SOLN...WILL KEEP THINGS LOW KEY FOR NOW. REINFORCING UPPER LOW DROPS INTO THE CENTRAL US TROF...DIGGING IT EVEN DEEPER. STRONG SHORT WAVE ROTATES AROUND THE LOW AS IT MOVES EAST FRI AND SAT. AT THE SFC...THERE MAY BE SOME LINGERING SHOWERS WED AS OCCLUDED FRONT MOVES ACROSS THE AREA. HIGHS ABOVE NORMAL AS DRIER...BRIEFLY WARMER AIR MASS MOVES IN. THE GULF LOW TRACK ON THE ECMWF HAS MOVED FARTHER OFF THE COAST...CLOSER TO THE GFS AND GEM TRACKS. THIS SHOULD HELP KEEP WED NITE DRY BEFORE THE NEXT SYSTEM APPROACHES. LOWS ABOVE NORMAL. AS THE UPPER LOW MOVES TOWARD THE AREA THU...A VERY COLD AIR MASS MOVES INTO THE AREA. THE GEFS HAS H85 TEMPS 1 TO 1.5 STANDARD DEVIATIONS BELOW NORMAL. ALONG WITH THE COLD IS LOW LEVEL MOISTURE MOVING IN FROM THE NW. THIS SETS UP THE POTENTIAL FOR A NW FLOW PRECIP EVENT FROM THU THRU FRI NITE. EVEN THOUGH THE H85 TEMPS REMAIN BELOW FREEZING...THE SFC TEMPS RISE ABOVE FREEZING DURING THE DAY. THEREFORE...HAVE PRECIP STARTING AS RAIN THU AFT...THEN CHANGING TO RAIN THU NITE. THIS TREND CONTINUES FRIDAY AS SNOW CHANGES TO RAIN DURING THE DAY...THEN BACK TO SNOW OVERNIGHT. SOME RAIN COULD DEVELOP OUTSIDE OF THE MTNS THU AFTERNOON...BUT PRECIP SHOULD REMAIN LIMITED TO THE NORMAL MTN LOCATIONS AFTER. KEPT POPS AT SLIGHT CHC FOR NOW GIVEN THE MDL TENDENCY TO OVER FORECAST THE PRECIP AND AMOUNT OF COLD AIR FOR THESE EVENTS IN THE MEDIUM RANGE. IT IS WAY TOO EARLY TO KNOW IF ADVISORY LEVEL OR HIGHER SNOW AMOUNTS WILL DEVELOP. HIGHS THU BELOW NORMAL WEST AND NEAR NORMAL EAST. TEMPS THEN BELOW NORMAL THU NITE THRU FRI NITE. HAVE FCST PRECIP ENDING FRI NITE...BUT IT COULD LINGER SATURDAY. DRY FCST SAT NITE. TEMPS REMAIN BELOW NORMAL. && .AVIATION /09Z SUNDAY THROUGH THURSDAY/... AT KCLT AND ELSEWHERE...UPSTREAM OBS AND SATELLITE IMAGERY INDICATE THAT SCT TO BKN CLOUDS IN THE 10-15 KFT LAYER ARE JUST NOW MAKING THEIR WAY ACROSS NORTH AND CENTRAL GA. AS SUCH...EXPECT THAT THROUGH LATE MORNING ALL TAF SITES WILL NOTHING MORE THAN SCT MID LEVEL CLOUDS WITH BKN TO OVC CIRRUS LAYER AND GENERALLY LIGHT NE FLOW. BIGGEST CHALLENGE OF THE PRESENT TAF PERIOD REVOLVES AROUND TIMING OF THE LOWERING OF THE CLOUD DECK AND ONSET OF PRECIP. AN INVESTIGATION OF SOUNDINGS ACROSS THE AREA INDICATE THAT THERE IS SUBSTANTIAL DRY AIR FROM THE SURFACE UP TO AROUND 600 MB...WHICH MEANS IT WILL TAKE A WHILE FOR EVEN A VFR LEVEL CIG TO DEVELOP. THIS BRINGS THINGS DOWN FIRST AT KAND WITH MVFR LEVEL CIGS AND -RA DEVELOPING AROUND NOON. I DO BRING IN MVFR DECK AT ALL SITES IN THE AFTERNOON AS DEEP LAYER MOISTURE INCREASES THROUGHOUT THE DAY. IN FACT MODEL SOLUTIONS SHOW THAT RAPID DETERIORATION OF CONDITIONS WON/T OCCUR UNTIL AFTER 00Z. MODELS ARE IN PRETTY GOOD AGREEMENT THAT THE GREATEST COVERAGE OF PRECIP WILL OCCUR LATE IN THE TAF PERIOD AS A SECONDARY SURGE OF ISENTROPIC LIFT SPREADS ACROSS THE REGION. WILL HINT AT THE DEVELOPMENT OF IFR CIGS WITH A MENTION OF FEW009 FROM KAND TO KCLT IN THE 01-02Z TIME FRAME. 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. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...NONE. NC...NONE. SC...NONE. && $$ SYNOPSIS...RWH NEAR TERM...BSH SHORT TERM...JAT LONG TERM...RWH AVIATION...BSH/PM