Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 011811 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 105 PM EST SUN FEB 1 2015 .SYNOPSIS... A STRONG COLD FRONT WILL APPROACHIN FROM THE WEST TONIGHT AND SWING ACROSS CENTRAL NC ON MONDAY. HIGHS PRESSURE WILL THEN BUILD OVER THE REGION THROUGH MIDWEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1025 AM SUNDAY... MID/UPPER LEVEL RIDGING OVER THE DEEP SOUTH IS FLATTENING THIS MORNING AS A VIGOROUS SHORTWAVE DIGS TOWARD THE MID-MISSISSIPPI VALLEY REGION. MID-LEVEL MOISTURE CONTINUES TO STREAM ACROSS THE AREA FROM THE SOUTHWEST...WITH EVEN A FEW ENHANCED RADAR RETURNS ABOVE 5-6K FT. THE SUB-CLOUD LAYER REMAINS VERY DRY WITH 15 TO 25 DEGREE DEWPOINT DEPRESSIONS AT 850MB ON MOST 12Z RAOBS AROUND THE SOUTHEAST US. AS THE ATMOSPHERE SLOWLY MOISTENS FROM TOP DOWN TODAY... EXPECT WE WILL CONTINUE TO SEE SOME ELEVATED RADAR ECHOES ASSOCIATED WITH WEAK UPPER DISTURBANCES ON THE THE EASTERN FRINGE OF THE STRENGTHENING WARM ADVECTION WEST OF THE APPALACHIANS. AN ISOLATED SPRINKLE IS POSSIBLE...BUT THE AFTERNOON AND MUCH OF THE EVENING SHOULD REMAIN DRY CWA-WIDE. STATISTICAL GUIDANCE TOPS OUT IN THE 52-59 RANGE...WHICH SHOULD BE ATTAINABLE FOR THE MOST PART GIVEN THAT VISIBLE IMAGERY SHOWS SOME BREAKS OF THINNER SPOTS IN THE OTHERWISE MOSTLY CLOUDY TO OVERCAST ALTOSTRATUS. -BLS TONIGHT: AFOREMENTIONED NORTHERN STREAM TROUGH WILL ADVANCE EASTWARD INTO THE OH/TN VALLEYS OVERNIGHT. ASSOCIATED DEEPENING SURFACE LOW...LOCATED ALONG THE LEADING EDGE OF INTENSE 180-200 H5 FALLS...WILL TRACK EWD ALONG THE MASON-DIXON LINE ...MOVING INTO THE MID ATLANTIC STATES MONDAY MORNING. STRONG DEEP MOISTURE TRANSPORT IN ADVANCE OF THE FRONT...WITHIN THE STRENGTHENING 60-65KT SOUTHERLY LLJ...WILL SUPPORT A 4-6 HOUR WINDOW OF CATEGORICAL POPS AS AN EASTWARD BAND OF SHOWERS MOVE EAST ACROSS THE AREA SUNDAY NIGHT- MONDAY MORNING BETWEEN 06Z IN THE WEST TO 15Z IN THE EAST. QPF AMOUNTS LOOK TO BE IN THE 0.25-0.50" RANGE... LIMITED BY THE INTRUSION OF A MID-LEVEL DRY AIR RACING IN FROM THE WEST. MODELS CONTINUE TO INDICATE MODEST MID-LEVEL LAPSE RATES ~6.5 C/KM WITH MUCAPE OF ONLY 100-150 J/KG ACROSS SOUTHERN/EASTERN PORTIONS OF THE FORECAST AREA...AND THUS VERY LOW PROBABILITY FOR SOME ELEVATED THUNDER. EXPECT A NON-DIURNAL TEMP TREND...WITH LOWS OCCURRING BEFORE MIDNIGHT BEFORE THE ARRIVAL OF THE RAIN AND STRONG WAA. LOWS SUNDAY NIGHT IN THE MID 40S NORTHEAST TO LOWER 50S SOUTH...RISING INTO THE 50S THROUGH THE PREDAWN HOURS. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... AS OF 250 AM SUNDAY... DEEP MOISTURE PLUME EMBEDDED WITHIN THE SOUTHERLY LLJ WILL SHIFT EAST AND OUT OF THE AREA AT OR SHORTLY AFTER 15Z MONDAY...WHICH SHOULD MARK THE BACK EDGE OF THE WIDESPREAD/CATEGORICAL POPS...WITH TRAILING SFC COLD FRONT AND LINGERING SMALL CHANCE OF SHOWERS LAGGING A FEW HOURS AFTERWARD. STRONG POST-FRONTAL DRY COLD AIR ADVECTION REGIME WILL RESULT IN WEST TO EAST CLEARING AND BREEZY/WINDY CONDITIONS DURING THE AFTERNOON AS BUFR SOUNDINGS INDICATE 35-40KTS AT THE TOP OF THE MIXED LAYER AND 25-30KTS JUST OFF THE SURFACE. HIGHS MONDAY SHOULD OCCUR AT OR BEFORE SOLAR NOON...RANGING FROM NEAR 50 NW TO UPPER 50S/NEAR 60 SE. TEMPERATURES WILL THEN FALL INTO THE 40S THROUGH THE AFTERNOON AS CONTINENTAL POLAR HIGH PRESSURE BUILDS INTO THE AREA MONDAY NIGHT AND INTO THE DAY ON TUESDAY. WINDS LOOK TO DECOUPLE OVERNIGHT...ESPECIALLY IN THE WEST...WHICH SHOULD HELP FOR A WIDE RANGE IN TEMPERATURES. LOWS TUESDAY MORNING IN THE LOWER TO MID 20S...WITH UPPER TEENS POSSIBLE IN THE TYPICALLY COLDER LOCATIONS ACROSS THE WESTERN PIEDMONT. && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 250 AM SUNDAY... TUESDAY AND TUESDAY NIGHT...THE GUIDANCE HAS BEEN CONSISTENT MOVING A MID-LEVEL SHORTWAVE ACROSS CENTRAL NORTH CAROLINA DURING THE DAY...WITH THE LEFT EXIT REGION OF A 140KT 300MB JET MOVING THROUGH THE AREA TUESDAY MORNING WITH A 500MB JET JUST TO OUR SOUTH. AHEAD OF THE SHORTWAVE...AND IN VICINITY OF THE JETS ALOFT BOTH THE NAM AND THE GFS PROVIDE FOR SOME MOSTLY MID-LEVEL CLOUDINESS TUESDAY MORNING WITH COLUMN DRYING TO FOLLOW FOR THE AFTERNOON. CENTRAL NORTH CAROLINA IS IN AN 850MB THETA-E TROUGH WITH K INDICES NEGATIVE...AND THE MOISTURE ALOFT DOES NOT CURRENTLY GET BELOW ABOUT -20C AND THE AIR MASS BELOW THAT IS QUITE DRY. A PERIOD OF POSSIBLY BROKEN CLOUDS IS ONLY ANTICIPATED EARLY TUESDAY BEFORE LATE MORNING AND AFTERNOON INCREASING SUN. SUBSIDENCE TUESDAY NIGHT UNDER SURFACE HIGH PRESSURE MOVING SOUTHEAST...WITH POSSIBLY A FEW CLOUDS OVERNIGHT ASSOCIATED WITH THE RIGHT ENTRANCE REGION OF A 70KT 500MB JET JUST TO OUR NORTH AND JUST MODEST MID-LEVEL MOISTURE. HIGHS TUESDAY AND LOWS TUESDAY NIGHT BOTH ABOUT A CATEGORY BELOW NORMAL...45 TO 50 FOR HIGHS TUESDAY AND MID TO UPPER 20S FOR LOWS TUESDAY NIGHT. WEDNESDAY THROUGH SATURDAY...PRIMARY CONCERN CONTINUES TO BE FOCUSED ON THE SYSTEM FOR THURSDAY...AS A COLD FRONT APPROACHES WEDNESDAY AND MOVES THROUGH MUCH IF NOT ALL OF CENTRAL NORTH CAROLINA WEDNESDAY NIGHT WITH A SURFACE LOW MOVING OVER SOME PART OF THE SOUTHEAST THURSDAY. THE GFS HAS TRENDED TOWARD THE PREVIOUS FEW VERSIONS OF THE ECMWF...WITH A DEEPER MID-LEVEL TROUGH MOVING SOUTHEAST ACROSS CANADA AND INTO THE GREAT LAKES WHICH SUPPRESSES THE SURFACE AND MID-LEVEL LOW TRACKS SUCH THAT CENTRAL NORTH CAROLINA WOULD RECEIVE LITTLE IF ANY PRECIPITATION. IT IS STILL CLOSE...THOUGH...AND FOR WHAT THEY ARE WORTH THE CANADIAN AND THE DGEX ARE STILL FARTHER NORTH AND WET FOR CENTRAL NORTH CAROLINA AT LEAST FOR THURSDAY. THE HIGHER QPF MODELS HAVE PARTIAL THICKNESSES THAT WOULD BE LIQUID ON THURSDAY FOR THE AREA...WHILE THE DRIER GUIDANCE IS COLDER. THE GFS HAS CERTAINLY TRENDED THE COLDER WAY...WITH HIGHS BY FRIDAY ON THE GFS MEX MOS GUIDANCE BARELY ABOVE FREEZING IN THE TRIAD. COMPLICATING THINGS...THE LATEST ECMWF IS SLOWER WITH THE TIMING OF THE MID-LEVEL TROUGH MOVING OUT OF CANADA...WITH A CORRESPONDINGLY SLOWER COLD FRONTAL PASSAGE AND A NOW SLIGHTLY FARTHER NORTH SURFACE LOW TRACK. LIKE THE CANADIAN AND THE DGEX...THICKNESSES ARE WARM FOR MUCH OF THURSDAY BEFORE COLDER AIR SETTLES IN. WHILE THE PROBABILITY OF PRECIPITATION MAY...OVERALL...HAVE LEANED SLIGHTLY LOWER...WITH THE OPERATIONAL GFS TRENDING PROGRESSIVELY DRIER IN EACH OF ITS LAST FOUR RUNS...GFS ENSEMBLES ON THURSDAY STILL HAVE SOME MEMBERS WITH A MORE MOIST AIR MASS AND PRECIPITATION. THE PRUDENT COURSE FOR THURSDAY IS TO MAINTAIN SOME CHANCES WITH SLIGHT CHANCES WEST OF ABOUT U.S. 1 AND CHANCES EAST...KEEPING PRECIPITATION LIQUID AND CONFINED TO THURSDAY UNTIL OVERALL FEATURES RESOLVE THEMSELVES MORE CLEARLY. THE WARMEST DAY SHOULD BE WEDNESDAY AHEAD OF THE COLD FRONT WITH THICKNESSES AND THE CURRENTLY EXPECTED DEGREE OF ANY MID- AND HIGH-LEVEL MOISTURE ALLOWING FOR HIGHS IN THE 50S. THERE HAVE BEEN HUGE SWINGS IN MOS GUIDANCE HIGHS FOR THURSDAY...40S TO 50S AND BACK AGAIN...AND 40S TO 50S TO 30S IN THE TRIAD ON PREVIOUS VERSIONS OF THE ECMWF MOS. BY FRIDAY SOME CONFIDENCE THAT MOST HIGHS SHOULD BE IN THE 30S MODERATING SOME FOR SATURDAY...BUT STILL BELOW NORMAL AND MOSTLY IN THE 40S THEN...AS 1000-850MB THICKNESSES RISE 40M TO 50M VERSUS VALUES OF AROUND 12Z FRIDAY. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... AS OF 105 PM SUNDAY... CONDITIONS ARE CURRENTLY VFR ACROSS CENTRAL CENTRAL NC WITH CLOUD BASES AT OR ABOVE 10K FT AND A LIGHT SOUTH-SOUTHWESTERLY WIND. THE PRESSURE GRADIENT WILL CONTINUE TO STRENGTHEN THIS AFTERNOON AHEAD OF A LOW PRESSURE SYSTEM MOVING INTO THE OHIO VALLEY...AND AS SURFACE WINDS INCREASE TO 8-12KT...A FEW WIND GUSTS TO 15-20KT MAY OCCUR...MAINLY FROM KRDU WEST TO KINT/KGSO. PRECIP ASSOCIATED WITH THE AFOREMENTIONED LOW PRESSURE SYSTEM LOOKS TO BE AHEAD OF THE FORECAST BY AN HOUR OR TWO...SO WILL INTRODUCE MVFR CEILINGS AND A CHANCE OF RAIN IN THE TAFS JUST A LITTLE EARLIER. EXPECT CEILINGS TO BE NEAR MVFR (3-4K FT) BY 03Z AT KGSO/KINT AND MORE TOWARD 06Z FROM KRDU EAST. THE MAIN RAIN BAND WITH THIS SYSTEM WILL CROSS THE AREA BETWEEN 06Z AND 15Z...WITH PREDOMINATELY IFR CEILINGS POSSIBLE DURING THIS PERIOD. SOUTHERLY WINDS WILL INCREASE TO 15-20KT AND GUST TO NEAR 30KT OVERNIGHT AS THE PRECIP AND COLD FRONT APPROACH....THEN SHIFT TO WEST- NORTHWESTERLY AND GUST INTO THE 30-35KT RANGE BEHIND THE FRONT ON MONDAY. OUTLOOK... NW BREEZE AT 10-15 KT WILL PERSIST MON NIGHT AS HIGH PRESSURE BUILDS TOWARD THE REGION FROM THE WEST. VFR CONDITIONS WILL RULE THROUGH MID-WEEK AS DRY HIGH PRESSURE BUILDS OVER THE CAROLINAS. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...CBL NEAR TERM...CBL/BLS SHORT TERM...CBL LONG TERM...DJF AVIATION...CBL/BLS

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