Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 180532 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 123 AM EDT SAT APR 18 2015 .SYNOPSIS...HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE NORTH TODAY... THEN SHIFT SLOWLY OFFSHORE SUNDAY AS A WARM FRONT APPROACHES FROM THE SOUTH. THE WARM FRONT WILL MOVE NORTH ON SUNDAY NIGHT. THIS WILL BE FOLLOWED BY A COLD FRONT THAT WILL PUSH WEST TO EAST ACROSS CENTRAL NORTH CAROLINA LATE MONDAY INTO MONDAY EVENING. && .NEAR TERM /TONIGHT/... AS OF 950 PM FRIDAY... A WELL-DEFINED SHORTWAVE TROUGH OVER NORTHERN AL/GA WILL MOVE GENERALLY EAST ACROSS THE SOUTHERN APPALACHIANS...SC...AND FAR SOUTHERN NC TONIGHT...TO A POSITION INVOF KILM BY 12Z SAT. AN EXPANSIVE AREA OF SHOWERS WILL ACCOMPANY THIS FEATURE AS IT MOVES EAST...WITH THE ASSOCIATED HIGHEST PROBABILITY OF RAIN OVER THE SOUTHERN PIEDMONT/SANDHILLS/SOUTHERN COASTAL PLAIN AFTER MIDNIGHT...WITH PROGRESSIVELY LOWER CHANCES TOWARD AND ESPECIALLY NORTH OF HIGHWAY 64. IT APPEARED THAT A COUPLE UPSTREAM CONVECTIVE CLUSTERS OVER VA...WHICH INITIATED ALONG A LEE SURFACE TROUGH...MAY MAINTAIN INTENSITY AS THEY PROPAGATED SOUTHEASTWARD ALONG THEIR ASSOCIATED OUTFLOW INTO A WEAK INSTABILITY AXIS CENTERED OVER THE NORTHERN NC PIEDMONT...BUT THAT ACTIVITY HAS MOSTLY DIMINISHED DURING THE PAST FEW HOURS. SO WHILE A SHOWER OR TWO CANNOT BE ENTIRELY RULED OUT OVER THE NORTHERN PIEDMONT AS BOTH PAIR OF OUTFLOW DRIFT SOUTH...THE PROBABILITY OF OCCURRENCE IS QUITE LOW RELATIVE TO THE INCOMING SHOWERS ASSOCIATED WITH THE AFOREMENTIONED SHORTWAVE TROUGH. LOWS CLOSE TO CURRENT SURFACE DEWPOINT TEMPERATURES...MOSTLY IN THE LOWER TO MIDDLE 60S. IF ANY APPRECIABLE BREAKS IN THE CLOUDS OCCUR...MOST LIKELY OVER THE NORTHERN PIEDMONT WHERE INFLUENCE FROM THE SHORTWAVE TROUGH AND ASSOCIATED LIFT/MOISTURE WILL BE LESS PREVALENT...THEN PATCHY FOG WOULD BE PROBABLE IN THOSE AREAS. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... AS OF 300 PM FRIDAY... SHOWERS WILL LINGER IN THE MORNING...ESPECIALLY IN THE SOUTHEAST... AS THE SHORT WAVE MOVES OFFSHORE. COOL AIR ADVECTION IN NORTHEAST FLOW WILL PROVIDE AN ISENTROPIC SURFACE TO INDUCE WEAK LOW LEVEL FORCING IN THE SOUTH. MEANWHILE...UPPER RIDGING TRANSITIONS ACROSS THE AREA DURING THE AFTERNOON TO EARLY OVERNIGHT...WHICH SHOULD BE ANOTHER AID TO LIMITING CONVECTION LARGELY TO THE SOUTHERN TIER IN THE AFTERNOON. WILL HAVE CHANCE POPS ACROSS THE FAR SOUTH TO SLIGHT CHANCE ELSEWHERE. HIGHS WILL HAVE TO BE TONED DOWN DUE TO INCREASING CLOUD COVERAGE AND WEAK COOL AIR ADVECTION. THICKNESSES SUPPORT A COUPLE OF DEGREES EITHER SIDE OF 80. THE UPPER RIDGING SHOULD DAMPEN ACTIVITY OVERNIGHT...BUT A WARM FRONT WILL BE LIFTING NORTH...WITH H85 FLOW VEERING TO SOUTHEAST...UPSLOPE...AND INCREASING. EXPECT PARTLY CLOUDY ACROSS THE NORTH...WITH MORE CLOUDINESS IN THE SOUTH OVERNIGHT...AND COULD SEE SHOWERS MIGRATE INTO THE FAR SOUTHWEST PIEDMONT BY MORNING. MINS WILL BE COOLER ACROSS THE NORTH...MID 50S...GRADUATED TO AROUND 60 ACROSS THE SOUTHERN TIER. && .LONG TERM /SUNDAY THROUGH FRIDAY/... AS OF 245 PM FRIDAY... SUN-MON NIGHT: A VERY WET AND POTENTIALLY STORMY PERIOD. THE NORTHERN STREAM SHORTWAVE TROUGH OVER SW CANADA WILL HAVE PICKED UP THE OPENING LOW THAT IS NOW OVER THE FOUR CORNERS REGION... WITH THE FORMER FEATURE AMPLIFYING OVER THE UPPER MIDWEST WHILE THE LATTER FEATURE IS TOSSED NORTHEASTWARD TOWARD LOWER MI. A BATCH OF MID LEVEL VORTICITY AND SUBTLE TROUGH NOW OFF THE COAST OF NW MEXICO WILL TRACK QUICKLY EAST THEN NE WITHIN THE STRONG SUBTROPICAL FLOW... AND IT IS THE MERGING OF THIS WAVE WITH THE OLD SOUTHWEST LOW INTO A DISTINCT TROUGH AXIS THAT WILL HELP TRIGGER WIDESPREAD RAIN OVER NC SUN INTO EARLY MON. THE MODELS HAVE TRENDED STRONGER WITH THESE TWO MERGED FEATURES AND THEIR RESULTANT TROUGH... AND THUS ARE STRONGER WITH AN ASSOCIATED SURFACE LOW NEAR THE MO BOOTHEEL SUN MORNING... EXPECT TO MOVE QUICKLY NORTHWARD THROUGH WRN MI THROUGH SUN NIGHT. MEANWHILE... THE BACKDOOR FRONT THAT DROPS SOUTHWARD TOWARD THE NC/VA BORDER -- PROPELLED BY AN INTENSE MID LEVEL SHORTWAVE TROUGH EXITING NEW ENGLAND AND COLD DENSE SURFACE HIGH PRESSURE CENTERED OVER SRN QUEBEC PUSHING SOUTHWARD -- NOW APPEARS LIKELY TO MAKE AT LEAST SOME PROGRESS DOWN THROUGH THE NC PIEDMONT. AND IT LOOKS LIKE THIS FRONT WILL MERGE WITH THE WEAK FRONTAL ZONE TO OUR SOUTH AS THE LATTER MOVES NORTHWARD... YIELDING A STRONGER SURFACE FRONTAL ZONE THROUGH NC BY LATE SUN. CONFIDENCE IS HIGH THAT WE`LL SEE A STRONG SURGE OF LOW LEVEL GULF- AND ATLANTIC-SOURCE MOISTURE INTO NC... STARTING FIRST IN SW NC AND SPREADING ENE SUN/SUN NIGHT IN CONJUNCTION WITH THE PRIMARY LIFT MECHANISMS FORCING ASCENT... INCLUDING MID LEVEL DPVA... UPPER DIVERGENCE... AND LOWER LEVEL (850-925 MB) MASS CONVERGENCE. MOISTURE SHOULD BE DEEP AND PLENTIFUL WITH PW WELL OVER 200% OF NORMAL AND A DEEP LCL-TO-0C LAYER NEAR 3.5 KM SUPPORTIVE OF WARM RAIN PROCESSES... AND A PERIOD OF HEAVY RAIN APPEARS LIKELY. OVERALL RAINFALL IS EXPECTED TO BE 1-2 INCHES... WITH THE LESSER VALUES EAST AND HIGHER TOTALS WEST. GIVEN SUCH DEEP LIFT AND ANOMALOUSLY HIGH MOISTURE CONTENT... AND IF MODELS TREND EVEN WETTER WITH HIGHER QPF OVER A LARGE AREA... WE MAY NEED TO CONSIDER A FLASH FLOOD WATCH ON TOMORROW`S SHIFTS. MODEL TIMING HAS BEEN TRENDING A BIT SLOWER WITH PRECIP ONSET BUT NOW APPEARS TO BE ZEROING IN ON A COMMON SOLUTION... AND WILL CONTINUE TO RAMP UP POPS TO LIKELY WEST/CHANCE NE SUN MORNING... GOING TO CATEGORICAL WEST/LIKELY CENTRAL/GOOD CHANCE EAST SUN AFTERNOON... AND CATEGORICAL EVERYWHERE LATE SUN AFTERNOON THROUGH SUN NIGHT... BEFORE TRENDING POPS DOWN WSW TO ENE MON MORNING. WHILE THE LARGE SCALE MODELS DON`T DEPICT MUCH INSTABILITY AT ALL SUNDAY WITH PRIMARILY MOIST ADIABATIC FORECAST PROFILES... WE DO HAVE SOME CONCERN ABOUT POCKETS OF CONVECTION AND AN ISOLATED THREAT OF A QUICK WEAK SPIN-UP ALONG AND NEAR THE AFOREMENTIONED BACKDOOR/WARM FRONT ACROSS NRN/WRN NC... ESPECIALLY LATE SUN AFTERNOON THROUGH SUN EVENING AND INTO THE EARLY OVERNIGHT HOURS... WHEN THE SURFACE FRONT SHOULD BE RETREATING BACK TO THE NNE... PROVIDING A FOCUS FOR ENHANCED LOW LEVEL VORTICITY. THIS CONCERN PEAKS SUN EVENING WITH THE COMBINATION OF 30-40 KTS OF DEEP LAYER SHEAR... AN UPPER DIVERGENCE MAXIMUM OVER THE SRN APPALACHIANS AND WRN/CENTRAL NC... INCOMING DRIER AIR IN THE MID LEVELS... AND A 40-50 KT 850 MB JETLET FROM THE SSE... AND FORECAST SOUNDINGS SHOW A STRONGLY CURVED HODOGRAPH. WILL CONTINUE TO MONITOR. WILL TAPER POPS DOWN MON MORNING WSW TO ENE AS THE MID LEVEL TROUGH AXIS AND CONVEYOR BELT OF PEAK MOISTURE PUSH TO OUR NORTHEAST... PLACING US FULLY IN THE WARM SECTOR WITH A PUNCH OF MID LEVEL DRY AIR ARRIVING FROM THE SW AND FLOW-MID LEVEL FLOW BECOMING MORE UNIDIRECTIONAL. MUCAPE IS EXPECTED TO REACH 1500-2500 J/KG MON AFTERNOON (AND COULD BE LOCALLY HIGHER IF WE GET MORE HEATING)... WITH BULK SHEAR NEAR 30-35 KTS AND SW 850 MB WINDS AROUND 30 KTS. DYNAMIC FORCING FOR ASCENT WILL HAVE DECREASED BY MON AFTERNOON... BUT WE`LL STILL BE BENEATH CYCLONIC MID LEVEL FLOW WITH WEAK DPVA... AND ANOTHER ROUND OF DECENT UPPER DIVERGENCE IN THE LEFT EXIT REGION OF THE STRAIGHT 140 KT SUBTROPICAL JET ACROSS TX AND THE GULF STATES. SO STILL EXPECT A FEW STRONG CELLS MON AFTERNOON INTO EARLY EVENING WITH STRAIGHT LINE WINDS THE PRIMARY THREAT. HIGHS SUN FROM THE MID 60S TO LOWER 70S WEST OF HIGHWAY 1... AND LOW-MID 70S FROM HIGHWAY 1 EAST. LOWS UPPER 50S NW TO MID 60S SE. STILL EXPECT HIGHS IN THE UPPER 70S TO LOWER 80S MON. LOWS MON NIGHT MID 50S NW TO LOWER 60S SE WITH COLD FRONTAL PASSAGE EXPECTED AFTER MIDNIGHT WITH DIMINISHING PRECIP CHANCES. TUE THROUGH FRI: A MAINLY QUIET PERIOD. LARGE AND DEEP MID LEVEL LOW PRESSURE CENTERED OVER AND NORTH OF THE NRN GREAT LAKES WILL COVER MUCH OF CENTRAL AND EASTERN NOAM... BRINGING SEASONABLY COOL TEMPS AS IT SITS AND SPINS THROUGH MID WEEK. HIGH PRESSURE WILL BUILD INTO OUR AREA FROM THE WEST TUE... PASS OVERHEAD EARLY WED... THEN SHIFT OFF THE COAST LATE WED INTO THU (GFS IS FASTER THAN THE ECMWF WITH THIS) WHILE A WARM FRONT MOVES NORTHWARD THROUGH NC. ENERGY EMANATING OUT OF THE BASE OF DEEP TROUGHING JUST OFF THE WEST COAST WILL CROSS THE DESERT SOUTHWEST THEN MOVE INTO OUR AREA LATE THU INTO FRI. WITH A SOUTHERLY LOW LEVEL FLOW ON THE BACK SIDE OF THE EXITING HIGH... WE SHOULD SEE INCREASING PW AND RETURNING CHANCES FOR SHOWERS LATE THU INTO FRI... HOWEVER THE MOISTURE INFLUX STILL DOESN`T LOOK GREAT WITH LIGHT AND DIFFLUENT LOW LEVEL FLOW... SO WILL KEEP POPS BELOW CLIMATOLOGY. TEMPS SHOULD HOLD NEAR OR JUST BELOW NORMAL THROUGH THE PERIOD. -GIH && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... AS OF 123 AM SATURDAY... VFR CONDITIONS ARE EXPECTED TODAY AND TONIGHT. HOWEVER... VFR TO MVFR CIGS CAN BE EXPECTED TODAY. THERE IS A CHANCE OF MVFR VSBYS THIS MORNING WITH A CHANCE OF SHOWERS MAINLY AT KFAY. A WARM FRONT WILL MOVE NORTH OVER NC SUNDAY. THIS WILL LOWER CIGS AND VSBYS SUNDAY AS RAIN ARRIVES FROM THE SOUTH DURING THE DAY. IFR TO LIFR CIGS AND VSBYS WITH RAIN AND FOG ARE EXPECTED LATE SUNDAY INTO SUNDAY NIGHT. MONDAY... CIGS WILL BREAK OUT INTO VFR DURING THE MORNING. THERE IS A CHANCE OF SHOWERS AND THUNDERSTORMS WITH THE COLD FRONT MONDAY AFTERNOON AND EVENING. THE OUTLOOK BEYOND MONDAY... A RETURN TO VFR CONDITIONS IS EXPECTED MONDAY NIGHT THROUGH FRIDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BADGETT NEAR TERM...RAH SHORT TERM...MLM LONG TERM...HARTFIELD AVIATION...BADGETT

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