Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 081831 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 230 PM EDT TUE JUL 8 2014 .SYNOPSIS...BROAD HIGH PRESSURE WEAKENS AS A COLD FRONT MOVES TOWARD THE REGION FROM THE GREAT LAKES. THIS COLD FRONT SHOULD MOVE INTO THE MID-ATLANTIC WEDNESDAY...WEAKENING AS IT MOVES INTO NORTH CAROLINA THURSDAY. A TROUGH OF LOW PRESSURE THEN PERSISTS OVER THE REGION AT LEAST THROUGH FRIDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 910 AM TUESDAY... THE LATEST SURFACE ANALYSIS SHOWED BROAD HIGH PRESSURE MOSTLY OVER THE MID-ATLANTIC AND THE CAROLINAS WITH A WEAK SURFACE TROUGH AMONG THE BROAD RIDGE OVER THE CENTRAL PIEDMONT. THE SPC MESOANALYSIS SHOWED A NOTICEABLE MINIMUM OF PRECIPITABLE WATER VALUES OVER THE WESTERN PART OF THE STATE...SIMILAR TO WHAT WAS FORECAST BY THE MONDAY GUIDANCE. THE RAP FORECASTS THIS MINIMUM TO MOVE ACROSS CENTRAL NORTH CAROLINA DURING THE DAY...AND FOR THE MOST PART RAP SOUNDINGS ARE SIMILAR TO SOUNDINGS FORECAST BY THE GFS MONDAY... QUITE STABLE TO DEEP CONVECTION DURING THE DAY. TWO CAVEATS TO THIS ARE CURRENTLY...AND VERY LATE TODAY. CURRENTLY...PRECIPITABLE WATER VALUES ARE AT OR ABOVE 1.5 INCHES OVER A LARGE PART OF CENTRAL NORTH CAROLINA...AND RAP SOUNDINGS SHOW THE PRESENCE OF MID-LEVEL INSTABILITY THAT WANES BY 18Z AS THE LOWER MOISTURE VALUES MOVE EAST. THE LATEST VISIBLE IMAGERY SHOWED A NARROW BAND OF MID-LEVEL CLOUDS THAT DEVELOPED FROM NEAR ROXBORO TO WADESBORO...AND THE HRRR WRF ACTUALLY FORECASTS A SHOWER OR TWO DEVELOPING FROM THIS. WATER VAPOR IMAGERY WOULD SUGGEST ENOUGH SUBSIDENCE TO PRECLUDE A SHOWER... BUT THE DEVELOPMENT OF THE CLOUDS PLUS THE PRESENCE OF WEAK INSTABILITY MAKES IT WORTHY OF NOTE HERE. LATE TODAY...THE RAP FORECASTS LIFT MOVING INTO THE FAR NORTHWEST PIEDMONT TOWARD KINT BY 23Z. RAP SOUNDINGS ARE STILL FAIRLY STABLE AT THAT POINT...AND QPF ON THE RAP IS NIL THROUGH 00Z WEDNESDAY. PRECIPITABLE WATER VALUES INCREASE QUICKLY ON THE RAP...TO NEAR 1.5 INCHES JUST AFTER 00Z WEDNESDAY...AS K INDICES RISE TO NEAR 40. LIKE THE GFS FORECAST MONDAY...MODEST MID-LEVEL COOLING COUPLED WITH MOISTURE ADVECTION MAY BE ENOUGH FOR A SHOWER OR THUNDERSTORM TO MOVE INTO THE WEST AND NORTHWEST PIEDMONT THIS EVENING. MOS GUIDANCE POPS ARE A FEW PERCENTAGE POINTS LOWER THAN THAT GUIDANCE OF MONDAY...AND WRF ARW GUIDANCE SUGGESTS LITTLE PRECIPITATION INTO THE EVENING. STILL...THE MOISTURE ADVECTION AND SLIGHT COOLING ALOFT... COUPLED WITH A WEAKENING MID-LEVEL SHORTWAVE MOVING INTO THE WESTERN PIEDMONT THIS EVENING...IS ENOUGH TO AT LEAST CONTINUE THE SMALL CHANCES WEST AS CURRENTLY FORECAST THIS EVENING...AND MAY NEED TO EXPAND SLIGHTLY FARTHER EAST. THE 00Z GFS APPEARED TO SUFFER FROM SOME MINOR CONVECTIVE FEEDBACK WHILE THE ECMWF HAS BEEN VERY CONSISTENT IN SUGGESTING THE BEST THREAT FOR OVERNIGHT CONVECTION TO OUR NW. IT SHOULD ALSO BE NOTED THAT THE CONVECTIVE ALLOWING MODELS VERIFIED WAY OVERDONE ACROSS THE OH VALLEY INTO THE MID ATLANTIC AT 06Z. HIGHS TODAY IN THE LOWER TO MID 90S. WARM OVERNIGHT WITH LOWS NEAR 70 TO THE LOWER 70S. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... AS OF 310 AM TUESDAY... MID LEVEL SHEAR AXIS ASSOCIATED WITH THE NORTHERN STREAM S/W AND ITS ATTENDANT SURFACE BOUNDARY WILL DRIFT SEWD INTO CENTRAL NC WEDNESDAY AFTERNOON-WEDNESDAY NIGHT. THIS SYSTEM WILL INTERACT WITH STRONG HEATING AND AVAILABLE MOISTURE (PRECIPITABLE WATER VALUES IN THE NEIGHBORHOOD OF 1.67-1.9 INCHES) TO INITIATE AND SUSTAIN SCATTERED CONVECTION...ESPECIALLY WEDNESDAY AFTERNOON-WEDNESDAY EVENING. SOME CONVECTIVE PARAMETERS SUGGEST SOME POTENTIAL FOR ORGANIZED CONVECTION IN THE FORM OF BROKEN CONVECTIVE SEGMENTS. IF THESE SEGMENTS WERE TO DEVELOP...COULD SEE A DAMAGING WIND THREAT WITH THE STRONGER CELLS. THIS THREAT APPEARS GREATEST ACROSS THE NORTHERN PIEDMONT INTO THE NORTHERN COASTAL PLAIN (GENERALLY NORTH OF I-40) WHERE BULK SHEAR VALUES APPROACH 30 KTS. DUE TO PRESENCE OF SHEAR AXIS AND SFC BOUNDARY...EXPECT SCATTERED CONVECTION TO PERSIST WELL INTO THE NIGHT THOUGH OVERALL COVERAGE AND INTENSITY WILL DIMINISH AS NEAR SURFACE AIR MASS UNDERGOES NOCTURNAL STABILIZATION. HIGH TEMPS WEDNESDAY DEPENDENT UPON AMOUNT OF INSOLATION AND CONVECTIVE COVERAGE. IF SUN LIMITED DUE TO EXTENSIVE CLOUD COVERAGE OR IF THE GFS IS CORRECT AND SCATTERED CONVECTION IS OCCURRING AT THE THE START OF THE DAY...THEN MAX TEMPS ACROSS THE NORTH COULD END UP BEING 5-6 DEGREES COOLER THAN FORECAST. DUE TO ANTICIPATED TIMING...BELIEVE THAT THE SOUTHERN HALF OF THE FORECAST AREA STANDS A GOOD SHOT OF SEEING TEMPS RETURNING TO THE MID 90S. MIN TEMPS WEDNESDAY NIGHT IN THE UPPER 60S TO AROUND 70 NORTH AND LOWER 70S SOUTH. && .LONG TERM /THURSDAY THROUGH TUESDAY/... AS OF 230 PM TUESDAY... FOR THU THROUGH FRI NIGHT: THU STILL APPEARS TO BE THE BUSIEST WEATHER DAY IN TERMS OF STORM COVERAGE. A SURFACE TROUGH WILL HOLD OVER CENTRAL NC THU... WITH ELEVATED LOW LEVEL MOISTURE TRANSPORT MAINLY EAST/SOUTH OF THE TRIAD. ALOFT... BROAD TROUGHING SETTING UP JUST TO OUR WEST WILL DRAW IN NRN STREAM ENERGY AS WELL AS PULL IN PERTURBATIONS FROM AN UPPER LEVEL WEAKNESS OVER THE WRN GULF OF MEXICO. WHILE THE TROUGH ITSELF WILL BE SOMEWHAT WEAK AT THIS LATITUDE WITH MINIMAL HEIGHT FALLS (10 M AT MOST ON THU) AND MLLR VALUES UNDER 6.5 C/KM... THE ADDED DYNAMIC FORCING FOR ASCENT SHOULD SUPPORT AT LEAST SCATTERED CONVECTION (MAXIMIZING IN -- BUT NOT RESTRICTED TO -- THE AFTERNOON/EVENING) DESPITE MARGINAL VALUES OF INSTABILITY DUE TO LAYERS OF A MOIST ADIABATIC PROFILE (NAM MLCAPE TOPPING OUT AT 500-1000 J/KG WITH GFS MUCAPE OF 1000-1500 J/KG IN THE EAST THU). FORECAST DEEP LAYER SHEAR VALUES ARE MORE FAVORABLE THAN YESTERDAY`S MODEL RUNS... NOW AROUND 25-35 KTS OVER NRN/WRN NC... INDICATING THE POTENTIAL FOR MORE ORGANIZED CONVECTION... ALTHOUGH THIS BETTER SHEAR WILL NOT QUITE BE SPATIALLY ALIGNED IN AN IDEAL MANNER WITH THE GREATER INSTABILITY. NEVERTHELESS... PW VALUES WILL REMAIN ABOVE NORMAL (1.7-2.0 IN.)... AND THIS MOISTURE COMBINED WITH LOW MBE TRANSLATIONAL SPEEDS AND A DECENT WARM CLOUD DEPTH NEAR 3.5 KM SUGGESTS THAT SOME SLOW-MOVING CELLS WITH EFFICIENT RAIN PROCESSES MAY GENERATE LOCALLY HEAVY RAINFALL. WILL BUMP UP POPS TO LIKELY... HIGHER EAST THAN WEST... ON THU EXTENDING INTO EARLY THU NIGHT... UNTIL THE MID LEVELS BEGIN TO DRY OUT A BIT. THE MID LEVEL TROUGH AXIS SHIFTS EAST OF THE SRN APPALACHIANS FRI... KEEPING ERN NC IN THE CROSSHAIRS OF SUFFICIENTLY DEEP MOISTURE AND MARGINAL SHEAR AND INSTABILITY... ENOUGH TO SUPPORT PRIMARILY AFTERNOON AND EVENING SHOWERS AND STORMS... WITH THE BEST CHANCES EAST OF I-95... ALONG/EAST OF WHERE THE SURFACE TROUGH SETTLES. EXPECT LOWER COVERAGE OVER THE REST OF CENTRAL NC WITH PW SLIPPING TO NEAR OR JUST BELOW NORMAL AND LOWER DEEP LAYER SHEAR (15-20 KTS)... ALTHOUGH GFS MUCAPE PEAKS ONCE AGAIN AT 1000-1500 J/KG OVER CENTRAL NC... SO CAN`T RULE OUT SCATTERED STORMS. WILL KEEP POPS RANGING FROM 25% NW TO 40-50% SE FRI. AN APPROACHING SHORTWAVE TROUGH... POTENT BUT SLOWLY WEAKENING... WILL DROP ESE THROUGH THE LOWER GREAT LAKES/OH VALLEY LATE FRI NIGHT... LIKELY LEADING TO CONTINUED PARTLY TO MOSTLY CLOUDY SKIES DOWNSTREAM OVER NC OVERNIGHT. THICKNESSES ARE PROJECTED TO BE NEAR NORMAL THU... WHICH WITH CONSIDERATION OF GOOD CONVECTIVE CLOUD COVERAGE WOULD SUPPORT HIGHS OF 86-92. THU NIGHT LOWS NOT FAR FROM NORMAL... 67-72. SLIGHTLY LESS WARMTH ON FRI WITH BELOW-NORMAL THICKNESSES POINTING TO HIGHS OF 86-90. FOR SAT-SUN: THE SURFACE TROUGH OVER ERN NC IS LIKELY TO DISSIPATE SAT AS IT IS OVERTAKEN BY THE ATLANTIC RIDGE BULGING WESTWARD... WITH FORMATION OF A NEW WEAK LEE TROUGH OVER THE PIEDMONT AND SOME ATTENDANT MINOR RECOVERY OF PW. THE AFOREMENTIONED WEAKENING MID LEVEL WAVE WILL CROSS THE MIDATLANTIC REGION SAT... ALTHOUGH MODEL DISPARITY EMERGES AS THE ECMWF IS SLOWER/STRONGER THAN THE GFS AND THEREFORE GENERATES MORE CONVECTION OVER CENTRAL/ERN NC. WILL RETAIN CHANCE POPS SAT... HIGHER EAST THAN WEST... GENERALLY FOLLOWING THE TYPICAL DIURNAL TREND. THE GFS DEPICTS FURTHER RECOVERY OF PW VALUES SUN WITH ANOTHER MINOR WAVE CROSSING THE REGION WITHIN VERY WEAK CYCLONIC FLOW AND A RETENTION OF THE PIEDMONT SURFACE TROUGH... AND WE SHOULD SEE YET ANOTHER ROUND OF MAINLY SCATTERED DIURNALLY-DRIVEN STORMS IN THE MID AFTERNOON INTO EARLY EVENING... WITH COVERAGE AND INTENSITY LIMITED BY THE WEAK DEEP LAYER SHEAR. FOR MON-TUE: THE GFE HAS COME INTO AGREEMENT WITH THE ECMWF`S SOLUTION (CONSISTENT OVER THE LAST FEW RUNS) REGARDING THE DEEPENING MID LEVEL VORTEX WHICH DRIFTS ACROSS THE GREAT LAKES/SE ONTARIO EARLY NEXT WEEK. THE PIEDMONT SURFACE TROUGH WILL SHARPEN AND PUSH A BIT TO THE SOUTHEAST IN RESPONSE TO THE APPROACHING SYNOPTIC COLD FRONT... EXPECTED TO PROGRESS SOUTHEAST TOWARD NW NC BY LATE TUE. PW REMAINS ABOVE NORMAL AREAWIDE MON... THEN THE HIGHER VALUES SHIFT TO OUR EAST TUE WITH THE SHIFTING TROUGH AND STRENGTHENING LOW AND MID LEVEL FLOW FROM THE WSW. WILL RETAIN CLIMATOLOGICALLY TYPICAL POPS MON (SLIGHTLY LOWER IN THE TRIAD AND HIGHER TO THE SOUTH/EAST... FOCUSED ON THE AFTERNOON INTO MID EVENING)... THEN TREND POPS BACK DOWN A TAD IN THE WEST TUE. THICKNESSES REBOUND BACK CLOSER TO NORMAL SO WILL NOT DEPART MUCH FROM SEASONAL NORMALS MON/TUE (WITH NORMAL HIGH/LOW OF 90/70 AT RDU AND 89/69 AT GSO). -GIH && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... AS OF 155 PM TUESDAY... VFR CONDITIONS ARE EXPECTED THROUGHOUT MUCH OF THE 18Z VALID TAF PERIOD. AS MOISTURE INCREASES AGAIN OVER THE REGION FROM THE WEST...SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS SHOULD OCCUR PARTICULARLY TOWARD THE TRIAD VERY LATE THIS AFTERNOON INTO THE EVENING. WITH UNCERTAINTY IN THE LOCATION OF ANY THUNDER ONLY INCLUDED A TEMPO FOR SHOWERS IN THE TAFS FOR KINT AND KGSO FROM ABOUT 23Z TO 04Z. ISOLATED SHOWERS OR SPRINKLES ARE POSSIBLE OVERNIGHT THEN CHANCES FOR SHOWERS INCREASE DURING WEDNESDAY WITH AT LEAST TEMPO CONDITIONS ANTICIPATED AROUND THE TRIAD DURING THE MORNING. SREF MODEL PROBABILITY OF IFR CONDITIONS ARE LOW BUT PROBABILITIES OF MVFR CONDITIONS ESPECIALLY OVER THE NORTHWEST PIEDMONT INCREASE AFTER 12Z WEDNESDAY AND HAVE INCLUDED SUCH CEILINGS IN THE TEMPO CONDITIONS AT KINT AND KGSO WEDNESDAY MORNING. GUSTY SOUTHWEST WINDS SHOULD DIMINISH BUT REMAIN NOTICEABLE OUT OF THE SOUTH TO SOUTHWEST OVERNIGHT...WITH A FEW GUSTS DEVELOPING MAINLY TOWARD KFAY WEDNESDAY MORNING WHERE HEATING TO START THE DAY SHOULD BE A LITTLE BETTER RELATIVE TO THE REST OF CENTRAL NORTH CAROLINA. BEYOND THE 18Z VALID TAF PERIOD...AT LEAST SCATTERED SHOWERS AND THUNDERSTORMS...AND THEIR ASSOCIATED SUB-VFR CONDITIONS...CAN BE EXPECTED OVER CENTRAL NORTH CAROLINA AT LEAST INTO THE END OF THE WORK WEEK. A COLD FRONT WEAKENS AS IT APPROACHES THE STATE THURSDAY...BUT A SURFACE TROUGH THEN LINGERS AT LEAST THROUGH FRIDAY AND LIKELY INTO AT LEAST PART OF THE WEEKEND. COVERAGE OF PRECIPITATION OVER CENTRAL NORTH CAROLINA SHOULD BE GREATER THURSDAY AND FRIDAY AS COMPARED TO THE UPCOMING WEEKEND. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...DJF NEAR TERM...WSS/DJF SHORT TERM...WSS LONG TERM...HARTFIELD AVIATION...DJF

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