Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 041909 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 310 PM EDT TUE AUG 4 2015 .SYNOPSIS...AN AREA OF LOW PRESSURE WILL TRACK NORTHEASTWARD ALONG THE SOUTHERN COAST AND SOUTHERN OUTER BANKS OF NORTH CAROLINA THROUGH TONIGHT. MEANWHILE... A COLD FRONT WILL APPROACH FROM THE NORTHWEST... AND SETTLE INTO NORTH CAROLINA ON WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 240 PM TUESDAY... THE TWO MAIN AREAS OF CONCERN THROUGH TONIGHT ARE THE POTENT SURFACE LOW JUST SOUTH OF HOLDEN BEACH EXPECTED TO TRACK TO THE NORTHEAST ALONG OUR SOUTHERN SHORES TONIGHT... AND THE ISOLATED STORMS NOW FORMING OVER THE HIGHER TERRAIN JUST TO OUR NW. REGARDING THE FORMER... THE NATIONAL HURRICANE CENTER IS INVESTIGATING THIS LOW TO DETERMINE IF IT POSSESSES ANY TROPICAL CHARACTERISTICS. UNTIL THIS IS DETERMINED... WE MUST TREAT IT AS NON-TROPICAL... BUT REGARDLESS... ITS IMPACT ON OUR CWA WILL CONSIST OF BROKEN BANDS OF ISOLATED TO SCATTERED TROPICAL-TYPE SHOWERS (AND PERHAPS A LIGHTNING STRIKE OR TWO) SPREADING OUT TO THE WEST AND NW... WITH INDIVIDUAL CELLS GRADUALLY DISSIPATING AS THEY TRACK FURTHER INTO THE PIEDMONT DUE TO DRY AIR ENTRAINMENT. COVERAGE SHOULD BE NO GREATER THAN SCATTERED. TO THE NW... AS THE HRRR/NCAR ENSEMBLE/SPC SSEO INDICATE... WE SHOULD SEE THE HIGH-ELEVATION CONVECTION TRANSLATE TO THE WEST OR WSW WITH THE MEAN STEERING FLOW INTO THE NW PIEDMONT OVER THE NEXT FEW HOURS... WORKING INTO THE NE AND SRN PIEDMONT BY EARLY EVENING BEFORE FALLING APART AS HEATING WANES... LEADING TO LOWERING OF CAPE VALUES AND INCREASING CINH. AREAS FURTHER EAST WILL ALSO BE UNDER THE INFLUENCE OF LARGE SCALE WEAK SUBSIDENCE ON THE WEST AND SW SIDES OF THE COASTAL LOW... LIKELY REDUCING POTENTIAL FOR UPSCALE GROWTH OF CELLS. BUT... DESPITE US BEING ON THE SOUTHERN END OF THE MAIN BELT OF WESTERLIES... THE INVERTED-V LOOK TO FORECAST SOUNDINGS AND IMPRESSIVE CALCULATED D-CAPE (1100-1500 J/KG OVER CENTRAL NC) ALONG WITH DECENT EFFECTIVE DEEP LAYER SHEAR OF 25- 35 KTS AND MLCAPE AROUND 2000 J/KG WILL MEAN A RISK OF A FEW STRONG STORMS WITH DAMAGING DOWNBURST WINDS POSSIBLE OVER THE NEXT SEVERAL HOURS... MAINLY ACROSS THE NORTH WHERE SHEAR AND INSTABILITY ARE GREATEST. FORECAST WILL HAVE SCATTERED SHOWERS/STORMS THERE UNTIL EARLY EVENING... THEN WILL SHIFT POPS SLOWLY EASTWARD WHILE INDICATING A DOWNWARD TREND TO COVERAGE. EXPECT LOWS CLOSE TO THIS MORNING`S... 69-74... WITH PATCHY FOG POSSIBLE IN THE EAST AS WINDS DIMINISH OVERNIGHT. -GIH && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
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AS OF 310 PM TUESDAY... THE COLD FRONT TO OUR NW IS EXPECTED TO DROP TO THE SSE THROUGH WED MORNING... LIKELY ENDING UP STRETCHED ROUGHLY ALONG OR JUST SOUTH OF THE NC/VA STATE LINE. THE LOW LEVEL FLOW FROM THE WNW SHOULD ALLOW DEWPOINTS TO DROP DOWN INTO THE 60S WITH DEEP MIXING ANTICIPATED BY EARLY TO MID AFTERNOON. SO WE SHOULD INITIALLY BE IN A RELATIVE PRECIP LULL OF BRIEF FLAT FLOW OR WEAK SHORTWAVE RIDGING... BEHIND THE DEPARTING LOW AND ITS ASSOCIATED SHORTWAVE TROUGH... AND AHEAD OF THE NEXT SHORTWAVE TROUGH NOW STRETCHING FROM NRN WY SE TO NE OK. AS THE LEADING EDGE OF THIS FEATURE APPROACHES LATE IN THE DAY AND INTO WED NIGHT... MID AND UPPER LEVELS WILL SLOWLY MOISTEN... AND THE INCREASING DYNAMIC FORCING FOR ASCENT ALONG WITH THE IMPROVING DEEP LAYER WIND FIELD SHOULD FACILITATE ISOLATED TO SCATTERED STORMS... DESPITE THE LATE DAY ARRIVAL. WILL TREND POPS UP TO CHANCE ESPECIALLY ACROSS THE NORTH AND WEST DURING THE MID TO LATE AFTERNOON... KEEPING A 20-30% CHANCE THROUGH THE NIGHT WITH CONTINUED RISING PW VALUES AND MID LEVEL HEIGHT FALLS. EXPECT RATHER HOT TEMPS DUE TO THE DEEP MIXING... ABOVE NORMAL THICKNESSES... AND GOOD INSOLATION FOR MUCH OF THE DAY... SUPPORTING HIGHS FROM 93 NORTH TO 99 SOUTH. LOWER DEWPOINTS WILL KEEP HEAT INDEX VALUES FROM GETTING TOO DANGEROUS... BUT STILL EXPECT WIDESPREAD VALUES AROUND 100-102 IN THE SOUTH AND EAST. LOWS WED NIGHT 68-74 WITH PARTLY CLOUDY SKIES AND SCATTERED SHOWERS AND A FEW STORMS PERSISTING OVERNIGHT. -GIH
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&& .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 410 AM TUESDAY... THE COLD FRONT FORECAST TO BE NEAR THE NC-SC BORDER THURSDAY MORNING WILL MEANDER BACK TO THE NORTH ON THURSDAY...AS A WAVE OF LOW PRESSURE TRACKS FROM THE MID-MISSISSIPPI RIVER VALLEY REGION TOWARD THE OHIO VALLEY REGION IN RESPONSE TO A SHORTWAVE MOVING EAST FROM THE CENTRAL ROCKIES. THERE ARE STILL SIGNIFICANT MODEL DIFFERENCES IN THE AMPLITUDE/TIMING THE SYSTEM THAT RESULT IN BELOW AVERAGE FORECAST CONFIDENCE FOR LATE WEEK. THE NAM AND ECMWF SEEM TO BE MORE CONSISTENT IN SHOWING A DEEPER DISTURBANCE AND AND NOTICEABLY STRONGER SURFACE LOW THAT TRACKS JUST NORTH OF CENTRAL NC LATE THURSDAY INTO EARLY FRIDAY...WHILE THE GFS SHOWS A VARIETY OF DISTURBANCES IN WEST-NORTHWESTERLY FLOW ALOFT THAT EVENTUALLY EVOLVE INTO A DEEPER SHORTWAVE TROUGH CROSSING OUR REGION LATE FRIDAY. WILL CONTINUE BEST CHANCE POPS THURSDAY EVENING THROUGH FRIDAY AFTERNOON GIVEN THE AFOREMENTIONED CONSISTENCIES IN THE ECMWF AND NAM...THOUGH THE BEST COVERAGE MAY ULTIMATELY END UP TO OUR NORTH WITH THE RETREATING FRONTAL ZONE. WHILE THE STRONGEST MID-LEVEL WESTERLIES WILL RESIDE TO OUR NORTH DURING THIS PERIOD...THE AMPLITUDE OF THE DISTURBANCE DEPICTED IN THE ECMWF (ALBEIT IMPACTING THE AREA AT A POOR TIME DIURNALLY) AND THE PRESENCE OF THE FRONTAL ZONE SUGGEST A SEVERE THREAT ISN`T OUT OF THE QUESTION. THE TRAILING COLD FRONT WILL THEN CROSS THE AREA BY FRIDAY EVENING...USHERING IN SOME DRIER AIR AND LEAVING MOST OF THE CWA DRY AS THE FOCUS MOVES TOWARD THE COASTAL AREA FOR THE WEEKEND THE COMBINATION OF CLOUD COVER AND PERIODS OF SHOWERS/STORMS SHOULD LEAD TO HIGHS A BELOW NORMAL BY FRIDAY....REMAINING AT OR JUST BELOW NORMAL SATURDAY BEFORE SLOWLY TRENDING WARMER EARLY NEXT WEEK BENEATH RENEWED NORTHWESTERLY FLOW ALOFT. && .AVIATION /18Z TUESDAY THROUGH SATURDAY/... AS OF 100 PM TUESDAY... OF MOST IMMEDIATE CONCERN TO AVIATION INTERESTS ARE THE BANDS OF SCATTERED SHOWERS AND ISOLATED STORMS OVER THE COASTAL PLAIN OF NC... AN OUTWARD EXPANSION OF THE RAIN SHIELD ASSOCIATED WITH POTENT LOW PRESSURE NOW JUST OFF THE NRN SC COAST NEAR MYR. AS THIS LOW TRACKS TO THE NE JUST OFF THE SRN NC COAST AND SRN OUTER BANKS THROUGH EARLY EVENING... WE SHOULD CONTINUE TO SEE ISOLATED CELLS NEAR RWI/FAY AND PERHAPS NEARING RDU AS WELL. BRIEF MVFR TO HIGH-END IFR CONDITIONS ARE EXPECTED IN THESE SHOWERS. ELSEWHERE... ISOLATED TO SCATTERED STORMS MAY IMPACT INT/GSO LATE AFTERNOON... PERHAPS REACHING RDU BY EARLY EVENING BEFORE FIZZLING OUT BY MID EVENING AS THEY PROGRESS TO THE EAST. LOCALIZED WIND GUSTS OVER 40 MPH AND MVFR CONDITIONS ARE POSSIBLE IN/NEAR THESE SHOWERS/STORMS. VFR CONDITIONS SHOULD THEN DOMINATE INTO THE EARLY OVERNIGHT HOURS... BUT MVFR FOG IS POSSIBLE AT RWI/FAY AFTER 06Z TONIGHT... LIFTING/DISSIPATING BY 14Z WED MORNING. LOOKING BEYOND 18Z WED... MUCH OF WED SHOULD BE DRY WITH VFR CONDITIONS THROUGH EARLY EVENING... THEN THE WEATHER BECOMES MORE ACTIVE AS A STRONG UPPER LEVEL DISTURBANCE APPROACHES FROM THE WNW AND MOVES THROUGH THE REGION WED EVENING THROUGH EARLY FRI MORNING. WHILE VFR CONDITIONS WILL BE OBSERVED THROUGH THE MAJORITY OF THIS PERIOD... SCATTERED TO NUMEROUS SHOWERS AND STORMS ARE EXPECTED AT ANY TIME... ESPECIALLY LATE THU AFTERNOON INTO EARLY FRI MORNING... AND SUB-VFR CONDITIONS WILL BE POSSIBLE IN/NEAR ANY OF THESE SHOWERS AND STORMS... WITH POSSIBLE SUB-VFR STRATUS AND FOG BETWEEN BOUTS OF RAIN. IMPROVING CONDITIONS TO MAINLY VFR IS EXPECTED FRI AFTERNOON THROUGH SAT AS HIGH PRESSURE BUILDS IN. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD SHORT TERM...HARTFIELD LONG TERM...22 AVIATION...HARTFIELD

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