Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 041836 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 100 PM EDT TUE AUG 4 2015 .SYNOPSIS...AN AREA OF LOW PRESSURE WILL TRACK FROM NEAR MYRTLE BEACH NORTHEASTWARD ALONG THE 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 955 AM TUESDAY... FORECAST IS IN GOOD SHAPE. LATEST SURFACE ANALYSIS SHOWS SURFACE LOW PRESSURE OFF THE NRN SC COAST POISED TO MOVE TO THE NORTHEAST TODAY NEAR THE SRN NC COAST AND SRN OUTER BANKS. A RATHER IMPRESSIVE SHIELD OF CONVECTION ACCOMPANIES THIS LOW... AND SOME OF THESE ELEMENTS HAVE SPREAD NORTHWESTWARD INTO THE SE CWA. THIS BEHAVIOR IS EXPECTED TO PERSIST THROUGH TODAY... RESULTING IN SCATTERED SHOWERS AND STORMS OVER THE SOUTHEAST COASTAL PLAIN EAST OF I-95. THIS IS IN LINE WITH NEARLY ALL COARSE AND HI-RES GUIDANCE INCLUDING THE SPC SSEO... NSSL WRF... AND NCAR ENSEMBLE OUTPUT. SUBSIDENCE ON THE WEST SIDE OF THIS FORMIDABLE LOW SHOULD HELP TEMPER MUCH OF THE CONVECTION MORE INLAND (NW OF A FAY-WILSON LINE)... HOWEVER FARTHER NW OVER THE NW AND FAR NRN PIEDMONT... SHEARED VORTICITY SPREADING ESE FROM NE/IA/MO CONVECTION INTO THE BROAD BASE OF THE MEAN LONGWAVE TROUGH WILL SPREAD INTO ERN KY/TN AND WRN VA/NC LATER THIS AFTERNOON THROUGH EVENING... LIKELY INSTIGATING ISOLATED TO SCATTERED CONVECTION ALONG EITHER AN OLD OUTFLOW AND/OR THE BAGGY PIEDMONT TROUGH... ALTHOUGH AS WAS THE CASE YESTERDAY... ENTRAINMENT OF DRY AIR WITHIN THE BELOW-NORMAL-PW ENVIRONMENT PERSISTING OVER THE WRN PIEDMONT OF NC WILL LIMIT COVERAGE/STRENGTH/LIFETIME OF ANY SUCH CONVECTION. THE HRRR AND NCAR ENSEMBLE PROBABILITIES BRING THIS CONVECTION INTO OUR NW CWA AROUND MID AFTERNOON... WITH A SLOW SOUTHEASTWARD DRIFT AND EVENTUAL DISSIPATION BY MID EVENING... IN LINE WITH THE CURRENT FORECAST WITH ONLY MINOR TWEAKS NEEDED. AFOREMENTIONED SUBSIDENCE SHOULD PROMPT GOOD HEATING PARTICULARLY OVER THE SRN AND ERN PIEDMONT AND WRN SANDHILLS (AWAY FROM THE COASTAL CLOUD SHIELD)... AND HIGHS IN THE MID-UPPER 90S APPEAR ATTAINABLE THERE... WITH LOW-MID 90S ELSEWHERE... COOLEST IN THE EXTREME ESE CWA. -GIH PREVIOUS DISCUSSION FROM 335 AM: A 1011 MB SURFACE LOW CENTERED JUST SOUTH OF KCHS IS FORECAST TO TRACK NORTHEASTWARD GENERALLY ALONG THE COAST OF THE CAROLINAS THROUGH TONIGHT. DEEP CONVECTION HAS BLOSSOMED DURING THE PAST COUPLE OF HOURS IN ASSOCIATION WITH THE LOW...AND EXTRAPOLATION OF THIS ACTIVITY (AND THE TRACK OF THE SURFACE LOW) SUGGESTS IT SHOULD REMAIN CONFINED FROM SAMPSON AND WAYNE COUNTIES AND ESPECIALLY POINTS EASTWARD...IN AXIS OF FOCUSED 925-850 MB MOISTURE TRANSPORT TO THE EAST OF AN INVERTED TROUGH AXIS FROM THE LOW CENTER. OTHERWISE...A PIEDMONT TROUGH WILL SHARPEN THIS AFTERNOON...AHEAD OF A COLD FRONT THAT WAS ANALYZED THIS MORNING FROM THE LOWER GREAT LAKES TO THE LOWER OH VALLEY. THE MODELS INDICATE THE COLD FRONT WILL SETTLE SOUTH ACROSS VA TONIGHT...TO NEAR THE NC BORDER BY WED MORNING. WILL RETAIN A 20-30 PERCENT CHANCE OF A LATE AFTERNOON AND EVENING STORM FROM ACTIVITY THAT COULD EITHER DEVELOP IN-SITU INVOF A PIEDMONT SURFACE TROUGH AND/OR THAT IS MORE LIKELY TO INITIATE UPSTREAM OVER THE NC/SW VA MOUNTAINS AND INVOF THE AFOREMENTIONED FRONT...WHICH WOULD THEN PROPAGATE AWAY FROM THOSE FORCING MECHANISMS AND INTO THE NC PIEDMONT LATE THIS AFTERNOON AND EVENING. STRONG DIURNAL HEATING OF A DEEPLY MIXED BOUNDARY LAYER...AND ASSOCIATED STEEP LOW LEVEL LAPSE RATES AND 25-30 C DEWPOINT DEPRESSIONS...WOULD SUPPORT A CONDITIONAL RISK OF STRONG TO DAMAGING DOWNBURST WIND GUSTS IF CONVECTION INDEED DEVELOPS OVER OR PROPAGATES INTO...CENTRAL NC. HOWEVER...MID LEVEL FLOW AT THIS LATITUDE/OVER CENTRAL NC WILL REMAIN ONLY MODEST TO THE SOUTH OF THE MAIN BELT OF WESTERLIES AT THE BASE OF A BROAD TROUGH CENTERED NEAR JAMES BAY...SO ANY SEVERE OCCURRENCE SHOULD BE ISOLATED. HIGH TEMPERATURES NEAR OR SLIGHTLY ABOVE THOSE OF MON GIVEN A SLIGHT UPTICK IN FORECAST LOW LEVEL THICKNESS VALUES - UPPER 80S/AROUND 90 WHERE CLOUDS SHOULD BE MOST PREVALENT FROM KCTZ AND KGSB AND POINTS EASTWARD...TO 90-98 DEGREES ELSEWHERE...HOTTEST FROM AFP TO FAY. LOWS GENERALLY 70 TO 75...AFTER ANY CONVECTION THAT DOES OCCUR MOVES EAST AND/OR DISSIPATES BY LATE EVENING. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... AS OF 350 AM TUESDAY... WHILE THE COLD FRONT WILL SETTLE SOUTH ACROSS CENTRAL NC AND SERVE AS A POSSIBLE TRIGGER FOR CONVECTION AGAIN WED AFTERNOON AND EVENING...GENERALLY WESTERLY FLOW ALOFT -INCLUDING A SIGNIFICANT DOWNSLOPE COMPONENT AT 850 MB- AND VEERED SURFACE FLOW INTO A PRE- FRONTAL TROUGH THAT THE MODELS INDICATE WILL HAVE DRIFTED INTO THE COASTAL PLAIN...SHOULD GENERALLY LIMIT COVERAGE. ANY SCATTERED OR WIDELY SO STORMS THAT DO FORM...HOWEVER...WOULD AGAIN POSE A RISK OF STRONG EVAPORATIVELY-ENHANCED WIND GUSTS. WEAK CAA NORTH OF THE BOUNDARY WILL TAKE THE EDGE OFF OF THE HEAT ACROSS THE NORTHERN PIEDMONT...WHERE LOWER 90S ARE EXPECTED...VERSUS MIDDLE TO UPPER 90S ONCE AGAIN OVER THE SOUTHERN PIEDMONT AND SANDHILLS. SLIGHTLY COOLER AND LESS HUMID AS THE FRONT SETTLES TO THE NEAR THE SC BORDER BY MORNING...WITH LOWS IN THE UPPER 60S TO AROUND 70 DEGREES. && .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...26/HARTFIELD NEAR TERM...HARTFIELD/26 SHORT TERM...26 LONG TERM...22 AVIATION...HARTFIELD

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