Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 020727 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 327 AM EDT TUE SEP 2 2014 .SYNOPSIS...AN AREA OF HIGH PRESSURE WILL EXTEND OVER THE REGION TODAY. A WEAK SURFACE FRONT WILL SETTLE SOUTHWARD ACROSS CENTRAL NC ON WEDNESDAY. HIGH PRESSURE WILL BUILD BACK OVER THE AREA FOR THE REMAINDER OF THE WORK WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 300 AM TUESDAY... BERMUDA HIGH PRESSURE REMAINS IN CONTROL OVER THE REGION AND WILL CREATE ANOTHER HOT AND HUMID DAY ACROSS CENTRAL NC. THE THERMAL RIDGE...WHERE H85 TEMPS VERIFIED AT 19C AT 00Z...WILL EXPAND ACROSS THE PIEDMONT TODAY...AND GUIDANCE IS IN VERY GOOD AGREEMENT ON HIGHS OF 93-97 WITH JUST ISOLATED STORMS AT BEST DURING THE AFTERNOON HOURS. DEWPOINTS WILL AGAIN MIX OUT A LITTLE MORE IN THE WEST...WITH HIGHER HEAT INDEX VALUES AROUND 100 DEGREES EAST OF US HWY 1. MEANWHILE...A SHORTWAVE OVER MID-MISSISSIPPI RIVER VALLEY REGION WILL CROSS THE UPPER OHIO VALLEY AND GREAT LAKES REGION THIS EVENING...LEADING TO WEAK HEIGHT FALLS AS FAR SOUTH AS THE NC/VA BORDER. AS THE ASSOCIATED COLD FRONT SLIPS SOUTH INTO VA THIS EVENING...MODELS INDICATE ONGOING PREFRONTAL CONVECTION CROSSING THE MOUNTAINS AND POTENTIALLY CONTINUING INTO AT LEAST THE WESTERN AND NORTHERN PIEDMONT BY MIDNIGHT AS PW INCREASE TO NEAR 2 INCHES. HOWEVER... FORCING WILL MUCH WEAKER THIS FAR SOUTH AWAY FROM THE MAIN SHORTWAVE...SO COVERAGE IS STILL A LITTLE UNCERTAIN. WEAK SHEAR AND NOCTURNAL STABILIZATION SHOULD LIMIT THE INTENSITY OF THE CONVECTION...BUT WITH ONLY ISOLATED STORMS EXPECTED THIS AFTERNOON...THERE SHOULD BE SOME LINGERING INSTABILITY AS DEWPOINTS RECOVER DURING THE EVENING. THUS...IF CONVECTION CAN CONTINUE INTO THE AREA...A STRONG TO SEVERE STORM MAY STILL BE POSSIBLE THIS EVENING AND OVERNIGHT. POPS WILL INDICATE THE INCREASING CHANCE THROUGH THE EVENING HOURS...DECREASING WITH SOUTHERN EXTENT AFTER MIDNIGHT. LOWS IN THE UPPER 60S AND LOWER 70S. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... AS OF 305 PM MONDAY... FOR WED/WED NIGHT: THE WEAK SURFACE REFLECTION THAT REMAINS FROM THE COLD FRONT APPROACHING CENTRAL NC WILL BECOME EVEN MORE WASHED OUT AS IT SHIFTS INTO THE LEE TROUGH OVER CENTRAL NC. MODELS SHOW A VERY WEAK VORTICITY LOBE ASSOCIATED WITH THIS FRONT PUSHING ESE THROUGH NC EARLY WED... AND ITS APPROACH ALONG WITH LINGERING STRONG LOW LEVEL MOISTURE TRANSPORT OVER ERN NC SHOULD SUPPORT AN AREA OF ATYPICAL MORNING SHOWERS/STORMS OVER THE ERN AND ESPECIALLY SE CWA WED MORNING. THE DEPARTURE AND DAMPENING OF THE MEAN MID LEVEL TROUGH WELL TO OUR NE WILL RESULT IN MODEST RISING HEIGHTS (15-25 M) WITHIN THE FLAT (W-E ORIENTED) MID LEVEL RIDGE ACROSS NC THROUGH WED NIGHT. THE LATEST NAM RUN IS CONSISTENT WITH PREVIOUS RUNS IN BRINGING LOWER PW (UNDER 1.5") INTO MUCH OF THE CWA FROM THE NW WITH A BIT STRONGER 850-700 MB NW WIND AS COMPARED TO THE GFS... WHICH KEEPS PW VALUES UP TO 1.7-1.9". GIVEN THE FACT THAT THE MID LEVEL TROUGH WILL BE DAMPENING WITH LITTLE REASON TO SUPPORT A STRONG PUSH OF DRY AIR PAST THE MOUNTAINS... THE GFS`S MORE SUBDUED TROUGH INFLUENCE APPEARS MORE LIKELY... BASED ON THE PERSISTENCE OF THE STRONG RIDGE. MODERATE INSTABILITY IS EXPECTED OVER ALL BUT PERHAPS THE FAR NW... WITH THE GFS SHOWING MUCAPE PEAKING AT 1000-2500 J/KG. WILL STAY CLOSE TO THE GFS/ECMWF SOLUTION WITH SCATTERED AFTERNOON THROUGH EVENING STORMS... WITH BEST COVERAGE ACROSS THE SOUTHERN CWA AND ALONG/EAST OF THE PERSISTENT LEE TROUGH... AS WELL AS ALONG THE INLAND-TRACKING SEA BREEZE. WITH ABOVE-NORMAL PW AND WEAK MID LEVEL FLOW... SLOW-MOVERS AND HEAVY-RAINERS ARE POSSIBLE. WITH THICKNESSES A TAD LOWER THAN TUE BUT REMAINING 12-20 M ABOVE NORMAL... EXPECT WARM AND STICKY HIGHS OF 91-95... DESPITE A GOOD CHANCE OF DEBRIS CLOUD COVER THROUGH THE DAY. CONVECTION CHANCES SHOULD RECEDE WED NIGHT BUT THE GFS INDICATES PLENTY OF ELEVATED BUOYANCY POTENTIAL OVERNIGHT... INCLUDING MLCAPE OF 500-1000 J/KG RESULTING FROM VERY WARM 960-920 MB TEMPS. WILL HOLD ONTO CHANCE POPS MAINLY SOUTH HALF OVERNIGHT. MUGGY LOWS IN THE LOW-MID 70S. -GIH && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 325 AM TUESDAY... THE SUB-TROPICAL RIDGE WILL BRIEFLY EXPAND NORTHWARD...INTO THE OH VALLEY AND MIDDLE ATLANTIC...THROUGH FRI. MEANWHILE...A MID LEVEL SHEAR AND MOIST AXIS...THE TAIL END OF A TROUGH ALOFT FORECAST TO CROSS THE NORTHEAST US AND SOUTHEAST CANADA...WILL REMAINS DRAPED ACROSS THE CAROLINAS THROUGH THE MIDDLE OF THIS WEEK. MEDIUM RANGE ENSEMBLE GUIDANCE SUGGESTS THE SUB-TROPICAL RIDGE WILL THEN WEAKEN AND BECOME SUPPRESSED...IN PROGRESSIVE FLOW ALOFT...BY ANOTHER TROUGH FORECAST TO CROSS THE NE US AND SE CANADA THIS WEEKEND... BEFORE YET ANOTHER ESTABLISHMENT OF THE RIDGE ACROSS THE SOUTHEAST THROUGH THE MIDDLE OF NEXT WEEK. THE EBB AND FLOW OF THE PATTERN ALOFT...AND ASSOCIATED PERIODIC RELAXATION OF THE SUB-TROPICAL RIDGE...WILL ALLOW A SFC COLD FRONT TO SETTLE INTO THE CAROLINAS SUN-MON. THE FAVORED ECMWF ENSEMBLE MEAN SOLUTION SUGGESTS THE FRONT WILL SETTLE SOUTH THROUGH CENTRAL NC SUN AND SUN NIGHT...THEN STALL INVOF THE EASTERN CAROLINAS/ ADJACENT GULF STREAM WATERS...AS IT MEETS RESISTANCE FROM RENEWED SUB-TROPICAL RIDGING EXPANDING FROM THE SW ATLANTIC TO THE GOM EARLY NEXT WEEK. THU: THE PRESENCE OF THE AFOREMENTIONED MID LEVEL SHEAR/MOIST AXIS THROUGH THU WILL PROVIDE FOR A DEEPLY MOIST ENVIRONMENT...ONE CHARACTERIZED BY PWAT VALUES BETWEEN ONE AND THREE QUARTERS AND TWO INCHES...WHICH SHOULD SUPPORT SHOWER AND THUNDERSTORM GROWTH IN A MODERATELY UNSTABLE AND WEAKLY INHIBITED REGIME OVER OUR REGION. WITH CONSIDERABLE MID AND HIGH CLOUDS ACCOMPANYING THE SHEAR AXIS ALOFT...AND CONVECTION...TEMPERATURES ARE APT TO CLIMB SHORT OF WHAT CONTINUED WARM H85 TEMPS OF AROUND 18C WOULD SUPPORT - HIGHS AROUND 90. IF MORE SUNSHINE WERE REALIZED...HIGHS WOULD BE A CATEGORY WARMER. FRI-SAT NIGHT: A PATTERN OF WEAK SYNOPTIC-SCALE ASCENT FRI-SAT NIGHT...AHEAD OF THE AFOREMENTIONED COLD FRONT...WILL THEN FAVOR NEAR CLIMO PROBABILITIES OF DIURNALLY; PIEDMONT TROUGH, AND SEA BREEZE-DRIVEN CONVECTION...WITH HIGHS EDGING INTO THE LOWER 90S BENEATH THE BRIEFLY BUILDING SUB-TROPICAL RIDGE. SUN-MON: THE BEST CHANCE OF SHOWERS AND STORMS DURING THE LONG TERM PERIOD WILL ACCOMPANY THE ARRIVAL/PASSAGE OF THE COLD FRONT SUN-SUN NIGHT...WITH LESSENING PROBABILITIES/DRYING FROM NW TO SE...ON MON. COOLER INVOF AND BEHIND THE FRONT...WITH HIGHS GENERALLY IN THE LOWER TO MIDDLE 80S. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... AS OF 140 AM TUESDAY... VFR CONDITIONS CURRENTLY OBSERVED ACROSS CENTRAL NC. EXPECT A FEW AREAS OF STRATUS WILL BE POSSIBLE THIS MORNING BETWEEN 09Z AND 12Z...MAINLY FROM KFAY NORTH TO KRWI. HOWEVER...BASED ON NEAR TERM GUIDANCE...CONFIDENCE IS INCREASING THAT THE AREAL COVERAGE OF STRATUS WILL BE RATHER LIMITED. LATER TODAY...ISOLATED STORMS WILL BE POSSIBLE...WITH A BETTER CHANCE THIS EVENING AND INTO THE OVERNIGHT HOURS AS A WEAK COLD FRONT SLIPS INTO NC FROM THE NORTH. AT THIS TIME... CONFIDENCE IN THE TIMING OF STORMS IS TOO LOW FOR MENTION IN THE TAFS BUT INCREASE WITH SUBSEQUENT TAF ISSUANCES. OUTLOOK...TYPICAL SUMMERTIME CONDITIONS ARE EXPECTED TO PERSIST THROUGH THE PERIOD...FEATURING DIURNAL CONVECTION EACH AFTERNOON/EVENING AND PATCHY FOG/LOW CLOUDS DURING THE PRE-DAWN MORNING HOURS. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...BLS SHORT TERM...WSS/HARTFIELD LONG TERM...MWS AVIATION...KRD/BLS

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