Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 042349 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 749 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/... 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 && .LONG TERM /THURSDAY THROUGH TUESDAY/... AS OF 315 PM TUESDAY... OVERALL THE SYNOPTIC PATTERN THROUGHOUT THE LONG TERM PERIOD WILL FEATURE RIDGING OVER THE SOUTH-CENTRAL/SOUTHWEST CONUS AND TROUGHING (WITH VARYING STRENGTHS) OVER THE EAST. GIVEN THIS UPPER LEVEL FLOW PATTERN...MUCH OF OUR WEATHER WILL BE DICTATED BY NUMEROUS SHORTWAVES (WHICH ARE IMPOSSIBLE TO ACCURATELY PREDICT THIS FAR OUT). TWO DISTURBANCES ARE PROGGED TO CROSS THE REGION DURING THE LATE THURSDAY INTO FRIDAY TIME FRAME. THE GFS AND ECMWF STILL DIFFER QUITE A BIT...LEADING TO A LOW CONFIDENCE FORECAST. WITH REGARDS TO THE FIRST WAVE THURSDAY NIGHT INTO EARLY FRIDAY...THE GFS IS WEAKER AND DISORGANIZED AND THE ECMWF/NAM ARE SIGNIFICANTLY STRONGER. THE GFS SHOWS A STRONGER WAVE LATE FRIDAY INTO EARLY SATURDAY...WHILE THE OTHER MODELS ARE MUCH WEAKER WITH THIS PARTICULAR FEATURE. REGARDLESS OF SOLUTIONS...PRECIP CHANCES ARE EXPECTED TO RAMP UP LATE THURSDAY INTO FRIDAY WITH THE APPROACH OF THE DEEPER SHORT WAVE/SURFACE FRONT BEFORE DECREASING LATE FRIDAY NIGHT INTO SATURDAY AS THE SECOND WAVE PUSHES THE FRONT EAST. GIVEN THE MODEL DIFFERENCES...PRECIP TIMING (STARTING AND ENDING) AND EXACT COVERAGE VARY...BUT THE SAME OVERALL TREND IS THERE. BY THE WEEKEND...BOTH MODELS ARE THEN IN FAIRLY GOOD AGREEMENT WITH THE FRONT BEING PUSHED TO OUR EAST...AND BECOMING NEARLY STATIONARY THERE. HIGH PRESSURE WILL BUILD IN AND THIS SHOULD RESULT IN A MOSTLY DRY FORECAST...WITH ONLY SOME ISOLATED DIURNAL TYPE ACTIVITY...MOSTLY ACROSS THE EAST IN CLOSER PROXIMITY TO THE BOUNDARY. THE HIGH WILL BEGIN TO SHIFT OFFSHORE EARLY NEXT WEEK AND THEREFORE PRECIP CHANCES WILL SLOWLY BEGIN TO INCREASE. TEMPS WILL BE RATHER WARM TO START THE PERIOD (HIGHS IN THE LOW/MID 90S...LOWS IN THE LOW/MID 70S)...BUT BY THE WEEKEND THEY SHOULD FALL SOME BEHIND THE FRONT (HIGHS IN THE MID/UPPER 80S...LOWS IN THE MID/UPPER 60S). && .AVIATION /00Z WEDNESDAY THROUGH SATURDAY/... AS OF 745 PM TUESDAY... VFR CONDITIONS ACROSS THE AREA ARE LIKELY TO CONTINUE THROUGH MUCH OF THE 24 HOUR PERIOD. THERE IS SOME POTENTIAL FOR SUB-VFR CONDITIONS AT KFAY AND KRWI WITH FOG IN THE MOISTER AIR MASS IN THE EASTERN PART OF STATE... OR SOME SUB-VFR CIGS REACHING KRWI ASSOCIATED WITH LOW PRESSURE MOVING ALONG THE COAST... BUT CONFIDENCE REMAINS LOW IN EITHER POSSIBILITY AT THIS TIME. WINDS WILL REMAIN LIGHT... BECOMING GENERALLY WESTERLY WED AFTERNOON. 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...KRD AVIATION...30/HARTFIELD

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