Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 160540 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 140 AM EDT TUE SEP 16 2014 .SYNOPSIS...A COLD FRONT APPROACHING THE REGION FROM THE WEST TONIGHT WILL TRACK SLOWLY SOUTHWARD THROUGH THE CAROLINAS TODAY AND TONIGHT. THE FRONT WILL GRADUALLY MOVE OFFSHORE THE SOUTHEAST COAST ON WEDNESDAY AND THURSDAY AS HIGH PRESSURE STRENGTHENS OVER THE GREAT LAKES AND EXTENDS SOUTHWARD THROUGH THE MID ATLANTIC. && .NEAR TERM /OVERNIGHT/... AS OF 1045 PM MONDAY... OVERVIEW: CENTRAL NC IS SITUATED ON THE NORTHEAST PERIPHERY OF A GULF COAST RIDGE...AT THE SOUTHERN FRINGE OF THE WESTERLIES IN BROAD CYCLONIC FLOW ALOFT. 02Z WV IMAGERY AND RAP DATA INDICATED SMALL AMPLITUDE SHORTWAVE ENERGY OVER EASTERN TN AND FAR SOUTHWESTERN NC. PRECIPITATION: COMPACT DPVA IN THE PRESENCE OF LOW-LEVEL MOISTENING/ WARM ADVECTION AND RESULTING DESTABILIZATION ALLOWED CONVECTION TO BLOSSOM OVER THE MOUNTAINS/FOOTHILLS BETWEEN 21-00Z. THIS ACTIVITY HAS PERSISTED AND PROGRESSED EASTWARD TO THE YADKIN RIVER BY 03Z AND APPEARS TO BE EITHER 1) ELEVATED OR 2) HIGH-BASED WITH CONVECTIVE CEILINGS AT 7-10 KFT AND OBSERVATION SITES REPORTING SPRINKLES/LIGHT RAIN WITH 7-10SM VISBYS AS PRECIP FALLS THROUGH A DRY MID-LEVEL AIRMASS (AS SEEN ON THE 00Z GSO SOUNDING). THIS ACTIVITY WILL TRACK EAST TOWARD THE HWY 1 CORRIDOR THROUGH 06Z IN ASSOC/W THE APPROACHING SHORTWAVE...THOUGH IT WILL ENCOUNTER AN INCREASINGLY UNFAVORABLE THERMODYNAMIC ENVIRONMENT AND THUS APPEARS LIKELY TO WEAKEN WITH EASTWARD PROGRESSION. WILL INDICATE A SLIGHT TO LOW CHANCE OF SHOWERS/SPRINKLES THROUGH 06Z WEST OF I-95...WITH THE BEST CHANCE IN THE WESTERN PIEDMONT. -VINCENT && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... AS OF 300 PM MONDAY... FOR TUE/TUE NIGHT: THE WEAK SURFACE TROUGH WILL BE IN PLACE OVER ERN NC TUE MORNING... AND WILL EXTEND A SLIGHT CHANCE OF SHOWERS IN THE SOUTHEAST INTO TUE TO REFLECT THE TROUGH`S PRESENCE AND THE DEPARTING MID LEVEL WAVE. WITH SUBSEQUENT NORTHWESTERLY DOWNSLOPE 925-850 MB FLOW... WE SHOULD THEN BE FAIRLY DRY FOR SEVERAL HOURS... UNTIL THE NEXT MID LEVEL VORTICITY MAX AND ACCOMPANYING STRONGER SURFACE COLD FRONT APPROACH FROM THE NW BY EARLY-MID AFTERNOON. SURFACE-925 MB LOW PRESSURE ALONG THIS FRONT WILL APPROACH FROM THE NW AND BECOME BETTER DEFINED AS IT CROSSES THE MOUNTAINS INTO THE PIEDMONT OF NC DURING THE AFTERNOON. MODELS SHOW A POCKET OF 6+ C/KM MID LEVEL LAPSE RATES CROSSING SRN NC LATE TUE ALONG WITH NEGATIVE LI VALUES. MUCAPE SHOULD PEAK AT JUST 750-1500 J/KG FOCUSED ON THE SOUTHEAST... AND DEEP LAYER SHEAR IS MARGINAL AT ABOUT 20-25 KTS... BUT THESE NUMBERS COMBINED WITH LOW LEVEL MASS CONVERGENCE SHOULD STILL SUPPORT SCATTERED SHOWERS AND ISOLATED STORMS LATE TUE AFTERNOON THROUGH TUE NIGHT. CONFIDENCE IN THE COVERAGE AND PLACEMENT IS NOT GREAT HOWEVER... AS THERE IS LITTLE AGREEMENT IN QPF AND POPS AMONG THE NAM/GFS/ECMWF. BUT GENERALLY EXPECT THE BEST COVERAGE TO BE IN THE SOUTHEAST CWA... WHERE MOISTURE TRANSPORT AND INSTABILITY WILL BE BEST... FROM LATE AFTERNOON THROUGH THE EVENING... TAPERING DOWN TO ISOLATED SHOWERS OVERNIGHT. THICKNESSES ADJUSTED FOR CLOUDS AND POSSIBLE SHOWERS LATE SUPPORT HIGHS FROM 82 TO 86. LOWS 60-65 TUE NIGHT AS COOLER AND DRIER AIR STARTS TO FILTER IN POST-FRONT FROM THE NNW. -GIH WEDNESDAY AND WEDNESDAY NIGHT...WESTERLY FLOW ALOFT WILL INDUCE PROGRESSIVE TOP DOWN DRYING THROUGH WEDNESDAY NIGHT...LESSENING THE DEPTH OF MOISTURE...WHILE NORTHEAST LOW LEVEL FLOW MAINTAINS MOISTURE THROUGH ABOUT 5KFT THROUGH THURSDAY MORNING. A SHORT WAVE WILL BE MOVING ACROSS THE SOUTHERN PERIPHERY OF THE AREA ON WEDNESDAY...ACCOMPANIED BY AN H85 WAVE THAT WILL ENHANCE LIFT VIA CONVERGENCE AND WEAK ISENTROPIC LIFT AT THE TOP OF THE MOISTURE COLUMN. HENCE WILL MAINTAIN A CHANCE POP FOR SHOWERS ACROSS THE SOUTH AND A SLIGHT CHANCE ACROSS THE NORTH THROUGH WEDNESDAY... DIMINISHING TO A LINGERING SLIGHT CHANCE IN THE EAST INTO THURSDAY. COOL AIR ADVECTION WILL COMMENCE LATE DAY AS THE SHORT WAVE PASSES AND WITH THE DAMPNESS AND CHANCE OF SHOWERS...HIGHS WEDNESDAY WILL RANGE FROM 75 TO 80...WITH SOME LOWER 70S POSSIBLE ACROSS THE NORTHEAST WHERE COOL AIR WILL ARRIVE A LITTLE SOONER. LOWS WEDNESDAY NIGHT WILL BE MAINLY IN THE UPPER 50S. -MLM && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 245 PM MONDAY... A LONG WAVE TROF SETS UP ACROSS THE EASTERN CONUS BY LATE WEEK... CONCURRENT WITH STRONG HIGH PRESSURE BUILDING INTO EASTERN CANADA AND DOWN THE EAST COAST ON FRIDAY WITH THE RESULTING DAMMING SCENARIO LINGERING THROUGH THE WEEKEND. LOW AMPLITUDE MID LEVEL RIDGING SHOULD INHIBIT PRECIP CHANCES THROUGH THE WEEKEND...WHILE THE PROLONGED EAST TO NORTHEAST LOW LEVEL FLOW OFF THE ATLANTIC WILL SUPPRESSES HIGH TEMPS INTO THE LOW AND MID 70S THROUGH SATURDAY. A STRONG TROF MOVING ACROSS THE MIDWEST WILL NUDGE THE SURFACE HIGH FURTHER OFFSHORE. THE WEAKENED FLOW WILL ALLOW THE AIRMASS TO MODERATE ON SUNDAY...WITH HIGHS MOSTLY IN THE UPPER 70S. FLOW VEERS TO SOUTHWEST BY MONDAY AHEAD OF THE UPPER TROF AND SURFACE FRONT...WITH INCREASING MOISTURE IN THE RESULTING RETURN FLOW AND A CHANCE OF SHOWERS BY LATE DAY MONDAY. HIGHS MONDAY WILL BE WITHIN A DEGREE OR TWO OF 80. MORNING LOWS THROUGH THE PERIOD WILL BE MOSTLY FROM 55 TO 60 DEGREES. -MLM && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... AS OF 140 AM TUESDAY... AVIATION CONDITIONS AT 0530Z VARY FROM VFR TO MVFR ACROSS CENTRAL NC. A DETERIORATING TEND ANTICIPATED THROUGH 10Z WITH IFR/LIFR CEILINGS HIGHLY PROBABLE AND WIDESPREAD MVFR VISIBILITY DUE TO FOG. THE ADVERSE AVIATION CONDITIONS SHOULD LINGER THROUGH 14Z WITH AN IMPROVEMENT TO VFR CONDITIONS MOST LOCATIONS BY 16Z. SURFACE WINDS WILL BE LIGHT AND VARIABLE...BECOMING NORTH NORTHWEST AT 5KTS OR LESS AFTER 14Z AS A WEAK COLD FRONT DRIFTS ACROSS THE REGION. PATCHES OF LIGHT RAIN WILL OCCUR AHEAD OF THIS FEATURE. LATER THIS AFTERNOON...ISOLATED SHOWERS AND POSSIBLY A THUNDERSTORM MAY OCCUR...MAINLY IN THE VICINITY OF KFAY. VFR CONDITIONS ANTICIPATED TONIGHT THROUGH WEDNESDAY WITH A BRIEF PERIOD OF MVFR CEILING/VISIBILITY POSSIBLE EARLY WEDNESDAY MORNING. THE PERIOD THURSDAY THROUGH SATURDAY APPEARS TRANQUIL WITH MAINLY VFR CONDITIONS. A BRIEF INSTANCE OF MVFR CEILING OR VISIBILITY MAY OCCUR EACH MORNING...MAINLY IN THE VICINITY OF KRWI AND KFAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS/VINCENT NEAR TERM...VINCENT SHORT TERM...HARTFIELD/MLM LONG TERM...MLM AVIATION...WSS

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