Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211921 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 320 PM EDT MON JUL 21 2014 .SYNOPSIS...A LOW PRESSURE AREA WILL HOLD OVER THE DEEP SOUTH THROUGH TUESDAY... RESULTING IN A MOIST ATLANTIC FLOW FROM THE SOUTHEAST INTO NORTH CAROLINA... AND UNSETTLED WEATHER TO START THE WORK WEEK. && .NEAR TERM /THROUGH TUESDAY NIGHT/... AS OF 315 PM MONDAY... A CUTOFF LOW DEVELOPING OVER THE DEEP SOUTH HAS BEEN EJECTING IMPULSES AND A DEEP PLUME OF MOISTURE NORTH ACROSS THE AREA TODAY. THESE IMPULSES HAVE PROVIDED ADDITIONAL SUPPORT FOR CLUSTERS AND LINES OF HEAVY SHOWERS AND THUNDERSTORMS ABOVE THE COOLER AND STABLE SURFACE AIRMASS IN PLACE ACROSS THE AREA. CONCURRENTLY...SOUTHEAST LOW LEVEL FLOW HAS STRENGTHENED...WITH WIDESPREAD LIGHT RAIN BREAKING OUT DUE TO THE ENSUING ISENTROPIC LIFT. AS SUCH...CATEGORICAL POPS ARE IN ORDER ACROSS THE SOUTHERN TIER...GRADUATED TO CHANCE POPS ACROSS THE NORTH. CONVECTION HAS BEEN WANING AS THE STABLE RAIN-COOLED SURFACE BASED LAYER HAS DEEPENED. THIS WANING TREND WILL CONTINUE THROUGH THE EVENING...BUT THE THREAT OF MERGERS AND TRAINING HEAVY SHOWERS WILL LINGER FOR THE NEXT FEW HOURS. ISENTROPIC LIFT WEAKENS OVERNIGHT...AND WILL SCALE POPS BACK TO CHANCE IN THE WEST...WITH SLIGHT CHANCES EAST BY MIDNIGHT...WITH A MILD HUMID MORNING ON TAP WITH LOWS WITHIN A DEGREE OR TWO OF 70. PRECIPITABLE WATER REMAINS HIGH AS WE KICK OFF THE DAY WITH IN-SITU DAMMED AIRMASS ACROSS THE AREA. GUIDANCE HIGHS TOMORROW ON THE GFS REACH THE LOW 90S...WHICH IS QUESTIONABLE GIVEN MORNING LOW CLOUDINESS AND EAST TO NORTHEAST SURFACE FLOW. WILL TREND TOWARDS MID 80S WITH MOSTLY CLOUDY SKIES. POP-WISE... THE UPPER LOW WILL RETROGRADE BACK TO THE MISSISSIPPI DELTA AREA BY LATE TUESDAY...MAINTAINING A CHANCE OF MAINLY DIURNAL CONVECTION...ESPECIALLY IN THE SOUTHWEST. DEEPER RIDGING WILL RETROGRADE INTO THE AREA TUESDAY NIGHT... VEERING THE LOW LEVEL FLOW...WEAKENING THE ISENTROPIC LIFT TO ONLY SLIGHT CHANCE POPS. WITH NO AIR MASS CHANGE...MINS AGAIN WILL BE AROUND 70. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/... AS OF 305 PM MONDAY... AN UPPER LEVEL TROUGH WILL DIVE FROM THE WESTERN GREAT LAKES REGION WEDNESDAY INTO THE SOUTHERN APPALACHIANS BY THURSDAY MORNING. THE ASSOCIATED COLD FRONT WILL STAY WEST OF THE APPALACHIANS THROUGH WEDNESDAY EVENING. THE AIR MASS ACROSS CENTRAL NC ON WEDNESDAY AFTERNOON WILL BE WARM AND UNSTABLE WITH WEAK TO MODERATE INSTABILITY VALUES OF AROUND 1000-2000 J/KG. THE AIR MASS WILL BE MOIST WITH PRECIPITABLE WATER VALUES OF 1.75 TO 2.0 INCHES. CONVECTIVE COVERAGE IS NOT EXPECTED TO BE OVERWHELMING AND LIKELY MOST FOCUSED ACROSS THE COASTAL PLAIN...EAST OF THE PIEDMONT TROUGH AND TO THE WEST ACROSS THE HIGHER TERRAIN. HIGH TEMPERATURES IN THE 88 TO 92 RANGE ARE SUPPORTED BY CONSENSUS THICKNESS VALUES AND IN BETWEEN THE WARMER MAV AND COOLER MET GUIDANCE. SCATTERED CONVECTION IS APT TO CONTINUE IN THE EARLY EVENING HOURS AND THEN BECOME ISOLATED OVERNIGHT...AGAIN THE BEST COVERAGE IS EXPECTED ACROSS THE COASTAL PLAIN AND PERHAPS MORE SO IN THE WESTERN PIEDMONT CLOSER TO THE UPPER TROUGH AND AS CONVECTION INITIATED NEAR THE MOUNTAINS MOVES EAST. OVERNIGHT LOWS SHOULD BE MODERATED BY CLOUD COVER AND SOME MIXING AHEAD OF THE APPROACHING WITH LOWS IN THE LOWER 70S. THE UPPER TROUGH REACHES THE SOUTHERN APPALACHIANS ON THURSDAY MORNING AS THE COLD FRONT SLOWLY MOVES FROM THE FOOTHILLS INTO THE PIEDMONT DURING THE MORNING AND AFTERNOON. THE AIR MASS ACROSS CENTRAL NC IS POSSIBLY EVEN MORE MOIST THAN ON WEDNESDAY WITH PRECIPITABLE WATER VALUES AROUND OR IN EXCESS OF 2 INCHES. EXPECT A GOOD AMOUNT OF CLOUD COVER WHICH MAY LIMIT INSTABILITY A BIT. THE APPROACHING TROUGH WILL RESULT IN STRONGER FLOW ALOFT AND BULK SHEAR VALUES WILL INCREASE INTO THE 20-30 KTS RANGE AND SUPPORT MORE CONVECTIVE STORM ORGANIZATION AND A SLIGHTLY ELEVATED SEVERE THREAT. POPS HAVE BEEN INCREASED TO THE HIGH CHANCE CATEGORY. MAX TEMP GUIDANCE IS EVEN WARMER COMPARED TO WEDNESDAY WITH THE WARMER MAV GUIDANCE SUGGESTING S HIGHS IN THE 94-95 RANGE AT RDU AND FAY. NOT READY TO GO THAT HIGH BUT WE HAVE INCREASED MAX TEMPS A BIT AND IF CLOUDS COVER IS LESS THAN EXPECTED...WARMER TEMPERATURES AND INCREASED INSTABILITY CAN BE EXPECTED. THE THUNDERSTORM THREAT CONTINUES INTO THURSDAY EVENING WITH THE BEST COVERAGE IN THE EAST. HIGHS THURSDAY SHOULD RANGE IN THE 88 TO 93 RANGE WITH LOWS IN THE UPPER 60S TO LOWER 70S. THE FRONT SLOWLY CLEARS CENTRAL NC FRIDAY AFTERNOON AND THEN STALLS ALONG THE NC COAST AND EXTENDS BACK INTO CENTRAL SC BY LATE FRIDAY NIGHT. A CONTINUED THREAT OF SHOWERS AND THUNDERSTORMS PERSISTS ON FRIDAY WITH THE GREATEST CHANCES ACROSS THE COASTAL PLAIN. HIGHS WILL BE NOTICEABLY COOLER THAN ON THURSDAY WITH FRIDAY MAXES IN THE MID TO UPPER 80S. LOWS WILL RANGE IN THE MID 60S TO THE NORTHWEST AND UPPER 60S TO THE SOUTHEAST. -BLAES && .LONG TERM /SATURDAY THROUGH MONDAY/... AS OF 320 PM MONDAY... THE COLD FRONT LINGERS SOUTH OF OUR AREA ON SATURDAY WITH HIGH PRESSURE EXTENDING INTO THE REGION. SATURDAY SHOULD BE THE BETTER DAY OF THE WEEKEND WITH A LIMITED THREAT OF CONVECTION...MAINLY ACROSS THE SOUTHWESTERN PIEDMONT...SANDHILLS AND SOUTHERN COASTAL PLAIN DURING THE TYPICAL AFTERNOON/EVENING PERIOD. ANOTHER UPPER LEVEL TROUGH AND ASSOCIATED COLD FRONT APPROACHES ON SUNDAY AND BRINGS AN INCREASED THREAT OF MAINLY AFTERNOON AND EVENING THUNDERSTORMS. GUIDANCE DIFFERS ON MONDAY WITH THE ECMWF BRINGER THE UPPER TROUGH THROUGH FASTER THAN THE GFS...FOR NOW WILL OPT FOR THE DRIER ECMWF SOLUTION AND DECREASE POPS FOR MONDAY. TEMPERATURES DURING THE LONG TERM RETURN TO MORE SEASONABLE VALUES WITH HIGHS IN THE MID 80S TO AROUND 90 AND MORNING LOWS IN THE UPPER 60S TO LOW 70S. -BLAES && .AVIATION /18Z MONDAY THROUGH SATURDAY/... AS OF 143 PM MONDAY... LOTS OF UNCERTAINTY AS TO SHORT TERM DETAILS AS WIDESPREAD LIGHT RAIN... WITH SCATTERED HEAVIER SHOWERS AND THUNDERSTORMS...IS EXPECTED IN THE MOIST AND QUITE UNSTABLE ENVIRONMENT OVER CENTRAL NORTH CAROLINA. CEILINGS AND VISIBILITY WILL BE LARGELY VFR WITH MVFR TO IFR CONDITIONS IN RAIN AND SCATTERED CONVECTION. THE PRECIPITATION WILL DIMINISH IN THE EVENING...AFTER 02Z...BUT CONDITIONS WILL GRADUALLY DETERIORATE AS WE COOL OVERNIGHT. MVFR VISIBILITY AND IFR TO LIFR CEILINGS WILL BE WIDESPREAD IN THE USUAL 08-13Z TIME FRAME...POTENTIALLY LINGERING INTO THE MID MORNING BEFORE LIFTING TO VFR VISIBILITY AND MVFR-VFR CEILINGS BY THE END OF THE TAF PERIOD. IN THE LONGER RANGE...WE REMAIN IN THE UNSETTLED PATTERN THROUGH FRIDAY. SCATTERED MAINLY LATE DAY CONVECTION IS EXPECTED AGAIN TUESDAY AND WEDNESDAY...THEN A BETTER CHANCE OF WIDESPREAD CONVECTION IS EXPECTED THURSDAY AND THURSDAY NIGHT AS A COLD FRONT MOVES SOUTHEAST THROUGH THE AREA. VFR CONDITIONS ARE EXPECTED FRIDAY AND SATURDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...MLM SHORT TERM...BLAES LONG TERM...BLAES/DJF AVIATION...MLM

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