Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 260612 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 210 AM EDT SAT JUL 26 2014 .SYNOPSIS...A SURFACE TROUGH WILL DEVELOP OVER THE WESTERN PIEDMONT THIS WEEKEND...RESULTING IN A VERY WARM SOUTHWEST FLOW. A STRONG COLD FRONT WILL CROSS THE AREA ON MONDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 210 AM SATURDAY... SHEARED S/W TROUGH AXIS WILL TRAVERSE THE AREA THIS MORNING... RESULTING IN SCATTERED TO OCCASIONALLY BROKEN MID AND HIGH CLOUDS. SUBSIDENCE WILL FOLLOW IN ITS WAKE...COINCIDENT WITH PEAK AFTERNOON HEATING...WHICH SHOULD LARGELY SUPPRESS CONVECTIVE RAIN CHANCES TODAY AS FORCING WILL OTHERWISE BE CONFINED TO VERY SHALLOW CONVERGENCE ASSOCIATED WITH THE DEVELOPING PIEDMONT SFC TROUGH. LOW-LEVEL THICKNESSES ARE PROGGED TO REBOUND 20M FROM YESTERDAY AND DESPITE SOME MORNING CLOUDS FROM BOTH S/W MOVING THROUGH THE AREA ALONG WITH SLOW LIFTING/DISSIPATION OF MORNING STRATUS ANTICIPATE WE SHOULD REACH FULL SUN READINGS. HIGHS IN THE UPPER 80S/NEAR 90 NORTH TO LOWER 90S SOUTH. LOWS TONIGHT UNDER CLEAR SKIES IN THE LOWER TO MID 70S. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 300 PM FRIDAY... SUN/SUN NIGHT: A SHORTWAVE TROUGH MOVING OUT OF CANADA AND ACROSS THE GREAT LAKES SUNDAY WILL BEGIN THE AMPLIFICATION OF THE LONGWAVE PATTERN FOR NEXT WEEK. EXPECT CONVECTION CONVECTION TO BE ONGOING OVER THE CENTRAL APPALACHIANS EARLY SUNDAY....WHICH SHOULD CONTINUE EAST INTO VA AND MAY BLEED SOUTH ALONG OUTFLOW INTO THE NORTHERN PORTIONS OF THE CWA. THE 12Z GFS BACKED OFF SIGNIFICANTLY ON THE COVERAGE OF CONVECTION OVER VA...SO CHANCE POPS ACROSS THE NORTHERN PIEDMONT AND COASTAL PLAIN ARE STILL A LITTLE UNCERTAIN. THE BIGGER STORY ON SUNDAY WILL BE THE HEAT AND HUMIDITY...AS DEEP MIXING AND 850MB TEMPS IN EXCESS OF 21C WILL LEAD TO HIGHS IN THE MID AND UPPER 90S. THE GFS EVEN SUGGESTS 100 IN A FEW SPOTS. MIXING WILL DROP DEWPOINTS A BIT...ESPECIALLY WEST OF THE PIEDMONT TROUGH...BUT TO THE EAST DEWPOINTS ARE FORECAST TO REMAIN IN THE UPPER 60S TO AROUND 70. THE RESULTING HEAT INDEX VALUES ARE IN THE 100-105 RANGE FOR A FEW HOURS AND MAY NECESSITATE A HEAT ADVISORY. A SOUTHWEST WIND WILL CONTINUE OVERNIGHT SUNDAY NIGHT AND LOWS WILL BE MUGGY IN THE MID TO EVEN UPPER 70S. MON/MON NIGHT: A STRONG COLD FRONT APPROACHING FROM THE NORTHWEST WILL CROSS THE CWA ON MONDAY AS ADDITIONAL SHORTWAVE ENERGY DIVES THROUGH THE BACKSIDE OF THE UPPER TROUGH. UNSEASONABLY STRONG 40- 60M HEIGHT FALLS OVERSPREADING WHAT IS EXPECTED TO BE A MOIST AND MODERATELY UNSTABLE AIRMASS WILL AID IN THE DEVELOPMENT OF STORMS ALONG AND AHEAD OF THE FRONT. BASED ON 40-50KT OF 0-6KM BULK SHEAR ASSOCIATED WITH THE DEEP PUSH OF THE STRONG WESTERLIES AND LONG...THERE IS GOOD CONFIDENCE THAT SUPERCELLS WITH A LARGE HAIL AND DAMAGING WIND THREAT WILL BE POSSIBLE. THE BIGGEST QUESTION WILL BE EXACTLY WHERE THE LEE TROUGH SETS UP AND HOW MUCH DEWPOINTS MIX OUT AS WEST-SOUTHWESTERLY LOW-LEVEL FLOW STRENGTHENS. EAST OF THE TROUGH...MOST LIKELY FROM US HWY 1 EAST...MODERATE INSTABILITY IS EXPECTED WITH FAIRLY STEEP MID-LEVEL LAPSE RATES OF -6C/KM TO MAYBE EVEN -7C/KM. FORECAST SOUNDINGS ALSO SHOW RATHER DRY MID- LEVEL AIR...THOUGH THE FORCING AND INSTABILITY SHOULD BE ABLE TO OVERCOME THIS...AND THE DRY AIR WILL LIKELY ENHANCE DAMAGING WIND THREAT. AT THE MOMENT...CONFIDENCE IS STRONG THAT SEVERE WEATHER WILL BE POSSIBLE...BUT THE UNCERTAINTY LIES HOW FAR EAST STORMS WILL DEVELOP AND THE OVERALL COVERAGE. HIGHS MONDAY WILL BE IN THE LOW TO MID 90S. -BLS && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 300 PM FRIDAY... IN THE WAKE OF THE THE FRONT ON MONDAY MEDIUM RANGE ENSEMBLES AND DETERMINISTIC MODELS SHOW AN UNSEASONABLY DEEP UPPER TROUGH DEVELOPING OVER THE EASTERN US BY MID WEEK WITH AN UPPER LOW CENTERED JUST SOUTH OF THE HUDSON BAY. MOST OF THE WEEK APPEARS TO BE STABLE WITH HIGH PRESSURE SETTLING ACROSS THE MID-ATLANTIC STATES AND DEWPOINTS IN THE UPPER 50S AND LOWER 60S. LOW-LEVEL THICKNESSES ARE PROGGED TO DIP BELOW 1390M...WHICH SUGGESTS HIGHS IN THE LOW/MID 90S AND LOWS IN THE LOW/MID 60S... POSSIBLY TOUCHING THE UPPER 50S IN THE COOLEST SPOTS. MORE UNCERTAINTY ARISES LATER IN THE WEEK WITH MODELS SHOWING SOME DEGREE OF FLOW SEPARATION WHERE AN UPPER LOW CUTS OFF AND DRIFTS SOUTH. WHETHER OR NOT THIS OCCURS REMAINS TO BE SEEN...SO AT THIS POINT WILL JUST HAVE A SLIGHT CHANCE POP BY FRIDAY AS MOISTURE STARTS TO INCREASE BACK ACROSS THE AREA. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... AS OF 130 AM SATURDAY... 24-HR TAF PERIOD: RESIDUAL LOW-LEVEL MOISTURE AND LIGHT SELY WINDS WILL RESULT IN STRATUS OVERNIGHT AND POCKETS OF FOG OVERNIGHT. CEILINGS OF IFR TO MVFR ARE POSSIBLE WITH GUIDANCE SUGGESTING THE BEST FOG POTENTIAL IN THE EAST...NEAR KFAY AND KRWI...WHERE SFC DEWPOINTS HAVE REMAINED IN THE LOWER 70S. PERHAPS SOME LINGERING MVFR STRATOCUMULUS COULD LINGER INTO THE LATE MORNING BEFORE VFR CONDITIONS RETURN BY EARLY AFTERNOON WITH OVERALL DRY CONDITIONS EXPECTED. LOOKING AHEAD: A COLD FRONT WILL APPROACH FROM THE NW SUNDAY/EARLY NEXT WORK WEEK... BRINGING THE POTENTIAL FOR SHOWERS/STORMS AND SUB- VFR CONDITIONS LATE SUNDAY (IN THE NORTHWEST) INTO MONDAY... PARTICULARLY MONDAY (ESPECIALLY EAST). VFR CONDITIONS ARE EXPECTED TO RETURN BEHIND THE FRONT ON TUESDAY AND CONTINUE THROUGH AT LEAST MID WEEK. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...CBL SHORT TERM...VINCENT/BLS LONG TERM...BLS AVIATION...CBL

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