Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 261840 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 240 PM 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 1105 AM SATURDAY... LINGERING LOW CLOUDS ACROSS OUR CENTRAL ZONES ARE SLOWLY LIFTING/ DISSIPATING WITH HEATING. THE 12Z GSO SOUNDING SHOWS THE LOW LEVEL MOISTURE ASSOC WITH THE AFOREMENTIONED CLOUDS...HOWEVER ALSO NOTED A DRY LAYER BETWEEN H6-H7 AND DRY ABOVE H5...ALONG WITH W-NW FLOW THROUGHOUT MUCH OF THE SOUNDING. MODIFYING THE SOUNDING SUGGESTS THE CURRENT LOW CLOUDS WILL TRANSLATE TO SHALLOW- TO PERHAPS SOME MODERATE CU THIS AFTERNOON. HOWEVER...DRY AIR ALOFT AND SUBSIDENCE IN THE WAKE OF THE DEPARTING SHORT WAVE SHOULD PRECLUDE ANY SHOWER ACTIVITY THIS AFTERNOON. THE SOUNDING ALSO SUGGESTS HIGHS IN THE UPPER 80S TO AROUND 90. CURRENT FORECAST IN GOOD SHAPE WITH NO SIGNIF UPDATES THIS MORNING. PREVIOUS NEAR TERM DISCUSSION 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/FOG 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/...
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AS OF 225 PM SATURDAY... SUNDAY: THE REMNANTS OF THE TSTM ACTIVITY CURRENTLY MOVING ACROSS THE MIDWEST WILL CROSS THE WVA AND VA MOUNTAINS AROUND SUNRISE SUNDAY. THERE`S GOOD MODEL AGREEMENT THAT ANY MIDLEVEL CIRCULATION ASSOC WITH THIS COMPLEX WILL STAY TO OUR NORTH...AND ANY SHOWER OR TSTM ACTIVITY ON THE SOUTHERN PERIPHERY OF THIS COMPLEX WILL WEAKEN OR PERHAPS DISSIPATE BEFORE AFFECTING OUR CWA. LATER IN THE DAY...WE`LL TURN OUR ATTENTION TO THE NEXT ROUND OF SHOWERS/TSTMS PROGGED TO DEVELOP UPSTREAM OVER THE OHIO VALLEY IN ADVANCE OF THE NEXT SHORT WAVE TROUGH AND ASSOC SFC FRONT. RIGHT NOW THERE`S GOOD MODEL AGREEMENT THAT ANY REMNANT ACTIVITY...DRIVEN MOSTLY BY OUTFLOW BOUNDARIES MOVING IN FROM THE WEST...WOULD AFFECT MAINLY OUR NORTHERN ZONES LATE IN THE DAY SUNDAY. BOTH THE 12Z NAM AND GFS HAVE LITTLE IF ANY QPF INDICATED DURING THE DAYTIME THROUGH THE EVENING SUNDAY SOUTH OF HWY 64. AS SUCH..WILL CONTINUE OUR CURRENT FORECAST WHICH INDICATES THE HIGHEST DAYTIME POPS (20-30%) ACROSS OUR NORTHERN ZONES TRENDING TO ONLY 10% ACROSS OUR SOUTHERN ZONES. IN TERMS OF STORM IMPACTS...DESPITE STEEP LOW AND MID LEVEL LAPSE RATES...FORECAST SOUNDINGS SUGGEST HIGH LFC LIMITING OVERALL CAPE. BUT WITH DECENT CAPE IN THE HAIL GROWTH ZONE...LARGE HAIL AND ISOLATED DAMAGING WIND GUSTS STILL CAN`T BE RULED OUT WITH ANY OF THE STRONGEST STORMS THAT DEVELOP ACROSS OUR AREA. SUNDAY NIGHT...THE PREFRONTAL SFC TROUGH IS PROGGED BY THE GFS AND NAM TO CROSS THE MOUNTAINS AROUND 06Z MONDAY THEN MOVE INTO OUR WESTERN ZONES BY 12Z MON. DESPITE THIS LOW LEVEL FORCING...THE MODELS HAVE LITTLE IF ANY QPF ACROSS MOST OF OUR CWA DURING THE OVERNIGHT HOURS...PERHAPS DUE IN PART TO A DRY WESTERLY FLOW PRECEDING IT AND LOW LEVEL NIGHT-TIME STABILITY. ANY CONVECTION THAT CAN GET GOING OVERNIGHT WOULD LIKELY BE ELEVATED...BUT STILL WORTH CLOSE WATCHING. FOR NOW WILL CONTINUE SLIGHT CHANCE POPS ACROSS THE ENTIRE CWA SUNDAY NIGHT. THE OTHER MAIN CONCERN FOR SUNDAY IS TEMPS AND HIGH HEAT INDICES. GUIDANCE CURRENTLY HAS TEMPS RANGING FROM AROUND 94 NW TO AROUND 98 SE. WITH DWPTS RANGING FROM THE MID 60S NW TO AROUND 70 SE...HEAT INDICES WILL LIKELY RANGE FROM 100-103 ACROSS OUR SOUTHERN COASTAL PLAIN ZONES. WHILE THIS IS BELOW HEAT ADVISORY CRITERIA...WE HAVE HAVE THIS HIGHLIGHTED IN OUR CURRENT HWO. LOWS SUNDAY NIGHT IN THE LOWER TO MID 70S. -NP MONDAY AND MONDAY NIGHT: THE UNSEASONABLY STRONG SHORTWAVE TROUGH/LOW TRAVERSING THE GREAT LAKES THIS WEEKEND WILL MOVE NE THROUGH NY AND ALONG THE U.S./CANADA BORDER THROUGH MONDAY NIGHT. ITS ASSOCIATED COLD FRONT WILL MOVE THROUGH THE AREA MONDAY AFT/EVE...RESULTING IN INCREASED CHANCES FOR SEVERE WEATHER. THE GFS AND ECMWF HAVE COME INTO BETTER AGREEMENT WITH THE TIMING AND LOCATION OF THE FRONT...HOWEVER THE CHANCES FOR CONVECTION HAVE DECREASED SOMEWHAT. THE BEST CHANCES ARE STILL MAINLY ALONG AND EAST OF I-95 FROM 18Z MONDAY THROUGH 06Z TUESDAY. IN THIS FAVORED REGION...MODELS ARE FORECASTING MUCAPE IN THE 1500-2500 J/KG RANGE...0-6 KM BULK SHEAR OF 40-50 KTS...LOW LEVEL LAPSE RATES OF 8- 8.5 DEG/KM...AND MID LEVEL LAPSE RATES OF 6.5-7 DEG/KM. LOW LEVEL SHEAR REMAINS WEAK. GIVEN THAT ENVIRONMENT...EXPECT CONVECTION... WHERE IT DEVELOPS...TO BE STRONG TO SEVERE...WITH THE MAIN THREATS BEING LARGE HAIL AND DAMAGING WINDS. THERE CONTINUES TO BE UNCERTAINTIES WITH RESPECT TO COVERAGE OF CONVECTION AND WHETHER THERE WILL BE MUCH OVER CENTRAL NC. SOME OF THE MODELS INDICATE THAT THE CONVECTION WILL FALL APART AS IT CROSSES THE APPALACHIANS... WITH SOME REDEVELOPMENT ALONG THE COAST LATE MONDAY AND/OR REMAIN NORTH OF THE NC/VA BORDER. THE GFS CONTINUES TO FORECAST THE BEST UPPER LEVEL FORCING WELL TO THE NORTH OF THE AREA. THUS...ALTHOUGH THE CHANCE FOR CONVECTION DEFINITELY EXISTS AND SHOULD IT DEVELOP ITS LIKELY THAT STORMS WILL BE STRONG/SEVERE...CONFIDENCE IS DECREASING WITH REGARD TO WHETHER STORMS WILL DEVELOP OVER THE AREA. ALSO...RESIDUAL CLOUDINESS AND OUTFLOW BOUNDARIES FROM CONVECTION SUNDAY/SUNDAY NIGHT (SHOULD IT OCCUR) MAY ALSO PLAY A ROLE IN LIMITING CONVECTION. HIGHS WILL BE MAINLY IN THE UPPER 80S NW TO MID 90S SE WITH OVERNIGHT LOWS...DEPENDING ON THE PROGRESSION OF THE FRONT...MAINLY IN THE LOW 60S NW TO UPPER 60S SE. -KC
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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AS OF 235 PM SATURDAY... THE UPPER LEVEL TROUGH WILL REMAIN OVER...TO JUST WEST OF THE REGION THROUGH THE PERIOD. AT THE SURFACE...HIGH PRESSURE WILL BUILD INTO THE AREA BEHIND THE FRONT...BRINGING COOLER AND DRIER AIR INTO CENTRAL NC THROUGH THE END OF THE WEEK. THIS WILL RESULT IN BELOW NORMAL TEMPERATURES...WITH HIGHS IN THE LOW TO MID 80S THROUGH THE WEEK AND LOWS FROM THE UPPER 50S TO MID 60S TUE/WED NIGHTS AND LOW TO MID 60S THU/FRI NIGHTS. WITH THE SUBSIDENCE IN THE WEST/NORTHWEST FLOW ALOFT AND SIGNIFICANTLY DRIER AIR ADVECTING INTO THE MID/UPPER LEVELS...EXPECT MUCH OF THE WEEK TO REMAIN DRY...WITH SOME SLIGHT CHANCES IN THE NW FRI/SAT AS THE UPPER LEVEL TROUGH SHIFTS WEST AND THE PIEDMONT TROUGH TRIES TO DEVELOP OVER THE AREA ONCE AGAIN.
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&& .AVIATION /18Z SATURDAY THROUGH THURSDAY/... AS OF 150 PM SATURDAY... MAINLY VFR CONDITIONS WILL CONTINUE THE REST OF THIS AFTERNOON AND INTO THIS EVENING WITH SHALLOW TO MODERATE CU DEVELOPING IN THE MOIST/UNSTABLE LOW LEVELS. CAN`T RULE OUT A LOCALIZED PATCH OR TWO OF BKN CU AROUND 3K FT...OR PERHAPS EVEN A LIGHT/BRIEF SPRINKLE... BUT THIS WILL BE VERY LOCALIZED AND BRIEF. VFR CONDITIONS SHOULD CONTINUE TONIGHT WITH SCT MID-HI CLOUDS AND LIGHT WIND. CAN`T RULE OUT A COUPLE PATCHES OF FOG...ESP INVOF THE CLIMATOLOGICALLY FAVORED LOCATIONS ACROSS THE NORTHERN COASTAL PLAIN. DURING THE DAY SUNDAY...LOOK FOR MOSTLY VFR CONDITIONS TO CONTINUE. LATER IN THE DAY...A BRIEF SHOWER OR TSTM WITH LOCAL IFR CONDITIONS WILL BE POSSIBLE MAINLY ACROSS THE NORTHERN HALF OF CENTRAL NC...AHEAD OF AN APPROACHING PREFRONTAL TROUGH. BEYOND THE 24 HOUR TAF PERIOD...A COLD FRONT WILL MOVE ACROSS CENTRAL NC ON MONDAY...BRINGING THE CHANCE FOR SHOWERS AND TSTMS AND ASSOC REDUCED FLIGHT CONDITIONS...ESP ALONG AND EAST OF A LINE FROM KRDU TO KFAY. VFR CONDITIONS ARE EXPECTED TO RETURN BEHIND THE FRONT FOR THE MIDWEEK PERIOD. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...NP/CBL SHORT TERM...NP/KC LONG TERM...KC AVIATION...NP

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