Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 050840 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 439 AM EDT SUN JUL 5 2015 .SYNOPSIS...
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A FRONTAL ZONE WILL REMAIN QUASI-STATIONARY NEAR THE VA AND NC BORDER TODAY...AHEAD OF AN UPPER LEVEL TROUGH AND ACCOMPANYING AREA OF SURFACE LOW PRESSURE THAT WILL DRIFT INTO THE CENTRAL APPALACHIANS THROUGH THIS EVENING. THE FRONT WILL THEN RETREAT NORTHWARD WITH THE MIGRATION OF THE SURFACE LOW THROUGH THE MIDDLE ATLANTIC STATES ON MON.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 415 AM SUNDAY... A WELL-DEFINED SHORTWAVE TROUGH CENTERED OVER WESTERN TN THIS MORNING WILL MOVE ONLY SLOWLY NE TO A POSITION OVER EASTERN KY OR SOUTHERN OH BY 12Z MON...SLOWED BY UPSTREAM SMALLER-SCALE IMPULSES AND ASSOCIATED POSITIVE VORTICITY MAXIMA FORECAST TO AMPLIFY FROM THE PLAINS STATES INTO-AROUND THE BASE OF THE TROUGH. THESE SMALLER SCALE DISTURBANCES...INCLUDING AN MCV OVER THE SC UPSTATE AT 08Z...WILL BE DIRECTED AROUND THE TROUGH IN SW FLOW ALOFT...ACROSS NC. THESE DISTURBANCES...INCLUDING THE SC MCV THAT IS FORECAST TO LIFT THROUGH THE WESTERN AND NORTHERN PIEDMONT BETWEEN 12-18Z...WILL BE MIGRATING THROUGH A FIELD OF OTHERWISE RISING HEIGHTS ALOFT OVER THE MIDDLE ATLANTIC STATES TODAY...IN THE WAKE OF A STRONG SHORTWAVE TROUGH LIFTING THROUGH THE NORTHEAST. MEANWHILE IN THE LOW LEVELS AT 08Z...A QUASI-STATIONARY FRONT --A DEEP ONE THAT EXTENDED THROUGH THE 925-850 MB LAYER PER REGIONAL VWP DATA-- EXTENDED EAST THROUGH SW AND SOUTHERN VA...FROM A 1015 MB SURFACE LOW JUST NORTH OF NASHVILLE TN. THE MODELS INDICATE THE LOW WILL DRIFT INTO THE CENTRAL APPALACHIANS TODAY...WHILE THE FRONT GENERALLY REMAINS NEAR THE VA/NC STATE LINE...THOUGH LIKELY MODULATED SOUTHWARD BY CONVECTIVE OUTFLOW FROM STORMS THAT FORM ALONG...AND/OR MOVE TOWARD...IT. A LEE TROUGH...MEANWHILE...WILL EXTEND SOUTH FROM THE APPROACHING LOW...THROUGH THE WESTERN CAROLINAS TO EASTERN GA. HI-RES SIMULATED REFLECTIVITY GUIDANCE SUGGESTS ARCS/BANDS OF MULTI- CELL CONVECTION WILL PIVOT NORTH ACROSS CENTRAL NC...THE FIRST OF WHICH WILL LIKELY ACCOMPANY THE AFOREMENTIONED MCV...AND WHICH SHOULD GRADUALLY INCREASE IN INTENSITY AS IT LIFTS NE THROUGH A DIURNALLY-DESTABILIZING ENVIRONMENT OVER THE PIEDMONT AND NEARS/CONCENTRATES ALONG THE FRONTAL ZONE. ADDITIONAL SCATTERED STORMS ARE APT TO FIRE IN THE WAKE OF THIS PROBABLE LEAD ACTIVITY...WITH THE RELATIVE GREATEST CONCENTRATION OVER THE WESTERN AND NORTHERN PIEDMONT...IN CLOSEST PROXIMITY TO BOTH THE FRONT AND WEAK INFLUENCE FROM THE SHORTWAVE TROUGH. THERE TOO...SCATTERED SHOWERS AND ISOLATED STORMS ARE APT TO LINGER TONIGHT FOR THE SAME REASONING..THOUGH WITH AN OVERALL DECREASE IN COVERAGE AND INTENSITY. HIGHS IN THE 80S - WARMEST NEAR 90 DEGREES OVER THE SANDHILLS AND SOUTHERN-CENTRAL COASTAL PLAIN. LOWS AROUND 70.
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&& .SHORT TERM /MONDAY AND MONDAY NIGHT/...
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AS OF 435 AM SUNDAY... THE SHORTWAVE TROUGH/CLOSED MID LEVEL LOW INITIALLY OVER THE TN VALLEY WILL CONTINUE TO LIFT SLOWLY NE AND DEAMPLIFY ACROSS THE CENTRAL APPALACHIANS THIS PERIOD...TAKING WITH IT THE ASSOCIATED FORCING FOR ASCENT TO THE NW OF CENTRAL NC. THE LIFTING OUT OF THE TROUGH WILL CAUSE THE SURFACE FRONT INITIALLY OVER SOUTHERN VA TO RETREAT NORTH THROUGH THE MIDDLE ATLANTIC STATES...LEAVING BEHIND A LEE/PIEDMONT TROUGH OVER CENTRAL VA AND THE CENTRAL CAROLINAS. HEIGHT RISES BEHIND THE DEAMPLIFYING TROUGH ALOFT AND WSW LOW LEVEL FLOW ON THE WEST SIDE OF THE PIEDMONT TROUGH SUGGEST CONVECTIVE COVERAGE SHOULD BE MINIMAL OVER THE SOUTHERN AND WESTERN PIEDMONT...WITH SCATTERED CONVECTION OTHERWISE EXPECTED ALONG AND EAST OF THE PIEDMONT TROUGH...AND IN ASSOCIATION WITH THE SEA BREEZE. HIGHS SIMILAR TO THOSE OF SUN...THOUGH UP TO A COUPLE OF DEGREES HIGHER OVER THE SOUTHERN PIEDMONT...CLOSE TO WHERE THE MODELS INDICATE THE DEVELOPMENT OF A LOW LEVEL THERMAL RIDGE CENTERED NEAR CLT. LOWS AGAIN AROUND 70...WITH MAINLY DRY CONDITIONS OVERNIGHT.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 405 AM SUNDAY... WITH THE DEPARTURE OF THE INCREASINGLY SHEARED UPPER LOW OVER THE SOUTH-CENTRAL APPALACHIANS ON TUESDAY...THE PATTERN OVER THE SOUTHEAST US WILL SHIFT BACK INTO A ORE TYPICAL SUMMERTIME REGIME...WITH THE SUBTROPICAL RIDGE BUILDING ACROSS THE SOUTHERN US. MEANWHILE...PROGRESSIVE FLOW ACROSS THE NORTHERN US WILL ALLOW A SERIES OF SHORTWAVES TO CROSS THE GREAT LAKES REGION... AND TO SOME DEGREE KEEP HEIGHTS ALOFT FROM RISING TOO QUICKLY OVER THE CAROLINAS. THE FIRST SHORTWAVE WILL CROSS THE GREAT LAKES ON WEDNESDAY...WITH A TRAILING COLD FRONT SINKING SOUTH INTO THE MID- ATLANTIC REGION...BUT GIVEN THE FACT THAT MODELS HAVE TRENDED A LITTLE STRONGER...AND WARMER...WITH THE SUBTROPICAL RIDGE....EXPECT THE FRONT TO REMAIN NORTH OF OUR AREA. A LEE TROUGH WILL BE THE MAIN FOCUS FOR ISOLATED TO WIDELY SCATTERED SHOWERS AND STORMS EACH DAY...WITH THE POTENTIAL FOR DISTURBANCES TRACKING WEST TO EAST NEAR THE FRONTAL ZONE TO PROVIDE SOME ADDITIONAL FORCING AS THE FRONT EFFECTIVELY TRIED TO SINK SOUTH INTO THE AREA BY THE WEEKEND. THIS WILL BE DEPENDENT ON HOW THE RIDGE EVOLVES...AND THE MODELS ARENT IN FULL AGREEMENT ON HOW QUICKLY THE CENTER OF THE RIDGE WILL BUILD WEST OVER THE SOUTHERN PLAINS...WHICH WOULD ALLOW HEIGHTS TO FALL AGAIN ALONG THE EAST COAST. FOR NOW...WILL CONTINUE TO SHOW MAINLY SLIGHT CHANCE OF LOW END CHANCE POPS EACH DAY...WITH HIGHS INCREASINGLY IN THE 90-95 RANGE. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... AS OF 225 AM SUNDAY... GENERALLY LIGHT SOUTH TO SOUTHWEST LOW LEVEL FLOW WILL PREVAIL OVER CENTRAL NC...ON THE SOUTH SIDE OF A SURFACE FRONTAL ZONE FORECAST TO SETTLE TO NEAR THE VA/NC STATE LINE LATER THIS MORNING. THE FRONT IS THEN FORECAST TO BECOME QUASI-STATIONARY AND FOCUS SCATTERED SHOWERS AND STORMS THIS AFTERNOON...INITIALLY MOST PROBABLE AT TRIAD TAF SITES AND RDU...IN CLOSEST PROXIMITY TO BOTH THE FRONT AND AN UPPER LEVEL TROUGH FORECAST TO DRIFT SLOWLY NORTHEAST ACROSS THE TN VALLEY. THE TROUGH ALOFT...AND PRECEDING WEAK IMPULSES IN SOUTHWESTERLY FLOW ALOFT...WILL PROBABLY TRIGGER A NORTH TO SOUTH- ORIENTED BAND OR TWO OF ADDITIONAL SHOWERS AND STORMS THROUGH THIS EVENING...BUT CONFIDENCE IN LOCATION AND TIMING IS LOW AT THIS TIME. OTHERWISE...THE HI-RES RAPID REFRESH MODEL (HRRR) SUGGESTS POCKETS OF IFR-MVFR STRATUS WILL EXPAND FROM AL/GA NORTHEASTWARD ACROSS SC...AND INTO SOUTHERN NC (INCLUDING FAY) BETWEEN 10-15Z. ALTHOUGH THE CONSENSUS OF OTHER MODEL GUIDANCE MAINTAINS VFR CONDITIONS AT FAY AND ELSEWHERE...THE RECENT GOOD TRACK RECORD OF THE HRRR VERSUS OTHER GUIDANCE WILL BE FOLLOWED; AND A TEMPO GROUP FOR MVFR CEILINGS HAS BEEN INCLUDED AT KFAY FOR A FEW HOURS LATER THIS MORNING. OUTLOOK: THE AFOREMENTIONED UPPER LEVEL TROUGH OVER THE TN VALLEY WILL CONTINUE TO LIFT SLOWLY NORTHEAST THROUGH THE APPALACHIANS AND DIRECT A MOIST AND WEAKLY PERTURBED SOUTHWEST FLOW ALOFT ACROSS NC THROUGH TUE. ABOVE AVERAGE PROBABILITIES OF MAINLY AFTERNOON-EARLY NIGHTTIME SHOWERS AND STORMS --AND ASSOCIATED SUB-VFR CONDITIONS-- WILL RESULT...WITH THE RELATIVE BETTER CHANCES ON MON. SUB-TROPICAL RIDGING WILL THEN EXPAND NORTH THROUGH MID-LATE WEEK...WITH ASSOCIATED MAINLY DRY AND WARMER/HOT CONDITIONS. && ..RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...26 NEAR TERM...26 SHORT TERM...26 LONG TERM...22 AVIATION..26

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