Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 040823 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 423 AM EDT SAT JUL 4 2015 .SYNOPSIS... A SERIES OF DISTURBANCES ALOFT WILL MOVE OVERHEAD AND INTERACT WITH A FRONTAL ZONE THAT WILL WAVER ACROSS VA AND NC THROUGH THE HOLIDAY WEEKEND. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 415 AM SATURDAY... WARMER AND BREEZY...WITH SCATTERED STORMS. AT 08Z...A 1009 MB SURFACE WAVE WAS LOCATED NEAR THE MOUTH OF THE CHESAPEAKE BAY...WITH A TRAILING FRONT ANALYZED NEAR/JUST NORTH OF THE VA/NC BORDER TO NEAR KMTV...WHERE THE FRONT ARCED NW TO A 1010 MB SURFACE WAVE OVER NORTHERN WV. THE TRAILING COLD FRONT STRETCHED ACROSS THE LOWER OH VALLEY TO THE CENTRAL PLAINS. THE MODELS INDICATE THE TWO SURFACE WAVES WILL TRACK OFF THE VA COAST THROUGH THIS EVENING...WITH THE TRAILING COLD FRONT SETTLING ONLY SLOWLY SOUTH INTO THE NORTHERN NC PIEDMONT LATE TONIGHT...AND PRECEDED BY A SHARP LEE TROUGH..AND CONVECTIVE OUTFLOW...OVER THE CAROLINAS. MEANWHILE ALOFT...A PRIMARY SHORTWAVE CENTERED OVER NORTHERN KY WILL LIFT ACROSS WV AND THE NORTHERN MIDDLE ATLANTIC STATES...WITH ASSOCIATED FORCING FOR ASCENT PASSING TO THE NORTH AND WEST OF CENTRAL NC. HOWEVER...WSW TO SW FLOW THROUGH THE BASE OF THE ASSOCIATED POSITIVELY-TILTED L/W TROUGH AXIS WILL AGAIN BE ORIENTED FAVORABLY TO DIRECT UPSTREAM MCV/S AND IMPULSES ACROSS THE CAROLINAS...INCLUDING A MOST NOTABLE ONE FORECAST TO TRACK FROM NE AL TO CENTRAL NC THROUGH AROUND 18Z...WHILE A TRAILING SHEAR AXIS AND POSSIBLE ADDITIONAL IMPULSES WILL LINGER OVER NC THROUGH TONIGHT. THERE IS A CONSENSUS SIGNAL FROM HI-RES SIMULATED REFLECTIVITY GUIDANCE THAT A CONVECTIVE CLUSTER WILL LIKELY ACCOMPANY THE LEAD FEATURE AND CROSS SOUTH-CENTRAL ROUGHLY BETWEEN 15-21Z...WHICH SEEMS REASONABLE SINCE AN EXPANDING INSTABILITY AXIS WITH DIURNAL HEATING WOULD FAVORABLY INTERCEPT THE APPROACHING DISTURBANCE AND PROBABLE CONVECTION DURING THAT TIME. REGARDLESS OF WHETHER OR NOT A SEMI- ORGANIZED CLUSTER OF STORMS INDEED ACCOMPANIES THAT FEATURE... ADDITIONAL SCATTERED STORMS ARE APT TO FIRE INVOF THE LEE TROUGH OVER THE CENTRAL CAROLINAS...AS WELL AS UPSTREAM ALONG THE AFOREMENTIONED COLD FRONT...THE LATTER OF WHICH WILL LIKELY PROPAGATE ALONG ASSOCIATED OUTFLOW AWAY FROM THE SYNOPTIC FRONT AND DRIFT TOWARD-INTO THE NORTHERN NC PIEDMONT LATE THIS AFTERNOON AND THIS EVENING. CONTINUED SEASONABLY STRONG SW MID LEVEL FLOW IN THE 30-35 KT RANGE WILL FAVOR ORGANIZATION...AND DCAPE SHOULD BE HIGH WITH STEEP LOW LEVEL LAPSE RATES AND SURFACE DEWPOINT DEPRESSIONS AROUND 25 DEGREES...SO ANY STORMS THAT DO FORM WILL BE CAPABLE OF PRODUCING STRONG TO SEVERE WIND GUSTS...AND PERHAPS MARGINALLY SEVERE HAIL. OTHERWISE...A RELATIVELY STRONG PRESSURE GRADIENT BETWEEN THE AREAS OF LOW PRESSURE MOVING ACROSS THE VIRGINIAS AND THE DELMARVA...AND HIGH PRESSURE ALONG THE GULF COAST...WILL RESULT IN THE DEVELOPMENT OF BREEZY CONDITIONS BY 14-15Z...AS SOUTHWEST WINDS STRENGTHEN INTO THE 10-20 KT RANGE WITH GUSTS IN THE 20S KTS - HIGHEST FROM THE EASTERN SANDHILLS OT THE COASTAL PLAIN. A SLIGHT TO CHANCE PROBABILITY OF SHOWERS AND STORMS WILL LINGER THROUGH TONIGHT...MAINLY OVER THE NORTHERN PIEDMONT AND NORTHERN COASTAL PLAIN - IN CLOSEST PROXIMITY TO THE SYNOPTIC FRONT SETTLING SOUTH THROUGH VA. LOWS AROUND 70.
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&& .SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
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AS OF 340 PM FRIDAY... A CLOSED MID-LEVEL LOW WILL DRIFT NNE ACROSS THE SOUTHERN AND CENTRAL APPALACHIANS ON SUNDAY...WHILE A SFC BOUNDARY REMAINS ALONG THE NC/VA BORDER. AS THE CLOSED LOW LIFTS TO THE N...SO WILL THE SFC BOUNDARY...MOVING N INTO VA SUNDAY NIGHT. AS SUCH...THE BEST CHANCE FOR RAIN AND GREATEST COVERAGE OF SHOWERS/TSTMS DURING THE DAY SUNDAY WILL BE INVOF OF THE BOUNDARY...BASICALLY AREAS N OF HWY 64. FORECAST SOUNDINGS SHOW MODEST CAPE AND SHEAR...WITH INSTABILITY LIMITED BY EXTENSIVE CLOUD COVERAGE. BUT WITH HIGH PWAT (>1.75") AND RELATIVELY SLOW STORM MOTION...WILL HAVE TO KEEP A CLOSE WATCH ON LOCALIZED FLOOD POTENTIAL.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/... AS OF 410 AM SUNDAY... A SHORTWAVE TROUGH AXIS...ATTENDANT TO THE UPPER LOW OVER THE OHIO VALLEY REGION MONDAY MORNING...WILL LIFT ACROSS CENTRAL NC ON MONDAY...WHILE A WEAK FRONTAL ZONE AT THE SURFACE SHIFTS NORTH INTO VA. FORCING ASSOCIATED WITH THE TROUGH AXIS AND A CONTINUED MOIST AIRMASS AND PW AROUND 1.8" SHOULD RESULT IN SHOWERS AND AND ISOLATED STORMS ACROSS THE WEST EARLY MONDAY...POTENTIALLY EXPANDING WITH TIME TO THE NORTH AND EAST WHERE AFTERNOON DESTABILIZATION IS EXPECTED TO BE MAXIMIZED GIVEN THE TIMING OF THE FORCING AND A SLIGHTLY BACKED SOUTH-SOUTHEASTERLY WIND OVER THE COASTAL PLAIN. RELATIVELY WEAK MID TROPOSPHERIC FLOW SHOULD LIMIT THE OVERALL SEVERE THREAT...BUT A CONCERN OF SOME LOCALIZED FLOODING MAY STILL EXIST IN THE ACTIVE PATTERN. THE UPPER LOW IS THEN FORECAST TO OPEN UP AND SHEAR OUT ON TUESDAY AS THE SUBTROPICAL RIDGE TRIES TO BUILD BACK ACROSS THE SOUTHEAST US. HOWEVER...PROGRESSIVE FLOW AND A SERIES OF SHORTWAVE CROSSING THE NORTHERN US WILL MAY KEEP HEIGHTS FROM RISING TO STRONGLY OVER OUR REGION...WITH A COLD FRONT MOVING INTO THE OH/TN VALLEY BY MIDWEEK. WHILE THE FRONT MAY NOT MAKE IT ALL THE WAY INTO THE NC...WE SHOULD SEE A SHARPENING LEE TROUGH AND FAIRLY TYPICAL SCATTERED AFTERNOON STORMS...WITH SOME INFLUENCE FROM WEST-EAST MOVING DISTURBANCES TO OUR NORTH BY LATE WEEK. HIGHS MONDAY WILL REMAIN BELOW NORMAL...WITH A WARMING TREND ENSUING TUESDAY ONWARD...THOUGH HIGHS WILL LIKELY REMAIN JUST A DEGREE OR TWO ON THE WARMER SIDE SIDE OF NORMAL. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... AS OF 250 AM SATURDAY... THE THREAT OF IFR-MVFR CEILINGS WILL CONTINUE IN THE VICINITY AND ESPECIALLY NORTH OF A FRONTAL ZONE DRAPED NEAR THE VA/NC BORDER THIS MORNING...WHILE THE PROBABILITY OF VFR CONDITIONS WILL INCREASE WITH SOUTHERN EXTENT FROM THE FRONT (IE. TOWARD KFAY). MEANWHILE...A SERIES OF DISTURBANCES OVER THE NORTHERN GULF COAST STATES TODAY WILL TRACK ENE ACROSS THE CAROLINAS THROUGH THIS EVENING...WITH AN ASSOCIATED CONVECTIVE CLUSTER PROBABLY ACCOMPANYING EACH...THE FIRST OF WHICH MAY AFFECT FAY/RDU/RWI BETWEEN 16-21Z BASED ON EXTRAPOLATION OF PAST MOVEMENT. STABILIZING EFFECTS OF EACH PASSING CLUSTER OF STORM SUGGESTS MUCH LOWER PREDICTABILITY WITH ANY SUBSEQUENT DISTURBANCE AND STORM CLUSTER FROM MID AFTERNOON ONWARD. OTHERWISE...A RELATIVELY STRONG PRESSURE GRADIENT BETWEEN LOW PRESSURE MOVING ACROSS THE DELMARVA AND HIGH PRESSURE ALONG THE GULF COAST WILL RESULT IN THE DEVELOPMENT OF BREEZY CONDITIONS BY 14- 15Z...AS SOUTHWEST WINDS STRENGTHEN INTO THE 10-20 KT RANGE WITH GUSTS IN THE 20S KTS - HIGHEST AT FAY AND RWI. OUTLOOK: THE FRONT WILL DRIFT SOUTH INTO NC LATE TONIGHT AND EARLY SUN. STRATUS WILL AGAIN BE POSSIBLE NEAR AND ESPECIALLY NORTH OF THE FRONT...NEAR AND MORE LIKELY JUST NORTH OF NORTHERN CENTRAL NC TAF SITES SUN MORNING. OTHERWISE...AN ABOVE AVERAGE PROBABILITY OF SHOWERS AND STORMS AND ASSOCIATED SUB-VFR CONDITIONS WILL ACCOMPANY THE APPROACH/PASSAGE OF AN UPPER LOW THROUGH THE SOUTHERN AND CENTRAL APPALACHIANS SUN-MON...BEFORE A RETURN TO MORE TYPICAL SUMMERTIME CONDITIONS FOR THE MIDDLE OF THE UPCOMING WEEK. && ..RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...26 NEAR TERM...26 SHORT TERM...WSS LONG TERM...22 AVIATION...26

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