Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 030842 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 440 AM EDT FRI JUL 3 2015 .SYNOPSIS... SURFACE LOW PRESSURE WILL TRACK EAST ACROSS NC AND VA LATER TODAY AND TONIGHT...ALONG A FRONTAL ZONE THAT WILL LINGER OVER THE REGION THROUGH THE HOLIDAY WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 415 AM FRIDAY... A PRIMARY SHORTWAVE TROUGH OVER THE MID MS VALLEY THIS MORNING WILL MAKE ONLY MINIMAL EASTWARD PROGRESS ACROSS THE TN VALLEY THROUGH TONIGHT...AND KEEP THE ASSOCIATED FOCUSED HEIGHT FALLS/FORCING FOR ASCENT OVER THE TN VALLEY AND CENTRAL APPALACHIANS THROUGH THE PERIOD. HOWEVER...WSW TO SW FLOW THROUGH THE BASE OF THE ASSOCIATED L/W TROUGH AXIS WILL BE ORIENTED FAVORABLY TO DIRECT UPSTREAM MCV/S AND IMPULSES ACROSS NC AND VA...INCLUDING A WELL-DEFINED ONE FORECAST TO TRACK FROM THE WESTERN TN VALLEY VALLEY THIS MORNING TO WEST-CENTRAL NC BETWEEN 21-00Z. ADDITIONAL IMPULSES MAY FOLLOW FOR THE OVERNIGHT...INCLUDING AN APPARENT ONE WITH A CONVECTIVE CLUSTER OVER OK THIS MORNING...BUT PREDICTABILITY OF SUCH FEATURES BEYOND ABOUT THE FIRST 12 HOURS IS RELATIVELY LOW. MEANWHILE IN THE LOW LEVELS...A FRONTAL ZONE --DEEP THROUGH THE 925- 850 MB LAYER PER 00Z RAOB DATA AND MORE RECENT REGIONAL VWP DATA-- HAS SETTLED SOUTH INTO THE NORTHERN NC PIEDMONT. THE MODELS INDICATE IT WILL RETREAT NORTH INTO VA AND ALLOW A SOUTH SOUTHWEST FLOW TO ENVELOP CENTRAL NC TODAY...IN ADVANCE OF A 1010 MB SURFACE LOW FORECAST TO MIGRATE ACROSS THE APPALACHIANS TODAY AND VA TONIGHT. HOWEVER...THE COMBINATION OF BOTH LOW STRATUS THIS MORNING AND CONVECTION MIDDAY ONWARD...SUGGESTS THE EFFECTIVE FRONT...OR AT LEAST SEGMENTS THEREOF...WILL BE MODULATED SOUTHWARD AND REMAIN OVER PORTIONS OF CENTRAL NC THROUGH TONIGHT. CONVERGENCE AND DIFFERENTIAL HEATING ABOUT THE FRONT...AND ISENTROPIC UPGLIDE ACROSS IT; THE ENE MIGRATION OF THE AFOREMENTIONED IMPULSE FROM THE WESTERN TN VALLEY; AND LOWER THAN PREVIOUS DAYS LCL/LFC HEIGHTS AND CINH...WILL SUPPORT THE DEVELOPMENT OF NUMEROUS SHOWERS AND STORMS BY MIDDAY-EARLY AFTERNOON. CONTINUED SEASONABLY STRONG MID LEVEL FLOW AROUND 30 KTS WILL SUPPORT ADDITIONAL MULTI-CELL STORM ORGANIZATION WITH AN ATTENDANT PRIMARY THREAT OF DAMAGING WET MICROBURST WIND GUSTS...AND LOCALIZED FLOODING FOR STORMS TRAINING ALONG THE GENERALLY EAST TO WEST-ORIENTED FRONT/OUTFLOW. HOWEVER...A FEW STORMS MAY DISPLAY TRANSIENT SUPERCELL/ROTATIONAL CHARACTERISTICS OWING TO ENHANCED LOW LEVEL SHEAR INVOF THE BOUNDARY...PARTICULARLY BETWEEN 21-03Z...FROM THE SANDHILLS AND EASTERN PIEDMONT...TO THE COASTAL PLAIN...WHEN 925 MB FLOW IS FORECAST TO ACCELERATE INTO THE 25-30 KT RANGE...WITH THE EMERGENCE OF THE FRONTAL WAVE INTO THE LEE OF THE APPALACHIANS. ASSOCIATED EFFECTIVE SRH WILL LIKELY INCREASE INTO THE 150-250 M2/S2 RANGE THERE...SUPPORTIVE OF AN ISOLATED TORNADO. WHILE THE BRUNT OF THE SHOWERS AND STORMS ARE LIKELY TO MOVE NE OF CENTRAL NC IN ASSOCIATION WITH THE PASSING FRONTAL WAVE FORECAST TO TRACK TO NEAR THE CHESAPEAKE BAY BY SAT MORNING...HIGH PWAT VALUES AND MINIMAL CINH...DESPITE PRIOR CONVECTIVE OVERTURNING/WEAK INSTABILITY...WARRANTS A CONTINUED SLIGHT-LOW CHANCE OF SHOWERS AND STORMS OVERNIGHT. LOWS IN THE UPPER 60S TO LOWER 70S. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... AS OF 435 AM FRIDAY... THE MODELS CONTINUE TO INDICATE THE FRONTAL ZONE WILL REMAIN JUST TO THE NORTH OF CENTRAL NC ON SAT...WITH A SHARP LEE TROUGH AND A BREEZY SOUTHWEST FLOW AND MODEST MIXING OUT OF BOUNDARY LAYER MOISTURE OVER THE CAROLINAS. TEMPERATURES SHOULD CONSEQUENTLY WARM...INTO THE MID 80S TO LOW 90S...WITH THE FOCUS FOR AFTERNOON AND EVENING CONVECTION OVER THE NORTHERN AND NW NC PIEDMONT...IN CLOSEST PROXIMITY TO THE FRONTAL ZONE. 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. ALTHOUGH THE MODELS INDICATE LIMITED QPF SAT NIGHT...THE FRONT IS FORECAST TO DRIFT SOUTH INTO CENTRAL NC LATE SAT NIGHT-EARLY SUN...SO A SLIGHT CHANCE OF A SHOWER OR STORM OVERNIGHT SEEMS JUSTIFIED. LOWS AGAIN AROUND 70. && .LONG TERM /SUNDAY THROUGH THURSDAY/... AS OF 345 PM FRIDAY... A LOW AMPLITUDE SHORTWAVE CURRENTLY OVER THE US NORTHERN ROCKIES WILL DIVE INTO THE BASE OF THE BROAD EASTERN US TROUGH ON SATURDAY BEFORE ESSENTIALLY CUTTING OFF FROM THE FLOW AND DRIFTING UP THE APPALACHIANS ON SUNDAY AND MONDAY...WHILE THE PERSISTENT SURFACE FRONT/TROUGH FROM EARLIER IN THE WEEKEND REMAINS DRAPED ACROSS CENTRAL NC. THERE MAY BE SOME UNCERTAINTY IN INSTABILITY GIVEN CONSIDERABLE CLOUDINESS EXPECTED EARLY SUNDAY...BUT THE COMBINATION OF THE UPPER LOW...ALBEIT WEAK...AND SURFACE BOUNDARY AMIDST PW OVER 1.75" SHOULD LEAD TO NUMEROUS SHOWERS AND STORMS SUNDAY AND INTO SUNDAY NIGHT. BY THE MONDAY THE FRONT IS FORECAST SHIFT NORTH INTO VA AND THE FOCUS OF SHOWERS/STORMS MAY SHIFT MORE TOWARD THE COASTAL PLAIN. THE LOW/MID LEVEL FLOW IS MUCH WEAKER SUNDAY/MONDAY AND SEVERE STORMS MAY BE LESS OF A THREAT...BUT LOCALIZED FLOODING MAY REAR ITS HEAD...PARTICULARLY IN THE VICINITY OF THE BOUNDARY. CLOUDS AND PRECIP WILL LIKELY KEEP HIGHS LITTLE BELOW NORMAL IN THE MID TO UPPER 80S...SLIGHTLY WARMER ON MONDAY. BEYOND MONDAY... THERE ARE SOME SIGNS OF WARMING FOR THE MIDDLE OF NEXT WEEK AND A LITTLE LESS PRECIP COVERAGE AS THE PROGRESSIVE PATTERN EVENTUALLY YIELDS SOME REESTABLISHMENT OF THE SUB-TROPICAL RIDGE OVER THE SOUTHEAST US WITH A COLD FRONT DYING JUST TO OUR NORTH AROUND MIDWEEK. HOWEVER...THE OVERALL PATTERN IS NOT VERY AMPLIFIED AND TEMPS SHOULD REMAIN WITHIN A COUPLE DEGREES OF NORMAL. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... AS OF 230 AM FRIDAY... THE PRESENCE OF A SURFACE FRONT DRAPED ACROSS THE NORTHERN NC PIEDMONT --AND ASSOCIATED MOISTURE CONVERGENCE-- WILL LIKELY RESULT IN THE CONTINUED DEVELOPMENT AND LOWERING OF IFR-MVFR STRATUS THIS MORNING. THE STRATUS CLOUDS WILL GRADUALLY LIFT AND MORPH AFTER DAYBREAK INTO A CUMULUS FIELD...WHOSE BASES ARE APT TO FLIRT WITH THE 3000 FT/MVFR THRESHOLD THROUGH MIDDAY-EARLY AFTERNOON. PRIOR CONVECTION AND ASSOCIATED AIR MASS STABILIZATION OVER CENTRAL NC WILL CAUSE UPSTREAM CONVECTION CROSSING THE SOUTHERN APPALACHIANS TO WEAKEN AS IT APPROACHES...THOUGH A FEW REMNANT SHOWERS CANNOT BE RULED OUT IN THE 10-16Z TIME FRAME. HOWEVER...A BETTER CHANCE OF SHOWERS AND STORMS WILL OCCUR WITH THE COMBINATION OF DIURNAL HEATING AND THE APPROACH OF A DISTURBANCE ALOFT INITIALLY OVER THE WESTERN TN VALLEY...AND AND INTERACTION WITH THE AFOREMENTIONED FRONTAL ZONE...BETWEEN 16Z-00Z. OUTLOOK: THE AFOREMENTIONED FRONT WILL STALL OVER VA/NC AND RESULT IN ABOVE AVERAGE PROBABILITIES OF SHOWERS AND STORMS AND ASSOCIATED SUB-VFR CONDITIONS THROUGH MON...WITH THE RELATIVE HIGHEST PROBABILITY SUN-MON. PERIODS OF MVFR CEILINGS WILL BE POSSIBLE EVEN OUTSIDE OF STORMS DURING THAT TIME...ESPECIALLY DURING THE MORNING TO EARLY AFTERNOON HOURS. && ..RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...26 NEAR TERM...26 SHORT TERM...26 LONG TERM...22 AVIATION...26

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