Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 021441 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1040 AM EDT THU JUL 2 2015 .SYNOPSIS... A SURFACE TROUGH WILL LINGER OVER THE PIEDMONT THIS AFTERNOON. MEANWHILE...A COLD FRONT WILL SETTLE SLOWLY SOUTH AND STALL OVER THE MIDDLE ATLANTIC STATES TONIGHT THROUGH THE HOLIDAY WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1040 AM THURSDAY... INITIAL WEAK S/W LIFTING NEWD AND EXITING OUR COASTAL PLAIN COUNTIES AT 14Z. EARLIER ISOLATED SHOWER ACTIVITY HAS PRETTY MUCH DRIED UP AND EXTENSIVE DECK OF MID LEVEL CLOUDS HAS BEGUN TO ERODE/DIMINISH ACROSS THE AREA. WATER VAPOR IMAGERY DEPICTS A VORTICITY MAXIMUM OVER EASTERN TN. THIS SYSTEM CURRENTLY HANDLED WELL BY NEAR TERM MODELS. PARTIAL SUN OVER THE AREA EARLY THIS AFTERNOON SHOULD PRODUCE ADEQUATE SURFACE BASED INSTABILITY TO INITIATE/SUSTAIN CONVECTION. THE APPROACH OF THE MID LEVEL VORT MAX SHOULD ENHANCE THE CONVECTION SO THAT WE SHOULD SEE DECENT COVERAGE OF CONVECTION...PRIMARILY OVER THE WESTERN AND NORTHERN PIEDMONT WHERE THE 12Z 850MB ANALYSIS DEPICTS AN ELONGATED SW-NE ORIENTATED TROUGH. LATEST SPC MESO SCALE ANALYSIS DEPICTS MODEST BULK SHEAR ON THE ORDER OF 20-25KTS OVER A SMALL PART OF THE PIEDMONT. ENOUGH SHEAR MAY EXIST TO CAUSE CONVECTION TO FORM IN BROKEN BANDS WHICH MAY CONTRIBUTE TO AN INCREASE RISK FOR STRONG/LOCALLY DAMAGING WIND GUSTS. TEMPS THIS AFTERNOON STILL APPEAR ON TRACK TO REACH THE MID-UPPER 80S. HOWEVER...IF CONVECTION BECOMES SCATTERED PRIOR TO 19Z...SOME PLACES MAY SEE MAX TEMPS NEAR 80/LOWER 80S. -WSS TONIGHT: INITIAL SHOWERS AND STORMS WILL GRADUALLY DIMINISH/MOVE ENE THIS EVENING. HOWEVER...A TRAILING SHORTWAVE TROUGH AND SEPARATE CONVECTIVE CLUSTER/MCV OVER THE NORTHERN PLAINS THIS MORNING WILL AMPLIFY... AMIDST CONTINUED CYCLONIC FLOW ALOFT...INTO THE TN VALLEY AND SOUTHERN-CENTRAL APPALACHIANS BY FRI MORNING. ASSOCIATED RENEWED FORCING FOR ASCENT WILL PROVIDE FOR SHOWER AND STORM REDEVELOPMENT OR MAINTENANCE FROM UPSTREAM...PARTICULARLY OVER THE NORTHERN PIEDMONT/NEAR THE VA BORDER...IN CLOSEST PROXIMITY TO THE SYNOPTIC/DEEPER FRONTAL ZONE FORECAST TO SETTLE SOUTH THROUGH VA DURING THE NEXT 24 HOURS. CONSIDERABLE CLOUDINESS OVERNIGHT WILL LIKELY RESULT IN LOW TEMPERATURES A DEGREE OR TWO ABOVE GUIDANCE - 69-74. && .NEAR TERM /FRIDAY AND FRIDAY NIGHT/... AS OF 425 AM THURSDAY... WHILE THE MODELS INDICATE THE SYNOPTIC FRONTAL ZONE WILL REMAIN NEAR THE VA BORDER...NUMEROUS OUTFLOW BOUNDARIES WILL MODULATE THE EFFECTIVE FRONT AND LIKELY CAUSE IT TO SAG SOUTH INTO CENTRAL NC THIS PERIOD. CONVERGENCE AND DIFFERENTIAL HEATING ABOUT THE FRONT(S); THE EASTWARD MIGRATION OF THE AFOREMENTIONED SHORTWAVE TROUGH ACROSS THE CENTRAL APPALACHIANS; 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. WHILE THE BRUNT OF THE SHOWERS AND STORMS ARE LIKELY TO MOVE NE OF CENTRAL NC IN ASSOCIATION WITH A FRONTAL WAVE FORECAST TO TRACK ALONG THE FRONT AND OFFSHORE THE VA COAST FRI NIGHT...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. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... AS OF 330 AM THURSDAY... THE ACTIVE WEATHER PATTERN WILL CONTINUE THIS WEEKEND AND INTO AT LEAST EARLY NEXT WEEK AS A BROAD UPPER TROUGH PERSISTS OVER THE EASTERN US. A SERIES OF DISTURBANCES IN THE WEST-NORTHWEST FLOW ALOFT WILL BRING PERIODS OF ENHANCED CONVECTIVE COVERAGE THAT WILL LIKELY BE A LITTLE BETTER FOCUSED NEAR A STALLED FRONT AND CONFLUENCE ZONE THAT IS FORECAST TO MEANDER FROM SOUTHERN VA INTO CENTRAL NC. CONFIDENCE IN THE TIMING AND AMPLITUDE OF THESE WAVES IS LOW GIVEN THE EXPECTED COVERAGE OF UPSTREAM CONVECTION EACH DAY...BUT THE ECMWF AND GFS BOTH SUGGEST THE POTENTIAL FOR A STRONGER SHORTWAVE ON SUNDAY THAT MAY SHIFT THE BEST COVERAGE FROM THE NORTHERN CWA ON SATURDAY TO MORE AREAWIDE ON SUNDAY... AND THEN TO SOUTHERN AND EASTERN AREAS ON MONDAY. HIGH PW AND MODEST MID- LEVEL FLOW ON THE EASTERN PERIPHERY OF THE UPPER TROUGH WILL SUPPORT MAINLY A DAMAGING WIND SEVERE THREAT AND AT LEAST SOME MINOR URBAN FLOODING POTENTIAL DEPENDING ON RAINFALL AMOUNTS IN PRECEDING DAYS. HIGHS EACH AFTERNOON WILL BE A LITTLE BELOW NORMAL OWING TO THE PERIODS OF CONVECTIVE ACTIVITY AND DEBRIS CLOUDING...WITH MOSTLY MID 80S NORTHWEST TO UPPER 90S SOUTHEAST EACH DAY SATURDAY THROUGH MONDAY. LOWS WILL BE IN THE UPPER 60S AND LOWER 70S. 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. HOWEVER...THE OVERALL PATTERN IS NOT VERY AMPLIFIED AND TEMPS SHOULD REMAIN WITHIN A FEW DEGREES OF NORMAL. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... AS OF 710 AM THURSDAY... CONSIDERABLE MID-HIGH CLOUDS...AND VIRGA OR VFR SHOWERS/ SPRINKLES...WILL SPREAD EAST ACROSS EAST-CENTRAL NC (INCLUDING RWI) THIS MORNING IN ASSOCIATION WITH A PASSING MID LEVEL DISTURBANCE. AN ADDITIONAL DISTURBANCE OR TWO WILL CROSS NC TODAY...AND ANOTHER LATE TONIGHT. THE PASSAGE OF THESE FEATURES...IN CONJUNCTION WITH THE APPROACH OF A COLD FRONT AND/OR OUTFLOW BOUNDARIES FROM UPSTREAM CONVECTION...WILL RESULT IN AN INCREASE IN COVERAGE AND INTENSITY OF SHOWERS AND STORMS THROUGH LATE THIS AFTERNOON-EVENING; AND SOME MAY LINGER OR REDEVELOP OVERNIGHT. OTHERWISE...AN INITIALLY LIGHT SSW SURFACE WIND WILL INCREASE INTO THE 10-15 KT RANGE WITH GUSTS IN THE UPPER TEENS TO AROUND 20 KTS THIS AFTERNOON. OUTLOOK: THE AFOREMENTIONED FRONT WILL STALL OVER VA/NC AND RESULT IN ABOVE AVERAGE PROBABILITIES OF SHOWERS AND STORMS AND ASSOCIATED SUB-VFR CONDITIONS FRI-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...WSS/26 SHORT TERM...26 LONG TERM...22 AVIATION...26

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