Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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590 FXUS62 KRAH 030807 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 405 AM EDT TUE MAY 3 2016 .SYNOPSIS... LOW PRESSURE WILL MOVE OFF THE MIDDLE ATLANTIC COAST EARLY TODAY. A SECONDARY WAVE OF LOW PRESSURE WILL DEVELOP ALONG THE TRAILING COLD OVER NC THIS AFTERNOON AND EVENING...BEFORE MOVING SLOWLY TO THE COAST AND OFFSHORE LATE TONIGHT AND WED. && .NEAR TERM /THROUGH TONIGHT/... AS OF 400 AM TUESDAY... AN AREA OF LOW PRESSURE NOW OVER MD WILL MOVE OFFSHORE EARLY TODAY. A SECONDARY LOW WILL DEVELOP OVER SOUTHERN VA/CENTRAL NC ALONG A TRAILING LEE SURFACE TROUGH AND SYNOPTIC COLD FRONT THAT WILL STRETCH THROUGH THE WESTERN CAROLINAS THIS AFTERNOON...IN RESPONSE TO HEIGHT FALLS /INCREASING LARGE SCALE FORCING FOR ASCENT/ ACCOMPANYING A POSITIVELY-TILTED TROUGH EVOLVING FROM SOUTHEAST CANADA TO THE CENTRAL PLAINS. SHOWERS AND A COUPLE OF ISOLATED MINI-SUPERCELLS OVER BOTH DILLON AND SUMTER COUNTY SC --ON THE LEAD OUTFLOW BOUNDARY AND IN A HSLC ENVIRONMENT CHARACTERIZED BY STRONG LOW LEVEL SHEAR /35 KTS OF 0-1 KM BULK AND 200-250 M2/S2 EFFECTIVE SRH/ AND AMIDST 35-40 KTS OF MID LEVEL FLOW PER REGIONAL VWP DATA...WILL MOVE NORTHEAST ACROSS EAST- CENTRAL NC DURING THE NEXT SEVERAL HOURS. ASSOCIATED MESO-VORTICES WILL BE CAPABLE OF PRODUCING LOCALLY DAMAGING WIND GUSTS AND/OR A WEAK TORNADO AS THEY TRACK NORTHEAST ACROSS CUMBERLAND/SAMPSON/WAYNE COUNTIES THROUGH AROUND 11Z. A COMPOSITE OUTFLOW BOUNDARY FROM WIDESPREAD CONVECTION FROM THE DELMARVA TO WESTERN NC WILL LIKELY INTERCEPT THE STORMS AND SERVE AS THE NORTHERN BOUND FOR THE SEVERE THREAT. OTHERWISE...PERSISTENT ANA-EFFECTIVE FRONTAL RAIN ON THE COOL SIDE OF THE OUTFLOW(S)...AT TIMES MODERATE TO HEAVY...MAY LEAD TO VERY LOCALIZED FLOODING. ALL OF THIS ACTIVITY SHOULD MOVE NORTHEAST OF CENTRAL NC WITH THE PASSAGE OF THE PARENT MID LEVEL DISTURBANCE NOW CROSSING EASTERN GA/WESTERN SC...BETWEEN 12-15Z. MUCH LIKE PREVIOUS DAYS...THE ATMOSPHERE WILL THEN DESTABILIZE WITH PARTIAL SUNSHINE...AND RISING TEMPERATURES TO NEAR 80 DEGREES...IN THE WAKE OF THE EARLY MORNING ACTIVITY...AND CONSEQUENTLY SET THE STAGE FOR THE RE-DEVELOPMENT OF SCATTERED TO NUMEROUS STORMS THAT WILL DEVELOP OVER WEST-CENTRAL NC - ALONG THE AFOREMENTIONED LEE SURFACE TROUGH AND/OR SYNOPTIC COLD FRONT. THESE STORMS WILL THEN CROSS CENTRAL NC THIS AFTERNOON AND EVENING. MID LEVEL FLOW AND ASSOCIATED EFFECTIVE SHEAR WILL STEADILY INCREASE FROM THE WEST INTO THE 40-60 KT RANGE WITH THE APPROACH OF THE AFOREMENTIONED UPPER TROUGH. THE CHARACTER OF THE STRONG SHEAR...INDICATED BY LONG/STRAIGHT HODOGRAPHS FROM THE SFC-6 KM...WILL FAVOR SPLITTING SUPERCELLS - ONES CAPABLE OF PRODUCING LARGE HAIL (SOME POSSIBLY VERY LARGE) AND WESTERLY WIND GUSTS UP TO 60-70 KTS. THE FRONTAL ZONE AND EMBEDDED WAVE OF LOW PRESSURE...AND ASSOCIATED DEEP MOISTURE AND SHOWERS...WILL MOVE GRADUALLY EAST OVERNIGHT... WITH JUST A LINGERING SLIGHT-LOW CHANCE OF SHOWERS EAST OF I-95 BY WED MORNING. DRY ELSEWHERE. COOLER WITH LOWS IN THE MID-UPPER 50S. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
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AS OF 405 AM TUESDAY... A PAIR OF NOTABLE CURLS IN WATER VAPOR OVER OVER IOWA AND NEBRASKA THIS MORNING WILL ELONGATE AND MOVE EAST BENEATH A DEEPER TROUGH DEVELOPING FROM A WAVE DIVING SOUTH OUT OF CENTRAL CANADA. THIS LEAD WAVE WILL CROSS CENTRAL NC EARLY WEDNESDAY... AND IN RESPONSE A BROAD WAVE OF LOW PRESSURE IS FORECAST TO DEVELOP OVER EASTERN NC WEDNESDAY AFTERNOON. DESPITE THE AIRMASS CHANGE IN THE WAKE OF TODAYS COLD FRONT... SLIGHTLY ELEVATED DEWPOINTS IN THE UPPER 50S IN THE COASTAL PLAIN AND WEAK LOW LEVEL MASS CONVERGENCE BENEATH STRONG COOLING ALOFT AND 60M HEIGHT FALLS SHOULD BE ENOUGH TO KICK OFF SOME SHOWERS AND ISOLATED STORMS...MAINLY IN THE NORTHERN COASTAL PLAIN. THE FREEZING LEVEL WILL DROP TO AROUND 9000 FT...SO SOME SMALL HAIL CANT BE RULED OUT WITH WEAK DESTABLIZATION. HIGHS WILL BE INT HE LOW/MID 70S...WITH FURTHER COOLING BENEATH AN UPPER LOW THAT WILL SETTLE OVER THE CAROLINAS LATE WEEK. ANY CONVECTION SHOULD DIE OFF AS THE UPPER FORCING DEPARTS TO THE EAST AND NOCTURNAL COOLING SETS IN. HOWEVER...WITH THE AFOREMENTIONED CANADIAN SHORTWAVE DROPPING THROUGH THE MIDWEST... SOME ADDITIONAL SHOWERS MAY DROP SOUTH THROUGH VA EARLY THURSDAY. MAINLY INT HE LOWER 50S.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/...
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AS OF 405 AM TUESDAY... A STRONG SHORTWAVE OVER MANITOBA THIS MORNING WILL DIVE SOUTH THROUGH THE MIDWEST WEDNESDAY AND CUT OFF OVER THE CAROLINAS ON THURSDAY...DEEPENING 3 TO 4 STD BELOW NORMAL THURSDAY AFTERNOON AS AN OMEGA BLOCK DEVELOPS OVER THE CONUS. STRONG HEIGHT FALLS AND A PERSISTENT AREA OF LOW PRESSURE/TROUGHING OVER NC SHOULD AGAIN PROMOTE THE DEVELOPMENT OF SHOWERS... SOME OF WHICH COULD PRODUCE A LITTLE GRAUPEL. H10-H85 THICKNESSES DIPPING TO AROUND 1340M SUPPORTS HIGHS IN THE MID 60S TO AROUND 70S ON THURSDAY...WHICH IS INCREASINGLY SUPPORTED BY MEDIUM RANGE GUIDANCE. THE CHANCE OF SCATTERED SHOWERS WILL CONTINUE FRIDAY AND DECREASE RAPIDLY INTO THE WEEKEND AS THE UPPER LOW BEGINS TO FILL AND MOVE EAST. RIDGING ALOFT WILL SHIFT EAST TOWARD THE REGION AND ALLOW FOR A WARMING TRENDING THROUGH THE WEEKEND AND INTO NEXT WEEK. THE GFS AND ECMWF THEN INDICATE A SHORTWAVE DIVING SOUTHEAST OUT OF CANADA...WHICH ULTIMATELY WEAKENS THE RIDGE AND ALLOWS A COLD FRONT TO APPROACH NC FROM THE NORTHWEST LATE SUNDAY AND MONDAY. GIVEN THE EXPECTED STRENGTH OF THE RIDGE...CONFIDENCE IN THE FRONT MOVING TO OUR LATITUDE IS A LITTLE LOW AT THIS POINT AND THE FORECAST WILL REMAIN DRY.
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&& .AVIATION /06Z TUESDAY THROUGH SATURDAY/... AS OF 230 AM TUESDAY... AN AREA OF SHOWERS AND ISOLATED STORMS OVER SC --AND PARENT MID LEVEL DISTURBANCE-- WILL LIFT NORTHEAST AND INTERACT WITH A LINE OF SHOWERS AND TRAILING RAIN NOW SETTLING SOUTHEAST ACROSS CENTRAL NC. THE RESULT WILL BE WIDESPREAD SHOWERS/RAIN...AND ASSOCIATED SUB-VFR CONDITIONS THROUGHOUT CENTRAL NC THIS MORNING. THIS REGIME WILL MOVE NORTHEAST AND OUT OF CENTRAL NC...WITH A RETURN TO DRY VFR CONDITIONS...GENERALLY BETWEEN 12-16Z. MUCH LIKE PREVIOUS DAYS...THE ATMOSPHERE WILL DESTABILIZE WITH PARTIAL SUNSHINE IN THE WAKE OF THE EARLY MORNING ACTIVITY...AND CONSEQUENTLY SET THE STAGE FOR THE RE-DEVELOPMENT OF SCATTERED TO NUMEROUS STORMS THAT WILL CROSS CENTRAL NC THIS AFTERNOON AND EVENING. LARGE HAIL...INCLUDING SOME POSSIBLY VERY LARGE...AND WESTERLY WIND GUSTS UP TO 60-70 KTS --IN SPLITTING SUPERCELLS-- WILL POSE AN ADDED RISK BEYOND TYPICAL SUB-VFR CONDITIONS IN SHRA/TSRA. DESPITE THE LIKELIHOOD OF OCCURRENCE OF SUCH STORMS AND CONDITIONS OVER NC...THE ASSOCIATED PROBABILITY OF SUCH OCCURRENCES AT ANY GIVEN POINT/TAF SITE IS TOO LOW TO INCLUDE IN THE TAFS...AT LEAST UNTIL STORMS ULTIMATELY DEVELOP. MULTIPLE SLOW-MOVING WAVES OF LOW PRESSURE ARE FORECAST TO DEVELOP IN THE VICINITY OF THE MIDDLE ATLANTIC COAST MID-LATE WEEK...WITH ASSOCIATED SUB-VFR CEILINGS AND SHOWERS/STORMS THAT WILL GROW IN COVERAGE AND INTENSITY WITH HEATING EACH AFTERNOON - ESPECIALLY AT EASTERN TAF SITES. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...26 NEAR TERM...26 SHORT TERM...22 LONG TERM...22 AVIATION...26

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