An unseasonably deep upper level trough allowed embedded shortwaves to rotate through the longwave pattern and across portions of central North Carolina. The interaction of these mid/upper level disturbances with and increasingly moist low levels of the atmosphere produced isolated severe storms.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS RAH wrote it up.
An unseasonably deep upper level trough allowed embedded shortwaves to rotate through the longwave pattern and across portions of central North Carolina. The interaction of these mid/upper level disturbances with and increasingly moist low levels of the atmosphere produced isolated severe storms.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Raleigh, NC wrote its last area forecast discussion before the first event at Aug 20, 9:37 AM EST, 2 hours 38 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1037 AM EDT THU AUG 20 2009 .SYNOPSIS... HIGH PRESSURE WILL LINGER OVER THE SOUTHEASTERN UNITED STATES TODAY. MOISTURE AND PRECIPITATION CHANCES WILL INCREASE LATER TONIGHT AND ESPECIALLY BY FRIDAY THROUGH SATURDAY... WITH THE APPROACH AND ARRIVAL OF AN UNSEASONABLY STRONG UPPER LEVEL TROUGH AND ASSOCIATED SURFACE COLD FRONT. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1025 AM THURSDAY... CONCERN FOR SEVERE WEATHER POTENTIAL TODAY WITH MANY PARAMETERS HIGH. HOWEVER LACK OF A SURFACE TRIGGER MAY MAKE INITIATION A PROBLEM. TODAY COULD BE A CASE OF ALL OR NOTHING... WHERE IT COULD BE TOTALLY DRY... OR ANYTHING THAT DOES DEVELOP COULD QUICKLY GO SEVERE. ONE POSSIBLE POINT AGAINST CONVECTION IS LOW LEVEL STRETCHING AND DIVERGENCE OF THE AIR MASS AS WEAK LOW LEVEL JET (20 KNOTS) PERSISTS OVER VIRGINIA TODAY WITH WEAKER WINDS SOUTH. LOW LEVEL WINDS OVER NORTH CAROLINA INCREASE TONIGHT AND SWITCH FROM ANTICYCLONIC TO CYCLONIC. WIND AND CYCLONIC SHEAR LOOK BEST IN THE WEST ALTHOUGH THE INSTABILITY OF THE AIR MASS IS FORECAST TO BE RELATIVELY UNIFORM ACROSS THE AREA. THUS STORMS... IF THEY DEVELOP MIGHT BE FAVORED TO PERSIST IN THE WEST INTO THE LATE EVENING THAN IN THE EAST. HATE LOWERING HIGH TEMPERATURES BUT RISKED A DEGREE OR SO DROP IN THE WEST NEAR THE CENTROID OF THE CURRENT STRATUS AIR MASS (IN OUR WEST PARTS). THE NORTHEAST IS ALREADY IN THE MID 80S AND MID 90S FOR THEM WELL WITHIN REACH. LOWS TONIGHT MOSTLY MID 70S. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... AS OF 315 AM THURSDAY... THIS SHOULD BE THE MOST ACTIVE PERIOD DURING THE NEXT SEVERAL DAYS... AS THE HIGHLY AMPLIFIED AND ENERGETIC TROUGH ALOFT OVER THE CENTRAL US THIS MORNING PROGRESSES EASTWARD. FRIDAY: MEAN MOISTURE WILL STEADILY INCREASE THROUGH THE DAY FRIDAY -- CHARACTERIZED BY A RISE IN PRECIPITABLE WATER VALUES TO IN EXCESS OF TWO INCHES BY 00Z SATURDAY -- IN RELATIVELY UNIDIRECTIONAL BUT SLOWLY STRENGTHENING SOUTHWEST FLOW ALOFT AHEAD OF THE TROUGH. WHILE THE STRONGEST FORCING ALOFT AND SURFACE COLD FRONT SHOULD REMAIN WEST OF THE MOUNTAINS DURING THE DAY FRIDAY... WEAK MID LEVEL HEIGHT FALLS (10 TO 20 METERS PER 12 HOUR) AND THE PASSAGE OF A SUBTLE MID LEVEL JET ATTENDING A LEAD SHORT WAVE TROUGH LIFTING OUT OF THE TROUGH BASE... SHOULD AID IN THE DEVELOPMENT OF SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS OVER THE WESTERN VIRGINIA AND NORTH CAROLINA PIEDMONTS DURING THE AFTERNOON. OTHER MORE ISOLATED TO SCATTERED ACTIVITY MAY DEVELOP OVER EASTERN SECTIONS... AMIDST A MORE TYPICAL SUMMERTIME REGIME. HIGH TEMPERATURES EXPECTED TO RANGE FROM THE MID 80S NORTHWEST TO LOWER 90S SOUTHEAST... AS CLOUD COVER... SHOWERS AND THUNDERSTORMS INCREASE FROM WEST TO EAST THROUGHOUT THE DAY. THE INCREASING DEEP LAYER MOISTURE SHOULD LIMIT MID LEVEL LAPSE RATES AND POTENTIAL/CONVECTIVE INSTABILITY... AND MAY RESULTANTLY TEMPER THE SEVERE THREAT. NONETHELESS... EFFECTIVE BULK SHEAR VALUES ARE PROJECTED TO INCREASE TO AROUND 25 KNOTS OVER THE NORTHWEST (TAPERING TO 15 KNOTS OR LESS SOUTHEAST)... WHICH COULD SUPPORT SOME MULTI-CELL (WEST) TO PULSE (EAST) DAMAGING WIND AND HAIL. FRIDAY NIGHT: THERE ARE MIXED SIGNALS FOR FRIDAY NIGHT. WHILE THE SURFACE COLD FRONT (PERHAPS DIABATICALLY REINFORCED FROM EARLIER CONVECTION) WILL MOVE INTO THE CENTRAL NORTH CAROLINA OVERNIGHT... THERE MAY BE A RELATIVE LULL IN FORCING ALOFT AS THE LEAD SHORT WAVE TROUGH AND JET ALOFT LIFT OUT AND A MORE VIGOROUS SHORT WAVE PIVOTS INTO THE TROUGH BASE JUST TO OUR WEST. WILL MAINTAIN HIGH CHANCE POPS OVERNIGHT FOR NOW... BUT THIS COULD BE OVERDONE FOR REASONING MENTIONED ABOVE. LOWS 69 TO 73. SATURDAY AND SATURDAY NIGHT: SATURDAY SHOULD AGAIN BE ACTIVE AS THE STRONGEST FORCING FROM THE UPSTREAM SHORT WAVE TROUGH (MID LEVEL HEIGHT FALLS ON THE ORDER OF 30 METERS PER 12 HOUR) AND RIGHT ENTRANCE OF THE UPPER JET ARRIVE OVER CENTRAL NORTH CAROLINA. HOWEVER... IF THE NWP MODELS ARE CORRECT IN THE TIMING OF THE LOW LEVEL (SURFACE TO 850 MILLIBAR) PASSAGE... THEN THE FOCUS FOR CONVECTION WILL SHIFT INTO THE EASTERN PIEDMONT AND SANDHILLS AND COASTAL PLAIN. WILL ACCORDINGLY GRADATE POPS FROM 30 TO 40 NORTHWEST TO 70 PERCENT SOUTHEAST). THE PRESENCE OF THE MID AND UPPER JET OVERHEAD WILL YIELD BULK SHEAR OF 20 TO 30 KNOTS... SO ADDITIONAL MULTI-CELL OR PERHAPS BRIEF SUPERCELL STRUCTURES WILL BE AGAIN CAPABLE OF DAMAGING WIND OR HAIL. HIGH TEMPERATURES NOT AS WARM AS PREVIOUS DAYS... GENERALLY 85 TO 90 DEGREES. CONVECTIVE COVERAGE SHOULD DIMINISH AS THE SURFACE FRONT SETTLES SOUTHEASTWARD... THOUGH CONTINUED MID LEVEL HEIGHT FALLS AND COOLING ALOFT THROUGH THE NIGHT WARRANTS AT LEAST A SLIGHT CHANCE POP. MID 60S NORTHWEST TO LOWER 70S SOUTHEAST... AS SLIGHTLY COOLER AND DRIER AIR WORKS INTO THE REGION BEHIND THE FRONT. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... AS OF 415 AM THURSDAY... MEDIUM RANGE GUIDANCE IN GENERAL AGREEMENT THAT THE SURFACE FRONT WILL SETTLE JUST SOUTHEAST OF CENTRAL NORTH CAROLINA AND LINGER... WHILE ROUGHLY 1020 MILLIBAR SURFACE HIGH PRESSURE WILL BUILD FROM THE GREAT LAKES TO THE MID ATLANTIC REGION. THUS... DESPITE THE CONTINUED PRESENCE OF THE TROUGH ALOFT... SOMEWHAT COOLER... DRIER... AND MORE STABLE CONDITIONS ASSOCIATED WITH THE INCOMING SURFACE RIDGE SHOULD KEEP PRECIPITATION CHANCES BELOW CLIMATOLOGY THROUGH EARLY NEXT WEEK... EXCEPT IN THE VICINITY OF THE STALLED AND DIFFUSING SURFACE FRONT OVER SOUTHERN NORTH CAROLINA. HIGH TEMPERATURES IN THE MIDDLE TO UPPER 80S EXPECTED. BY WEDNESDAY... THE MEDIUM RANGE MODELS INDICATE THE SURFACE RIDGE WILL WEAKEN AND GIVE WAY TO A PRONOUNCED LEE TROUGH... AS LOW LEVEL THICKNESSES RETURN TO THE 1420 TO 1430 METER RANGE AND SUGGEST A RETURN TO TEMPERATURES AT OR ABOVE 90 DEGREES. THE RETURN OF THE HEAT AND INCREASING HUMIDITY SHOULD ALSO YIELD IMPROVING CHANCES (NEAR 20 PERCENT) OF DIURNAL SHOWERS AND STORMS ON WEDNESDAY. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... AS OF 729 AM THURSDAY... CURRENTLY HAVE AN AREA OF STRATUS EXPANDING SLOWLY NORTH FROM THE SOUTHERN PIEDMONT AND SANDHILLS AT 11Z. NORTHERN EDGE MAY REACH KRDU AND THE TRIAD TERMINALS THEN MIX OUT BY 14Z. MAY SEE A REPEAT OF THIS EPISODE AGAIN FRIDAY MORNING. OTHERWISE...AN AREA OF HIGH PRESSURE ALOFT OVER EASTERN NORTH CAROLINA WILL REMAIN NEARLY STATIONARY THROUGH TONIGHT THEN SLOWLY WEAKEN ON FRIDAY. MEANWHILE AN AREA OF LOW PRESSURE WILL STRENGTHEN OVER THE GREAT LAKES AND OH VALLEY. THE CIRCULATION AROUND THESE TWO WEATHER SYSTEMS WILL ADVECT VERY MOIST AIR INTO CENTRAL NORTH CAROLINA TODAY THROUGH FRIDAY. MINOR IMPULSES EMBEDDED IN THIS FLOW COUPLED WITH AFTERNOON HEATING WILL TRIGGER SCATTERED CONVECTION...MAINLY OVER THE PIEDMONT COUNTIES...THIS AFTERNOON AND AGAIN FRIDAY AFTERNOON. MAY EVEN SEE ISOLATED SHOWERS OCCUR OVER THE WESTERN PIEDMONT OVERNIGHT TONIGHT INTO EARLY FRIDAY. MOST CEILINGS WILL REMAIN ABOVE MVFR CRITERIA EXPECT WHERE HEAVIER SHOWERS AND STORMS OCCUR IN WHICH MVFR CEILINGS AND VISIBILITIES WILL OCCUR. THE APPROACH OF AN UPPER LEVEL TROUGH FROM THE WEST AND A MOIST AIR MASS IN PLACE WILL RESULT IN SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS ACROSS THE REGION FRIDAY NIGHT INTO SATURDAY...AND OVER THE EASTERN PIEDMONT AND COASTAL PLAIN SATURDAY NIGHT. WEATHER CONDITIONS ARE EXPECTED TO GRADUALLY IMPROVE ON SUNDAY INTO MONDAY AS SURFACE HIGH PRESSURE BUILDS IN FROM THE NORTHWEST. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && SYNOPSIS... NEAR TERM... SHORT TERM...MWS LONG TERM...MWS AVIATION...WSS
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RALEIGH NC 1158 AM EDT THU AUG 20 2009 NCZ009>011-026>028-041>043-077-078-085-086-088-089-211000- VANCE-WARREN-HALIFAX-FRANKLIN-NASH-EDGECOMBE-WAKE-JOHNSTON-WILSON- HARNETT-WAYNE-SCOTLAND-HOKE-CUMBERLAND-SAMPSON- 1158 AM EDT THU AUG 20 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL NORTH CAROLINA. .DAY ONE...TODAY AND TONIGHT. SCATTERED THUNDERSTORMS WILL DEVELOP THIS AFTERNOON WITH THE POTENTIAL THAT A FEW MAY BECOME SEVERE. THE PRIMARY THREAT WILL BE DAMAGING DOWNBURST WINDS. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY. THE APPROACH OF AN UNSEASONABLY STRONG UPPER LEVEL TROUGH AND PASSAGE OF AN ASSOCIATED COLD FRONT WILL PROMOTE THE DEVELOPMENT OF SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS SATURDAY AFTERNOON. A FEW THUNDERSTORMS COULD BECOME SEVERE... MAINLY BETWEEN NOON AND 8 PM... WITH A PRIMARY THREAT OF DAMAGING WIND GUSTS. THE POTENTIAL FOR THUNDERSTORMS TO TRAIN OVER THE SAME AREAS MAY ALSO RESULT IN LOCALIZED URBAN FLOODING. .SPOTTER INFORMATION STATEMENT... SKYWARN SPOTTERS ARE ENCOURAGED TO REPORT ANY SEVERE OR SIGNIFICANT WEATHER ASSOCIATED WITH THESE STORMS. NCZ007-008-021>025-038>040-073>076-083-084-211000- PERSON-GRANVILLE-FORSYTH-GUILFORD-ALAMANCE-ORANGE-DURHAM-DAVIDSON- RANDOLPH-CHATHAM-STANLY-MONTGOMERY-MOORE-LEE-ANSON-RICHMOND- 543 AM EDT THU AUG 20 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL NORTH CAROLINA. .DAY ONE...TODAY AND TONIGHT. HAZARDOUS WEATHER IS NOT EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY. THE APPROACH OF AN UNSEASONABLY STRONG UPPER LEVEL TROUGH AND PASSAGE OF AN ASSOCIATED COLD FRONT WILL PROMOTE THE DEVELOPMENT OF SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS FRIDAY AND FRIDAY NIGHT. A FEW THUNDERSTORMS COULD BECOME SEVERE... MAINLY BETWEEN 3 PM AND 11 PM... WITH A PRIMARY THREAT OF DAMAGING WIND GUSTS. THE POTENTIAL FOR THUNDERSTORMS TO TRAIN OVER THE SAME AREAS MAY ALSO RESULT IN LOCALIZED URBAN FLOODING. .SPOTTER INFORMATION STATEMENT... SKYWARN SPOTTERS ARE ENCOURAGED TO REPORT ANY SEVERE OR SIGNIFICANT WEATHER ASSOCIATED WITH THESE STORMS.
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RALEIGH NC 112 PM EDT THU AUG 20 2009 NCZ022-023-201815- ALAMANCE-GUILFORD- 112 PM EDT THU AUG 20 2009 ...A STRONG THUNDERSTORM WILL MOVE ACROSS GUILFORD AND ALAMANCE COUNTIES THROUGH 215 PM EDT... AT 111 PM EDT...DOPPLER RADAR INDICATED A STRONG THUNDERSTORM OVER GREENSBORO...MOVING NORTHEAST AT 30 MPH. SOME LOCATIONS AFFECTED BY THIS STORM INCLUDE MCLEANSVILLE... MONTICELLO... GIBSONVILLE... ELON COLLEGE... ALTAMAHAW... GLEN RAVEN... UNION RIDGE...AND PLEASANT GROVE. GUSTY WINDS OF 30 TO 40 MPH...SMALL HAIL... AND DANGEROUS CLOUD-TO-GROUND LIGHTNING CAN BE EXPECTED WITH THESE THUNDERSTORMS. ANYONE OUTDOORS SHOULD MOVE INSIDE A SAFE BUILDING... AND WAIT UNTIL THE STORM HAS PASSED. GIH
The Roanoke radar (KFCX), 110 km away, was scanning. The volume nearest the first event began at 17:15 UTC.
2 thunderstorm wind. Local standard time, as filed.
Large tree limbs were blown down and two bradford pear trees were toppled on Briarmeade Road.
One tree was reported blown down on a home on Sink Circle.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in North Carolina in 2009Every state in 2009This day in weather historyWarnings in North Carolina, August 2009
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 193515, 193516.