620  
NOUS41 KPBZ 211609  
PNSPBZ  
PAZ021-073-212015-  
 
PUBLIC INFORMATION STATEMENT  
NATIONAL WEATHER SERVICE PITTSBURGH PA  
1109 AM EST TUE NOV 21 2017  
 
...TORNADO CONFIRMED NEAR PLUM TO MURRYSVILLE IN ALLEGHENY AND  
WESTMORELAND COUNTY WESTERN PENNSYLVANIA...  
 
LOCATION...PLUM TO MURRYSVILLE IN ALLEGHENY AND WESTMORELAND  
COUNTY WESTERN PENNSYLVANIA  
DATE...NOV 19 2017  
ESTIMATED TIME...1211 AM - 1215 AM EST  
MAXIMUM EF-SCALE RATING...EF1  
ESTIMATED MAXIMUM WIND SPEED...90 MPH  
MAXIMUM PATH WIDTH...125 YD  
PATH LENGTH...2.5 MI  
BEGINNING LAT/LON...40.4206N/79.7277W  
ENDING LAT/LON...40.4910N/79.6829W  
* FATALITIES...0  
* INJURIES...0  
 
* THE INFORMATION IN THIS STATEMENT IS PRELIMINARY AND SUBJECT TO  
CHANGE PENDING FINAL REVIEW OF THE EVENT(S) AND PUBLICATION IN  
NWS STORM DATA.  
   
..SUMMARY
 
 
THE NATIONAL WEATHER SERVICE IN PITTSBURGH PA HAS CONFIRMED THAT  
STORM DAMAGE ON NOV 19, 2017 THAT OCCURRED FROM PLUM TO  
MURRYSVILLE IN ALLEGHENY AND WESTMORELAND COUNTIES IN WESTERN  
PENNSYLVANIA WAS THE RESULT OF A COMBINATION OF TORNADIC AND  
STRAIGHT-LINE WIND.  
 
THE STORM SYSTEM THAT PRODUCED THE DAMAGING WIND IS KNOWN AS A  
QUASI-LINEAR CONVECTIVE SYSTEM (QLCS). THE LINE OF STORMS ON  
SATURDAY NIGHT FORMED IN CONDITIONS THAT WERE FAVORABLE FOR THE  
DEVELOPMENT OF SMALL, SHORT-LIVED DAMAGING CIRCULATIONS (CALLED  
MESOVORTICES) ALONG THE EDGE OF THE STORM OUTFLOW. SUCH  
CIRCULATIONS OCCASIONALLY CAN PRODUCE TORNADOES IN ADDITION TO  
EXTREME STRAIGHT-LINE WIND.  
 
ON SUNDAY AND MONDAY, A TEAM FROM THE NATIONAL WEATHER SERVICE IN  
PITTSBURGH SURVEYED DAMAGE ALONG AND ADJACENT TO SALTSBURG ROAD  
FROM PLUM TO MURRYSVILLE.  
 
IN SUMMARY: DAMAGE ALONG THE ENTIRE 3+ MILE PATH OF THE STORM WAS  
CAUSED BY A COMBINATION OF TORNADIC AND STRAIGHT-LINE WIND. AT ITS  
WORST, THE TORNADIC DAMAGE APPEARS CONSISTENT WITH PEAK WIND OF 90  
MPH, WITH A RATING OF EF1.  
 
CLIMATOLOGICALLY, TORNADOES IN THE OHIO VALLEY ARE RARE IN  
NOVEMBER. SINCE 1950, THIS IS ONLY THE SEVENTH NOVEMBER TORNADO  
DOCUMENTED, BUT THE SECOND NOVEMBER TORNADO THIS YEAR. DESPITE ITS  
SMALL SIZE AND SHORT DURATION, THE COMBINATION OF THE TIME OF  
YEAR, INTENSITY AND TIME OF DAY (OVERNIGHT) MAKES THIS TORNADO  
VERY UNUSUAL.  
 
THE SURVEY TEAM IS IMMENSELY APPRECIATIVE TO LOCAL AND COUNTY  
EMERGENCY MANAGEMENT/FIRE DEPARTMENT PERSONNEL AND THE PUBLIC FOR  
THEIR INVALUABLE ASSISTANCE IN THIS TWO-DAY EFFORT TO DOCUMENT,  
ASSESS AND PROVIDE ADDITIONAL DETAILS OF THE STORM DAMAGE.  
 
A DETAILED ANALYSIS OF THE EVALUATED STORM DAMAGE IS PROVIDED  
BELOW FOR INTERESTED READERS.  
 
***DAMAGE SURVEY DETAILS***  
 
A FOCUSED SWATH OF DAMAGE APPEARS TO HAVE BEGUN IN BOYCE PARK  
NEAR THE ENTRANCE ON NEW TEXAS ROAD, WHERE TREES WERE UPROOTED AND  
LIMBS WERE SNAPPED. THIS SWATH OF FOCUSED, BUT SPORADIC TREE  
DAMAGE CONTINUED ALONG THE STORM'S PATH GENERALLY PARALLEL TO  
SALTSBURG ROAD. BASED ON THE RADAR APPEARANCE OF THE STORM, THIS  
DAMAGE LIKELY WAS THE RESULT OF STRAIGHT-LINE WIND ON THE SOUTHERN  
FLANK OF THE INTENSIFYING MESOVORTEX.  
 
DAMAGE BECAME MORE CONCENTRATED AND HIGHER-END AS THE CIRCULATION  
APPROACHED KOCHER ROAD AND SALTSBURG ROAD, AT THIS POINT, DAMAGE  
SUGGESTS THAT A NARROW TORNADO BEGAN, WHERE LARGE HARDWOOD TREES  
WERE UPROOTED OR SNAPPED. AT A SENIOR RESIDENTIAL COMMUNITY ALONG  
SERENITY LANE, A VEHICLE WAS FLIPPED BY THE WIND AND DRAGGED  
WESTWARD AND AIR CONDENSER UNITS ON BOTH THE UPWIND AND DOWNWIND  
SIDES OF BUILDINGS WERE MOVED. BUILDINGS SUFFERED MINOR LOSS OF  
ROOFTOP SHINGLES AND DOWNWIND LOSS OF SIDING, AND SUBSTANTIAL  
TREE DAMAGE WAS OBSERVED.  
 
AS THE STORM PROGRESSED EASTWARD, LESS-CONCENTRATED TREE DAMAGE  
WAS NOTED UNTIL IT APPROACHED ABERS CREEK ROAD, WHERE FOCUSED  
AREAS OF SNAPPED TREES WERE DISCOVERED. TREES AT THE BASE OF A  
HILL ON THE NORTHERN END OF THE CLOVER COMMONS RESIDENTIAL  
COMMUNITY WERE HIT PARTICULARLY HARD, WITH SUBSTANTIAL SNAPPAGE  
OBSERVED.  
 
OF SPECIAL CONSIDERATION: A HOME AT THE TOP OF THIS SMALL HILL  
SUFFERED THRESHOLD DAMAGE AND LOST THE ROOF OF AN ATTACHED  
OUTBUILDING OWING TO AN OPEN WINDOW IN THE STRUCTURE. A PROPERLY-  
MOUNTED, HIGH-QUALITY WIND SENSOR AT THIS HOME MEASURED A PEAK  
WIND GUST OF 82 MPH FROM THE WEST DURING THE STORM ON THE OUTER  
PERIPHERY OF THE MESOVORTEX CIRCULATION.  
 
THE TORNADO/PARENT MESOVORTEX APPEAR TO HAVE WEAKENED BRIEFLY  
EAST OF THIS LOCATION, AS ONLY THRESHOLD WIND DAMAGE IN THE FORM  
OF LOW-END TREE DEBRIS WAS NOTED ALONG HAVANA ROAD (ALTHOUGH IT  
IS POSSIBLE THAT SUCH DAMAGE WAS HIDDEN FROM VIEW OF THE SURVEY  
TEAM).  
 
A REINTENSIFICATION OF DAMAGE WAS FOUND NEAR THE COUNTY LINE  
BETWEEN WESTMORELAND AND ALLEGHENY COUNTIES, NEAR AND EAST FROM  
LOGAN FERRY ROAD. CONCENTRATED TREE DAMAGE APPEARS TO HAVE BEGUN  
IN EARNEST NEAR A LUTHERAN CHURCH AT THE INTERSECTION OF ROUTE 286  
AND LOGAN FERRY ROAD. DAMAGE CONTINUED INTO THE ADJACENT  
NEIGHBORHOODS ON OLD LOGAN FERRY ROAD, LOTT COURT, CALLA DRIVE AND  
MARGARETTA DRIVE, WHERE TREES WERE UPROOTED AND LIMBS WERE  
SNAPPED.  
 
AS THE STORM EMERGED FROM LOTT COURT TOWARD SARDIS ROAD AND  
SALTSBURG ROAD, THE TORNADO REINTENSIFIED, PRODUCING THE MOST-  
SUBSTANTIAL TREE DAMAGE NOTED ALONG ITS PATH. IN THIS LOCATION, A  
FOCUSED, CONVERGENT, 125 YD-WIDE PATH WAS CUT THROUGH SEVERAL  
CLUSTERS OF HARDWOOD AND SOFTWOOD TREES. FULL-LEAF TREES WERE  
SNAPPED AT THE TRUNKS, AND OTHER TREES WITH NO LEAVES WERE  
UPROOTED. EVEN CONSIDERING THE PRE-CONDITIONED WET GROUND, WIND  
WAS QUITE STRONG IN THIS AREA, AS SHELTERED HOMES SAW MINOR  
ROOFTOP DAMAGE FROM THE WIND IN ADDITION TO THE LOSS OF SIDING  
(AND DAMAGE AFTER BEING PELTED BY AIRBORNE DEBRIS), POWER POLES  
SUFFERED MINOR DAMAGE AND TREE DAMAGE WAS CONSIDERABLE.  
 
ALONG SARDIS ROAD AND SALTSBURG ROAD, A CLASSIC INDICATION OF A  
QLCS TORNADIC MESOVORTEX WAS DISCOVERED, WITH A CONVERGENT DEBRIS  
FIELD NOTED TO THE NORTH OF A PROXIMATE DIVERGENT DEBRIS FIELD.  
THE WIDTH OF THE ENTIRE DEBRIS FIELD OF NOTE SPANNED PERHAPS  
300-400 YD ALONG SARDIS ROAD.  
 
THE CIRCULATION WEAKENED QUICKLY AFTER CROSSING SALTSBURG ROAD,  
WITH ONLY SPORADIC SNAPPAGE OF TREE LIMBS OBSERVED FROM AFAR IN A  
HEAVILY-WOODED AREA AND NO FOCUSED PATH CONTINUING THEREAFTER.  
 
THE DAMAGE NEAR LOGAN FERRY ROAD LIKELY WAS THE RESULT OF A  
DEVELOPING, SECOND SURGE OF THUNDERSTORM OUTFLOW (STRAIGHT-LINE  
WIND) AS THE MESOVORTEX RESTRENGTHENED. UPON APPROACHING/EXITING  
LOTT COURT, THE EARLIER TORNADO STRENGTHENED TO DAMAGING LEVEL ONCE  
AGAIN BEFORE WEAKENING AS IT CROSSED SALTSBURG ROAD.  
 
DESPITE THE DETAIL PROVIDED ABOVE, THE ENTIRE SWATH OF DAMAGE FROM  
PLUM TO MURRYSVILLE APPEARS TO HAVE OCCURRED OVER A FIVE-MINUTE  
PERIOD FROM 1210-1215 AM SUNDAY MORNING. THE TORNADO LIKELY WAS IN  
PROGRESS FROM 1211-1215 AM.  
 
AT MANY TIMES DURING THIS TORNADO'S EXISTENCE, THE STRONGEST WIND  
APPEARS TO HAVE OCCURRED AT ROOFTOP/TREETOP LEVEL, PERHAPS 30-50  
FT ABOVE GROUND. THIS CONCLUSION IS MOST EVIDENT TOWARD THE END OF  
THE PATH, WHERE CHILDREN'S PLASTIC PLAYHOUSES AND LIGHTWEIGHT  
YARD FURNITURE ON THE GROUND WERE UNAFFECTED, WHILE SHINGLES AND  
CHIMNEY STACKS WERE REMOVED AND TREES WERE SNAPPED AT THE TRUNK.  
 
ONE OF THE TALLEST SOFTWOOD TREES REMAINED STANDING WHILE ALL  
OTHERS AROUND IT WERE SNAPPED. THE VERY TOP OF THIS TREE RETAINED  
ITS EVERGREEN BRANCHES WHILE ALL LOWER BRANCHES WERE STRIPPED FROM  
THE TREE BY THE WIND.  
 
THIS INFORMATION ALSO CAN BE FOUND ON OUR WEBSITE AT  
WEATHER.GOV/PITTSBURGH.  
 
FOR REFERENCE: THE ENHANCED FUJITA SCALE CLASSIFIES TORNADOES  
INTO THE FOLLOWING CATEGORIES:  
 
EF0...WIND SPEEDS 65 TO 85 MPH  
EF1...WIND SPEEDS 86 TO 110 MPH  
EF2...WIND SPEEDS 111 TO 135 MPH  
EF3...WIND SPEEDS 136 TO 165 MPH  
EF4...WIND SPEEDS 166 TO 200 MPH  
EF5...WIND SPEEDS GREATER THAN 200 MPH  
 

 
 
KRAMAR  
 
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