000 NOUS41 KPHI 291913 PNSPHI DEZ001>004-MDZ008-012-015-019-020-NJZ001-007>010-012>027-PAZ054-055- 060>062-067>071-300300- PUBLIC INFORMATION STATEMENT - SEVERE WEATHER EVENTS NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 215 PM EST WED OCT 29 2003 ...THE FALL OF 2003 PRODUCES SEVERAL SEVERE WEATHER EVENTS... SEPTEMBER AND OCTOBER OF 2003 HAS CERTAINLY BROUGHT SEVERAL ROUNDS OF SEVERE WEATHER TO PARTS OF THE REGION. WHILE SOME PLACES RECEIVED LITTLE OR NO SEVERE WEATHER, OTHER PORTIONS OF THE REGION GOT HIT HARD BY DAMAGING WINDS AND EVEN SEVERAL TORNADOES. THE TORNADOES THAT DID TOUCH DOWN DURING THIS FALL SEASON'S SEVERE WEATHER OUTBREAKS WERE WEAK, HOWEVER CONSIDERABLE DAMAGE DID OCCUR IN SOME LOCALES. THE TORNADOES WERE RATED F0 TO F1 ON THE FUJITA SCALE. THE FUJITA SCALE IS A RATING SYSTEM BY WIND SPEED THAT STARTS AT F0 AND GOES UP TO F6 (REFER TO THE TABLE BELOW). THE WEATHER SYSTEMS THAT SPAWNED OUR SEVERE WEATHER THIS FALL WERE QUITE SIMILAR IN RESPECT TO THEIR ATMOSPHERIC SETUP. THE SEPTEMBER 23RD EVENT HAD A TOTAL OF 4 TORNADOES, ALL OF WHICH WERE RATED AN F1 ON THE FUJITA SCALE. THERE WERE NO TORNADOES DURING THE OCTOBER 14-15 EVENT, HOWEVER THERE WERE MANY REPORTS OF DAMAGE FROM STRAIGHT-LINE WINDS. THE MORE RECENT EVENT, OCTOBER 27TH, THERE WAS 1 CONFIRMED TORNADO IN BURLINGTON COUNTY, WHICH WAS RATED AN F0. ...THE FUJITA SCALE... F-SCALE INTENSITY PHRASE WIND SPEED (MPH) ------- ---------------- ---------------- F0 GALE TORNADO 40-72 F1 MODERATE TORNADO 73-112 F2 SIGNIFICANT TORNADO 113-157 F3 SEVERE TORNADO 158-206 F4 DEVASTATING TORNADO 207-260 F5 INCREDIBLE TORNADO 261-318 ------------------------------------------------------- *F6 INCONCEIVABLE TORNADO 319-379* * = THESE WINDS ARE VERY UNLIKELY. IN GENERAL, THE FUJITA SCALE IS REFERENCED FROM F0 TO F5. BELOW IS A GENERALIZED SUMMARY OF EACH SEVERE WEATHER EVENT. ...SEPTEMBER 23, 2003... A POWERFUL COLD FRONT APPROACHED FROM THE WEST AND MOVED THROUGH THE DELAWARE VALLEY AROUND DAYBREAK, THEN CONTINUED TO MOVE EAST AND THEN OFF THE NEW JERSEY COAST BY LATE MORNING. ATMOSPHERIC CONDITIONS WERE SUCH THAT THE WIND FIELD SEVERAL THOUSAND FEET ABOVE THE GROUND WAS IN EXCESS OF 60 MPH. THERE WAS NOT A LOT OF INSTABILITY OR ENERGY IN THE ATMOSPHERE, HOWEVER THE VERY STRONG WIND FIELD, COUPLED WITH THE COLD FRONT ITSELF PRODUCED AN INTENSE LINE OF WHAT IS CALLED "LOW-TOPPED CONVECTION". LITTLE IN THE WAY OF THUNDER AND LIGHTNING TYPICALLY OCCURS WITH THESE TYPE OF LINES, AS THE CLOUDS DO NOT EXTEND VERY HIGH INTO THE ATMOSPHERE. THE CLOUDS DID HOWEVER EXTEND HIGH ENOUGH TO TAP THE STRONGER WINDS ABOVE THE GROUND. THESE STRONG WINDS WERE THEN TRANSPORTED DOWN TO THE GROUND, RESULTING IN DAMAGING WIND GUSTS. ALONG THE LEADING EDGE OF THE LINE, CHANGING WIND DIRECTIONS WITH HEIGHT PRODUCES A TURNING MOTION IN THE LOWER PART OF THE ATMOSPHERE, KNOWN AS WIND SHEAR. THIS ENHANCED LOW-LEVEL TURNING OR ROTATION WAS THEN TILTED VERTICALLY INTO THE LINE, PRODUCING BRIEF F1 TORNADOES. MAXIMUM WINDS IN THE F1 TORNADOES DURING THIS EVENT RANGED FROM 75 TO 85 MPH. BRIEF TORNADOES CAN ALSO OCCUR ON THE LEADING EDGE OF A GUST FRONT. A GUST FRONT IS THE LEADING EDGE OF GUSTY WINDS PRODUCED BY THE RAIN-COOLED AIR FROM A THUNDERSTORM. WIND DIRECTIONS CAN CHANGE QUICKLY ALONG A GUST FRONT, THEREFORE PRODUCING BRIEF SPIN-UPS OR WEAK TORNADOES. ...OCTOBER 14-15, 2003... THIS EVENT WAS SIMILAR TO THE SEPTEMBER 23RD EVENT AS ANOTHER STRONG COLD FRONT APPROACHED AND CROSSED THE ENTIRE AREA. ONCE AGAIN THIS OCCURRED DURING THE EARLY MORNING HOURS, GENERALLY CENTERED AROUND MIDNIGHT. THIS EVENT HOWEVER WAS A LITTLE FARTHER SOUTH THEN THE PREVIOUS EVENT, WITH SOUTHERN NEW JERSEY, DELAWARE AND EASTERN MARYLAND TAKING THE BRUNT OF THE SEVERE THUNDERSTORMS. AGAIN, A NARROW LINE OF INTENSE THUNDERSTORMS DEVELOPED ALONG OR JUST AHEAD OF THE COLD FRONT. THIS LINE WAS ABLE TO TAP THE STRONG WINDS ABOVE THE SURFACE AND TRANSFER THEM DOWN TO THE GROUND. THIS RESULTED IN THE DOWNING OF MANY TREES AND POWER LINES. ONE AREA PARTICULARLY HARD HIT WAS ABSECON, NEW JERSEY (ATLANTIC COUNTY) WHERE A MACROBURST OCCURRED. A MACROBURST IS AN INTENSE WIND GUST THAT RUSHES DOWNWARD FROM A SEVERE THUNDERSTORM. THIS WIND HITS THE GROUND AND THEN SPREADS OUTWARD FROM THE THUNDERSTORM, RESULTING IN A PATH OF DESTRUCTION. SOMETIMES MACROBURST'S CAN BE MISTAKEN TO BE TORNADOES. WITH A MACROBURST, THE DAMAGE IS LAYING DOWN IN NEARLY ONE DIRECTION, OR SOMETIMES IS IN A FANNED OUT PATTERN. A TORNADO ON THE OTHER HAND PRODUCES DAMAGE IN A MORE CHAOTIC PATTERN. TYPICALLY IN OUR AREA, DAMAGE FROM A MACROBURST CAN MEET OR EXCEED DAMAGE CAUSED BY A TORNADO. THERE WAS ONE FATALITY WITH THIS EVENT. AN INDIVIDUAL WAS KILLED WHEN STRONG WINDS DOWNED A TREE ONTO THEIR VEHICLE. ...OCTOBER 27, 2003... MOST RECENTLY, THIS EVENT OCCURRED DURING THE AFTERNOON. COMPARED TO THE PREVIOUS EVENTS DISCUSSED ABOVE, IT WAS THE TIMING THAT WAS MOSTLY DIFFERENT, AS THE PREVIOUS EVENTS TOOK PLACE LATE AT NIGHT OR DURING THE EARLY MORNING HOURS. THE OCTOBER 27TH EVENT HAD SIMILAR ATMOSPHERIC CONDITIONS WHEN COMPARED TO THE EARLIER ONES. YET ANOTHER STRONG COLD FRONT WAS APPROACHING FROM THE WEST. A LARGE SHIELD OF RAIN FELL ACROSS THE REGION, THEN AS THE FRONT ITSELF APPROACHED, A LOW-TOPPED LINE OF CONVECTION (SOME LIGHTNING DID OCCURRED) DEVELOPED AND RAPIDLY MOVED EAST. MOST OF THE DAMAGE OCCURRED ACROSS NEW JERSEY, ESPECIALLY ACROSS CENTRAL AREAS. ONE DIFFERENCE WITH THIS EVENT WAS THAT A WAVE OF LOW PRESSURE DEVELOPED ON THE FRONT AND TRACKED NORTHEASTWARD. INCREASINGLY HUMID AIR SURGED INTO THE REGION AHEAD OF THE FRONT, WHICH ALLOWED FOR AN INCREASE IN SOME INSTABILITY. WHILE THE OVERALL INSTABILITY AGAIN WAS NOT IMPRESSIVE, THE WIND FIELDS WERE RATHER STRONG. THE CONVECTION EMBEDDED WITHIN THE LINE WAS ABLE TO TAP THIS WIND AND TRANSPORT IT DOWN TO THE GROUND. THE APPEARANCE OF THIS EVENT WAS ALSO SIMILAR TO EARLIER ONES THIS FALL AS THE LINE WAS ACCOMPANIED BY SOME LOW-LEVEL SHEAR. AGAIN, THIS TURNING OF WIND DIRECTION WITH HEIGHT, ALLOWS FOR ROTATION TO DEVELOP. AS THE CONVECTION RUNS OR TAPS INTO THIS, WEAK TORNADOES DEVELOP ALONG THE LEADING EDGE. ONE WEAK TORNADO (AN F0) WAS CONFIRMED IN HAINESPORT, NEW JERSEY (BURLINGTON COUNTY). WINDS WERE ESTIMATED TO BE 70 MPH WITH THIS F0 TORNADO. A FEW FUNNEL CLOUDS WERE ALSO SIGHTED DURING THIS EVENT. ONE FATALITY OCCURRED WITH THIS EVENT. ONE PERSON WAS KILLED WHEN STRUCK BY A LARGE TREE LIMB. ...IN SUMMARY... THE THREE SEVERE WEATHER EVENTS THIS FALL WERE RARE. "NORMALLY" ONLY ONE SEVERE WEATHER EVENT TAKES PLACE IN OUR AREA EACH FALL SEASON. THE ATMOSPHERIC SETUP WITH ALL THREE SEVERE WEATHER EVENTS THIS FALL WERE NOT EXACTLY THE SAME, HOWEVER THERE WERE SEVERAL FACTORS THAT WERE. THE STRONG WIND FIELDS THAT ACCOMPANIED THE COLD FRONT OF EACH EVENT, COMBINED TO PRODUCE SEVERE WEATHER. THE COUNTIES THAT WERE IMPACTED THE MOST WERE NEARLY THE SAME ONES IN ALL THREE EVENTS. STRONG COLD FRONTS DURING THE FALL SEASON, COUPLED WITH A VERY STRONG WIND FIELD RESULTS IN WHAT IS TYPICALLY KNOWN AS A "COLD FRONTAL RAINBAND". THESE RAINBANDS ARE MADE UP OF LOW-TOPPED CONVECTION WHICH MANY TIMES DO NOT PRODUCE LIGHTNING AND THUNDER, HOWEVER THEY ARE STRONG ENOUGH TO BRING DOWN THE STRONG WIND FIELD FROM ABOVE, TO THE SURFACE. THE RESULT IS WIND DAMAGE. SMALL SCALE SHEAR ZONES (AREAS WHERE THE WIND IS CHANGING DIRECTION WITH HEIGHT) DEVELOP ALONG THE LINE OF CONVECTION, PRODUCING BRIEF SPIN-UPS OR WEAK TORNADOES. **NOTE: THE TERM "THUNDERSTORM" HAS BEEN REFERENCED ABOVE, HOWEVER THERE WERE MANY OCCURRENCES IN THE EVENTS DISCUSSED THAT THE DAMAGING WINDS, AND EVEN TORNADOES WERE NOT ACCOMPANIED BY ANY THUNDER AND LIGHTNING. SINCE THE WIND DAMAGE ASSOCIATED WITH THESE TYPE OF EVENTS ARE DUE TO CONVECTION (LOW-TOPPED), SEVERE THUNDERSTORM AND/OR TORNADO WARNINGS WERE ISSUED. $$ FOR COMPLETE WEATHER INFORMATION, VISIT OUR WEB SITE AT: WWW.WEATHER.GOV/ER/PHI (IN LOWERCASE LETTERS). MICHAEL GORSE METEOROLOGIST NWS MOUNT HOLLY NJ