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Marblehead Massachusetts multiple microburst 357-430 PM

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  • Bill Scanlon
    Statement as of 3:11 PM EDT on July 14, 2006 Compilation of two storm surveys for severe thunderstorms July 11 2006. ... Marblehead Massachusetts multiple
    Message 1 of 1 , Jul 14, 2006
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      Statement as of 3:11 PM EDT on July 14, 2006

      Compilation of two storm surveys for severe thunderstorms July 11
      2006.

      ... Marblehead Massachusetts multiple microburst 357-430 PM
      Tuesday July 11 2006...

      A National weather storm survey of storm damage has reached a
      preliminary conclusion that multiple wet microbursts affected
      Marblehead Neck and the adjacent waters between approximately
      357 PM and 430 PM on Tuesday July 11th.

      This survey included visual assessment... interviews with many along
      the primary damage path... receipt of wind instrument winds speeds...
      newspaper accounts and correlation with National climatic data
      center /ncdc/ archived Taunton radar reflectivity... velocity and
      spectrum width data.

      Westerly winds of about 90 miles an hour occurred in the core damage
      zone centered from Marblehead Harbor southwest of the corinthian
      yacht club /cyc/ cutting across corinthian Lane then across the
      southern portion of Barker Lane and out to sea. The land damage path
      was short... primarily because the land is only about 700 feet wide
      from the Point of impact and exit across Marblehead Neck.

      There were no known injuries.

      The main damage path was approximately 150 feet wide. It consisted of
      primarily tree damage and comparatively minor structural damage along
      with substantial damage to sailing vessels and at least one auto.

      Sporadic tree damage occurred about 600 feet north of the street
      surveyed core damage path... near Manley street... as well variable
      distances to the south and southwest of the core path... beginning on
      Foster street near The Harbor Avenue intersection then up to the
      eastern yacht club finally to ocean Avenue near its intersection with
      Harbor Avenue.

      There was a tight gradient to the primary damage core.

      Taunton radar implied strong rotation via velocity data... and also
      strong shear in spectrum width data... indicating turbulent flow aloft
      in the interface between a portion of the updraft and the wet
      microburst downdraft from a constantly enlarging storm system.

      Multiple eyewitness accounts spoke of a wind driven damage from west
      to east.

      There was one report of a waterspout from a patron at restaurant
      across The Harbor but we were not able to interview that person.

      This 4 PM storm reportedly did have hail preceding it... estimated 1.5
      inch diameter at approximately 355 PM... but this was clearly a
      separate storm from the 305-320 PM three inch diameter hailstone
      storm... the second largest diameter hailstones known to have occurred
      in Massachusetts.

      It is possible... after more data arrives... including evaluation of
      storm relative motion data... barographs... additional wind damage data
      and further visual accountings... that an updated Post event
      evaluation would reveal a rain wrapped tornado was embedded in the
      initial violent westerly wind. However the preponderance of
      information gleaned through 3 PM Friday July 14th... suggests that was
      a straight line wind event.

      The following is time approximate and may need to be adjusted in the
      final report found in the National climatic data center document
      titled... storm data. Storm data will also reflect later updated time
      information on the events already listed.

      At about 340 PM to 345 PM... apparent northeast wind storm outflow
      from storms traveling west to east... just north of Marblehead...
      arrived at the mouth of Marblehead Harbor causing sea spray. For
      those reviewing velocity data in the 0.4 degree slice... the
      Centerpoint of the Taunton radar beam at this distance intersects the
      atmosphere/storms at about 2000 feet. The northeast surface outflow
      probably was much shallower and undercut the wind fields seen at 2000
      feet.

      Sometime between 357 PM - 4 PM... a white tempest was reported to
      have developed over Marblehead Harbor on the neck side of The
      Harbor... estimated by the cyc race chair to begin about 300 yards
      upstream from The Dock... and advanced toward the corinthian yacht
      club /cyc/ lifting 30 foot sailing vessels approximately 20 feet in
      the air and catapulting them end over end toward The Dock. An
      anemometer on the cyc dock was viewed to reach 95 mph before it blew
      off its mast. A sailing regatta had just finished and there were
      reports of people being pinned to the yacht club porch wall by the
      wind as safety was sought by many. At the club itself an anemometer
      topped out at 60 mph.

      One anemometer on corinthian Lane at 401 PM recorded 74 mph... time
      approximate... while a family member was watching branches Peel off a
      tree at about 414 PM... again time estimated.

      Police logs indicate the first call for trees down was at 416 PM.

      Wind and or debris blew out some windows on homes along corinthian
      Lane and much of the shorn tree damage with branches estimated 9
      inches to a foot in diameter... were torn off the mid and upper
      portions of trees either side of corinthian Lane and then across
      Harbor Avenue onto properties south of Barker Lane.

      There were many reports of excessively heavy rain accompanying or
      just following this burst of damaging wind... visibility down to 5
      feet... windows fogging and at least one report ears popping... the
      latter possibly related to a rapid change in air pressure near the
      time of this event.

      Enhanced fujita scale estimates for both hard and softwood combined
      with anemometer readings that were not checked for calibration both
      in time and wind speed... strongly imply wind speeds of near 90 miles
      an hour.

      That was the first microburst...

      Winds continued to blow strong after the initial damage burst..then
      there was at least one report of a sudden shift to a southerly wind
      component probably sometime between 420 PM and 425 PM causing further
      damage on corinthian Lane and possibly confusing debris pattern
      assessment. The report below also supports this secondary
      microburst event.

      Reports from weatherflow wind instruments on children's island about
      1 mile to the northeast of Marblehead Neck and kindly shared with the
      National Weather Service were as follow...

      425pm 285 degs 11 gust 26 mph
      430pm 230 degs 48 gust 73 mph
      435pm 195 degs 18 gust 47 mph
      440pm 92 degs 16 gust 24 mph.

      We will continue to accept baraograph traces... detailed anemometer
      information and eyewitness accounts both verbal and video.

      We extend appreciation to the numerous officials /police-fire/
      Skywarn support... eyewitness accounts-reports from the corinthian...
      eastern and pleon yacht clubs as well as those along corinthian and
      Barker lanes who willingly shared a recounting of events toward a
      better understanding of the processes involved.


      Now to the tornado in Wendell Massachusetts below...

      ... Microburst and F2 tornado confirmed in Wendell Massachusetts on
      Tuesday July 11...

      A damage survey was conducted in Wendell Massachusetts today by the
      National Weather Service in Taunton... in cooperation with the Skywarn
      amateur radio coordinator for western Massachusetts... the
      Massachusetts emergency management agency... the Massachusetts
      department of conservation and recreation... and the Athol Fire
      Department.

      Based upon the damage survey... interviews with eyewitnesses and
      Doppler radar data... the severe thunderstorm produced a combination
      of straight line wind damage and a tornado... which has been rated as
      a strong F2 with wind speeds near 155 mph.

      Damage began around 230 PM EDT... about 200 yards west of Montague
      Road. Straight line wind damage extended from Montague Road 1.5
      miles east to wicket pond in the Wendell State Forest. Large
      Oak... Maple and Pine trees were uprooted and snapped in this area.
      Some Oaks just over two feet in diameter were snapped about 10 to
      15 feet from the ground. Damage from the microburst extended along a
      path of one and a half miles in length... and anywhere from 50 to
      300 yards wide. Wind speeds were estimated as high as 90 mph.

      Tornado damage first appeared on the northeast corner of wicket
      pond. An eyewitness reported seeing a 6 foot wave form on The Pond.
      In addition... the park supervisor reported that the level of The Pond
      was lowered 6 to 8 inches by the storm. On the west side of wicket
      pond many trees snapped 15 to 20 feet above the ground... with debris
      in a chaotic pattern.

      The next area of damage was on wicket pond Road where the most severe
      damage occurred. Trees as large as 3 feet in diameter were uprooted.
      Bark was stripped off trees and a house had part of its roof torn
      off. The tornado tracked to the east along wicket pond Road...
      passing over depot Road which is in Wendell center. Part of a roof
      was torn off an old barn and many trees were uprooted.

      After crossing depot Road... the tornado continued to track to the
      east... passing north of Morse Village Road. A construction storage
      trailer was completely destroyed and its roof was wrapped around
      a tree. Trees were also uprooted or snapped in this area. Damage
      came to an end about one half mile east of New Salem Road near a
      power line.

      The path length of the tornado was approximately 2.9 miles long.
      Its average width was 200 yards... varying from 100 to 300 yards.


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