Damage Survey Results
Squall Line with Embedded Supercells
8 July 2002 |
| |
| Staff Participating in Survey: |
Julie Adolphson (MIC)
Andy Pohl (IT)
Jesse Hystad (STEP Student) |
| |
| Date Completed: 9 July 2002 |
| |
| Discussion: |
| South End of Bonnie Street in Glasgow |
| The team departed at approximately 9:00am and drove to Bonnie Street, which
is just west and south of the Glasgow High School. We met with Mr. Larry Cote
and Mrs Dave Watson Jr. Mr. Cote had called the office to report a
shed blown into the Watson's yard, which is located just to the north of
his yard. |
| The shed was approximately 14' X 14' and was anchored to concrete just to
the west of Watsons'. It was made of aluminum and looked to be at least 10
years old. The horizontal distance that the shed traveled was less than 10 yards,
and there were three telephone/electrical wires that the shed either passed in
between or over. A witness believed that the shed was high enough to clear
the wires. The vertical distance over the wires was approximately 35 feet.
Based on the structural integrity of the shed, and the direction from which
it originated, as well as other minor damage nearby, the damage was ruled as straight-line
wind gust. |
| |
| Downtown Hinsdale |
| At approximately 10:00am the team arrived on the east side of Hinsdale,
and turned north to survey the Nemont Telephone Cooperative building. This
building was made of cinder block with an aluminum roof. The size of the building
was approximately 15' X 15' and contained communications switching equipment.
The roof was completely blown off and traveled to
the northeast approximately 30 yards. The roof was crumpled in such a way
that it was believed to roll over on itself as it blew across a vacant lot.
The team noticed a splattering of insulation (blown-type) on the north and east wall
of the building. The insulation also blew into a house directly east of the
building. Torrential rain soaked the equipment inside the telephone building
and caused a lot of the insulation to splatter up from the ground onto the
lower north wall. |
| The team headed west down the street from the Nemont building, where
a large cottonwood tree had fallen on Leora Jones' house. According to
Mrs. Jones, the tree was well over 50 years old. The location of the break
in the tree was an area of considerable decay. Given the tree's decay and direction
of fall, and other less significant damage in the area, the team determined
the cause of the damage to be a straight-line wind gust from the southwest or west. |
| |
| West of Hinsdale |
| Next, the team headed west on US Highway 2, west of Hinsdale. Approximately five
miles out of town, at the Dull family farm, signs
of damage were noted. Mr Dull met us and described what had occurred.
First, a small metal shed was picked up and spun around in place for a few
seconds and then toppled over on its side. Next 10' X 12' three-sided metal
livestock stall was damaged. The front on the building was open to the southwest.
It had the roof, which was well-anchored in the center of the building (with
a 12-inch diameter solid wood beam), ripped off and strewn approximately
100 yards to the northeast into a pasture. The beam in the center of the building
was incased in three feet of concrete. The debris from the stall spread out
and turned counterclockwise into the field. Mr Dull could not see because
the visibility was poor, so he was unable to tell if the damage was due to a tornado
or straight-line winds. Given the type of damage and direction of the debris
field, it was determined that an F0 tornado had occurred at the Dull farm. |
| |
| Park Grove |
| The team then headed back east towards Park Grove (near Fort Peck) to survey
reported damage. Three fallen trees were noted approximately
three miles north of Park Grove. These trees were all lying towards the
northeast and were likely the result of straight-line winds. In
Park Grove the team visited with the Baker family who had significant damage
to the area across the street from their home. Substantial damage was done
to their garage and its contents. Some of the damage was a direct result of
debris which had come from the southwest, where a roof was taken off a modular
home. Of particular note was a small (5 inch-diameter) tree which was sheared
off with aluminum wrapped around it, this tree was directly to the southwest
of the garage. A picnic table lost its top, entirely, with no evidence of wood
left on the top. The garage door and frame was noticeably broken and listing.
The metal from the larger portion (to the west of the above mentioned portion
of the garage) was extremely mangled. As in Hinsdale, the visibility was near
zero in rain, so that the witnesses to the storm were unable to see rotation.
The entrance to the storm cellar was significant damaged, and the residents
did not attempt to enter the cellar before or during the storm. The path
of damage was quite narrow, but it was difficult to detect if there was indeed
rotation associated with the Bakers' damage. |
| About a half-mile to the southwest of the
Bakers' home was the modular home, owned by the Bryans. This modular home
appeared to be around 20 years-old, with reasonable construction. It was
located on a point overlooking water and then more open space to the southwest
through northwest. Just a year ago, the home had sustained considerable
hail damage, and the roof was replaced. The roof was lifted off from the southwest,
as debris was noted left over in the northeast corner of the home. On the
west (front of the home) wall, some windows were broken, but one was lifted
out of its frame and placed perfectly upright between two twin beds, with
its glass intact. Very little debris was deposited close to the home. Some
strips of insulation were found at least 40 feet high into the trees located
directly behind (northeast) the home. A 5' X 6' shed was pushed over in the
northeast corner of the back yard. The majority of the debris appeared to have
hit the Bakers' garage mentioned above. Although not ruled out, the team could
not determine with certainty whether a tornado was the cause at this time.
In the area to the immediate northeast of the Bakers' was additional debris,
such as aluminum siding noted on top of a pick up truck, which had been parked
under a tree for protection. |
| North or northwest of the Bryans' home was
an area of trees which had considerable limb breakage. This area was about
50' X 50' and showed signs of rotation. Limbs where strewn in a convergent and
even circular pattern. Away from the center of the circular pattern, was
a more distinct convergent pattern, with limbs to the south lying to the
northwest, with the limbs near Bryans' home lying to the northeast. In addition,
there was a well-constructed (very heavy) 8'X8' shed that was rotated off its
cinder block, but not damaged in any other way. The team determined that
the above was conclusive evidence that there was indeed an F0 tornado responsible
for some of the damage in Park Grove. However, the many other residents interviewed
could not confirm seeing rotation, but all mentioned the visibility was low
during the highest incidence of wind. Many also noted seeing some low-level
rotation prior to the onset of precipitation. |
| |
| Meteorological Information |
| The WSR-88D performance was fair during this event. The
majority of the base and derived products indicated a significant shear line ahead
of the convection. Also noted was several supercells that evolved into
the bowing line. Although it may be premature to say without further analysis
of the radar data, the weak tornadoes may have been rain-wrapped vortices
associated with mini-supercells. Another possibility, is that the weak tornadoes
formed along the leading edge of the gust front. However, given that the
witnesses all said the winds were associated with the rain, it seems less likely
that the latter would be the case. |
| One other note of interest was that once the line became more parallel to
the mid-level flow, the winds were noticeably weaker, and severe wind reports decreased.
A number of TVSs were detected, including at or near the time of the damage reported
here, but the locations of the TVSs were not in conjunction with the areas of damage noted. |
www.weather.gov 
