WAYNE AND CAYUGA COUNTY TORNADO - AUGUST 21,
During the late afternoon of Sunday August
21st, 2011 severe weather developed rapidly across the Finger
Lakes Region of New York State in advance of a cold front
crossing the Lower Great Lakes Region. A severe thunderstorm
produced extensive damage across portions of Wayne and Cayuga
counties. A subsequent damage survey conducted by the
National Weather Service in coordination with Emergency
Management offices from Wayne and Cayuga counties confirmed that
an EF-2 tornado touched down and was responsible for the bulk of
the damage. This web page provides a brief review of the
meteorological factors that contributed to the severe weather that afternoon.
The photographs of damage at the bottom of this report were
taken by the WFO Buffalo Storm Survey Team.
pattern on Sunday afternoon August 21st featured a cold front that
extended from a Low in Quebec to another Low over western Lake Erie
(Fig 1). Strong winds aloft and an atmospheric thermodynamic
profile that featured a very unstable environment combined to
elevate the threat for severe weather during the late afternoon
hours. NOAA's Storm Prediction Center had outlined an area
just to the east of the affected counties to be under a Slight Risk Area for severe weather that afternoon
Figure 1: NCEP Surface Analysis
Sunday August 21st at 18z.
Figure 2: 12hr
forecast valid 00z Mon August 22, 2011 of the NAM 200mb Height,
Divergence contours and image of Wind Speed.
|Severe thunderstorms are often
fueled by strong winds aloft and are more likely in particular
quadrants of the Upper level Jet. In this case, the Finger
Lakes Region was under the
Exit Region of the Upper Level Jet as shown in Figure 2.
This region is often associated with increased upward motion and
when combined with other factors, an increased threat for severe
thunderstorm development. The image show the 200 mb height
field in thicker green lines, the divergence field in light brown
and the image is wind speed which outlines the 200mb jet.
|As the afternoon progressed a cluster of
thunderstorms moved across WNY. As you will see in the
animation below, one particular storm among a cluster of showers and
embedded thunderstorms becomes stronger and actually turns slightly
to the right of the prevailing movement as it crosses eastern Wayne and Cayuga counties.
Right turning storms often produce severe damage.
WSR-88D 0.5 degree reflectivity loop from 1713z - 1950z
Sunday August 11, 2011. Note the cell
bows out and turns to the right in
eastern Wayne county.
|Figure 4 shows a
Relative Velocity (SRM) image taken about the time of the
damage. The drawing within the image attempts to explain how
the radar detects a circulation from the SRM data. The radar
can only detect motion that comes toward or away from it.
Therefore, a circulation will show a specific signature, in this
case, red colors show motion away from the radar and green show
motion toward the radar. If adjacent radar pulses shows
strong reds next to strong greens, then there is some evidence that
a rotation exists in that spot. The forecaster working the
severe weather desk will use this information along with several
other indicators to assess the potential for rotation and
subsequently a tornado. Figure 5 is an animation which shows the development of the
rotation, a tightening of the rotation during the time of the
tornado damage as it moves across eastern
Wayne county and eventually it weakens as it heads east of Cayuga
Figure 4: WSR-88D 0.5
degree SRM August 11, 2011 at 1922z. Note the strong opposing
velocity signatures adjacent to each other along the Wayne-Cayuga
WSR-88D 0.5 degree SRM August 11, 2011 loop from 1859z-1945z shows
the tightening of the circulation as it moves across eastern Wayne
and western Cayuga counties.
|Figure 6 shows the damage path that resulted
from the EF-2 tornado on the Enhanced
Fujita Scale . A Survey Team from the National Weather
Service met with Emergency Managers from Wayne and Cayuga counties
who escorted them to sites where damage was reported. Based on
examination of the evidence and comparison with the WSR-88D radar
data, the Team determined that an EF-2 Tornado with wind speeds of
approximately 115-120mph cut a swath about 200 yds. wide along a
path of 11 miles. Each of the points along the damage path in
the figure represent locations where damage was examined.
Figure 6: Damage path
determined from the
survey conducted by NWS and Emergency
Damage Photos Taken by NWS Survey Team
|The four photos above are of a 2-story frame farmhouse
in Savannah, NY. The roof on an addition was torn off,
a barn was destroyed across the street and an aluminum boat
with motor was carried several hundred yards into a field.
|Damage to homes on Drable St. in Savannah. The
first two photos show a manufactured home whose roof was
partially removed. The third photo is another
manufactured home that was moved off its foundation and
sustained significant damage.
|This home on Taylor St. had its roof completely
torn off, the pool deck was tossed on top of the
garage roof and an outbuilding was tipped over.
|The first photo shows an entire stand of
pine trees snapped off about halfway up
their trunks. The second photo shows
the tangled mess of trees and a flatbed
trailer. Finally a stately farmhouse
in Conquest had its entire roof torn off.
|The damage path ended in Cato
just east of Rte 34 where the a
beautiful backdrop of fair weather
cumulus clouds outline a barn whose
roof was torn off just the day