Download HAZARD: TORNADO TORNADO PROFILE

HAZARD: TORNADO
TORNADO PROFILE:
A tornado is defined by Strahler in his Physical Geography Text as a violently rotating
column of air extending from a thunderstorm to the ground. Normally thunderstorms and
associated tornadoes develop in warm, moist air in advance of strong eastward moving
cold fronts in late winter and early spring. Tornadoes can also occur along a “dryline”
which separates very warm, moist air to the east from hot, dry air to the west. Both of
these scenarios are common in the Central Plains. Another way that tornadoes can be
created occurs when warm moist air flows upslope. Under the right temperature and
moisture conditions, intense thunderstorms can produce tornadoes in higher terrain.
As shown on Figure 29, tornadoes can occur in every state, although the mid-west states
have by far the greatest potential for this type of event. According to the Maryland
Hazard Analysis, the state had 210 tornado touchdowns reported between 1950 and 1998.
The most recent tornado outbreak occurred in the LaPlata vicinity in 2002 as shown on
Figure 30.
Tornadoes can be ranked by intensity by using the Fujita Scale devised by Dr. Theodore
Fujita at the University of Chicago in 1971. This scale is shown on Figure 28, and is
broken into 6 categories from F-0 to F-5. F-0 relates to a tornado having a wind speed up
to 72 miles per hour, while an F-5 tornado would have winds up to 318 mph.
COUNTY PERSPECTIVE AND HISTORY:
As shown in the Maryland Hazard Analysis, Garrett County has a composite tornado risk
of 4 on a scale of 1-5. The local planning committee agrees with this risk assessment.
Even though Garrett County is located in mountainous terrain it still has been subjected
to violent storms including tornadoes. Between 1950 and 1998 there were 8 reported
touchdowns of tornadoes in Garrett County as shown on Figure 31. Two of these events
were rated Class F-3 and the remainder were F-1 or F-2. In 1980 Garrett County suffered
a string of tornadoes which caused damage to a number of homes in Crellin. In 1998,
two outbreaks of tornado activity occurred at the border of Garrett County and Somerset
County just to the north. Both of these events were related to thunderstorms developing
from passing cold fronts. The combination of warm moist air flowing up slope from the
southwest and the cold front passing from the north and west created ideal conditions for
tornado activity. One of these tornadoes was rated F-4 after it crossed the county line and
hit Frostburg in Allegany County as shown on Figure 30.
MUNICIPAL PERSPECTIVE:
As is the case with most other weather related events, municipalities in Garrett County
share the same concerns as the county. Two municipalities, Grantsville and Accident, are
located on high, relatively flat land, and are probably more susceptible to wind events
than municipalities like Friendsville and Kitzmiller, which are located in a valley setting
affording some protection by surrounding mountains.
PREVIOUS MITIGATION MEASURES:
While mitigating tornado damage is nearly impossible, Garrett County does have a state
mandated Building Code which includes wind loading requirements and tie-down
requirements for mobile homes as shown on Figure 24. Additionally, the county’s hazard
warning system can be activated following notification of impending severe weather by
NOAA.