Table 5. Ice storm history in the region hit by the January 510, 1998 ice storm.
March 36, 1991
NY: devastating ice storm in western and northern NY
VT: power crews kept busy for several days
NH: numerous outages from ice-laden power lines in southern NH
ME: significant freezing rain and sleet storm in central portions
February 1415, 1986
NH: fiercest ice storm in 30 years over higher elevations in the Monadnock Region in 10-
mile-wide swath from MA border to New London
January 825, 1979
ME: trees and power lines coated w > 2 in. of ice; heaviest storm in many decades
NH: major disruption to power and transportation
March 25, 1976
NY: worst ice storm in memory in western NY: outages lasted longer than 10 days
December 22, 1969January 17, 1970
MA: severe ice storm
NH: power disruption to many communities
VT: "havoc unbelievable" to forests and utility lines
ME: worst ice storm in many years in southern half
December 411, 1964
NY: one of the most devastating freezing-rain storms of record in eastern NY
MA: destruction compared to 1921 and 1942 ice storms
December 2930, 1942
CT, MA, VT, NH: glaze storm of severe intensity
NY: one of the most severe glaze storms of record, St. Lawrence valley to Albany
December 1720, 1929
NY: one of worst of record in Buffalo and western NY
NH: unprecedented disruption and damage to telephone, telegraph, and power systems
ME: worst ice storm in half a century; weeks to repair utility lines
this storm, are presented in the following subsection. The return periods of storms like this one
are also estimated. The use of regional values, rather than point values, of extreme ice loads is
discussed in Section 7.4 for transmission lines. The large horizontal extent of many high-voltage
lines makes them more vulnerable to damage from ice and wind storms that hit anywhere along
the line route, so they should be designed for heavier ice loads. Systems of communication
towers that depend on all towers being operational should also be designed for regional ice and
wind loads rather than point loads.
7.1 Peaks-over-threshold method
Researchers often use the epochal method to determine the parameters of an extreme value
distribution. They pick the maximum value (of wind speed, snow depth, ice load, etc.) for each
year in the period of record, and then use these annual maxima to determine the parameters of a
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