Extreme ice thicknesses from freezing rain
Final Report
The maps of extreme ice thicknesses should not be interpreted as predictions of the future. They
are simply an evaluation of the risk based on current information. Rare ice storms can and do
occur now. Because structures are designed for specified risk levels that correspond to relatively
long return periods, we need to evaluate the severity of ice storms with large equivalent radial ice
thicknesses based on the information now available. For example, the 1998 ice storm in the
northeast appears to be consistent with a mean recurrence interval of about 250 years in the
Montreal area. As time goes by, and no other extraordinary ice storms occur, then the estimate of
that mean recurrence interval will increase. Or, on the other hand, if another storm as severe as
the 1998 storm occurs 20 years from now, a reanalysis of the data will indicate a shorter mean
recurrence interval. Any nonstationarity in the climate, whether natural or anthropogenic, can
certainly further affect the estimates of extremes as well.
September 2004
Page 6
Previous Page
