Resolution No. 4814 - Laserfiche WebLink

Home Browse Search

7,0 WINTER STORMS 7.1 Overview Winter storms affecting the Eugene/Springfield Metro area are characterized by a combination of heavy rains and high winds. Heavy rains can result in flooding, as well as debris slides and landslides. High winds commonly result in tree falls which primarily affect the electric power system, but which may also affect buildings and vehicles. This chapter deals primarily with the rain and wind effects of winter storms. Larger scale flooding is addressed in Chapter 6. Debris flows and landslides are addressed in Chapter 8. Winter storms can also involve ice and snow, most commonly at higher elevations than the immediate Eugene/Springfield Metro Area. The most likely effects of snow and ice events on the Eugene/Springfield Metro Area are road closures limiting access/egress to/from the Eugene/Springfield Metro Area, especially roads to higher elevations such the highways into the Cascades or over the Coast Range. Winter storms with heavy wet snow and ice storms also may result in power outages from downed transmission lines and/or poles. Average annual snowfall in the Eugene/Springfield Metro Area (Eugene Airport weather station) is 6.0". Since the weather station was established in 1939, maximum monthly snowfall has been 47.1" (January 1969), with maximum seasonal snowfall also of 47.1" (1969). Maximum monthly snowfalls for other months for February, March, November, and December are 8.8", 10.8", 6.0" and 10.2", respectively. Major snow storm events do occur occasionally. Major snow storms affecting the Willamette Valley occurred in 1884, 1892, 1909, 1916, 1919, 1937, 1950, 1969, 1989 and 2004. January 1950 snowfalls were especially high, with 54" in Albany and 36" in Eugene. In January 1969, Eugene had 47" of snow. Thus for Eugene, most winters result in little snowfall, with major storms of 10" or more snow occurring typically about every 10 or 20 years. There are few practical mitigation actions for such infrequent major snow storms, other than commonsense measures applicable to many hazards, such as encouraging residents to maintain emergency supplies of food and water for a few days and emergency generators for critical facilities. For completeness, we also briefly address other severe weather events, including hail, lightning strikes and tornadoes. Hail events are possible in the Eugene/Springfield Metro Area, generally during summer thunderstorms, with the most recent significant event being August 4, 1999. However, hail damage is generally minor and few practical mitigation alternatives are applicable to hail. Lightning strikes also occur in the Eugene/Springfield Metro Area. Lightning strike damage to buildings or infrastructure is generally relatively minor and few practical mitigation alternatives are applicable to lightning, other than installing lightning arrestors on critical facilities subject to lightning damage. However, nationwide NOAA data show that lightning causes about 90 deaths per year, with at least 230 injuries (NOAA Technical Memorandum NWS SR-193, 1997). Lightning injuries appear to be systematically underreported and thus the actual injury total is most likely significantly higher. For Oregon, however, casualties from lightning are very Iow, with totals of Public Review Draft: August 6, 2004 7-1