THE MAP ROOM: One Hundred Inches in One Hundred Hours

Abstract

rom 22–27 November 2001, two complex Intermountain storm systems produced 108 inches of snow at Alta ski area in the Wasatch Mountains of northern Utah (Fig. 1; Steenburgh 2003). Since 100 in. fell in 100 h, local news media coined the phrases “100 inches in 100 hours” and “Hundred-Inch Storm Cycle” to describe the event (a storm cycle is a period where multiple winter storms occur in rapid succession). The storm cycle was the largest at Alta since 1991, provided a boost for preparations for the 2002 Winter Olympics, and produced substantial lowland precipitation. Salt Lake City International Airport (SLC) observed 1.27 in. of rain on 22 November, a record for a calendar day in that month, while during colder periods, up to 33 in. of snow fell in the Salt Lake City metropolitan area. The event provided an excellent example of the complex evolution of Intermountain winter storms, with storm stages delineated by the passage of large-scale weather features and their accompanying changes in stability and precipitation processes. Contrasts between mountain and lowland precipitation varied from stage to stage and storm to storm, illustrating the limitations of applying climatological precipitation–altitude relationships for short-range quantitative precipitation forecasting. The first storm system moved through Utah from 0600 UTC 22 to 0700 UTC 24 November, producing 50 in. of snow at Alta. Time–height sections for SLC, created from hourly National Centers for Environmental Prediction (NCEP) Rapid Update Cycle (RUC2) analyses, showed an intrusion of low-θe air aloft several hours ahead of a surface-based cold front (Fig. 2). Widespread valley rain and mountain snow ONE HUNDRED INCHES IN ONE HUNDRED HOURS The Complex Evolution of an Intermountain Winter Storm Cycle