Utilizing Standardized Anomalies to Assess Synoptic Scale Weather Events in the Western U.S

Standardized anomalies were computed from the global re-analysis data for the period of 1 January 1948 through 31 December 2006 for the western United States. The computations were done in 6-hour increments with anomalies computed for heights, temperatures, winds, specific humidity at mandatory levels and surface based variables such as mean sea level pressure and precipitable water. The base climatology for the means and standard deviations was computed for the period 30 year period of 1971-2000.

Following the methodology presented by Hart and Grumm (2001), the western United States events are ranked objectively based upon their standardized anomalies method of pressure weighted anomalies by variable. The degree of rarity for an event is determined by the departure of these fields from climatology. The overall ranking was computed using the average for pressure weighted values for each variable. This identified the top 20 most anomalous events to affect the region since 1948. The top 10 events will be summarized in a table with select images to define the events.

The top 10 events by variable will also be presented. Select cases for the largest wind, height, thermal, and moisture anomalies will be presented. Preliminary research suggests that many of the top events identified by this method were associated with events in the literature, such as the Columbus Day Windstorm of 1962, the Big Thompson Flood event of 1976, the Yellowstone/Teton Tornado of 1987, and the California New Year's Flood of 1997.

The top ten anomalous events for the western United States, from the Front Range to the eastern Pacific are examined from a synoptic-scale perspective. The goal of this research is to improve upon our ability to anticipate significant or rare events by event type in the western U.S. Specific event types include heavy rain events, Pacific Northwest windstorms, and heat waves.