Western Montana Snow Squall Climatology and Synoptic Patterns, 2000–2020

Abstract

The rapid onset of whiteout conditions, from strong winds, blowing snow, and heavy snow, associated with snow squalls often results in hazardous travel conditions. Snow squalls bring pronounced impacts to the transportation sector, leading to accidents, fatalities, and significant travel delays. Given these impacts, historical frequencies, and the synoptic environments associated with snow squalls in western Montana were examined to develop forecast aides, primarily through synoptic pattern recognition, for meteorologists to identify and communicate snow squalls. A 20-yr climatology was constructed to identify events characterized by wind gusts ≥26 kt (30 mph) and visibility ≤0.8 km (0.5 mi). 74 snow squall events were identified from 2000 through 2020 across three ASOS sites: Missoula (KMSO), Kalispell (KGPI), and Butte (KBTM). The median duration of heavy (moderate) snow during snow squalls was 26 (34) min. A composite study utilizing these events was conducted using the NCEP North American Regional Reanalysis. The composite study along with surface observations, revealed three distinct snow squall patterns and types: orographic snow bands, Pacific cold fronts, and Canadian arctic fronts.