Synoptic Variability of Extreme Snowfall in the St. Elias Mountains, Yukon, Canada

• Main Author: Andin, Caroline
• Format: Bachelor Thesis
• Language: English
• Published: Uppsala universitet, Institutionen för geovetenskaper 2015
• Subjects: Snow; glaciers; Yukon; synoptic meteorology; Aleutian Low; Bering Sea; Canada; Gulf of Alaska; Pacific; aleutian low; glacier*; Subarctic; Alaska
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-253449

Glaciers of southwestern Yukon (Canada) and southeastern Alaska (USA) are presently experiencing high rates of annual mass loss. These high melt rates have mainly been investigated with respect to regional temperature trends, but comparatively little is known about how climate variations regulate snow accumulation on these glaciers. This study examines the synoptic weather patterns and air flow trajectories associated with extreme snowfall events in the central St. Elias Mountains (Yukon). The analyses are based on data retrieved from an automated weather station (AWS) between 2003 and 2012, which provide the longest continuous records of surface meteorological data ever obtained from this remote region. The AWS data reveal that 47 extreme snowfall events (> 27 cm per 12 hours) occurred during this period, of which 79 % took place during the cold season months. Air flow trajectories associated with these events indicate that a vast majority had their origin in the North Pacific south of 50°N. Less frequent were air masses with a source in the Aleutian Arc/Bering Sea region and the Gulf of Alaska, and in a few rare cases precipitating air was traced to continental source regions in Western Canada and Alaska. Composite maps of sea-level pressure and upper-level winds associated with extreme snowfall events revealed a frequent synoptic pattern with a low-pressure area centered over the Kenai Peninsula (Alaska), which drives strong southerly winds over the Gulf of Alaska towards the St. Elias Mountains. This pattern is consistent with AWS data wind recordings during snow storms. The most typical synoptic configurations of the North Pacific low-pressure area during extreme snowfall events are either elongated, split, or single-centered, and these situations represent possible seasonal analogues for the different states of the Aleutian Low in the subarctic North Pacific. However, neither the geographical position or intensity of negative sea-level pressure anomalies, nor surface pressure gradients associated with ...