Weather Patterns for Significant Snowfall Events in Prince William Sound, AK

This project is composed of two different studies. The first looks at patterns leading to large snowfall events that differ in accumulation across three cities within close proximity. The second looks at the climatology of snowfall events over the last 95 years in Valdez, AK. The first study uses snowfall data from Cordova, Thompson Pass, and Valdez, AK. Sixteen cases were selected with varying snowfall occurring at each of the sites on the same day. Each case was analyzed using the North American Regional Reanalysis (NARR) data. Parameters studied include air temperature, wind speed, wind direction, geopotential height, stability and precipitable water both at the surface and aloft. The Weather Research and Forecast (WRF) model was run for specific cases to further investigate the synoptic evolution at a higher resolution.

The second study uses data from the Valdez Weather Service Office taken from the National Climatic Data Center. Frequency of large snowfall events (>12in) by year, month, and snowfall totals were examined for long term trends and patterns over a period of 95 years. Correlations were studied between these patterns and the Pacific Decadal Oscillation (PDO). The top twenty large snowfall events were studied further using the NARR data with similar parameters to those for study one.

Reanalysis of the sixteen cases from Cordova, Thompson Pass and Valdez did not reveal any clear cause for varying snowfall amounts among the three cities. WRF output was looked at for more evidence. Preliminary results from the Valdez, AK climatology study indicate the greatest frequency of large snowfall events occur between December and February despite the typical winter season running from October through March. Preliminary results also show years with fewer large snowfall events coincide with warmer sea surface temperatures in the Pacific Ocean associated with the PDO. Reanalysis of the top twenty cases resulted in the placement of the cases into distinct categories based on the location of the surface low pressure and 500mb height pattern. This allows forecasters to identify these events and sea surface temperature anomalies in the Pacific such that the potential severity of snowstorms may be anticipated on a seasonal timescale.

Snowfall distribution in Southern Alaska during large events is complex and likely dependent on several small-scale factors. Output from high resolution WRF simulations will provide further insight into factors that may contribute to differences in precipitation patterns over Prince William Sound.