Precipitation characteristics and associated weather conditions on the eastern slopes of the Canadian Rockies during March-April 2015

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<p><strong>Abstract.</strong> Precipitation events that bring rain and snow to the Banff–Calgary area of Alberta are a critical aspect of the region's water cycle and can lead to major flooding events such as the June 2013 event that was the second most costly natural disaster in Canadian history. Because no special atmospheric-oriented observations of these events have been made, a field experiment was conducted in March and April 2015 in Kananaskis, Alberta, to begin to fill this gap. The goal was to characterize and better understand the formation of the precipitation at the surface during spring 2015 at a specific location in the Kananaskis Valley. Within the experiment, detailed measurements of precipitation and weather conditions were obtained, a vertically pointing Doppler radar was deployed and weather balloons were released. Although 17 precipitation events occurred, this period was associated with much less precipitation than normal (<span class="inline-formula">−35</span><span class="thinspace"></span>%) and above-normal temperatures (2.5<span class="thinspace"></span><span class="inline-formula"><sup>∘</sup></span>C). Of the 133<span class="thinspace"></span>h of observed precipitation, solid precipitation occurred 71<span class="thinspace"></span>% of the time, mixed precipitation occurred 9<span class="thinspace"></span>% and rain occurred 20<span class="thinspace"></span>%. An analysis of 17<span class="thinspace"></span>504 precipitation particles from 1181 images showed that a wide variety of crystals and aggregates occurred and approximately 63<span class="thinspace"></span>% showed signs of riming. This was largely independent of whether flows aloft were upslope (easterly) or downslope (westerly). In the often sub-saturated surface conditions, hydrometeors containing ice occurred at temperatures as high as 9<span class="thinspace"></span><span class="inline-formula"><sup>∘</sup></span>C. Radar structures aloft were highly variable with reflectivity sometimes <span class="inline-formula">&amp;gt;30</span><span class="thinspace"></span>dBZe and Doppler velocity up to <span class="inline-formula">−1</span><span class="thinspace"></span>m<span class="thinspace"></span>s<span class="inline-formula"><sup>−1</sup></span>, which indicates upward motion of particles within ascending air masses. Precipitation was formed in this region within cloud fields sometimes having variable structures and within which supercooled water at least sometimes existed to produce accreted particles massive enough to reach the surface through the relatively dry sub-cloud region.</p>




Thériault, J. M., Hung, I., Vaquer, P., Stewart, R. E., & Pomeroy, J. W. (2018). Precipitation characteristics and associated weather conditions on the eastern slopes of the Canadian Rockies during March-April 2015. Hydrology and Earth System Sciences, 22(8), 4491–4512.

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