June 19 - Thunderstorm and mixed precipitation at Fortress

An eventful night at Fortress Top

Hilary and Juris arrived at Fortress at 0542 MDT. Skies were clear with most of the action occurring to the east and north of us. ECCC issued a snowfall warning for Jasper National Park. 

Shortly after arrival the newest GEM 2.5 runs came out and the amount of precipitation expected decreased substantially. Most of the precipitation was occurring further north of our location, where several snowfall and rainfall warnings were issued For Wednesday and Thursday, with the main event occurring Wednesday early morning from 0300-0600 AM. 

I (Juris) took the first shift, updating radar to see what was in the horizon. Observations began at 0750 UTC, when I noticed a cell to the west of the divide moving towards Fortress. At 0800 UTC it looked as though the smallest of particles were slowly falling, but being swirled around and staying suspended in the air for long. 
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GEM 2.5 timing for precipitation beginning at 0900 UTC was very close and started at Fortress around 0940 UTC. A thunderstorm continued across the continental divide during Hilary’s shift with a few loud thunder claps with its passing. The thunderstorm lasted for approximately half an hour, and, at certain points, the timing of the lightning and thunder was very close together. Winds were fairy strong during the storm. The thunder seemed to be extra loud in the mountains. Definitely an exciting part of the night!
 
The second round of precipitation that GEM 2.5 predicted was also very close in timing and accurate with the type of precipitation, which was forecasted as mixed. At 1420 UTC Juris observed a couple of ice pellets that were translucent in colour and then shortly after what appeared to be liquid core pellets with a very thin outer shell. Graupel then began around 1425 UTC which both Hilary and Juris noticed to resemble a diamond, though this was short lived and ended at 1430 MDT. Mixed precipitation then began and we were able to get some pictures of graupel.  Winds were pretty strong, with strong gusts, with moderate visibility and precipitation was falling as strictly solid precipitation, with some occasional larger aggregates. By 1500 UTC the system had passed us, heading southeast. Both Hilary and Juris left shortly afterwards to head home to BGI. 

- Hilary & Juris

Field Participants: Hilary Smith & Juris Almonte