Observation: Avalanche Professional

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Weather Summary

April 24th-28th 2023: This past week's weather forecast was mostly accurate with an unexpected moderate storm on Wednesday, April 26th. Overcast skies and moderate precip on Monday, April 24th quickly faded to very light precip, mostly snow above 3:500', light winds, seasonal temps, and obscured skies with valley fog base est at 4:500'. On Tuesday, April 25th, cloud bases gradually rose and greenhouse warming was noticed through broken cloud cover. Eventually, visibility increased and temps rose. The unexpected Wednesday storm progressed in the forecast, starting with a subtle mention in the NOAA fx discussion on Sunday, April 23rd, then progressing to a small chance (20 percent rain) on Tuesday, April 25th, to moderate winds and light snow early, then steady moderate rain at approx. 6,300' for about 20 hours ending early Thursday morning on April 27th. Early morning fog quickly developed then faded on Thursday, April 27th. The overnight rain (4/26-4/27) and then clearing skies dropped temps and left frozen surface conditions down to approx 4,800'. Temps rose in a seasonable way throughout the day on Thursday, softening surface conditions. Clear skies overnight allowed a suitable freeze in the alpine and near treeline elevations by the morning of Friday, April 28th. With another seasonable warming regime to follow.

April 24th-28th 2023: Many overlapping and dynamic avalanche problems created an interplay that was intriguing to observe. These typical spring avalanche problems create random triggers and release with narrow margins for error. From small D1 loose wet near and below treeline to very large D3 glide near treeline, and D2 wet slabs and cornice collapse in near treeline and low alpine elevations (less than 7,000' ). With very large tracks starting in the alpine and extending to below treeline anticipating terrain and the associated overhead hazard was incredibly difficult. The most active and random releases occurred at elevations near and below 5,000' where very deep winter snow bases meet warming spring temps and alpine-like terrain and bed surfaces. For example, very few trees and rock slabs. Some climax glide crown depths were hard to estimate but often looked more like calving and crevassed glaciers than 85-120 percent of the avg winter snowpack. Furthermore, the interconnectivity of avalanches was on full display. Cornice collapses triggering wet loose and/ or wet slabs that are carried onto lower elevations, triggering glide avalanches, illustrated the interconnectedness. While many avalanches were older by the time we observed them (before April 24th pic #7 and #8) a few new releases occurred due to the rain (approx 4-5 new) on Wednesday, April 27th (pic #4 and #5) and subsequent warming on April 28th. Throughout the week, we observed several releases each day (+/- 7) most of which were D2 or smaller but very pushy and powerful for their relative size and destructive force. View photos for examples and video link, in the media attachments section above, for a loose wet avalanche and spring Cascadia exemplified.