Date of Observation: 01/01/2023
Name: Irwin Guides
Zone: Northwest Mountains
Route Description: Irwin Tenure
Observed avalanche activity: Yes
Avalanches: Widespread Touchy Storm Slabs yesterday 12/31. There was a notable natural avalanche cycle on the Upper Upper West Wall that produced 3-5 large avalanches. This terrain has not been mitigated or skied this season and was predominantly scoured down to rock prior to 12/28. Lingering Storm Slabs were more resistant to explosive and skier testing in our core westerly terrain today. However, easterly start zones that were previously Unreactive reached a tipping point: a single hand charge cleared out almost all of Candies and Sonic to the ground (SS-AE-R2-D2-G FC (100cm x 75m x 150m)). This is southeasterly terrain from about 12k. We also had a small but impressive natural event today on The Crotch apron in a recently wind loaded pocket (HS-N-R2/D1.5-O/G 50-100 cm x 10m x 40m). This is SSW terrain at 11.8k and ran O/G with a crown of 1m at its apex.
Snowpack: We received 45″ of snow with 3.5 inches of water over two storm cycles since 12/28. The second cycle was notable for very warm temps, multiple riming events that laid down thin friable crusts at lower elevations, and several hardness inversions in the new snow.
Estimated avalanche date: 01/01/2023
Number of Avalanches: 1
Location
Location: Lake Irwin (Robinson Basin, Owen, Ruby)
Location Specific:
Start Zone Elevation: NTL: Near Tree Line
Aspect: SE
Characteristics
Trigger: Explosive
Trigger modifier:
Type: Soft Slab
Failure Plane: Ground
Size
Relative Size: R2 small
Destructive Size: D2 – could bury, injure, or kill a person
Avg. crown height (inches):
Avg. width (feet):
Avg. vertical run (feet):
Involvements
# of people caught:
# of partial burials:
# of full burials:
Additional comments: Candys/Sonic
Estimated avalanche date: 01/01/2023
Number of Avalanches: 1
Location
Location: Lake Irwin (Robinson Basin, Owen, Ruby)
Location Specific:
Start Zone Elevation: NTL: Near Tree Line
Aspect: S
Characteristics
Trigger: Natural
Trigger modifier:
Type: Hard Slab
Failure Plane: Ground
Size
Relative Size: R2 small
Destructive Size: D1.5
Avg. crown height (inches):
Avg. width (feet):
Avg. vertical run (feet):
Involvements
# of people caught:
# of partial burials:
# of full burials:
Additional comments:
Estimated avalanche date: 01/01/2023
Number of Avalanches: 4
Location
Location: Lake Irwin (Robinson Basin, Owen, Ruby)
Location Specific:
Start Zone Elevation: NTL: Near Tree Line
Aspect: W
Characteristics
Trigger: Natural
Trigger modifier:
Type: Unknown
Failure Plane:
Size
Relative Size:
Destructive Size: D2 – could bury, injure, or kill a person
Avg. crown height (inches):
Avg. width (feet):
Avg. vertical run (feet):
Involvements
# of people caught:
# of partial burials:
# of full burials:
Additional comments: Upper Upper Westwall
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