Monday December 30, 2019

Wednesday January 1, 2020
Tuesday December 31, 2019
Monday December 30, 2019
Confidence: High - Weather models in agreement and good field data.

Main Concerns

Wet Slab, Loose Wet - view Avalanche Problems for detailed information.

Travel & Terrain Advice

Avoid thin shallow areas at treeline and alpine elevations, especially on northern aspects. These spots have a much higher likelihood of triggering the mid snowpack weak layers.

Watch for hazards such as rocks and open creeks at below treeline elevations, due to the very shallow snow pack. Very little snow down low means low avalanche danger but many other dangers exist hidden just under the surface….

Stay away from all avalanche terrain at treeline and alpine elevations when the rain starts to fall as it will certainly trigger large avalanches, of both the loose wet and wet/persistent slab types.

Avalanche Summary

No new avalanche activity has been reported over the past few days.

Avalanche Problems

Wet Slab

The rain forecast to fall at all elevations on Tuesday will add significant load the the weak layers that still exist in our mid snowpack. These layers are mainly found on north east to north west aspects at treeline, but may still linger in wind sheltered zones in the alpine as well . It is very likely that the additional load (by rain and/or loose wet avalanches passing over the weak layers “step down”) will result in many large naturally triggered (size 2 to size 3) wet slab/persistent slab avalanches, and that human triggering is likely to possible also.

Loose Wet

Loose wet avalanches will result as rain saturates the upper snowpack on Tuesday. We are almost certain that these avalanches will exist in the alpine and treeline on all aspects and will range from size 1 to size 3. These avalanches will be touchy (very easy to trigger) and will trigger both naturally and with human activity.

Snowpack Summary

Rain up to 1700m has moistened the upper snowpack, while the mid snowpack remains dry with a few preserved weak layers. So we have a nasty upside down cake (heavy over weak).

Snowpack Details

SurfaceThin rain crust from a freezing rain event Sunday in the below treeline and treeline elevations
UpperMoist snow approx 10 to 20 cm down depending on elevation
MidA few preserved weak layers in dry snow
LowerMainly well settled and bridged, but a weakness near the ground from early season still exists.

Past Weather

Small amounts of snowfall Friday were replaced with light rain Saturday. Sunday the temperatures went above zero at below treeline and near zero at treeline. Rain at these elevations resulted in a freezing rain ice crust and began to moisten the upper snowpack. Only the very high (above 1700m) has escaped the rain effects.

Weather Forecast

Sorry folks.. It does not look good for the next three days… Wet wet then freeze…

Monday - 3 to 10 mm of precip (mix of snow and rain), winds moderate SW rising to strong S to SW, temps 0 to -3, freezing level 1000 m to 1500 m.

Tuesday - Oh here it is! 25 to 45 mm of precip (mainly all rain at all elevations), winds moderate SW rising to strong SW overnight, temps +1 to +5 (ouch!), freezing level 2500 m to 2000 m.

Wednesday - 3 to 20 mm of rain fallowed by 2 to 5 cm of snow as temps drop mid day, winds strong SW dropping to moderate SW, temps +2 to -6, freezing level 1500 m to 800 m

Posted on Monday December 30, 2019 by Bill Phipps

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