Avalanche Forecast
Issued: Apr 12th, 2021 2:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Cornices, Loose Wet and Wind Slabs.
Jesse Percival,
VIAC
A few loose wet on steep south were observed during daytime observation flight over 5040 and Mount Arrowsmith. Additionally widespread wind effect was evident on all upper alpine terrain. Cornices remained intact and are large and looming.
No new avalanche observations were summitted or observed in the norther zone of the forecast region.
Summary
Past Weather
This weekend continued with winter weather, cool temperatures and between 20 and 30 cm's of new snow all combined with moderate to strong south wind.
Weather Forecast
A ridge of high pressure will introduce warm air, provide clear sky and sunshine for the entire forecast period. Expect freezing levels and temperature to continue to rise daily.**Monday:** No new precipitation Winds light from the North East , Freezing levels at sea level rising during the daytime to 1600 meters. Temps at 1500 meters up to 1 degrees.**Tuesday:** No new precipitation, Winds light to moderate from East North East, Freezing levels 1800 meters. Temps at 1500 meters 3 degrees.**Wednesday:** No new precipitation, Winds light from the East North East, Freezing levels 2800 meters. Temps at 1500 meters 7 degrees.
Terrain Advice
**Please respect the current closures at Mount Washington, no access is permitted at anytime on the ski areas slopes or terrain.**During periods of intense warming and sunshine avoid solar aspect terrain.Avoid travelling both above and below cornices.
Snowpack Summary
New snow between 20 and 30 cm overlies a previously well developed surface crust. Warming daytime temperatures and moderate settlement of this new snow has promoted bonding of this new layer of snow. Highly wind effected upper alpine areas and continued cornice growth is evident. Expect in lee areas that wind slab depths could easily exceed a meter. The mid and lower snowpack are well settled and dense. Forecast temperature values are expected to rise rapidly and overnight cooling and snowpack recovery (refreeze) will begin to diminish. With these factors, the snowpack will begin to rapidly settle and is likely to become during the height of the warmth, very unstable. Expect cornice collapse, glide slab failures, waterfall ice failures and perhaps other anomalous geo hazard events to occur as the mountains are going to see a rapid change from winter conditions to near summer like conditions in a 72 hour period.
Snowpack Details
- Surface: Variable surface conditons dependant on aspect and elevation.
- Upper: Reactive crusts at 30 cm and 100 cm
- Mid: Well settled and dense.
- Lower: Well settled and dense.
Confidence
Moderate - Weather forecast models are very well aligned and provide support to forecast avalanche problems. **Avalanche danger ratings reflect the highest danger level expected over the course of the day.**
Problems
Cornices
Cornices continued to grow with the last snow fall and strong south west wind, Expect this problem become increasingly sensitive as daily temperatures and freezing level rise. The probability of natural cornice failures occurring in the heat of the day on Wednesday are near certain.
**Location:** Predominantly north aspects at ridge top in the Alpine and Tree line.
**Possibility:** Triggering of this avalanche problem is likely to very likely from light loads such as skiers. Natural avalanches are very likely.
**Size:** If triggered expect these avalanches to be large size 2, on isolated terrain features very large, size 3
Likelihood
Expected Size
Loose Wet
The loose wet avalanche problem will become widespread as overnight temperatures are forecast to not provide enough cooling to refreeze the upper snowpack, expect south facing terrain to become rapidly unconsolidated as temps rise and the sun begins to directly radiate surfaces.
**Location:** South Aspects at all elevations
**Possibility:** Triggering of this avalanche problem is very likely from light loads such as skiers. Natural avalanches are very likely.
**Size:** Expect widespread size 1 to 2 avalanches
Likelihood
Expected Size
Wind Slabs
Wind slabs in isolated lee terrain at higher elevation will continue to gain strength and settle but may still continue to present in terrain well protected from the sun.
**Location:** North East thru to North West aspects and found in the Alpine
**Possibility:** Triggering of this avalanche problem is possible from light loads such as skiers. Natural avalanches are unlikely.
**Size:** If triggered expect these avalanches to be large size 2 and in isolated terrain very large size 3.
Likelihood
Expected Size
Valid until: Apr 13th, 2021 2:00AM
