Wayne Flann Avalanche Blog: February 21, 2021

YESTERDAY:

Unsettled early Saturday morning.

Patches of blue in the am.

Challenging visibility at times.

With decreased visibility Blue Line offered a smooth option.

Nice turns in the Harmony area.

Powder to the People, Shale Slope.

Looking down the rib on Mondays.

Saturday Feb 20, 2021. 14:00 Hrs. -8 with a 20-45 KPH South wind. +1 in the valley.

Satellite image from the same timeframe as above.

Modis satellite image of the AR event.

Snowing in the valley Saturday afternoon.

Weather Observations for February 21, 2021 taken at 06:00 Hours.

2240 meters -6, Winds were 50-65 KPH S--Horstman Hut

2180 meters -6, Winds were 70-90 KPH SE--Whistler Peak
1860 meters -4, Winds were 30-45 KPH SE --Rendezvous

1835 meters -3, Winds were 40-65 KPH SE--Round House

1650 meters -1, 2 cm in 12 Hrs, 3 cm in 24 Hrs, Base 247 cm --Pig Alley
1570 meters -3, 5 cm in 12 Hrs, 6 cm in 24 Hrs, Base 184 cm--Catskinner

660 meters 0, Valley Temp, Max temp Yesterday was +1.9, 0.6 mm of precip yesterday.

As of 07:00 Hrs we have overcast skies, variable visibility and its snowing lightly.

FORECAST:

An approaching warm front will bring periods of light-heavy precip in a Westerly flow aloft. The FL is expected to top out at 1500 meters. Strong alpine winds will reach or exceed 100 KPH. Another warm front with a trailing cold front on Monday after a short lived dry out Monday morning. . The FL should drop to surface by Monday night. Periods of light precip expected on Monday, should ease to flurries by Monday afternoon and dry out into Tuesday. Unsettled weather Tuesday with a mixed bag. Some weak ridging will bring some sunny breaks and flurries. Wednesday is also looking unsettled at this time. Guesstimates: 20-30 cm by Monday am, 2-6 cm by Tuesday am, 1-3 cm by Wednesday am.

GOES IR image from this am. Much drier last night than I thought. Not much of an AR.

Wet warm windy day. FL will likely get to 1500 m.

West/North Westerly flow aloft.

Not really a pineapple express, Westerly flow should keep the FL at an acceptable height.

NW flow for Monday, with cooler temps later in the day..Warm front-trailing cold front.

Much cooler Tuesday, weak upper trough moves East.

AVALANCHE ACTIVITY:

Update on the avalanche that killed a snowboarder in Wyoming. Article below. Net Pic

Update on the avalanche that killed a snowmobiler in Wyoming. Article below. Net Pic

Snowmobilers witnessed large destructive avalanche in the Beaverhead Mtns.,Co. Article below.

Avalanche mitigation on Whistler Saturday produced some Sz 1 storm slabs up to 50 cm. Xe Sc

No new avalanches observed on Blackcomb. Sz 1 from a Nc (natural cornice drop).

From the Sea to Sky Avalanche Advisory:

Avalanche Summary

The main story on Sunday will be new storm and wind slabs with the incoming storm.

A small 15 cm storm on Friday resulted in in several small (size 1) human triggered storm and wind slabs, with explosive control producing some larger (size 2) avalanches on bigger terrain features.

There was some notable avalanche activity a week ago after a bout of northerly winds formed wind slabs in unusual places (eg. south, southeast, and southwest facing slopes). On Feb 11, two skiers were caught in a natural wind slab avalanche in a couloir on Mamquam Mountain, resulting in serious injuries. On Feb 12, a fatal avalanche was triggered by skiers at 2200 m on a west-facing slope on Phalanx Mountain (a size 2.5 wind slab). On Feb 12, another fatal avalanche was triggered by skiers at 1700 m on a treed southwest-facing slope in the Brandywine valley (a size 1 wind slab). See the incident reports here and here for details. These old wind slabs have decreased in reactivity over the past the week, however may still present as a problem with the stress of new snow and wind.

Snowpack Summary

Forecast snowfall amounts are variable across the region with 40 cm expected in coastal areas like Squamish and the Sunshine Coast and closer to 20 cm further inland near Whistler and Pemberton. The new snow and wind will form reactive slabs at all elevations, while rain could be expected up to 1400 m.

The new snow adds to 15 cm of recent snow sitting above a potentially reactive interface consisting of surface hoar layer at treeline, a crust below 1800 m, sun crusts on steep south slopes, and faceted surfaces in the alpine. These interfaces could be failure layers during the storm.

A lingering persistent weak layer from late January is 80-120 cm deep and consists of facets at upper elevations and surface hoar in sheltered areas. Although this structure is suspect, we have no recent reports of avalanches on this layer.

INFORMATION & OBSERVATIONS:

It is very easy to find yourself in a touchy situation. Would only take a Sz 1 to mess up the day.