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Weekend conditions update — Friday Jan. 15

 | January 15, 2021

Every weekend SPIN will present the current avalanche forecast and hazards as well as weather for the Interior. Tune in at the end of each week to get the forecast before your weekend adventures begin.

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A clear start to the weekend may tempt some to get out and explore bigger terrain, but don’t be fooled by the sun’s rays as snowpacks, including those adjacent to the Sun Peaks area, pose potentially consequential conditions.

Weather

A high pressure system over B.C. will weaken as the weekend creeps closer while a cold front will begin to encroach over the South Coast region Friday morning after high freezing levels coupled with precipitation in the form of rain will fall.

Freezing levels in the Interior will begin to drop late Friday but no further than 900 -1100 metres depending on where you are. The Coquihalla freezing level is forecasted to rise as high as 2300 metres producing variable to poor snow conditions. Saturday should see freezing levels drop to valley bottom for the Interior before rising again on Sunday.

When the cold front moves in early on in the weekend it will bring partly cloudy skies and isolated flurries with five to 10 centimetres of snow to the Interior while light to moderate winds shift from westerly to southerly/southwesterly in both the Columbia and Southcoast Inland regions while the Cariboo region will see similar direction but stronger winds.

As the weekend continues the front will gain strength which means clear, cold, dry days for the B.C. Interior.

Weather specific to Sun Peaks will see cloudy skies with sunny breaks Friday with increasing cloud Saturday and Sunday with periods of light snow expected later in the weekend. On average temperature lows will be around -10C and on average highs of -5C but don’t forget to factor in the wind, which is forecasted to come from the southeast at five to 15 kilometres per hour Friday and 10 – 20 kilometres an hour Saturday.

Avalanche Forecast

Both the North and South Columbia region avalanche danger ratings are forecasted at considerable in the alpine and at treeline while below treeline is moderate for Friday. Saturday the danger rating will ease off overall as the treeline elevation band will move from considerable to moderate while other elevation bands remain the same as the day before. Sunday’s danger rating will revert back to Friday’s with considerable ratings at alpine and treeline and moderate below treeline.

The Cariboo region forecast shows a considerable danger rating for both the alpine and treeline elevation bands while below treeline the rating is considered moderate for Friday. Saturday the treeline rating will change to moderate before bouncing back to considerable while both the alpine remains at considerable and below treeline remains at moderate all weekend.

The South Coast Inland region is forecasted to be considerable at both the alpine and treeline elevation bands while below treeline the danger is reduced to moderate all weekend. However, Avalanche Canada said the danger is a step lower for the Coquihalla region because the persistent slab avalanche concern (described below) is less of a problem in the area.

For the North and South Columbia regions, the number one avalanche concern is storm slab avalanches which are said to be very likely at all elevations, on all aspects and could produce avalanches from size 1-2.5 thanks to 20-70 centimetres of snow and strong winds that were delivered by a storm on Tuesday. Areas that are exposed to the wind will likely have thick, reactive wind slabs on leeward slopes and sheltered areas will host a touchy storm slab. Both the storm and wind slabs overlie a surface hoar layer or crust.

A persistent slab problem is second on the list for the North and South Columbia regions and also exists on all elevation bands, aspects and is unlikely to be triggered but if it is, the consequences could be dire as size 2-3.5 avalanches are possible. In the North the persistent slabs lie on a spotty surface hoar layer which exists 80-150 centimetres deep and another decomposing surface hoar layer and/or a crust down 120-200 centimetres in the snowpack. In the South the persistent slab avalanche problem is similar but the slab depths differ by approximately 10 centimetres. Be aware there is potential for avalanches to step down to deeper weak layers, hence the large sized avalanche estimation. 

In the Cariboos, similar avalanche problems exist with storm slabs at all elevations and aspects likely to trigger size 1-2 avalanches in the region due to recent snow loading of 15-40 centimetres from the Tuesday storm that also brought strong winds. The storm slabs will vary with elevation and terrain exposure to the wind while storm slabs exist in sheltered areas and are touchy due to the underlying surface hoar. A persistent slab avalanche problem exists at treeline and below on all aspects but is not very likely to be triggered, however, if it is, it will be big, as it is projected to be a size 2-3.5 avalanche. Buried, spotty surface hoar is down 30-100 centimetres and decomposing surface hoar and/or a crust is buried 80-140 centimetres deep. Both are the cause of this problem and are highly variable. There is potential for these types of avalanches to step down causing larger, more destructive avalanches.

Storm slabs will also be a concern for the Coquihalla area over the weekend at all elevations and aspects. Be careful as they will be very sensitive to human triggering and could produce size 1-2.5 sized avalanches. As described above the persistent slabs aren’t as prevalent in the Coquihalla area but wet-loose avalanches at treeline and below on all aspects will be a problem, with the freezing levels rising up to 2300 metres on the Coquihalla, and could release sized 1-2 avalanches especially on steeper terrain exposed to the sun.

Be aware that Avalanche Canada’s confidence in the above danger ratings are for the South Coast Inland and Cariboo regions due to limited observations and the difficulty inherent to forecasting likelihood of persistent slabs

Avalanche Canada’s general travel and terrain advice for the Coquihalla area is to make conservative choices and avoid overhead hazards such as cornices, be aware of the potential for persistent slabs to step down and when a thick, melt-freeze crust is present, avalanche activity is unlikely. For the Cariboo and Columbia regions, conservative terrain choice is also advised while storm snow settles but watch for those reactive wind slabs in exposed terrain and use low consequence slopes to test the bond of the new snow.

For more information, visit avalanche.ca

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