Clarify the SPAW issued by CAC

Hi Everyone,
Just a short note to clarify the Special Public Avalanche Warning (SPAW) which was issued by the Can Avalanche Centre for last weekend.
Ian Stokie and I had a discussion about it as he was wondering why the Danger was dropped to Considerable when there was a special warning issued. Ian figured that the danger should at least be High to coincide with the warning.
In fact, the issuance of a SPAW is based on several factors:
1) a snowpack condition which is ‘tricky’ in that it varies over terrain, aspect and elevation and may not be easily recognizable to the majority of recreationists
2) the forecast weather, which may have an affect on the number of backcountry users and their terrain choices
3) the time period, ie the weekend, when most recreationists with Mon-Fri jobs can get out, but on balance, may not have the experience and knowledge to assess and understand the nature of the avalanche problem

When the DANGER LEVEL is rated as High, it is presented in a bright red colour and presents to the public an elevated and serious hazard in the backcountry. The red flag is up!

The SPAW warns of avalanche conditions which may cause numerous accidents in the backcountry even though there may not be widespread large natural avalanches as in the case of High Danger.

Obviously the shift from High to Considerable is based on a judgement by the forecasters. In this case it was related to the fact that the Feb 9 surface hoar layer was buried from 20 to 60 cm in the SRockies Region. Some areas had already slid, some areas would likely slide with a human trigger and some features could possibly slide naturally.

The Bulletin expressed a lack of confidence in the weather forecast and the amount of new snow which would be forthcoming. ‘Snowfall amounts are uncertain on Sunday’. Obviously a metre of new snow Sat night and Sunday was not anticipated and definitely created a High or Extreme Avalanche Danger, certainly in the Lizard Range. Once that amount of storm snow had arrived the forecasters realized that the 3 x Considerable rating was not accurate and upgraded to High in the Lizard Range.

The South Rockies region has been separated from the Lizard Range because of the incredible amounts of storm snow which may fall specifically there but not necessarily in the S Rockies. We have divided our region into:
Flathead / Elk Valley South / Elk Valley North / Crowsnest South / Crowsnest North

We recognize that in many cases the Flathead and Elk Valley South sub-regions can be very close to the Lizard Range in terms of snowfall and snowpack structure. This is a problem with forecasting for the S Rockies as an entire region and we do our best to make note of this in the Forecast Details on the Bulletin.

Hope this helps to clarify the SPAW scenario.

Gord Ohm
Avalanche Technician
South Rockies