North Columbia Avalanche Forecast Date/Time issued: Wednesday, March 26, 2008 at 4:00 PM Valid until: Friday, March 28, 2008 at 6:00 PM Next Scheduled Update: Friday, March 28, 2008 ---------- Monashees & Selkirks ---------- Thursday Friday Saturday Alpine 3 - CONSIDERABLE 3 - CONSIDERABLE 2 - MODERATE Treeline 2 - MODERATE 2 - MODERATE 2 - MODERATE Below Treeline 2 - MODERATE 2 - MODERATE 2 - MODERATE Confidence: Good. Primary Concerns: * Wind Slab: Slabs from the weekend wind event remain in many areas. * Persistent Slab: Persistent weak layers (PWLs) from February and March remain in the Monashees and Selkirks. These seem to be less of a problem in the Cariboos. * Solar Radiation: Even brief exposure to sun can significantly destabilize the snowpack, even when air temperatures remain cool. Special Message: The snowpack remains complex and variable in the Monashees and Selkirks where I’d be worried about a surface slab (even a small one) overloading and stepping down to deep PWLs on slopes that have not avalanched recently. It’s colder than normal so settlement and bonding are slower than usual for this time of year. There were a number of close calls in this region over the weekend, a reminder to remain vigilant. In the Cariboos: windslab problems appear less critical while March and especially February PWLs seem to be less of an issue than farther south. Travel Advisory Issued: Wed, Mar 26 Next Scheduled Update: Fri, Mar 28 Recent S’ly winds have loaded N and NE aspects at and above treeline. Layers of firm snow on the surface (or just below recent new snow) and drifts are signs of new windloading. Recent avalanches, whumpfing, and cracking are obvious clues of unstable snow. Solar radiation rapidly decreases stability of slopes or cornices. I suggest avoiding travel on or exposure to windloaded slopes, especially if the sun is shining. Watch terrain above and around you even on wind-sheltered, cold, shaded slopes at lower elevations. The biggest challenge is the PWLs (I know I’m nagging), which are increasingly difficult to trigger but continue to produce large and destructive avalanches on terrain generally considered low risk. Good local information is required if you intend to venture onto steep or complex terrain in areas where PWLs are known or suspected, notably in the Monashees and Selkirks. If you trigger one of these layers, fractures will exceed 100cm and chances of survival are slim if caught on large or ccomplex terrain. This report describes an incident that could happen in many areas of the interior right now and it remains applicable to present conditions in this region. Avalanche Activity Issued: Wed, Mar 26 Next Scheduled Update: Fri, Mar 28 A cycle of natural avalanches, almost all on N’ly quadrant, up to size 4.5, in the last few days including windslabs and step-down avalanches on March and February layers. Large avalanches triggered by explosives at the tail end of the natural cycle. Most activity was in the Monashees and Selkirks, south of Blue River to highway 1. Snowpack Issued: Wed, Mar 26 Next Scheduled Update: Fri, Mar 28 Where winds occurred over the weekend, slabs remain on slopes that did not avalanche in the recent cycle. While natural avalanches are becoming less likely, I suspect these slabs remain susceptible to human and solar radiation triggering. PWLs were triggered (often as step-down avalanches) as recently as Monday and there’s no reason to believe these layers have improved significantly since then. Windslabs appear less widespread and PWLs don’t seem as big a problem in the Cariboos. View Avalanche Observation Summary (NEW!) Weather Issued: Wed, Mar 26 Next Scheduled Update: Fri, Mar 28 0-5cm today, tonight, and Thursday. Locally moderate amounts possible due to convection in unstable W’ly flow. Wind S30kph today, SW30 tonight through Thursday afternoon except W20 Thursday afternoon in the Cariboos. Freezing levels at valley bottom. Little change Friday. Issued by: Karl Klassen