January 1, 1998 SOUTH COAST & VANCOUVER ISLAND WEATHER: Leading up to the weekend, the Coast saw mild temperatures, moderate snowfall, and brisk SW winds; text book weather to build surface slabs in the alpine. There will be some moisture from a Pacific flow Thursday and Friday. Once the system passes, a high pressure ridge in the interior will begin to feed air toward the coast, bringing clearing skies and slightly cooler temperatures. Watch for a shift in winds from SW to East to signal the beginning of this event. SNOWPACK: The warm weather leading up to this report tended to promote settlement and the overall strength of the lower snowpack likely improved in most areas. The snow and rain that accompanied the warm air caused a relatively widespread instability in the upper storm snow, and in many areas this has avalanched. Wind has built a 20-30cm slab now in most alpine areas, and the coming weather will add to this. As temperatures drop, we are likely to build a crust in lower elevation areas. AVALANCHES: The size and frequency of the storm snow avalanches has been decreasing throughout the last few days of 1997, although most stations are still reporting some activity, mostly to size 2 or less. The wind and snow coming just before the weekend will cause an increase in natural activity, but once the temp drops, this should taper off. DANGER: Considerable. TRAVEL ADVISORY: The weekend is going to be tricky on the Coast. Natural avalanche activity should drop right off as skies clear, but there will still be a lingering surface slab instability waiting for a human trigger. The best bet this weekend is to dig a profile, and assess the surface slab stability, since there is not likely to be much for clues from natural avalanche activity. BULLETIN SPONSORED BY: Canadian Avalanche Centre Staff NORTH COLUMBIA WEATHER: Warm temperatures to mountaintop, half a metre of storm snow, and light to moderate winds have been the weather pattern for the last days of December. An Arctic Airmass has roared into Alberta, and will spill over the divide, clearing things up the first day of 1998, but not for long. A Pacific low on the coast will be forced over top of the cold dense air, and anytime you have a moist Airmass forced upwards, that spells snow. Snowfall will increase in intensity as you progress eastward, and since the arctic air is still slumping southward rapidly, will be heavier as you move south also. With these airmasses converging, local instabilities will be everywhere, so impress visiting relatives by using the, "This is the mountains, just wait 5 minutes and the weather will change!" adage, and you won't go wrong. SNOWPACK: There are two lingering problems in the lower snowpack, the crust from around November 20th, and the buried surface hoar from December 8th. The crust is down almost 2 metres in most areas, and is breaking down but still easily seen. The surface hoar is around 100-140cm down, and is a little harder to pick out, but much more of a problem than the crust. All of the recent avalanche activity has been starting in the storm snow. The new snow coming will likely bond well after a day or two of settlement, but what will the added weight do to the interface at the buried surface hoar? AVALANCHES: North of this region, up in the Boweren Lakes, Barkerville area, highway crews reported no natural activity, but almost 100% success producing large avalanches on the November crust using helibombing. Natural and explosives activity is also the order of the day north of Smithers. In the North Columbias proper, the storm snow cycle has ended Jan 1, with only some whumpfing reported. DANGER: Considerable. TRAVEL ADVISORY: The December surface hoar interface is weak and more weight keeps getting added. If something goes, it will likely be big and propagate widely. Dig a pit in valley bottom down to the November crust, and check the strength of the facet crystals above and below it. If they are weak, watch out, particularly in the north country around Valemount and beyond. If the crust looks ok, then definitely take the time to find the December surface hoar higher up around treeline before committing to any tiger terrain. If you are having trouble locating the Dec layer, try isolating it with a Rutschblock or shovel compression test, then zero in on it and assess stability. January 1, 1998 SOUTH COLUMBIA WEATHER: The south country has seen new snow and warm temperatures to end 1997. An Arctic Airmass is pouring over the divide from Alberta January 1st, and will cause a sharp drop in temperatures. A Pacific low is heading inland, and will be forced over the dome of cold air, making for a big dump of snow to start off 1998. The Pacific air will be inland by late Friday, and skies will be clear and temperatures around -20. The arctic air will begin to slowly mix, and temperatures will be a little warmer each day. Pronounced instability will produce swirling winds at the airmass interface, while areas in Pacific air will have moderate west winds and areas in the arctic air will be relatively calm. SNOWPACK: The avalanche cycle from the storm snow last week is still going on, and more snow will fall on that. Instabilities are most pronounced in the upper 40cm, but many avalanches are stepping down into lower problem layers. Crusts, facets, weak layers bridged by thin strong layers, buried surface hoar, the south Columbias has it all right now. The most dangerous layer is the December surface hoar down about 75-100cm, which in one case produced an avalanche 1km wide in the New Denver area. AVALANCHES: Widespread natural and skier triggered activity still being reported January 1, before the heavy snow begins. Activity will increase as new snow is added rapidly, then taper off later in the weekend. DANGER: High, improving through the weekend to Considerable by Sunday. TRAVEL ADVISORY: Watch out, here comes a big one! Although things will tighten up and natural activity taper off by Saturday, use caution before you rip into the dump with that new sled or board you got for Christmas. BULLETIN SPONSORED BY: Kelowna Mountain Weather Centre Staff ROCKIES WEATHER: A strong outbreak of Arctic air began slumping southward Wednesday, and many areas were seeing a drop of more than one degree Celsius per hour by the time the partiers were cheering in the new year. The cold airmass is progressing southward Jan 1st, and some air is spilling over the divide. A Pacific low is tracking westward, and will be forced over top of the cold air, producing heavy snow throughout Friday and into the night. The extreme east slopes of the Rockies are also seeing air being forced upwards by the Arctic passage, so locally heavy snow from this east slope uplift is adding to the dump. SNOWPACK: The Rockies has suffered through a dreadful drought of snowfall up to this point. The snowpack is shallow and weak. Now we have a dandy dump of new snow over the entire region. Some areas have a rain crust topping the snowpack off, and a big dump spells an interface weakness for the storm snow. The sandwich of lower snowpack problem layers will definitely act up also. AVALANCHES: Some light activity was still being reported before the new snow, mostly with explosives. Parts of the region were just tapering off from a smaller than expected cycle the last days of 1997, and now things will pick up again during the storm. DANGER: High during the first few days of 1998, tapering off to Considerable later in the weekend. TRAVEL ADVISORY: With this being the first big dump of the winter for many parts of the region, it is going to be very hard to resist the temptation to just charge headlong into the powder once skies clear. Be very careful, conditions up until this point have been weakening what snow we did have throughout December. When natural avalanche activity drops off late in the weekend, make sure you still assess the snowpack with a pit to ground. Lift serviced skiing should be excellent to outstanding, and is certainly the best bet during the pending avalanche cycle.