0430 temp. at 6350’ in Carnelian Bay: 42 deg. & 50% RH

0515 temp. at 8650’ Tamarack TH: 34 deg.

Backcountry Obs.:

I got out this morning to see what the incoming snow will fall upon and as expected, crusts cover all elevations and aspects from 8600’-9000’ in the Rose backcountry. On windward and solar aspects, these firm surfaces are not even penetrable with the blunt end of a pole. In sheltered areas and NE aspects, crusts are generally 1/2-1” thick and semi supportable. Cold snow lays beneath.

Why does this matter? The crusts create a new bed layer upon which instabilities may form and run in future avalanche cycles. With the early season PWL (persistent weak layer) now less of a concern, most issues will occur from the current surface up.

The big question with the incoming storm today is how well the new snow bonds with the current surface snow. At this point, the storm looks to start warm and finish cold, which in general bodes well for bonding and stability.

The skiing today: hateful, survival combat. A week’s worth of traffic, complete with deep ruts, dinosaur tracks – and who knows, maybe even a mule train or two – on refrozen firm surfaces that occasionally give way, made for a tiring descent. Good thing a fresh start is inbound.

Weather and forecast thoughts:

Today dawned with moderate winds, foreboding skies, and warm temps. Winds ahead of the system have mixed out the inversions of the past few days, improving air quality, but also raising temps and lowering humidities. The storm is already appearing on radar over the North Coast and should begin impacting the Sierra late this afternoon/early evening. NWS Reno issued a Winter Storm Warning yesterday which still remains in effect from 10am today through 10am Fri. Expect a windy day today with increasing clouds, temps in the 40’s, and rain/snow moving into the area late in the day.

Precip. will begin falling as rain around the lake, quickly transitioning to snow and picking up in intensity late tonight through tomorrow morning. Snow levels still look on track to start around 7000′, then fall quickly through lake level and down into the 5500-6000′ range on Thurs. Updated model projections for the storm have trimmed down snow totals a bit for tonight-tomorrow evening to 12-18″ above 7000′, up to 6″ in mountain communities.

The angle of the storm up against the Sierra is a big factor in trimming the snow totals. As the storm hits the range, the flow will be shadowed, meaning more precip. will fall on the western slopes. The crest and areas along CA 89 will get the most, falling off considerably the further east you move.

Behind the opening salvo, a moist flow off the Pacific will promote snow showers continuing Thurs. PM, Fri, and into Sat. Some of these could be convective, giving them an extra punch with some snow bursts freshening up the mountains each day, especially during afternoon hours. A rumble of thunder isn’t out of the question along the crest either.

Looking at the next system, this morning some of the models suggest things getting going Sat. night and lasting into Tues. This one is giving strong signs of being a classic dump machine with the ability to deliver feet to the mountains and maybe even at the lake. There is plenty of cold air in place, so snow will fall at all elevations for Tahoe communities and backcountry zones.

This system is looking pretty complex as it combines a strong AR (atmospheric river) of subtropical moisture phasing with colder air as a closed low drops down the Pacific coast. The strong low will help provide dynamic lift to the moist air as it hits the Sierra, wringing out its contents as heavy snow.

I expect quite a few revisions to the forecast in the next few days. Closed lows are notorious for wobbling about as they travel due to being disconnected from the jet stream and larger upper flow. This makes predictability for specific impacts challenging. Any change in the track of the low a hundred miles one way or another, could significantly alter which parts of the Sierra receive the heaviest snowfall. It’s going to be fun to watch.

For now, snow moves in tonight giving the backcountry a welcome refresh. Never waste a powder day!