Tahoe Backcountry Snow

Backcountry obs.:

Heading out Tuesday (1/20) on tour in the Mt. Rose area revealed a largely thrashed snow pack, severely degrading morale. Weeks of high user traffic, coupled with melt-freeze crusts on all but the shadiest N and NE aspects, have created firm, chattery, and sometimes breakable surface conditions not good for much more than honing survival ski skills. Due southerly aspects do host supportable melt-freeze surfaces, softening on sunny, warmer days providing buttery corn to relieve those weary of the snow drought blues.

Since midweek high clouds and increased humidity in the middle elevations likely baked any remaining soft surface snow on N and NE aspects, which has since refrozen into breakable crusts now that cold air has returned to the Tahoe Sierra. Lower humidity on the snow pack at the highest elevations could have potentially preserved a few sheltered pockets of cold snow on N and NE aspects, but whatever does exist is likely small and worth no more than a few turns. Good luck finding the pot o’ gold!

Weather and forecast thoughts:

The last measurable snowfall in Tahoe was on Jan 8. Looking at the coming week it’s increasingly likely that January will close out without additional measurable precip. Expect the cool NE flow over the area this weekend to moderate early in the work week (1/26-1/27) under mostly sunny skies as a ridge of high pressure restrengthens overhead. Late Tues and into Weds (1/27-1/28), a system tries to nudge into the area, but looks to be largely blocked by the resident high. The result may be an uptick in winds, especially over the higher terrain, cloud cover and potentially a few flurries, but without meaningful accumulations. Behind the shortwave, model guidance shows a ridge of high pressure rebuilding over CA holding into the coming weekend (1/31-2/1).

Expect high temps across the backcountry this week to be in the upper 20s to mid 30s on Sunday and Monday, climbing into the upper 30s to low 40s around midweek. Inversions are likely at the beginning of the week, so ridges and summits could be 10-15°F warmer than surrounding valleys in the stable air mass. Late week backcountry temps look to moderate well into the 40s each day as another ridge takes hold. Expect inversions to return, as well.

Here’s a snapshot of the big picture pattern for the week:

Diving a bit deeper into the midweek disturbance, models disagree on how much miniscule moisture makes it to the Sierra, further degrading confidence in the forecast. The Euro ensemble brings more moisture in while the GEFS retains a drier solution.

Where there is agreement is that any disturbance that does arrive will be little more than that: just a nudge to the airmass bringing some wind, clouds and maybe a flurry or two. The dynamics (mid level vorticity) to wring out moisture are very weak.

And there just won’t be much moisture to wring out.

So on the midweek storm, an amazing surprise of good fortune might be an inch or two in the backcountry, but such an outcome looks highly unlikely.

After the midweek disturbance, another ridge of high pressure builds in setting the stage for more sunny, dry weather.

Looking out into February, models have recently been quite inconsistent between runs. The strong ridge from earlier this month doesn’t look to return with the same strength as in January, but a trend towards high pressure and above average temps looks more likely than not, at least for the first week of the month. There are some hints at a pattern of undercutting lows that could bring precip to the Sierra. But strong signals of a significant pattern change yielding impactful storms just haven’t appeared.

Meanwhile, the days of winter keep slipping away.

Backcountry obs.:

Touring deep on the West Shore this weekend, I found a snowpack closely reflecting the Juneuary weather of the past month.

Below treeline, N-E aspects host a combo of cold, soft snow interspersed with delicate breakable crust: delightful to defensive skiing within a few feet. Shaded valleys and creek depressions have remained well below freezing each night, pooling cold, moist air, perfect for growing delicate surface hoar that in some areas has accumulated multiple inches deep. Ski turns through this recycled pow shatter at once like fine crystal on marble, tinkling as they scatter across the snow surface. It’s a remarkable sound and feeling.

Venturing out into the sun from the cold backcountry hideaways, the snow wears heavy weeks of sun and heat. Breakable crusts atop heated mush are the main story in the trees, while open, due south facing areas hold supportable melt freeze crusts that under clear skies and light winds, have softened into smooth butter each afternoon. Buttery turns aren’t bad.

Up at the highest elevations, despite the warm temps, extremely dry air has kept snow surfaces mostly frozen. Ridges and summits host all forms of sculpted sastrugi, edgeable wind buff and occasional soft, textured, wind deposited snow. Carrying a whippet or axe is a wise idea in high consequence terrain where firm surfaces abound.

It’s a variable thrift shop of conditions out there. Add in the heavy holiday traffic and you’ll find popular zones thrashed with tracks, ruts, dinosaur tracks (snowshoes), and even some lamely poached snowmobile tracks.

As they dry days stack up and extend into the future, the calculus of skiing an ever degrading backcountry snow pack versus doing anything else fun becomes harder to pencil out.

Weather and forecast thoughts:

Looking ahead at the coming week (1/19-1/25) dry and warm weather will continue to exacerbate the growing snow drought in the Tahoe Sierra. No precip. throughout the entire week seems nearly guaranteed. Temperatures look to remain steady with only a few modest variations: edging up a few degrees by midweek, then cooling by a few degrees by the weekend.

Highs this week will generally wobble between the low to mid 40s through the work week and into next weekend above 7000′, under a very dry air mass. Low temps already a bit cooler than last weekend will drop into the low to mid 30s along higher terrain, with temps into the 10s and 20s in valleys and depressions each morning. Expect a bumper crop of surface hoar throughout the week. Shaded aspects should continue to hold onto vintage, dirty powder with the dry airmass.

Yee ole’ persistent dome of high pressure continues to defend the Sierra from any hint of a storm system. Around midweek ensembles do show a cut off low developing off SoCal and undercutting the ridge, but it will then move off into the desert Southwest without much trace for the Central Sierra. A few high clouds and breezes might be the only evidence of its passing.

As noted above, behind the low another ridge redevelops over CA, reinforcing warm, dry conditions going into next week (1/26-2/1).

An interesting, although grim, note about this pattern is its resilience. Looking at a model of the amount of spin half way up in the atmosphere (aka 500mb vorticity), it’s evident how the blocking ridge dissipates and largely deflects any storms that try to penetrate it. The below GFS model spans the North Pacific and goes out until 2/4. Storms are denoted by brighter colors showing areas of greater spin (vorticity). Note the path of disturbances as they approach the CA Coast.

A model going out this far will almost certainly play out differently than depicted above. However, it’s instructive in showing how persistent and entrenched the current pattern is and its ability to stave off perturbations.

Change will come, but it’s not looking likely until at least the beginning of February.

Backcountry obs.:

Tours around the Tahoe backcountry this week, both on the West Shore (1/13) and in the Mt. Rose area (1/15) revealed surprisingly resilient snow conditions, despite the recent dry, warm weather. Low January sun angles and very dry air are helping to preserve surface snow on shady, sheltered N and NE aspects. Above treeline, recent NE winds have hammered any unconsolidated snow into firm, frozen wind board, both supportable, and at times breakable.

Lower elevations and any aspect that receives sun has now crusted over into breakable solar crusts. Treed solar aspects also have breakable firm surfaces from refrozen tree drippings, while true, open, southerly aspects now hold supportable melt-freeze conditions.

Combine this grab bag of surface snow conditions with a week’s worth of skier traffic since the last snowfall (1/8), and you have truly sporty ski conditions varying from a downright hootenanny good time, to death crust, to slide for life, to “was that a corn turn?!” all within a single lap. It’s ideal for building character and encouraging exploration out into the deeper reaches away from the masses.

Weather and forecast thoughts:

Going into the MLK weekend, “persistence” jumps out as the weather theme of the holiday weekend. Clear skies, light winds, and warm days will prevail through the coming weekend and into the coming week, potentially lasting through the end of January. Peering way out towards the close of the month, there are some hints of change in the pattern, but specifics are impossible to foresee.

Today (1/15) through MLK Day (1/19) expect mostly clear skies, light winds and daily high temps into the 40s across the backcountry, with lows near to well-below freezing in drainages and depressions. Along ridge tops and in mid-slope areas, warmer overnight lows will struggle to drop beyond the upper 30s to low 40s and nightly light to moderate easterly winds could continue to expand wind board across open slopes and bowls. For example, this morning at 0607 at 9200′ in the Mt. Rose area it was 45.2°F with an 11.6°F dew point and 24% RH under clear skies and light easterly winds! Meanwhile it was 30°F at lake level. These classic, high pressure inversions will continue through the weekend and likely well into next week.

The culprit is a blocking ridge of high pressure that continues its big sit over the west.

The ridge does show signs of migrating NW into the Gulf of Alaska later next week, which could allow some energy to under cut its influence, but anything that does arrive looks starved for moisture. An uptick in winds and cooler temps would be the most likely result, but any appreciable backcountry refresh appears unlikely through next week (1/19-1/23).

Some ensemble guidance does pick up on some light precip. and cooler temps reaching the Sierra by next weekend (1/23-1/25), but it’s inconsistent and recent model runs have pulled back on the already light total precip. amounts, inspiring little, if any, confidence.

Looking way out towards the end of month and first few days of February, climate models do suggest changes in some key teleconnections that could favor a pattern change for the western US. The MJO (Madden Julian Oscillation) shows signs of potentially re-energizing and entering a phase favorable for unsettled weather in CA. Additionally, the weak La Niña in the equatorial Pacific appears to be breaking down and will continue to do so going into the spring. Changes are afoot. How and when they play out remains an open question.

So get used to the sunshine, warm days and increasingly spring-like snow conditions on southerly aspects. Juneuary is here for a while.