Tahoe Backcountry Snow

0400 wx at 6350′ in Carnelian Bay: 22.6 deg. / 14.4 deg. dew point / 70% RH / Light winds / Clear skies / 3″ new snow on 2/4 / 1.75″ rain on 2/5

0500 wx at 8400 Mt. Rose backcountry TH: 12 deg. / Moderate SW winds / Mostly clear skies

Backcountry obs.:

Despite waking to a disappointing surprise of no new snow at lake level, the Rose backcountry above 8400′ did not disappoint. 1.5′ – 2.5′ of new, wind-smeared, dense snow now sits atop rain crusts from the 1/31 – 2/3 AR event.

The new storm snow has an upside-down structure with notable density changes throughout. Colder, less-consolidated snow rests just beneath the denser, wind-massaged surface. Breaking trail is fairly laborious with a semi-supportable upper layer, breaking into the softer snow underneath, especially in wind sheltered areas. Wind-exposed zones near treeline offer more supportable snow and easier travel.

Wind-exposed aspects (SE-S-W-NW), especially near and above treeline hold heavily wind-affected snow with large pillows, drifts and fins of dense, yet edgeable snow. Lee aspects are wind textured, yet soft and supportable, offering plentiful opportunities to carve wide, buttery turns.

Weather and forecast thoughts:

The battle between cold air from the Gulf of Alaska and the central Pacific’s plentiful subtropical moisture has set up the recent boom or bust weather of the past two storms. While some cooler air had phased into the Tues (2/4) storm dropping snow levels to near 6000′, especially at the onset, it couldn’t beat out the deep warmth associated with the subtropical AR. Snow levels rose yesterday around midday to nearly 8000′ by nightfall, and didn’t recover their starting position until precip. ended overnight.

Today (2/5) offers a reprieve from the AR cycles. Sunny skies and cool temps will dominate as highs remain below freezing in the backcountry above 7000′. Brisk SW winds will hang on throughout the day and increase towards nightfall, presaging the arrival of the next storm.

Tomorrow morning (2/6), snowfall should begin around daybreak for all elevations in Tahoe. The incoming moisture will arrive into the resident cold air mass bringing snow to all elevations throughout tomorrow morning. However, as the day progresses, more robust moisture from the subtropics will filter in, nudging up snow levels to 6500-7000′ during the afternoon and evening. At the same time, a deep, cold, unstable low off the Pac NW will descend along the coast, phasing colder air into the moisture plume. The tension between these two air masses will create another round of high winds and intense precip. late tomorrow into early Fri (2/6), while also crashing snow levels back below 6000′ in the wee hours of Fri. AM. The timing and placement of the cold low will determine just how quickly snow levels fall.

By Fri AM, another 1-2’+ of new snow is likely in the backcountry above 7000′, with isolated spots in the alpine, especially near the crest, receiving up to 3′. Below 7000′, 4-12″ of new snow looks like a safe bet, with higher amounts along the west shore of Tahoe.

Cold, unstable air behind the storm passage will promote scattered convective snow showers throughout the day on Friday, adding a few more decorative inches. Temps will remain cold, not warming beyond the 20s above 7000′.

Looking ahead, the weekend is shaping up to be sunny and cold: bluebird.

0400 wx at 6350′ in Carnelian Bay: 39.6 deg. /25 deg. dew point / 56% RH / overcast skies / 24hr. rainfall: .50″ / 2.76″ rainfall since Fri (1/31)

0515 wx. at 8650′ Mt. Rose backcountry TH: 29 deg. / SW winds ~ 10mph / overcast skies

Backcountry obs.:

The weekend storm produced, just not below 8000′. Snow levels started off around lake level on Fri (1/31), but rose above 9000′ on Sat. night (2/1) before settling around 8200′ for much of Sun. (2/2).

As a result, there’s little new accumulation below 8000′ in the Mt. Rose area, but the snow stacks up, especially at and above 8500′ where 1-2′ of new, ultra dense snow fell, recharging the snowpack. The new snow has been heavily groomed by strong winds creating a supportable, yet delightfully edgeable — and ripable — surface. 1-3″ of soft, unconsolidated surface snow exists in sheltered treed areas while a few isolated wind-exposed areas host a 1/4″ breakable rain crust.

The quantity and spackle-like quality of the snow has dramatically improved coverage and skier confidence. Gone are the days of fearing knee snapping snags and stumps lurking just beneath the surface. The tide has risen! Let the fast, fearless turns begin!

Forecast and weather thoughts:

While round 1 of the prolonged atmospheric river (AR) brought the warm and wet, and the next two waves look to bring equally intense precip. rates, but with the gift of progressively colder temps. Expect the next round of heavy snow to impact the backcountry Mon PM (2/3) into Weds AM (2/5). There will likely be a brief break Weds AM – Weds PM, before the coldest wave in the series brings heavy snow to all elevations in Tahoe starting overnight Weds/Thurs (2/5) and lasting through Fri AM (2/6).

By Fri evening, model ensembles show total snowfall amounts between 2-4′ above 7000′. Locally higher amounts are plausible near the crest and at higher elevations.

Today’s break in the rain and snow will quickly end this evening as a plume of AR moisture descends upon the central Sierra from the north. Snow levels will initially start around 6500′, then gradually rise up to or slightly above 7000′ by Tues morning. Rain and snow will fall in earnest on Tues as a surface low and powerful upper level jet accompany the moisture plume, providing strong atmospheric dynamics for enhanced precip. rates, especially along the crest. By Tues evening, colder air works into the system dropping snow levels down to lake level. As precip. winds down Weds AM, 1-3′ of new snow is likely above 7000′, while anywhere from 4-12″ could coat areas below 7000′. Lower elevation snow totals will be highly dependent upon how fast cold air phases into the storm.

The daylight hours of Weds (2/5) will provide a brief reprieve before the final — and coldest — round of the sequence arrives Weds evening. Models are in good agreement for another strong and dynamic system with a deeper source of cold air, creating heavy snow Weds PM through Fri AM (2/7).

It’s taken a while, but winter finally looks to be turning on.

0400 wx obs. at 6350′ in Carnelian Bay: 32.0 deg. / 48% RH / 14.5 deg. dew point / light and variable winds

0515 wx. obs. at 8650′ Mt. Rose backcountry TH: 31 deg. / light to mod. winds from SW.

0640 wx. obs. from 9890′: 27.3 deg. / Overcast / Winds SW at 8mph, gusting to 12mph

Backcountry obs.:

I headed out this morning for a prestorm conditions check.

Below treeline, sun exposure largely determines snow quality. Shady NW-NE aspects still hold soft, light snow from last weekend’s (1/26) storm. The ultra light snow has consolidated and bonded to the crusts beneath leaving 3-6″ of fluff upon which to turn and giggle. Settling and bonding over the past week has replaced formerly scratchy turns with a dampened, bouncier feel underfoot.

Near treeline and above, frozen, scoured and wind affected surfaces reign on all aspects.

Solar aspects below treeline now host a 1″-2″ thick melt freeze crust that is largely supportable, especially on the sunniest SE-SW slopes. Surface texture in these areas resembles early corn, indicative of the snow drought, but also higher sun angles. Beneath this crust is a loose 2-5″ layer of unconsolidated facets resting atop hard crust.

Weather and forecast thoughts:

The largest storm cycle of the season to date is right on our doorstep. Heavy precip., high snow levels, and strong SW winds will impact the Tahoe backcountry through the weekend and into Monday. The 50th percentile of models suggests that by Mon. (2/3) several (3+) inches of rain will have fallen below 7000′ in the Tahoe Basin, while 1-3′ of heavy, dense snow is possible, especially above 8500′. Tues. – Thurs., snow levels drop to and below 6000′ as additional rounds of heavy precip. impact the Sierra Mon PM-Tues., and possibly again on Thurs. (2/6).

The action begins mid-late morning today (1/31) with strengthening SW winds and snow showers increasing in intensity. Snow levels will begin below 6000′ and steadily climb throughout the afternoon and evening. By sundown, heavy rain will likely fall up to 7000′ and continue climbing throughout the night.

By daybreak Sat (2/1) the fire hose will be upon us with moderate-heavy rain and snow clobbering the backcountry. Snow levels Sat. PM will climb up to 8000′ on the northern side of the basin, while slightly higher snow levels ~8500′ are likely further south. The deluge continues into Sat. night as snow levels remain high at or slightly above 8000′, likely peaking some time early Sun. morning.

Sun. (2/2), precip. will likely back off as the main focus of the moisture plume shifts to the north. However, very strong SW winds will take its place. Models show high probabilities for 40-60mph winds even below 7000′. Winds over 100mph are almost a certainty on ridgetops. Snow levels will also begin slowly creeping down mountain Sun. into the 7000′ level Sun night into early Mon. morning.

Colder air looks to continue slowly bleeding into the area through the day on Mon. (2/3), dropping snow levels to around 7000′ by the evening and steadily declining thereafter. By daybreak on Tues. (2/4), another round of moderate-heavy precip. comes in, just in time for snow levels to begin flirting with lake level.

Fear not! While round one looks to be a rain producer for all but the highest elevations, colder storms and signficant, snowpack building systems look likely for the middle to end of next week.