Global Snow & Avalanche Outlook #4
WEEK OF 11 DECEMBER 202
With winter officially underway in the northern hemisphere, large-scale atmospheric patterns are now pushing cold air and storm systems into key ski touring regions. A split polar vortex and persistent troughing over North America have delivered a robust cold pool and increased snow potential across multiple mountain chains. Europe’s high Alps maintain early coverage as Atlantic systems edge in, while Japan’s classic northwest monsoon begins to ramp up coastal snowfall. The Himalaya remains mostly dry with isolated high-elevation snow showers due to weak Western Disturbances.
NORTH AMERICA — UNITED STATES
Wasatch Mountains (Utah)
Observed Conditions
Since the last outlook, snowfall in the Wasatch has been relatively limited and uneven. Mid-mountain and upper terrain generally shows a modest base depth (~30–50 cm), with lower elevations thin or crusty from periodic warm spells. Persistent faceted basal layers from earlier weak snow events remain a structural issue beneath the current pack. Reports show a mix of dense slab over weak oct/novelex facets and consolidated wind-transported snow in alpine terrain.
Forecast (Next 5–7 Days)
Models continue to suggest a drier pattern directly over Utah through mid-week, with cold temperatures and limited precipitation. Snow chances improve marginally later in the period if Pacific moisture can translate inland ahead of strong jet dynamics moving into the Pacific Northwest (see PNW pattern below). Expected new snow through week’s end is low (< 10–15 cm) in isolated storms. Freezing levels near or slightly above 2500–2800 m at times may limit coverage and quality. Localised crust re-formation is likely with diurnal warming.
Pattern / Synoptic Summary
A displaced polar vortex lobe is funneling Arctic air into Western and Central North America. Combined with a blocking high over the eastern Pacific, this sets up a cross-continental trough that favours northwest flow aloft — typically a setup that allows periodic storm entries into the northern tier while leaving the central Wasatch in a relative precipitation shadow.
Avalanche Conditions
The Utah Avalanche Center currently indicates Moderate avalanche danger across steep terrain above ~2700 m in the Salt Lake and surrounding forecast regions. Persistent weak layers (facets from Oct/Nov) lie beneath thin slabs near treeline and above, so triggering a 30–60 cm slab remains possible on convex slopes. Wind drifted snow is also forming pockety slabs near ridges. Signs of instability like cracking and collapsing may be subtle but significant. Consistent block tests and careful terrain selection are essential.
Tetons & Bridger Ranges (Wyoming)
Observed Conditions
Early December brought a light cumulative snowpack in the Tetons; upper elevations show ~30–55 cm total with underlying crusts at mid elevations. Strong diurnal cycles have produced ice crusts at lower levels. Recent excursions noted wind-transported snow on leeward slopes. Local ranger posts and backcountry reports confirm a fragile mid-pack.
Forecast (Next 5–7 Days)
Some light snow accumulations are possible under weak synoptic forcing through mid-week, with potential for ~5–15 cm. Snow quality will be variable with crust-powder sandwiches likely below 2700 m. A stronger mid–late week disturbance may bring up to ~20–30 cm of fresh snow at upper elevations, especially on west aspects as jet dynamics amplify across the northern Rockies.
Pattern
The larger trough over western North America favours cold air through the Northern Rockies. However, higher precipitation focuses on areas with deeper Pacific moisture transport (e.g., PNW, northern Interior BC).
Avalanche Scenario
Wind slabs expected above ~2800 m on north and leeward aspects. Persistent weak basal layers remain a concern and pockets of storm slab instability could remain reactive after new snow. Hard slab development remains possible where winds accelerate snowfall onto leeward rolls. Local avalanche advisories should be checked for daily specifics.
Colorado Rockies (Northern / Central / Southern)
Observed Conditions
Snow totals have been modest, with ~15–35 cm reported over higher peaks since the start of the month. Lower mid-elevation slopes still expose rocks and limited coverage. Mid-pack faceting is ongoing with a pronounced weak layer near the base in many zones.
Forecast (Next 5–7 Days)
Expect a continued slow accumulation pattern. Forecast guidance suggests small disturbances bringing ~5–20 cm of new snow at higher elevations, especially across northern ranges. Central and southern sections may see similar light bands, with the possibility of ~10–25 cm by week’s end. Snow levels remain cold enough above ~2500–2700 m.
Pattern
The elongated trough over western North America combined with a sharp ridge over the Southeast U.S. supports northwest flow aloft. This maintains cold air but does not favour strong storm transfer into the Colorado interior until later in the outlook period.
Avalanche Scenario
The Colorado Avalanche Information Center continues to highlight persistent weak layers below recent accumulations. This means triggering large slabs remains possible in steep terrain where new snow adds load over these weak layers. Wind drifts can exacerbate problems on leeward slopes, and sensitivity to human triggers remains elevated. Terrain traps and convexities could be especially dangerous.
Sierra Nevada (CA / Eastern Sierra)
Observed Conditions
Recent storm activity has left the Sierra with a patchy early cover; upper elevations generally carry ~20–40 cm, with rain or crust at lower elevations. Snow-to-rain transitions have complicated accumulation patterns.
Forecast (Next 5–7 Days)
A Pacific storm train is expected to bring moisture into the Sierra, with ~15–35 cm of fresh snow above ~2400–2600 m possible by late week. Snow levels may fluctuate with each frontal passage, meaning rain-snow line timing will be key for quality.
Pattern
Atmospheric river activity is focussed on the PNW and northern California, with some moisture spilling into the central Sierras when trough interactions occur. The Pacific jet remains active.
Avalanche Scenario
Wind slabs and storm slabs remain the focus above treeline. Given the early season crust layers and rain events below, expect a complex snowpack with potential soft slabs over crust near mid-elevations and deeper slabs at higher terrain. Careful consideration of facet/crust interfaces and wind-loaded slopes is critical.
Pacific Northwest Cascades (WA / OR)
Observed Conditions
An active Pacific pattern has produced higher mountain snowfall in the northern Cascades, with many upper elevations accumulating ~30–60 cm over the past week as atmospheric rivers impact the region. Lower elevations have seen mixed rain/snow events, but high alpine snowfall has been significant given the jet strength.
Forecast (Next 5–7 Days)
The atmospheric river train continues, with another potent surge likely mid-week bringing heavy precipitation. Expect > 60 cm in upper elevation zones, with the potential for localized > 100 cm in favored orographically enhanced portions of the northern Cascade crest. Snow levels will be dynamic, dipping below ~1800–2000 m when cold air surges follow frontal passages.
Pattern
A strong subtropical plume feeding into the Pacific Northwest is tied to the active jet stream and blocked west coast ridge, driving moisture inland and enhancing snowfall on the windward slopes. The pattern reflects classic winter coastal storm impacts.
Avalanche Scenario
The Northwest Weather and Avalanche Center (NWAC) forecasts elevated avalanche danger due to deep snow accumulation with sustained winds. Expect widespread storm slabs and persistent wind slabs in many alpine areas. Heavy loading from atmospheric rivers followed by strong post-frontal NW winds will keep avalanche danger high, especially on leeward slopes and bowl features.
NORTH AMERICA — CANADA
Coast Mountains (BC – Whistler / Sea to Sky)
Observed Conditions
Recent Pacific systems have delivered significant snowfall in the northern Coast Mountains, with upper elevations reporting base depths well above early season normals (often > 50–80 cm). Obstructions remain where coverage is thin below treeline, but high alpine terrain is generally well established.
Forecast (Next 5–7 Days)
Persistent westerly flow will continue to feed moisture into the Coast Mountains. Expect intermittent heavy snow bands with ~30–60 cm fresh in favored locations by week’s end. Snow levels will remain predominantly low (below ~1500 m), enhancing snow continuity.
Pattern
A strong Pacific jet and repeated trough passages maintain an active storm track into western Canada. Orographic effects over the Coast Range amplify snowfall where the moisture plume intersects steep terrain.
Avalanche Scenario
Avalanche Canada’s forecasts show widespread wind slabs and storm slabs above treeline in coastal zones, with rapidly building early season snowpack. Travel in steep unsupported terrain should consider the potential for deep slabs and persistent weak layers at mid-pack interfaces.
Interior BC & Selkirks / Purcells
Observed Conditions
Interior BC ranges have enjoyed multiple storm cycles with ~30–70 cm over the past week in sheltered terrain, building more continuous coverage above ~1800–2200 m. Faceted layers near the bottom persist where early snow melted and refroze.
Forecast (Next 5–7 Days)
Expect continued moisture with trough interactions, delivering ~40–80 cm fresh snow in wind-favored zones above ~2000 m. Cold air remains entrenched inland, promoting dry powder with each band.
Pattern
Interior BC sits in the lee of Pacific moisture streams, with the active jet feeding high snowfall despite frequent ridge-trough oscillations.
Avalanche Scenario
Avalanche Canada indicates developing storm slabs and wind slabs above treeline with persistent weak layers at depth. In many alpine basins, slab thickness may exceed ~1 m, making natural and human-triggered avalanches probable on steep aspects.
Canadian Rockies
Observed Conditions
The Canadian Rockies have seen modest early accumulations (~15–35 cm) with stronger winds depositing snow in lee terrain. Snow coverage remains patchy below ~1800 m.
Forecast (Next 5–7 Days)
Mid-week disturbances bring ~10–25 cm of snow at higher elevations, with persistent NW flow helping preserve cold surface temperatures. Weekly totals may reach ~30–50 cm in favored alpine zones.
Pattern
Cold polar air combined with Pacific moisture supports an ongoing snow buildup trend across the Rockies, especially where orographic lift enhances snowfall.
Avalanche Scenario
Avalanche Canada analysts emphasise early season wind slabs and shallow slab problems on top of weak foundations. Even modest new loading can increase danger on north and east aspects with steep slope angle.
EUROPE — ALPS
French, Swiss, Austrian & Eastern Alps
Observed Conditions
The Alps have seen repeated snowfall events over the past week, with many high alpine stations reporting ~50–100 cm since early December. Swiss high elevations are showing strong early-season bases (often > 120 cm), although lower slopes still reveal crust and patchy coverage in places.
Forecast (Next 5–7 Days)
Atlantic storm systems will continue to graze the northern Alps. Expect ~20–40 cm of new snow at upper elevations during the active periods, with lighter snow mid-week. Snowlines may fluctuate between ~1500–1800 m depending on frontal placement.
Pattern
A series of Atlantic lows riding a southerly jet into Western Europe provides moisture, while cold air aloft keeps precipitation largely as snow at mid to high elevations.
Avalanche Scenario
SLF Switzerland reports persistent wind slabs and deeper slab layers in sheltered terrain, especially above ~2200–2400 m. These slabs can be reactive after new loading, particularly on lee slopes. In areas where snow cover is thinner, buried crusts and facets can also produce problematic persistent weak layers.
JAPAN — HOKKAIDO & HONSHU
Hokkaido
Observed Conditions
Early December snowfall on Hokkaido continues its gradual build, with repeated smaller snow events layering up ~15–30 cm above ~800–1200 m. Coastal stations show improving base depth, though lower slopes remain intermittent.
Forecast (Next 7 Days)
A classic northwest monsoon flow will persist, with widespread snow showers bringing ~30–60 cm of new snow through mid-week and a strong late-week front capable of adding ~40–70 cm or more in coastal, windward zones. Temperatures remain cold with good snow growth conditions.
Pattern
Cold continental air from Siberia passing over the warm Sea of Japan drives intense orographic snow production on Hokkaido’s western flanks — the textbook snow-belt mechanism.
Avalanche Scenario
Wind slabs above treeline and storm slabs atop crust layers remain primary concerns. With rapid snow growth, expect reactive slabs in alpine bowls and leeward slopes. Tree-well hazards and inconsistencies in coverage at lower elevations increase risk in sidecountry terrain.
Honshu (Hakuba, Myoko, Nozawa, Tohoku)
Observed Conditions
Initial snow pulses dropped ~10–30 cm in northern Honshu, with some upper basins already uphill of ~60 cm total. Snowpack remains variable lower down but improves with elevation.
Forecast (Next 5–7 Days)
Successive bands from the Sea of Japan will deliver ~50–70 cm widely, with heavier fringes ~80–100 cm possible if the strongest front stalls over westerly slopes. Deep alpine accumulations will build quickly in this synoptic regime.
Pattern
Persistent NW fetch over the Sea of Japan combined with mid-week frontal enhancement supports sustained orographic snow growth into Honshu’s classic snow belt.
Avalanche Scenario
Rapid base strengthening transitions early thin cover into significant storm-slab conditions. Wind slabs on ridgelines and cross-loaded bowls will form quickly during the heaviest snow. Expect tricky slab luck until several days post-storm.
HIMALAYA — INDIA / NEPAL / PAKISTAN
Western Himalaya (J&K, Himachal, Northern Pakistan)
Observed Conditions
High passes and ridgelines in the Western Himalaya have seen only isolated, light snow showers this past week; snowpack remains thin and discontinuous below ~3500–3800 m. Cold stable conditions prevail at lower elevations with clear skies and inversion patterns.
Forecast (Next 7 Days)
A weak Western Disturbance may produce scattered snow showers ~5–15 cm above ~3500–3800 m between now and late week. Most valleys and mid-slopes remain dry with patchy snow.
Pattern
Limited moisture embedded in a broad upper-level ridge and stable cold air suppresses deeper snow events, yielding only light scatter showers in the far western ranges.
Avalanche Scenario
Low overall avalanche activity. Light wind slabs may form in localized lee zones at high elevation, but deep slab cycles are unlikely this week. In very steep gully and ice features, isolated small loose avalanches could occur with fresh accumulation.
Central & Eastern Himalaya (Uttarakhand, Nepal, Sikkim)
Observed Conditions
Dry conditions dominate, with minimal fresh snow except at extreme high summits. Snowpack remains largely remnant and discontinuous outside permanent glaciers.
Forecast (Next 5–7 Days)
Mostly dry, with only trace accumulations possible on the highest peaks. Cold clear conditions persist across valleys and mid-slopes.
Pattern
A stable upper ridge suppresses storm systems from the west, leaving little moisture for snow in these sectors.
Avalanche Scenario
Very low avalanche hazard except on very steep glaciated terrain where isolated wind slabs or old frozen slabs may persist. Objective hazards remain related to ice and rockfall rather than fresh slab cycles.
SUMMARY & TAKEAWAYS
North America: Pacific Northwest and Western Canada remain the most active early-season snow producers with multiple atmospheric river bands and strong NW flow delivering deep accumulations. The Rockies and Wasatch continue building a patchy base with persistent weak layers. Avalanche problems include persistent facet layers with new snow, and wind slabs where transport is significant.
Europe – Alps: Deepening early bases reinforced by ongoing Atlantic storms; localized wind slabs and deeper persistent layers are the key avalanche drivers.
Japan: Classic northwest monsoon brings sustained snow to Hokkaido and Honshu, with potential for ~80–100 cm or more in upper terrain this week — avalanche hazard will rise accordingly.
Himalaya: Light, isolated snow only in the far western high passes; broader ranges remain dry and cold with minimal slab avalanche activity.
Overall, winter’s first major pattern shift is underway. Where storm cycles align with cold air and orographic enhancement, significant snow and avalanche risk are increasing — make sure to consult daily avalanche bulletins from local centres before heading into the backcountry.
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