The good news is decent moisture for the Sierra in the next 3-4 days. The bad news is warm temps will keep any appreciable totals at the summits. Everyone else gets scraps this week including the PNW. Colder air and an active pattern might take hold next weekend in the PNW. Low pressure might take hold in the extended forecast.
We are watching an intense storm for Europe due later this week, just in time for the holiday. If you want deep pow, I would jump a flight mid to late this week for the Alps. Keep an eye on snow levels as they start colder midweek followed by a slight warm-up Thursday followed by cooling Friday. You could also chase to Alaska where some decent totals will fall for the holiday period (Starts cold and finishes a bit warmer).
Below: My view from the cliffs near Lagos Portugal on Saturday. The surreal scene just after the sunrise before the crowds arrived (Kinda like the first chair). @powderchasersteve via Instagram.
For North America, the main focus is the storm spinning off the coast of California Monday morning. This system will move inland late Monday into Tuesday spreading light snowfall above 9000 feet to the Sierra. The American GFS is much wetter than the European (Still disagreement) with just over 2 inches of liquid through Wednesday. The European models show a maximum of 1 inch of liquid along the Sierra Crest. Averaging things out, I would expect 1.5 inches of moisture for the Sierra range (8-15 inches of wet snow at the summits). This might be a decent event for Mammoth (higher base elevation) or even the southern Tahoe basin near Kirkwood (Summit).
There will be 2 pieces to the Sierra storm with lighter amounts Monday-Tuesday and heavier snowfall possible Tuesday night to Wednesday. The snow levels will lower slightly for Wednesday morning (7500 feet). I don't expect any new snow at most of the base locations, with light or moderate amounts above 8,000 with moderate or heavier totals above 10,000. The Summit of Mammoth might be the best solution for a chase, especially for Wednesday morning. The Good: Lots of moisture possible (Model disagreement from 1-2.5 inches). Someone might score 10-15 inches up high. The Bad: Pesky high snow levels limiting rideable pow to mid-elevations or more likely the summits. West Sierra Cement (Most folks will take anything they can get right now). Ride higher elevations above 8500-9K.
Below: 10K foot temps are near freezing (0-Celcius) Monday from the PNW to the Sierra. Temps are even warmer in the Rockies. Snow early this week will only be confined to the summits. Is this April or December? Temps in the Sierra will drop by Tuesday night, but only by a few degrees pushing the snow level down to 8-8500. Wednesday morning could be a chase worthy surf pow day, especially for the southern Sierra. We don't usually even consider chasing the Sierra with temps any higher than -8C at 10K (Dry density at this point). Take what you can get, but the extended forecast might have better news.
Below: Total snowfall in the west through next Saturday, December 23rd. The American model is pretty bullish, especially for the southern Lake Tahoe area extending into Mammoth midweek (Above 8500 feet). Some summits are showing totals over 15 inches with this model (Snow ratio is 8:1). This storm drags south along the CA coast before weakening and spreading inland late this week toward AZ, UT, and NM (Light or moderate leftovers).
Below: The European Model is less optimistic about keeping snow totals lower for the Sierra summits (5-10) and teasers for mountains to the east in the 4 corners.
Below: The European ensembles show the low dragging of a piece of energy initially north (Some scattered snow showers possible for the PNW), and then heading south midweek.
Below: By Friday/Saturday, colder air for the PNW and a new area of low pressure will be overspreading Canada (Western areas are favored) and the Cascades by the weekend (Could be a moderate event).
The low from the CA storm will be moving inland over the 4 corners spreading some light or moderate leftovers into Arizona, southern UT, and New Mexico (Southern areas favored). Colder air will be confined to the northern tier of the PNW with the new area of low pressure. Map: Friday AM to Sunday PM (XMAS eve snowfall in a few areas of the 4 corners).
Below: Finally a cold front is on the horizon for the PNW and northern Rockies (Map is late Friday night December 22). Some high-quality snow showers will focus on Canada and the Cascades (Northern regions will be favored). Amounts will be upgraded in a future post (Does not look overly deep, but the cold temps could bring a few surprises). These temps are at 10K feet in C. Snow levels in the PNW will drop below the bases. Snow ratios will be decent (Good density).
Bottom Line: Aside from Europe or perhaps Alaska, we don't see any deep short-term chases aside from some surf snow at the summits in the Sierra midweek. The core of the Rockies gets weak leftovers favoring the southern mountains late this week. The PNW might deliver late next week or next weekend with a cold front.
We seem to be entering a bit of a stormier pattern, especially for the PNW after the holiday into late December. Some models show a very active pattern into early January that might benefit the PNW and finally the Sierra (Fingers crossed). Colder temps are also showing up on the ensembles for the west to close out December.
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