Weekly North America Forecast – Persistent Storms in the North, AR for the Sierras Leading Up to Xmas
Written Wednesday afternoon, 17th December (Pacific Standard Time)
Persistent storms continuing across Canada and the northern US will see another deep layer of snow build up over the course of the next 7-days. Warm temperatures will be an issue at times, especially in more southern locations.
In the lead-up to Christmas, an atmospheric river will hit Tahoe before expanding across the Sierra Nevada. A massive load of precipitation is expected, providing a much-needed boost of snow for the upper slopes at least. But again, snow levels will be an issue at lower elevations.
Further south, Utah and Colorado on the fringes will see much more modest accumulations, while Arizona and New Mexico will miss out entirely.
Thursday 18th & Friday 19th December
A storm passing over the north will bring moderate to heavy snowfall to the northern half of western North America during Thursday and Friday. However, for most resorts, especially those south of the US/Canada border, a large portion will fall within a warming airmass that will see snow levels rise, turning snow to rain at low elevations with dense snow higher up.
Cold air on the back of the system will improve things, but this will stop just short of the Tahoe resorts, where rain and high-elevation snow will develop on Friday. Thankfully, it shouldn’t be too heavy.
Saturday 20th & Sunday 21st December
Light to moderate snowfall will continue across Canada, Washington, and northern Idaho and Montana on Saturday, while it clears areas to the south.
From late Saturday, new storm systems pushing in from the west will see precipitation rates pick up and extend down into Tahoe once again, and also into northern Utah and western Wyoming, with a glancing blow to north Colorado. However, warm air will again be part of the package, especially in these more southern locales, with low-to-mid-level rain and dense snow expected.
Monday 22nd to Wednesday 24th December
In the lead-up to Christmas, synoptic charts will be a tangle of fronts and low-pressure systems as the storm cycle remains active across much of the west. Resorts in Canada and the northern US will do well with consistent light to moderate snowfall and cooler temperatures.
However, a narrow and persistent atmospheric river (AR) of warm, moist air affecting Tahoe and the northern Sierras will continue to dump low-level rain and dense high-level snow through Monday into Tuesday.
Then on Wednesday, Christmas Eve, models expect the AR to strengthen and expand northward into the Cascades and southward into the Southern Sierras. Precipitation rates could be off-the-chart heavy, and there is a hint temperatures will be a little colder too, so snow levels could creep closer to the lower slopes if we’re lucky. Over the three days, snow accumulation in the Sierras could approach or exceed 1.5m above snow levels. From zero to hero!
That’s all from me today, folks. Have a great week, and I’ll see you back here next Thursday for another weekly rundown of North America’s highlights and snowlights.
Grasshopper
