Thread by @Weather_West

Lot of hype right now regarding supposed potential for widespread "sea level snowfall" later next week NorCal.

That almost certainly isn't going to happen (for variety of reasons). But some unusually low elevation snowfall (to 1000-1,500 feet or so) is certainly possible. #CAwx

Yes, I know that the coarse-resolution ensemble models are showing accumulating sea level snowfall for SF/Sacramento. They are very likely wrong--and the same models' *own thermal profiles* are not supportive of snow in these areas with this pattern! #CAwx

It is *extremely* difficult to generate widespread snowfall to sea level in central/northern CA. Very cold air aloft sometime happens, but getting the freezing level all the way to the surface takes an exceptional weather pattern. #CAwx

Virtually the only plausible pathway--and the way it's happened on the handful of occasions it occurred in 20th century--is for an extremely cold continental polar Arctic airmass to "retrograde" (move westward, against prevailing winds) from the PacNW interior. #CAwx

It's essentially impossible for a sufficiently cold airmass to survive the overwater trek over Pacific. That's why the upcoming pattern simply does not fit the conceptual model for widespread "sea level snow" in NorCal--it's too moist, with too much overwater trajectory. #CAwx

All that said, major pattern change developing in about 6 days could well be disruptive. Heavy snow accumulations <1,500 feet elev in NorCal could cause significant problems in places that rarely see so much snow. And hail/graupel showers are plausible just about anywhere. #CAwx

I'll likely have a blog post and new virtual office hour session by early next week to discuss this dramatic pattern shift, plus why I think the models are not projecting the correct p-type (i.e., snow vs rain) from a given airmass. Stay tuned! #CAwx