Light snow is falling up in the high elevations of the Wasatch thanks to a weak reinforcing cold front. Honestly didn’t expect snow to fall, but cold air like this can squeeze out even marginal moisture. With KMTX radar down, it’s hard to say how much of this we can expect, but I think it’s reasonable to assume it will stop by this afternoon.
A cold day on Wednesday. Mountain snow moves into Northern Utah on Thursday and Thursday night. A break on Friday before more snow for Saturday.
Today (Wednesday) should be the coldest day of the year thus far. At 6AM, temps in the lower valleys are in the 20s with teens and even a few single digits in the mountains and mountain valleys. Highs today will struggle to reach freezing in many locations. It could be much worse however… Current temperature in Laramie, WY (6 hours to our east on I-80) is -19F. Rocky Mountains are blocking the worst of the cold air from making it to Utah.
Right now we have a massive ridge along the west coast of North America. That ridge will be undercut starting later today, bringing us rain and snow tomorrow to northern Utah. I’ve been asked a few times over the last few days what undercutting means. So let me briefly explain…
Here’s the ridge today:
The “warm” colors indicate high pressure. You can see the ridge of high pressure extending all the way up into the Yukon. The red arrows indicate the approximate storm track. Energy is forced well north before diving down into the central US after picking up lots of cold air. This pattern is considered highly amplified.
Here is the forecasted heights for tomorrow:
The ridge gets so stretched that it weakens and allows moisture and energy to “undercut” it. The green arrows indicate the rough path of moisture tomorrow. It’s essentially the atmospheric version of a river oxbow.
So how much snow will we get from this undercutting? Good question. Without dynamics to force the precipitation, it becomes difficult to predict. Snow will start tomorrow morning in the mountains (and possibly valleys as well). The NAM-WRF shows the following precip through midday Friday:
The highest elevations of the Wasatch on this map receive .5 – 1″ of liquid… which would translate to 6-12″… This seems overdone to me. The 4km NAM graph for the Upper Cottonwoods is similar.
I don’t buy this at all. The 12km resolution is much less optimistic and portrays only 2″ of snow for Alta. I think this is underdone. My best guess is somewhere in the middle — 3-6″ with up to 8″ in a few select areas by midday Friday. Snow levels will start out low, near valley floors, but should rise to at least 6,000 feet by Thursday night as the air modifies.
Friday is mostly a break day before the next wave moves in on Saturday. This wave looks to carry much colder air, so snow levels will likely lower back down to all valley floors. This wave has a bit more forcing but may be short-lived. Another 3-6″ (perhaps a bit more in places) will be likely on Saturday.
Overall, wouldn’t be surprised if we saw 6-12″ total by Sunday in favored locations of the Wasatch and Uintas. There is not a lot going for these systems except for their combined long duration. We’ll have moist flow tonight through early Sunday… If we can generate more lift than expected, then we might end up with better totals than mentioned above.
We clear out for early next week as the ridge re-establishes itself. Unfortunately the system that was advertised for mid next week is looking much weaker now in all models. The problem is that because we are only temporarily undercutting the ridge, it immediately returns and becomes difficult to break down again. The ridge is like Voldemort. If you don’t completely kill it, it’s only going to return to haunt you again.
The good news is that models still indicate we will finally break down the ridge by about November 22/23. This is still over 10 days away so a lot can change but I’m hopeful for an active pattern for the week leading up to Thanksgiving.