Friday, December 22, 2017

The Next Storm Could Surprise

Based solely on the large-scale pattern setting up for tonight and Saturday, one might not be very enthused about our snow chances.  There's a huge, high-amplitude ridge centered over Alaska and a ridge upstream of Utah with a short-wave trough moving across Montana.  Show this and nothing else to 10 meteorologists and ask them what will happen in Utah and they probably would say not much.

However, the Devil is in the details, and those details suggest this storm could surprise.  The pattern is highly unusual because of the size of the ridge over Alaska, and we end up in a situation in which two airmasses of dramatically different origin are coming together, one from the subtropics, the other from the high latitudes.  This leads to a strong mid-level front and plume of moisture that extends inland across Utah.

By itself, that probably wouldn't do much, but we have something going for us, the Wasatch Range.  The GFS forecast above shows that the terrain effects are very important, with strong modulation of precipitation as the moisture plume runs over the various topographic features of Oregon, Idaho, Utah, and Colorado.

So, what do the models spit out?  I'll focus on the period through 0600 UTC 24 December (11 PM MST Saturday), although the bulk of the precipitation is expected to fall tonight and during the first half of the day tomorrow (the end of the precip is a bit ill defined with some models calling for it to last longer than others).

For Alta, the 0Z Euro puts out about 0.4 inches of water, the 6Z GFS is just over an inch, and the 6Z NAM 0.8".  The downscaled SREF plumes below show a pretty wide spread, enough to give serious heartburn to any meteorologist, with a range from 0.1" up to 1.75" by 0600 UTC 24 December.

Before it retires in another week or so, we can also have a look at the NCAR ensemble, with a range from about 0.5 to 1.4 inches through 0000 UTC 24 December (5 PM Saturday).

Ultimately, much will depend on the location of the plume and the evolution of the flow.  The Euro and low-end of the ensembles say keep your expectations tempered, but even 0.4" of water would make this the 2nd biggest event since the 3 December storm that put down a season-saving 1.08" of water at Alta.  It's going to help.  Some of the ensemble members are putting out amounts much higher than anything we've seen in a while.  Those are not high probability possibilities, but they could come up with a lucky role of the dice.  Thus, let's see what happens and hope this storm surprises.

Skinny skiers should be happy as a little will go a long ways at Mountain Dell and North Fork Park and the precipitation should be all snow at both locations.

1 comment:

  1. Nice synopsis with the subtle upper air pattern. Have a Merry Christmas!