Tuesday, November 1, 2022

Ten-Day Snow Potential

The next ten days have tremendous potential to transform the early season skiing potential in the central Wasatch Mountains.  

We've already been blessed with a good October. The Snowbird SNOTEL sits at 3.9" of snowpack water equivalent, which is 390% of median. The warmth of the past few days has caused some snow losses on south and west facing slopes, but has also probably limited depth-hoar formation, which may help us stave off a persistent weak layer (note that I was not in the field yesterday or today so this is not an observation and it does not mean that surface facets, near surface facets, or other weak layers could prove problematic when the snow begins tomorrow).  

A best-case scenario now is for the snowpack to deepen, opening more terrain for touring and giving us some additional insurance against depth-hoar formation.  

Tomorrow is looking good.  A cold front is expected to stall over northern Utah, giving the central Wasatch a prolonged period of snow.  The situation at 1500 UTC 2 November (9 AM Wednesday) shows the 700-mb temperature contrast associated with the cold front parked right over the Central Wasatch.  Additionally, the flow in this area is confluent, with 700-mb (about 10,000 ft) inflow between south-southwesterly flow over southeast Utah and west-southwesterly flow over northwest Utah aligned right along the front and temperature contours (see lower left).  

Such a pattern is what meteorologists call frontogenetical, as it acts to strengthen the front.  Additionally, the vertical circulations associated with such a frontogenetical pattern are often favorable for precipitation, and the GFS both stalls the front and strengthens the associated precipitation during the day tomorrow.  

By 0600 UTC 3 Nov, the GFS has laid down just over 1" of water equivalent in the upper elevations of the central Wasatch.  

The GFS terrain is smooth, so it does not capture some of the fine-scale characteristics of precipitation in the central Wasatch.  I have noticed that it often produces more snow at the Park City resorts than Alta (as is the case above), even though that is typically not the case.  The Euro is also near or just over an inch through 0600 UTC 3 Nov near or just east of the Wasatch Crest.  

On the other hand, the HRRR has better terrain representation and puts out 1.33" at Ala Collins, 1.1" for Canyons-Daybreak, and 0.76" for Deer Valley-Ontario.  

There is some potential for orographic or lake-effect snow continuing Wednesday night and Thursday.  Right now, the flow directions and depth of the instability being advertised by the models are such that I don't expect this to be a major accumulation period for the central Wasatch, but that could change if the flow direction shifts. 

The latest 12Z GFS-Derived Little Cottonwood forecast just came in as I type this and it is consistent with the forecast above.  About an inch of mostly frontal precipitation (water equivalent) through  midnight Thursday and then a bit more through early Thursday morning and Thursday during the day.  

Applying our snow-to-liquid ratio algorithms to that gives about 13" of snow through midnight Thursday and 17" by Thursday night.

Based on these forecasts, I expect 10-18" of snow at Alta Collins by midnight Thursday and then perhaps another 3-6" after that through the Thursday afternoon.  

The forecast beyond that is also optimistic.  Through 5 PM next Tuesday, another 1.25 inches of water in the GFS.  Other models vary, but overall the pattern is one in which I expect to see more added to the snowpack.

Remember that the resorts are de facto backcountry right now.  Avalanche conditions will be changing dramatically tomorrow.  Let's be careful out there.    


  1. Loving the "Wasatch Front" graphics - are those new, or have I just been missing out for years? Either way, thanks very much for that.

    Looks like things changed overnight with the GFS favoring Deer Valley and the HRR favoring Powder Mountain? Seems like some atmospheric (or computational) weirdness going on.....

    1. Currently the HRRR and the GFS are different models. They use different approaches to divide up the atmosphere and produce a forecast. They run at different resolutions and the GFS is a global model whereas the HRRR only covers the continental US. Their forecasts can differ some, but you can't clearly count on one over the other. Any given forecast is a bit like a NASCAR race in which some teams might be better than others, but on any given day, one can win.

      In the central Wasatch, the GFS precipitation maximum is often too far east. This is due to its inadequate terrain resolution. I think we will see that more clearly with the new graphics.

      Yes, those graphics are new. I updated most of the products on weather.utah.edu over the summer, deleting some but adding many new ones.

    2. Hence the aggregating - I totally get it - we actually do something similar in my field of injury biomechanics using human body FE models.

      Jealous of the time you had to learn python and update all your code - I know full well what a lift that was - wish I had the time (or even the mental capacity)

      That said - is it within your skill set to make the iso contours slightly transparent so we can make out the terrain underneath? As a none-paying consumer of all your hard voluntary work, that would make me happy :)

  2. This is happening because I am trying to get concrete poured in my driveway. Now that it's all torn up there are no dry days for pouring concrete. You're welcome, I guess.

  3. somebody had to give it up

  4. 11" at my house in Park Meadows. And single digit temps this morning. Brr.