Thursday, January 29, 2015

The Snow Potential (or Lack Thereof) from Brush By Storms

If the forecast from the 0600 UTC GFS verifies, the central Wasatch will remain sandwiched between storms to our south or storms to our north over the next week, getting just what we can from brush-by precipitation events.

First we have the system moving into the southwest today and giving them precipitation through Saturday.  We are expected to be on the northern edge of this system.  

Once that system moves downstream, the we get brushed by systems to our north.  Again, we're right on the edge of the action.  

In situations like this, a slight shift in storm position can make a difference and I like to consult forecast ensembles to get an idea of range of possibilities.  Let's start with the Short Range Ensemble Forecast System (SREF), from which we can examine the potential for precipitation as the system affecting the southwest brushes by us the next couple of days.  There are 22 members of this ensemble, of which only 9 produce any precipitation at all at the Salt Lake City grid point, with two generating over 0.15".  

A forecast like that suggests we may see a few valley showers and mountain snow showers tonight through early Saturday morning, but accumulations will probably be minimal.  The odds of a few inches during this period in the upper Cottonwoods aren't zero, but they're pretty low (less than 10%).

For the next week, we can look at our ensemble of downscaled forecasts from the North American Ensemble Forecast System (NAEFS) for the 7-day period beginning yesterday afternoon and running through next Wednesday afternoon.  As can be seen below, the probability of at least 6 inches of total snow accumulation in this period is fairly low, maxing out in the central Wasatch at about 60 or 70%.  The odds of more than 24 inches isn't zero, but it's less than 10%.  We would need one of those systems to shift southward for that to happen.  

Here's another way to look at it.  Below we've extracted the accumulated water equivalent (top) and snowfall (bottom) from the downscaled NAEFS ensemble members for Alta.  The vast majority of the members are producing 8 inches or less of snow for the entire period.  There is one member, from the Canadian Ensemble, that is very excited about a huge storm late in the period (this always seems to be the case with the Canadian Ensemble.  The Canadians clearly love snow!).    

So, looking at all these ensembles, the most likely forecast scenario for the next week (i.e., through Wednesday) in the central Wasatch is that we continue to see drier than average weather, with just a few periods of snow showers or snow as we are brushed by systems to the south or north.  Although not zero, the odds of a major storm are low and would require a more direct hit than forecast by most of the ensemble members.  

REI Talk Tonight

I'll be giving a talk on my book Secrets of the Greatest Snow on Earth, including a look at topics such as the real reasons why Utah snow is so great, where to find deep powder around the world, and the avalanche history of Little Cottonwood Canyon, at 7 PM tonight (Thursday) at the Salt Lake City REI (3285 E 3300 S).  The talk is free and open to the public, although REI does request that you register by clicking here.  My friends from Weller Book Works will be selling copies of the book if you haven't picked one up yet.  I'll be happy to sign any copies you bring or buy at the event.  


  1. Jim,
    I have a suspicion that the publication of "Secrets" may have jinxed our ski season in the Wasatch. It's not a very well understood phenomena. I would like to be the first to site it with the name "Secrets of the Greatest Snow Oscillation". :)
    I really can't complain though. In my visits to ski in Park City, I have experiences some very nice snow conditions, especially the time between Christmas and New Years. Even last week, conditions were for the most part very good.... just not what I am accustomed to expect from skiing the Wasatch in January. Wish I knew how to create more chaos to change the long wave pattern. :)

  2. What does your gut tell you about the remainder of the season? Once we start down this path of crazy weather are we destined to deal with it for the remainder of the season? Or could we return to normal at some point and enjoy at least a month or two of good snow?

    1. I don't trust my gut, which is I why I use models and statistics :-). The dice aren't strongly loaded one way or the other as we look beyond a week or two. The CPC actually gives us slightly better odds of above average than below average precipitation, but I would call it even steven and say the odds of below, average, or above are fairly comparable. In other words, I don't know what to expect.

    2. I'm going to take that as a positive reply and keep hoping that winter will return. Thanks for sharing your thoughts. Your gut, however, probably knows more than you give it credit for!

  3. Hey Jim, is the title supposed to say "lake" or "lack"?

    1. Lack! More poor typing! Thanks for noting it. I did a quick correction.

  4. If you have not already, please encourage all readers to make a sacrifice to Ullr. Clearly he is angry and he needs satiating. I will give him beer and whiskey, and weed. That should help, I hope.

  5. Jim, in case you don't see my tweet due to privacy settings: "@ProfessorPowder Good call on what you deemed a "monsoon" several blogs ago. Getting pcpn from the S has got to be unusual midwinter in Utah"

    Chris Doyle (the Olympic guy in Vancouver). Still remember the great help you guys gave us.