Apologies for a detailed discussion, but we have a crazy and unpredictable storm at our doorstep, and I think a longer discussion than I normally do is warranted.  However, if you just want to see the model snow predictions, they’re 2” to 8”, but as explained below, take any model forecast with a large grain of salt.  

Quick background.  The biggest snow producers for our patrol zone are, in order, (i) upslope snow (i.e., winds from the east) caused by a low pressure south of our patrol zone; (ii) jet streaks; (iii) spillover effect from storms from the west; and (iv) the direct effect from fronts, low pressure systems, etc.  Right at the top of the continental divide, number (iii) above, the spillover effect, is more pronounced and would take top billing, but let’s face it, it’s rare for us to be skiing at the very top of the divide in our patrol zone. 

What makes this upcoming storm so complex is that it has elements of all four snow generators as part of it.

The first part of the storm (Thursday night to midday Friday) will be primarily spillover.  However, there is a strong low that develops to give us easterly winds from early afternoon Friday onwards.  So, the second half of the storm is an upslope.  The exact location, shape, and depth of the low pressure system all affect how much upslope we get, and this is hard to predict.  This is further complicated by the fact that this time of year low pressure systems move quickly towards Kansas (that’s why our biggest storms are in the spring when they don’t move quickly), so one should be somewhat skeptical of a big producing upslope this time of year.

Let’s add another complicating layer.  There will be a strong jet streak overhead on Friday and Saturday.  This will contribute to the snow.  However, the key sections of the jet streak for snow production (left entrance and right exit) don’t look to be exactly over our patrol zone, so the jet streak may not play in that much.  However, models struggle to accurately predict jet streaks snow production.

Two more ingredients to add to this complicated mix.  First, there is a front associated with the storm (which at least the models seem to do a good job of predicting snow associated with that portion).  The final factor is the temperatures.  Most models put the high on Saturday barely over 0 degrees at 10,000’.  As a general matter, the colder one gets, the more snow is produced, but only up to a point.  (Like everything, that’s an oversimplification, but still a helpful one sentence description.)  The cold temperatures would suggest that the models may underpredict the snowfall – but it’s always possible it may get too cold to produce good snow. 

Long story short, this will be a storm that the models will really struggle to accurately predict.  With that said, what are the models calling for?  They’re remarkably consistent, except for the WRF model.  The snowfall numbers are:

8” – Canadian, European, and RDPS Models

7” – American and NAM Models

6” – UK Met Model

2” – WRF Model

Regardless, odds are better for the northern portions (e.g. Rock Creek) than middle and southern portions (e.g. East Portal) getting the most snow.  By way of example, the UK Met Model is putting 10” on St. Vrain mountain and only 6” from Brainerd Lake to East Portal. And for what it’s worth, the American model is calling for 7” in Golden, and the Canadian model is calling for 5” in Golden.

Anyhow, quick discussion of what will happen next.  Starting on Sunday, we’ll be under a ridge of high pressure and more pleasant (boo!) weather for a bit.  Then, another round of snow may start around Wednesday January 5 and extend for the rest of the week.

Retrospective Discussion:

The Monday evening/Tuesday morning system produced 3” of snow per the Eldora Snow Stake Cam, meaning that except for the American Model that was too low, all other models right before the storm did a nice job with the WRF nailing this snowfall dead-on. 

An additional 5” by my count looking at the Eldora Snow Stake Cam fell between Tuesday afternoon and Thursday mid-day.  As such, the Canadian model’s optimism was right on the money, the European and UK Met models did okay, and the American and WRF models happily completely underpredicted the mid-week snow.

Happy New Year everyone!

-Jordan (Thursday 12/30 evening)

Note: Unless otherwise noted, all forecasts are for 10,000’ in exposed areas.  References to American Model are the American (GFS) Model.  References to the Canadian Model are the Canadian (GDPS) Model.  References to the WRF Model are the CAIC WRF Hi-Res Model.  References to the European Model are the European (ECMWF) Model.