Thoughts On The Upcoming Storm(s)

12/19/21 Sunday 7:10 am

I have spent a lot of time looking at models over the last 24 hours. Sometimes I need to try to sort out what I think I know from what I really don’t know. What I think I know at this point is that mountain locations above 8,500 feet are going to get a decent amount of snow between Thursday, December 23rd, and Tuesday, December 28th. The latest trend I am seeing is that travel should not be a problem during the daylight hours on Wednesday. I am still not sure about snow levels, how much precipitation will fall in the lower elevations, or when or if there will be a break between storms.

In the past, I have talked about my reliance on the ensemble weather models versus the operational models. I have explained that each major weather model I reference has an ensemble family of many members. The members each have slightly different data inputted into them.

The goal is to allow for changing weather conditions over time. The average output of all of that is called the ensemble mean. The general rule is that you rely on ensemble models until about 72 hours prior to the onset of the effects of the arriving storm.

That sounds good on paper, but if you follow this method 100% you can miss trends that are occurring in the operational models. Not only that, ensemble models are very low resolution and struggle with our terrain. For me personally, if I see excellent model agreement among the operational models, I am going to rely less on the ensemble mean solutions.

Right now, I am seeing a lot of problems in the “more reliable” ensembles than I am in the operational models. For example, the latest ensemble run of the Canadian model shows snow starting early Thursday morning and continuing every day through January 4th. January 4th is the end of the 16-day run time of that model. I would not mind if that happened, but it seems highly improbable. Ok, that’s enough with the ensembles already…

In my last post, I ended by saying I hoped that the Euro and Canadian models would stay “on the rails” with their forecasts. The Canadian and Euro model runs that came out after my last post were very ambitious. The overnight runs backed off a bit. The GFS run from that same time slot was anomalously low in precipitation, its next two runs recovered nicely.

Here are the latest operational runs from those three models, immediately followed by their previous model runs. This shows the precipitation through December 25th only.

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