A Storm With Unanticipated Intensity

Alta, Monday Afternoon.  Photo: Jake Hutchinson

On Monday, it was almost as if Mother Nature had stored up two weeks of snow and decided to see if she could puke it out in just a few hours.  Snowfall rates were high and sustained throughout the central Wasatch.  I felt like a kid in a candy shop watching the automated snow depth sensors (about the best I can do when I can't be there).  It was quite an event, and it exceeded all meteorological expectations.

I had the good fortune of not making a forecast for this event and I can tell you if I did I never would have gone for 16 inches (and 1.28" of water) in 10 8 hours (from 9 am to 5 pm) as was observed at Alta-Collins.  Official forecasts called for a 70% chance of 3-6" in the 5 am to 5 pm period, and a 30% chance of 7-9".  Note that they were calling for more after 5 PM, so overall, this was expected to be a pretty big event, but the early onset and intensity of the snowfall on Monday were not anticipated.

Source: NWS

The NWS forecast is specific with regards to time.  Although I couldn't find other forecasts online specific for the 5 am to 5 pm time period, I did find that most issued the night prior to the storm were calling for storm totals of no more than 15".  I might have gone for 4-8" in the 5 am to 5 pm period.  I am 100% certain I would not have gone for a foot by 5 PM.  

Such high intensity events are very hard to forecast, yet they are very important for public safety.  Avalanche danger escalates rapidly in high intensity storms, as occurred on Monday, and highway maintenance is far more difficult.  

We have a saying in meteorology, "live by the models, die by the models" and in this instance, none of the models were calling for such high snowfall rates.  Even the 4-km NAM, well known for overforecasting, was going for a storm total of about 9 inches through Tuesday morning and didn't start the precipitation in earnest until Monday afternoon when it started at 9 am.  

Thus, we clearly have more work to do, but you probably knew that already.  

I do, however, have a forecast that is sure to verify.  Unless we reach "too much of a good thing" accumulations tonight, you won't be seeing a new post on this blog Tuesday morning.