Sunday, February 22, 2015

Limitations of Long-Term Snowfall Records

This snowfall measurement brought to you by The Home Depot
In a season in which we are seeing seeing remarkable snowfalls in the east (a lot of snow) and in the west (not enough), I've been dealing with a number of questions concerning long-term snowfall trends and records.  Answering these questions is sometimes complicated by the warty nature of our long-term climate records.  We have a saying in meteorology that all observations are bad, but some are useful, and this is especially true for snowfall observations, which are probably the worst of the lot.

Here are just a few things that affect snowfall observations:
  1. On what surface was the snow depth measured?
  2. How frequently were observations taken?
  3. Was the measurement taken right after the storm or a couple hours later?
  4. Was the measurement taken right after the precipitation changed to sleet/freezing rain/rain or a couple of hours later?
  5. How hard was the wind blowing?
  6. Was the measurement location sheltered or wind affected?
  7. Was there any tree or building intercept?
  8. Who collected the data?

And, when we compare contemporary observations with those in the past, changes in observing techniques and site characteristics can make a big difference and in some (most) cases, these changes are poorly documented.  In addition, when one goes into the distant past, the measurement techniques can be far removed from what we do today, at least at some locations (e.g., Looking Back and the World 24-Hour Snowfall Record)

Based on the long-term record at the Utah Avalanche Center, we are making a run at the lowest February snowfall at Alta-Guard.  Those observations are collected today by the Utah Department of Transportation, and in the past by USFS Snow Rangers like Monte Atwater (Note: These are not equivalent to the ski area observations which, at least in recent years, have been collected independently).  The previous record is 34 inches in February 1950.  We are still below that, but have some potential to climb closer depending on how things play out the next several days.

Ultimately, comparing the two Februaries is perhaps not an apple to oranges comparison, but a bit of a gala to Braeburn comparison since the details of the snow measurements in February 1950 are probably lost in the sands of time (one of you historians should do some digging).  Assuming we get no more snow, we can probably say with some confidence that February 2015 was worse.  If we do get more snow, and we end up within a few inches of 34, it will be less clear which February is the "winner."  

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