A lot of people ask me why it seems to be that we never get a good start to the ski season in November. We all have memories of good starts to the ski season. Certainly it was better in the "good old days." But was it?
We have relatively short records of November snowfall in the Wasatch Range. There are actually records for Silver Lake/Brighton going back to 1916, but there are a large number of missing days prior to 1942, in some intermediate years, and then again since 2000. Thus, I'm going to use Alta Guard, which has a shorter but more continuous record of November snowfall, with only 1972/73 missing.
A look at the November snowfall shows three fairly distinct periods (the plot below is labeled by season, so 1945/46 denotes November 1945). Pre 1982/83, 1982/83 to 2003/04, and post 2003/04. The middle period of from 1982/83 to 2003/04 is the fat period when there is a high frequency of heavy November snowfalls and the six largest November snowfalls on record. The running five-year average (black line) was near or even above 100 inches during the middle of the period. For many people, I think these are the "good old days".
But those years were not reflective of most of the record. For the pre-1982/83 period, the five year running average was between about 45 and 70 inches. From 1953/54 to 1963/64 it was near 50 inches. That ten year period compares well to the 2008/09 to present period when we've been running around 50 inches. Maybe the old days weren't really so good?
For kicks and giggles, the red line is a linear trend line on the snowfall. It has a very slight downward trend that I suspect is not statistically significant. It sometimes makes sense to use linear trends, but for snowfall, which exhibits a great deal of year to year and even decade to decade variability, linear trends over such a short period of record make little sense. The fat years in the middle were not the result of a long-term trend, but instead what meteorologists refer to as decadal-scale variability, something that is very apparent if one looks at paleoclimate records over the western United States, such as tree rings, which show slow decadal-scale variations from wet to dry periods. Our instrumented record for the Wasatch Range is too short to identify these. The period from 1982/83 to 2003/04 (give or take a few years at the end) is one of the wet periods.
A critical question, however, is whether or not our recent string of poor November snowfalls reflects something new, namely human-caused climate change. Alternatively, are the odds of poor November snowfalls increasing due to human-caused climate change?
I don't have the time to answer that question today, but if you want some insights, see some of my older posts:
Very good post! Most people have terrible memories for past weather; always good to show the numbers.
ReplyDeleteVery interesting... 5yr trendline especially useful for visualization.
ReplyDeletePerhaps if you have the time and details you might be able to post on why CLN is so whacked? -327.7F at 0900, lots of caution and suspect readings... what kind of instrument issues cause this, how does one clean and use this kind of data for research, and how do they commonly get the instrumentation working again? I'd imagine this problem causes a few other knock-on effects that make things interesting to deal with on the analysis side.
I don't work with those instruments, so I don't know the answer to your question, but observational errors are something that must be dealt with continuously in my field, sometimes well, sometimes not so well. Quality control of observations is a critical part of the forecast process. Paraphrasing George Box, "All Observations are Bad, but some are useful."
DeleteI know we're looking at snow pack in November at Alta Guard but I think a better picture would be just precip in general. I think it was well into the 50 degrees F last week at Alta and that would have come down as rainfall not snow fall.
ReplyDeleteAnother thing to look at would be the avg. November temps here too.
See the links at the end of the post. Not specific to November, but applicable.
DeleteThere are no long-term records identifying precipitation type, snowpack depth, or snowpack water equivalent at Alta Guard or Alta ski area, so we cannot do such an analysis specifically for that location.
Good historical perspective.
ReplyDeleteThat 1953-1964 drought period also shows up in Los Angeles rainfall and Chilean snowfall in the Andes east of Santiago.