Does a Stormy Fall Mean a Snowy Winter?

By Yeti \ September 27 2016

This weather discussion and season outlook is provided by our friends at Wasatch Snow Forecast

Utah is coming off its first widespread snowfall of the season – a rather significant early season storm which brought copious precipitation to the state.

Above 8,000 feet, snow accumulated in earnest with 6-12” in the Wasatch Range and up to 15” in the Uinta Mountains.  With warm temperatures expected this week, it’s unlikely that the snow will last long.  Still, the return of winter weather got me thinking…  What, if any, correlation do early season storms have on how the winter plays out with regard to total seasonal snowfall?  I couldn’t just let this question sit unanswered, so I decided to have a look. 

Initially, I wanted to look at other previous storms in September, but found that significant precipitation events are rare, and therefore my datasets were too small to determine a correlation. I decided to use October as our key indicator instead.  Does an active October correlate to a better winter overall? In each of the past two years (2014 and 2015), we saw very little snowfall during October.  The Wasatch Crest Trail was rideable up to the end of the month in each year.  When you think of October snowfalls, perhaps the first thing that comes to mind is October 2004.  If you remember it, you probably remember unreal amounts of powder on Halloween. Brighton opened on October 29.  Alta had 122 inches of snow during the month.  It was unlike anything we had seen before or since.  Just how good was that October 2004? Put it this way, on Halloween of that year, we had 10.8” of Snow Water Equivalent (SWE) at the Snowbird snotel site.  Over our past five Winters (2011-2016), we’ve failed to reach that amount of SWE until much later in the season: 

The black line in the above image indicates that 10.8” of SWE.  It’s taken us until at least the first week of December to reach that point over the past 5 years.  In one case (2012), we didn’t match October 31, 2004’s base until the third week of January! 

But how did that season (2004-2005) turn out after our great start? Pretty darn well.  Alta received 553” from November 2004 thru April 2005.  The snowpack on April 1st, 2005 was at 160% of normal.  Of course, this is only one example.  I wanted to get a larger data set to compare.  Snotel data at Snowbird is available back to the 1989-90 season.  That gives me 27 years of data to play with.  I grabbed the total accumulated precipitation in each October to determine how “active” the month was.  Then I correlated that to how deep our snowpack was on April 1st of each of the respective following ski seasons.  Then, I put that into a scatter plot that would map out the correlation.  This is what I found:

Each dot represents a winter season.  The X-axis is how much precipitation Snowbird received during October leading into that season.  The Y-axis is the total snow water equivalent (SWE) on April 1st of that season.  The top 5 most “active” Octobers are indicated with blue dots.  You can see the previously mentioned October 2004 as the farthest dot to the right on the chart.  You can also see that it has the highest SWE on April 1.  Four of the five most active Octobers ended with a snowpack well above the mean (black line).   On the other side of coin, the five driest Octobers are indicated with red dots.  You can see that our worst snowfall season (2014-2015) is included in these driest Octobers.  However, three of the five driest Octobers actually ended up above the mean SWE on April 1, albeit marginally.  Overall, the end-of-season mean SWE for dry Octobers is only 0.5” below the overall mean – this equates to roughly 6 inches of snowfall.  The mean for the active Octobers is much higher than the overall mean, by 11.3” of liquid.  This is roughly 12-15 feet of snow. 

What does all this mean in the grand scheme of things? It means that there is a fairly strong positive correlation (red line in graph above) between how active October is and how good our ski season is.  It also means that even if we have a dry October, that doesn’t necessarily mean we are doomed to have a bad season.  A very wet and active October, on the other hand, makes it highly likely that our overall snowfall totals for the season will be above normal.  Of course, long range forecast models are just now starting to come into range of the first week of October.  There’s really no telling just what our October will bring this year, but we have already had one significant storm and early indications are that we could have an active start to October 2016.  If we see anything close to what we saw in October 2004, it might mean mouth-watering prospects for the rest of the season. 

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