How unusual is the current low PNW snowpack?

All I want for Christmas ...

... is a dump of 2+ feet!

Also, Amar's famous! From today's Mt. Baker Ski Area Snow Report :

According to a recent in depth study by University of Washington scientist Amar Andalkar, the weather that has occurred through mid December has very little to do with the upcoming weather for the rest of the winter season. He expects the most likely scenario is both near normal snowfall and April 1st snowpack, which is a huge amount of snow and far beyond other regions in the lower 48 states. Keep doing your best snowdance!

Amar's post made me want to make some graphs to take a look at the trend visually.


(numbers indicate years since 1900, thus year 113 was last year).

In general, mid-december snowpack (snow water equivalent) is correlated with April snowpack.  However, there's still lots of season left to make up for a poor start.  One way you might assess that is to look at the correlation between each month, and see how quickly it drops off.  In the graphs below, the brighter the green, the stronger the correlation.  You can see that for Stampede Pass and Paradise, the horizontal band of green at Dec 16 doesn't extend as far as it does when you follow January 16 out to the right (for instance).





I would interpret this as saying that often our heaviest snowfalls will come after the new year. However, once we run out of winter (March 1), we essentially will only maintain the snowpack, rather than have any more chance to build it.

Interestingly, in sites to the east of the crest, early season correlations appear to have a stronger influence on the late season.  At Hart's Pass,  even Nov 16 snowpack appears to correlate with May snowpack.  This may be because it is the coldest (receiving air from the BC interior), and highest site I considered.  This actually might also be true for Stampede Pass, which also seems to have more persistent correlations than Stevens Pass.

Methods:
I downloaded bi-monthly snow water equivalent from snotel using their report generator .  Records were from 1981-December 2013, except for a couple sites where records started in the mid-80s.
I defined the water year to be July1-Jun 31st (which I think is standard?).  If anyone is curious, here's some links to the data I used to generate the plots.

awesome analysis Amar, I love geeking out on hydrologic data. Thanks for putting the numbers to it.

Nice supplement andyrew...just FYI water years go from Oct1-Sept30. Roughly correlates to the break point at which rivers ceases running from the previous winter's snowpack, or vice-versa, when the rivers could begin running from fresh snowfall.

In the meantime, less bitching, more praying for snow!

Andyrew,
There has been a short term (<10 yr) shift towards later-season (post March 15) snowpack accumulation that would get buried in the noise of a longer historical analysis. IIRC, this affect appears to be more pronounced during El Nino years. Last time I checked (at least a year ago) no one in the field really knew why this was, but I believe a play between the various pacific ocillations (PDO/IPO) was a suspect.

Another analysis that would be fascinating is your correlation extended to basin-wide SWE models. Sometimes these tell a different story than individual SNOTEL sites because they are less susceptible to single-point conditions. I feel like your Hart's Pass analysis hints total SWE for a large portion of the Cascades may correlate rather strongly, because so much of our terrain is higher than the average SNOTEL site.

I love that some real analysis is going on at TAY!

While Amar’s analysis of past snowfall history is interesting, it should not be construed to imply a most likely outcome of this year’s snowpack.  What it does show is that this winter is similar to winters that have been observed in the past.  If you believe the climate modelers, what has been normal or typical in the past will become very abnormal in the near future. Correlations made now with past weather events will become meaningless in predicting the future.  It is quite possible that within the next few years we will begin to notice a very different regime of temperature and snowfall in the Cascades. That change could already be happening.