Wednesday, October 22, 2014

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Anti-Seasonal Outlook, Seasonal Outlook: Part III

What does El Nino mean for us?

By now you have probably been inundated with talk of the “forecasted El Nino” and thoughts of record breaking snowfall and epic years come to mind.  Well if you live in Northern Arizona, Southwestern Colorado or Northern New Mexico get ready, statistically, El Nino is all the rage but what about if you frequent the awe inspiring terrain of the Central Sierra.  For those of us who are lucky enough to have deep blue views of Lake Tahoe in our backyards, El Nino and ENSO in general can be much less of a sure thing.  In fact, except for during strong ENSO years there isn’t a strong relationship between El Nino and precipitation in the Central Sierra (see Figure 1).  According to the National Weather Service’s Sacramento Office, four out of five strong El Nino’s since 1950 have brought above average precipitation to the area.  Meanwhile five out of seven of the strong La Nina’s during the same time period have also brought above average precipitation.  The data and plots can be found here:

Figure 1 [click for larger image]
Figure 1 only includes strong ENSO data back to 1950 and it should also be noted that measurements prior to 1946 might be less accurate and thus the mean total snowfall and maximum snow depths may not be completely accurate.

So what does it mean for this winter???

Well in reality, it just means that we have no way of really knowing what is going to happen this winter in the Central Sierra.   In case this isn’t enough proof check out the October-March precipitation in Reno, NV (Figure 2, compliments of WRCC) and Blue Canyon, CA (Figure 3, compliments of NWS Sacramento) based on ENSO.  There is absolutely no relationship between ENSO and precipitation amount in Reno.  

Figure 2

Meanwhile in Blue Canyon when the October-March is broken into fall and winter, there is more precipitation in winter during El Nino and more precipitation in fall during La Nina.  

Figure 3 [click for larger image]
Bottom Line: The lack of signal between ENSO and precipitation makes it extremely difficult to predict this or any winter's snowfall in the Sierra/Tahoe region. 


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