After the last 4 years of drought, and 6 of the last 8 seasons below average for snowfall, I continue to be cautiously optimistic as we look towards next Winter.
The last post was purposely heavy on reasons why a strong El Nino is not a guarantee for big snow. I wanted to put these reasons out there before we started to look at all the signs of why we could see an average or above average snow season, and before putting out any official seasonal forecasts. Four of the last six strong El Nino seasons brought above average snowfall to the Tahoe mountains, but we don't want to overlook the 2 seasons that brought well below average snowfall.
It seems like a lot of forecasters are mainly comparing the upcoming season to 97-98, the last strong El Nino season, and saying that this upcoming season is a guaranteed big snowfall year since we are tracking along the same path as 97-98. In past posts, I pointed out that the warm blob of ocean water in the northeast Pacific may be responsible for the persistent ridge and lack of snowfall the last couple of seasons, and this warm water is still there. During the strong El Nino seasons of 81-82 & 97-98 seasons, the warm pool of water in the northeast Pacific was much weaker, thinner, and further South, closer to the West Coast, so it's tough to directly compare this year with 81-82 & 97-98.
When we put together a forecast that takes into account both El Nino and the warm blob of water in the northeast Pacific, we found that the seasons that most closely resembled the current setup were 86-87 and 91-92, which were moderate El Ninos with the warm blob. Those two seasons saw only 57% of average snowfall. That's not great news, but the thought among a lot of forecasters is that the strength of this upcoming season's El Nino will negate the affect of the warm blob of water, and that would be good news for Tahoe. That said, we haven't seen this situation (strong El Nino + strong blob) often in the historical record, so we can't test that theory very thoroughly.
It is true that this El Nino is tracking similarly to the 97-98 & 81-82 strong events, and is also forecast to peak in December. This is different than during the El Nino of 87-88, which peaked in October and brought only 58% of average snowfall.
Here is a look at the current SST's (Sea Surface Temps) and how they compare to average:
Making things more interesting is that the forecast models are at odds for the SST forecasts for the upcoming season. The European and other models show the SST's staying similar to where they are now.
While other models, like the CFSv2, shows the warm blob being broken down this Winter with cooler water near the coast.
I don't know that I would buy into any specific model, especially the CFSv2 which failed miserably with forecasts during the last 2 seasons. But the point is that Sea Surface temperatures, however they play out, can make a big difference for the weather pattern over Northern CA.
We have been working hard on the Winter forecast here at Opensnow, and have been using our own SST forecasts developed by our climatologist. This data shows a greater chance of a strong El Nino lasting through the Winter, with the warmest ocean water temperatures occuring close to the coast of South America. When we use this updated forecast of ocean water temperatures to forecast snow, we see a better chance of above-average snowfall for the Northern/Central Sierra compared to forecasts we made about one month ago.
In conclusion, I don't think anyone can forecast the snowfall for this or any upcoming season with 100% certainty. El Nino typical brings above average precipitation to our South and below average precipitaton to our North. The strength of El Nino has historically made a big difference for Tahoe, and the SST's over the rest of the Pacific can also make a big difference.
The question is: will the factors that make for a snowy Winter outweigh those factors that could disrupt the pattern and keep the heavy precipitation to our south? I am still riding on the cautiously optimistic train until we get closer to the Winter and see how things continue to evolve.
Also, I am stocking wood and winterizing the lodges I run on Donner Summit extra early this year to be safe. I am more optimistic for big and early snow than I have been since the Fall of 2010.
The graphic above is a peek at the Weatherbell.com snowfall forecast for this season, and you can see the heavy snow from CA across the South and up the East Coast. This precipitation pattern is typical of an El Nino pattern, but is a little conservative in the Northern Sierra.
Personally, I feel comfortable with this forecast made in August, and then reanalyzing and updating the data during the fall.
Fingers crossed, and I'll be posting more updates in the coming weeks and months.
Speaking of additional updates for Tahoe, if you enter your email address below, we will send you the summarized forecast plus some other goodies on Mondays during the fall and on both Monday and Thursday during the season. Hopefully we'll have plenty of storms to talk about and these emails can help you stay on top of them.
Stay tuned ...BA
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