2021 likely a below average snow year

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c9h13no3
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2021 likely a below average snow year

Post by c9h13no3 » Tue Feb 16, 2021 11:56 am

We're hitting the last half of the wet season, and the current snowpack is around ~50% of the April 1st average, as of 16-Feb. The current long range forecast for Feb-Mar-April from the NOAA climate prediction center has the La Niña pattern holding, giving most of California a drier than average outlook. So we're looking at a below average snowpack, but nothing terribly out of the ordinary.

The summer of 2021 will probably look like 2020/2018/2013/2012, which is pretty much business as usual. COVID is doing goofy things for the roads opening, so no guarantees there, but I'd expect early to mid-May for Sonora Pass. Peak melt will probably be the usual mid-May, mosquitoes should taper off by late July, and wildfires will be a problem late season.


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Wandering Daisy
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Re: 2021 likely a below average snow year

Post by Wandering Daisy » Tue Feb 16, 2021 1:16 pm

CDEC data today, snow water equivalent;

Northern Sierra 54%
Central Sierra 59%
Southern Sierra 40%
State-wide 69%

Much more snow in northern coast ranges brings up the statewide number.

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SirBC
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Re: 2021 likely a below average snow year

Post by SirBC » Tue Feb 16, 2021 6:00 pm

Is there a website that lists the percentage of normal for each year? Something along the lines of:

2020: X % normal
2019: Y % normal
2018: Z % normal
etc...
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Re: 2021 likely a below average snow year

Post by Wandering Daisy » Tue Feb 16, 2021 6:34 pm

http://cdec.water.ca.gov/snow/current/snow/index.html

Probably something here if you look around. Note that CDEC is designed for water resource management, so most data is for water equivalent, not snow depth. Nevertheless, this web page has a lot of good stuff.

The Tioga Road plowing report has what you want, but it is specific to Yosemite.

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Re: 2021 likely a below average snow year

Post by brandoge » Tue Feb 16, 2021 7:50 pm

I enjoy reading the Tahoe Open Snow forecast site, and they put together some nice statistical data at the end of each ski season about the snow pack. Below are a few graphs showing historical data for rainfall and snowfall for a given season (I think rain seasons are measured October-October). Looking at the graphs is interesting to me because it seems like our snowfall has a high variance, some years will be big while others small but most are quite different from average.
historical_snowfall.jpg
historical_rainfall.jpg
Here's a link to last year's report from Bryan Allegretto where I got the graphs: https://opensnow.com/dailysnow/tahoe/post/18867
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Re: 2021 likely a below average snow year

Post by mkbgdns » Tue Feb 16, 2021 9:16 pm

annual sierra snowfall has more of U-shaoed distribution than a "normal" (random) distribution, because it's not random, but dependent on cycles of ocean temps, the blocking high, etc. almost no winters are "average" (whether you measure central tendency as mean or median).

oh, and Daisy, you cited the regional percentages of April 1, but the statewide percentage as of today's date. doesn't make sense for the average water content in the sierra to be significantly lower than that of the state, since most of the state's water is in the sierra. state water supply currently 53% of April 1 average

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c9h13no3
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Re: 2021 likely a below average snow year

Post by c9h13no3 » Tue Feb 16, 2021 11:04 pm

mkbgdns wrote:
Tue Feb 16, 2021 9:16 pm
annual sierra snowfall has more of U-shaoed distribution than a "normal" (random) distribution, because it's not random, but dependent on cycles of ocean temps, the blocking high, etc. almost no winters are "average" (whether you measure central tendency as mean or median).
Yeah, pretty much this (not really U-shaped, but not normal either). The snowpack this year is below average, but still typical. Most years will be "below average", with some 2017/2019/2011 years that really skew the average high. This isn't a 2015 situation where you could drive across Tioga pass in January.

Was sharing this mostly for planning purposes.
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Re: 2021 likely a below average snow year

Post by TurboHike » Wed Feb 17, 2021 6:39 am

SirBC wrote:
Tue Feb 16, 2021 6:00 pm
Is there a website that lists the percentage of normal for each year? Something along the lines of:

2020: X % normal
2019: Y % normal
2018: Z % normal
etc...
I use this site: http://cdec.water.ca.gov/snowapp/swcchart.action

You can choose the years at the top of the page, then click "draw chart".

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Re: 2021 likely a below average snow year

Post by Wandering Daisy » Wed Feb 17, 2021 10:14 am

The website cited to turbohike is the one I got my statistics off of. I really like ALL of the CDEC data. Some is not the most user-friendly but I appreciate that this website, used a lot by water supply professionals, is also available to the general public. I think it is an example of really good work done with my tax dollars. I sure hope it remains well supported in the future.

I like it because you can put up many years and compare, both to annual % average and also look at the timing of the snow and spring melt. The spring melt is important to me for evaluating early season backpack trips.

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Re: 2021 likely a below average snow year

Post by SirBC » Wed Feb 17, 2021 11:04 am

Thanks all for the snow pack sites, that is what I was looking for :)
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