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Historic data for first Winter Storm Date

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Historic data for first Winter Storm Date

Postby fishmonger » Tue Apr 05, 2016 2:53 pm

This fall I am hoping to do a late fall trip to the Sierra. My window of opportunity is somewhere between middle of September to middle of October, but I need to settle on dates in the near future. I lean to a date as late as possible, risking snow, but obviously hoping to get by without a massive snowstorm and in return experience near total solitude on the trails.

Currently I hope to enter the mountains around Sept 27 and exit around Oct 14 (to make use of the moon light during that second week in Oct to extend my hiking hours)

Does anyone know where I could obtain dates of the last 10-15 years of snowfall with amounts by date? My own memory tells me there were few storms before Oct 15. Am I wrong?



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Re: Historic data for first Winter Storm Date

Postby maverick » Tue Apr 05, 2016 3:43 pm

See if this helps, it will not give you data from the High Sierra itself, but surrounding communities like Mammoth, Bridgeport, Yosemite Valley and Grant Grove for example, but could still be helpful in seeing when storms dropped snow on certain dates in specific years. http://www.theweathercollector.com/
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Re: Historic data for first Winter Storm Date

Postby Snowtrout » Tue Apr 05, 2016 5:00 pm

Not sure if this would work but mammoth mtn has been tracking monthly snow data since 1970. If anything, it can give you an idea how much snow has fallen in the past and could fall in the future.

http://www.mammothmountain.com/winter/m ... nd-weather

Then click on snow history.
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Re: Historic data for first Winter Storm Date

Postby dave54 » Tue Apr 05, 2016 5:22 pm

The issue is not the first snow, but the first snow of sufficient depth and duration to hinder travel. A light dusting that quickly melts may not be a problem.

I did something similar for my grad work, determining the probability of a fire ending precipitation event in the Caribou Wilderness. Using 30 years of weather data into the fire spread model, then into a probability distribution. Anyway the 50th percentile date for the Caribou Wilderness was Sept 27, but the event could be rain or snow.

It would be later further south.
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Re: Historic data for first Winter Storm Date

Postby rlown » Tue Apr 05, 2016 6:22 pm

this isn't what you want most likely. http://cdec.water.ca.gov/selectQuery.html

You can pick a station and go back as far as it lets you. I'm sure there's a clever way to pick 3 or 4 stations in the area you want, or download the data for each and put in an Excel spreadsheet and pivot as you wish.
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Re: Historic data for first Winter Storm Date

Postby fishmonger » Wed Apr 06, 2016 6:32 am

rlown wrote:this isn't what you want most likely. http://cdec.water.ca.gov/selectQuery.html

You can pick a station and go back as far as it lets you. I'm sure there's a clever way to pick 3 or 4 stations in the area you want, or download the data for each and put in an Excel spreadsheet and pivot as you wish.


I exported all the snow data from 2000 on for various sensor stations. I think only one year showed significant snow water content in mid October, which I feel can't be right. Many sensors have missing data for months at a time, or are simply not recording before Dec 1. However, when I did see snow depths, it was usually in November or even December (a the lower elevations where snow is being recorded).

Perhaps looking for rainfall events at those elevations is really what I should be looking at, as above 11,000 feet, most if not all of the rain that time of year is in fact snow, just that they don't sent John Dittli et a. up to the snow measuring courses before December to capture the high elevation levels. They only care about the aggregate for water planning so Dec 1 is fine as a starting date.

I will have a look at the Mammoth snow record. I now recall seeing that table in 2010 when snows went to new record levels. The ski folks definitely should care about the first day of the year that leaves some white on the mountain.
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Re: Historic data for first Winter Storm Date

Postby fishmonger » Wed Apr 06, 2016 6:52 am

Snowtrout wrote:Not sure if this would work but mammoth mtn has been tracking monthly snow data since 1970. If anything, it can give you an idea how much snow has fallen in the past and could fall in the future.

http://www.mammothmountain.com/winter/m ... nd-weather

Then click on snow history.


It helps to some extent - don't have the day, but I do see the monthly total

Code: Select all
               
Season   Sep Oct
1995-96   0   0
1996-97   5   25.5
1997-98   1   0
1998-99   5   0
1999-00   0   0
2000-01   0   38
2001-02   0   6
2002-03   3   0
2003-04   6   0
2004-05   0   85.6
2005-06   0   0
2006-07   0   4
2007-08   10   1
2008-09   0   10
2009-10   0   34
2010-11   0   10
2011-12   0   19.5
2012-13   0   18
2013-14   0   10
2014-15   0   0
2015-16   0   0



This shows Oct snow in 8 out of the last 10 years. Given it probably is more likely to snow later in October than early, and there is only one significant Sept snow event in those years, it probably isn't a big leap of faith to assume that less than half of those snow events happen in the first half of the month. Sure, there's going to be a good chance, probably 33% or better, but it's not that significant. Plus, I'd be further south in the later part of my hike, again decreasing the precip chance.

I could easily go a week earlier, or two, but I am actually looking at the moon phases during October, and the moonrise and illumination data for early October is perfect for my planned hiking pattern, which given the short days in Oct will require some significant night walking. With a near full moon, I will be able to see much better and make more progress. This, combined with the more or less deserted JMT highway adds up to enough of an argument to risk getting stuck in a tent for a while should it actually storm. I'll have a sat phone and daily weather updates anyway, so it won't catch me by surprise, allowing me to make an abort decision well before I get bogged down in deep snow, at least getting closer to exit points before it gets thick.

Still would like to locate those exact dates these recent October snowfalls actually happened. Perhaps reviewing the archive of the Whitney Webcam on the whitneyzone forum would be a source, but that's not publicly accessible. Maybe it should be... gotta go talk to Steve and maybe we can rig up some database driven camera archive, should he still have all files... I have about 100 of those files here on the laptop and use them as screen backgrounds. Of those, a number are October shots and show snow on Whitney including date in the image.
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Re: Historic data for first Winter Storm Date

Postby longri » Wed Apr 06, 2016 8:54 am

There is snow course daily data (snow wc, precip, temp) going back to 1979 at this site:
http://wcc.sc.egov.usda.gov/nwcc/rgrpt? ... t&state=CA
The stations are more northerly, although the one near Virginia Lakes (~9500 ft) could be used as a proxy for the Sierra.

For example, I can attest to the fact that there was snowfall in the Sierra on September 1, 2000 (SEKI at 10,000'). I'm 100% certain of the date and here's a photo:

Image

I heard there was 5-6 inches of snow at Donner Summit as well so it wasn't a local storm. Looking at the Viginia Lakes precipitation data it appears there was half an inch of water that day. (Edit: I misread the table. It actually says zero rain for that day.)

For what it's worth.

I've also been frustrated trying to find historical weather data. I have to believe it exists but isn't packaged for general consumption. If you find better sources post them, please?

Of course you can't predict the future based on the past, particularly since the climate is a moving target. But at least it's nice to know. I hope your trip goes well. That's got to be one of the best times of the year to be out there.
Last edited by longri on Wed Apr 06, 2016 6:42 pm, edited 1 time in total.
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Re: Historic data for first Winter Storm Date

Postby rlown » Wed Apr 06, 2016 10:29 am

fishmonger wrote:I exported all the snow data from 2000 on for various sensor stations. I think only one year showed significant snow water content in mid October, which I feel can't be right. Many sensors have missing data for months at a time, or are simply not recording before Dec 1. However, when I did see snow depths, it was usually in November or even December (a the lower elevations where snow is being recorded).


Several of the sensor towers get hit by lightning every year, so.. I reported the TES station being down this year. They didn't know it was down, but they can't fix it until the snow is gone :) I use the DAN station at 9800' now to just gauge what is happening up and around Tioga Pass. http://cdec.water.ca.gov/cgi-progs/staM ... ion_id=DAN

Some are manual sensors meaning monthly data only, by human observations where possible. I do like your rain strategy.
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Re: Historic data for first Winter Storm Date

Postby fishmonger » Wed Apr 06, 2016 1:44 pm

longri wrote:There is snow course daily data (snow wc, precip, temp) going back to 1979 at this site:
http://wcc.sc.egov.usda.gov/nwcc/rgrpt? ... t&state=CA
The stations are more northerly, although the one near Virginia Lakes (~9500 ft) could be used as a proxy for the Sierra.


Good starting point, even though the locations are limited. I picked Truckee/Donner Pass area as a likely worst case scenario measurement location (I really only care about Yosemite to Whitney), although when I looked at more accurate Mammoth data, I realized that there can be snow in Mammoth when it doesn't even rain in Truckee. I will update with other sources as I find them.

Interesting to see that even though the climate clearly warmed up over those decades, there's no clear trend as to when it snows first, other than significant snow accumulation before Oct 15 is a hit and miss - 50/50 chance I will get snowed on this fall. I think I'll just plan for it and take that chance (great photos, long boring days in tent).

The more accurate data from 2002 onward available for Mammoth shows that when it did snow heavily (3-4" water content for 30" of snow), it sometimes only took 5 days for most of that to melt away. Smaller storms with less than 2" of snow water equivalent when followed by sunshine will melt away completely in just 2 days. The really big events are storms followed by a second storm before the first wave is melted, and that only happened once in recent history (2004 late in the month). Even the big 10/13/2009 4" water content storm melted down to very dense snow in less than 2 days - see this plot of snow depth and density over a 6 day period

Image

10/31/90 0.1 (Sonora Pass)
10/15/81 0.3" (Sonora Pass)
10/26/82 0.4" (Truckee/Donner)
10/07/83 0.1" (Sonora Pass)
10/07/84 0.2" (Sonora Pass)
10/21/85 0.4" (Truckee/Donner)
10/12/86 0.9"' (Sonora Pass)
10/09/87 1.0" (Sonora Pass)
10/02/88 1.2" (Sonora Pass)
10/03/89 0.4" (Truckee/Donner)(Mammoth monthly)
10/31/90 0.0"
10/24/91 1.5" (Sonora Pass)
10/29/92 0.4" (Truckee/Donner)
10/27/93 3.5" (Sonora Pass)
10/08/94 1.0" (Mammoth ski resort earliest opening date ever, guess 1" as no record of snowfall)
10/16/95 0.5" (Sonora Pass)
10/05/96 1.1" (Sonora Pass)
10/31/97 0.0" (0.1" at Mammoth, day unknown)
10/19/98 0.5" (Sonora Pass)
10/31/99 0.0"
10/26/00 0.3" (Sonora Pass)
10/31/01 0.0"
10/20/02 0.8" (Mammoth)(Mammoth monthly)
10/06/03 0.1" (Mammoth)(Mammoth monthly)
10/18/04 0.15" (Mammoth)
10/31/05 0.0"
10/12/06 0.4" (Mammoth, rain precip)
10/06/07 0.15" (Mammoth)
10/31/08 0.0"
10/13/09 3.5 " (Mammoth) Big storm for more than one day video shows how it snowed in Yosemite on that day
10/07/10 0.15" (Mammoth)
10/07/11 1.3" (Mammoth) Whitney webcam view
10/14/12 1.3" (Mammoth)
10/09/13 0.5" (Mammoth)
10/31/14 0.0"
10/05/15 0.5" (Mammoth)

as a graph - I am pretty sure the lack of accurate data before 2002 explains why there are fewer early October snow events in the past than the last decade. The extended snow history in Mammoth for example lists a lot of months as 0 inches when there was significant snow in that month, except in many cases, the snow also melted away in less than 3 days, as 70F daytime temps in October at 8000 feet are quite normal.

Image

(updated 4-8-16)

The data corresponds nicely to some Whitney webcam images I saved - linked from the date when available
I think I'll update the list above over time as I find more data point, anecdotes, pictures with dates, etc - to get a better feel for when snow usually first hits the Sierra main crest
Last edited by fishmonger on Fri Apr 08, 2016 2:47 pm, edited 3 times in total.
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Re: Historic data for first Winter Storm Date

Postby Wandering Daisy » Wed Apr 06, 2016 1:56 pm

Looking at historical data alone will not get an answer. The NWS long term climatic forecasts (see link below) adds the probabilities of this specific year to be above or below normal. The models take into account both the historical data and the climatic patterns for this year. Unfortunately the information is not very detailed, but seems to indicate normal to above normal temperatures and normal precipitation, at least on the southeast side of the Sierra.

http://www.cpc.ncep.noaa.gov/products/p ... php?lead=5

Just form my own experience and reading trip reports here, it seems that late September to mid-October usually brings some short snow storms at the higher altitudes, but rarely a big storm. You just have to be prepared for snow. By mid-October there may be a skiff of snow from earlier storms on the higher elevations that has not melted.

I would just pick the time you really want to go and then keep an eye on shorter term forecasts as your trip date nears. When I choose late season times for trips, I go for the earlier, simply because I like more daylight hours. I am ready to cancel the trip if the short term forecast is not good a few days before I go out. End of September is sort of my end date for a longer trip because I hate all those dark hours. But that's just my preference, not because of snow.
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Re: Historic data for first Winter Storm Date

Postby Wandering Daisy » Wed Apr 06, 2016 2:38 pm

Here is another, albeit tedious, source of information. I actually like this the best because it is graphic and also is linked to actual snow station data.

http://www.nohrsc.noaa.gov/nsa/index.ht ... rra_Nevada

You can toggle through the dates for each year, for example, you are interested in Sept 15 to Oct 15. It goes back to 2003. It shows both the 24-hour snowfall and the cumulative snow on the ground for a given date. This helps because it shows if the snow stays or melts. It also shows "non-snow" precipitation (rain). When you find a day that has some snow, then you can click on "more" and it will show the actual station data.
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