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
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.
(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