[pct-l] Snow Predictitions 2 - long

[Bighummel at aol.com (Bighummel@xxxxxxx)]

For those of you planning a 2004 thru-hike and interested in this discussion 
of Sierra snow meltoff predictions and thus, estimating your starting date, 
read on, or, delete if not.

The following is where I collect the information, how I process it and then 
how I use this in order to make a wild assed guess about when the earliest date 
will be each year to enter the Sierras.

For a database from which to draw analogs from; I look through the available 
Sierra snow survey sites for ones which are 1) on or near the PCT in the 
Southern Sierra, 2) highest elevation, and 3) have fairly complete records going 
back to 1970 or 1972 when they started collecting the data.  The Bighorn Plateau 
(BGH) survey site has a complete data set, is on the PCT just south of 
Forester Pass and is at 11,350 feet of elevation, and, the Tyndall Creek (UTY) snow 
survey site is a bit higher at 11,400 feet, on the PCT, closer to Forester, 
and also has complete historical info.

I then took the historical information from BGH and UTY and looked for 
patterns late in the Winter, thus March 1, which might give an indication of the 
eventual meltoff.  June snow amounts were not always recorded, so May snow 
amounts were chosen as a LATE indicator of meltoff status.  

Thus I compiled an "early" indicator of snow status; March 1st from each 
year, and a "late" indicator of snow status; May 1st from each year.  I plotted 
these on a graph by year and looked at how the extremely wet and dry years look 
at the March 1st time to see if there was a correlation between the March 1st 
and May 1st amounts.  The weather patterns between these two dates are 
critical ones relative to the overall snowpack volume and meltoff scenario.

First, the dry years;
1971, 1972, 1976, 1977, 1981, 1987 thru 1992 stick out as the lowest (driest 
years) snow amounts by far.  None of these had more than just 36 inches of 
snow depth at March 1st at either BGH or UTY.  Of these dry years, only 3 had 
more snow in May than in March.  One of these 3, in 1976, had only 14 inches in 
May versus 13.4 inches in March.   Thus of these 11 dry years, you would have a 
82 percent chance (9 out of 11) of being correct in predicting that the 
meltoff would be significantly early (by possibly a month! i.e. May 15th!) by 
simply finding that less than 36 inches of snow was present at BGH on March 1.    
Just how early could be predicted by looking at the rate, on a daily basis, 
that the snow was melting off at the Tyndall Creek, Bighorn Plateau and other 
Kern River -  Southern Sierra snow survey sites in late April and early May.   

OF COURSE, a late Spring snowstorm in May can reverse the meltoff or delay 
it.  This happens about only 20% of the time.  By May 1st most thruhikers are 
already on the trail and tuned into the trail information network.   When a late 
Spring storm hits the Southern Sierra, it generally also hits the other 
Southern California mountains and the thru-hikers, therefore, they/you are likely 
to be able to guage at that point whether their/your schedule to hit the 
Sierras should be delayed or sped up.  

Now, the wet years;
1978, 1980, 1983, 1993, 1997, 1998 and 2000 all had more than 75 inches on 
March 1st at BGH (note BGH gets more snow on the average than UTY).  Two of 
these, 1978 and 1983, had even more snow in May than in March.  So, in "wet" years 
the predictions are not so easy, other than to say that entry dates will 
definately be late and possibly very late.  It is important to point out that in 
many of these "wet" Sierra years, the Pacific Northwest is dry, thus a North to 
South hike is worth considering in these years.

The rest of the years fall into an "average" category which, on March 1st may 
be;
- on the dry side and melt off early, or
- on the dry side and gets late storm systems that delay the meltoff until 
later, or
- on the wet side and melts off early, or
- on the wet side and gets late storms systems that delay the meltoff until 
later, or
- on an average meltoff schedule and stay that way.

Only 6 of these did the last "average" meltoff, 3 of the 6 in last ten years. 
 Thus a June 15th entry date for the Sierras is going to be significantly off 
very often based upon this database.

The UTY database gives daily information going all of the way back to 1970.  
Thus it gives the zero snow depth date (only at that location, not the entire 
Sth Sierras, of course, but can be used loosely as a "near zero snow date" for 
the Southern Sierra).  The earliest, in 1976 is May 8th, the latest date is 
July 28th in 1983.  This is a 11 1/2 week spread!  Yep, the average date works 
out to June 13th.  In 16 years out of the 33 years in record, you would be 
either more than two weeks early or more than two weeks late entering into the 
Sierras on June 13th.  So, Ray Jardine's recommendation that you enter the 
Sierras on or about June 15th is correct in one way of looking at it, however, way 
off in reality.

>From all of this on a given year, I find the amount of snow at both UTY and 
BGH on March 1 and compare it to similar years in the historical database, 
consider the El Nino weather effects for that year in order to guage whether late 
storm systems are likely or not, and then make a wild assed guess.  I have 
percentages and statistics on my side that make this an educated - wild - assed 
-guess, but clearly recognize that I do not have a crystal ball and anything 
can happen between March 1st and the date that the snow mostly melts off.  

The date that I gave this year was June 10th.  Yep, that is very close to the 
average and I made that prediction because the amounts of snow at BGH and UTY 
was in the "average" range and the El Nino effect was not a significant 
player this Spring.  I have heard from several thru-hikers who entered the Sierras 
on or about this date and found generally no snow at lower elevations and snow 
and ice at the high passes.  Those are the conditions that I caveated my 
prediction with as I believe, IMHO,  that is the best time to enter the Sierras. 

Tom Reynolds uses a different method and a different entry date definition 
(one with little or no snow at the passes) that he can explain in detail if 
anyone is interested.  He and I keep it fun, recognizing that this is all highly 
variable and subject to all sorts of errors on our part and on the part of the 
weather (the weather makes errors too!  I just couldn't be THAT wrong!).  Yet, 
we both try to give it a bonafided, serious look for your benefit.  It is 
what we would do if we were going to be joining you next year.

Have fun with it.  As someone said, "Statistics are what you make of them."  

Best regards,

Greg Hummel
"Strider"

Remember when you're feeling very small and insecure 
how amazingly unlikely is your birth . . .  
and pray that there's intelligent life somewhere up in space 
cause there's damn near none here on earth!
                    Monty Python "The Meaning of Life"