Cascade Melt Out

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There are few more important questions for Northwest hikers:  when will their favorite trails melt out and the hiking season begin in earnest?  

And few more important questions for those concerned about the local impacta of global warming:  is the Cascade snowpack melting out earlier, thus providing evidence of the effects of increasing greenhouse gases in the atmosphere. 

This truth may surprise some and depress others.  

It turns out that the Cascade snowpack has been trending to melt out LATER during the past thirty years, with the last few years being particularly late.  For example, Stevens Pass finally melted out yesterday--3 weeks later than normal.

Here is a plot of the melt-out date at Stevens Pass from 1981 through this year (courtesy of UW atmospheric scientist Mark Albright).  The y axis shows the melt-out day (days into the year) and the purple line shows a 5-year running average.  The overall trend is clearly for a later melt out.
The mean melt-out dates by decade illustrate this trend:

1980s:  30 May
1990s:  1 June
2000s:  2 June
2003-12:  6 June

Three of the five latest melt-out dates have been during the past five years:

1 July 2011 THE LATEST!
25 June 2008
25 June 1999
24 June 2012
23 June 1997

Paralleling the late snowpack melt-out is the April 1 snowpack amount, which has not shown any decline over the past 30 years.

Does this trend in snow melt out  mean that the Northwest does not have to worry about greenhouse warming? The answer is no.  By the middle of this century the Northwest snowpack should clearly be on decline as the earth warms, but as I have mentioned many times in this blog, the entire world will not warm at the same rate.  Downstream of the eastern Pacific, the coastal portions of the Pacific Northwest (Cascade crest westward) will warm up more slowly than most places, since the eastern Pacific will take its time to heat up.

Let me illustrate this.  Here is the change in global temperature from 1980 through this year for the winter months (courtesy of Goddard Institute for Space Studies).  The eastern Pacific has COOLED, and we have cooled with it.  But we are the exceptions...most of the earth has warmed and the arctic region has really warmed.   So there is global warming (with some contribution from man-caused increasing greenhouse gases), but out neighborhood has cooled...temporarily.

Pretty interesting stuff and with important implications for us here in the NW...we have much more time than most to prepare for the effects of global least the temperature/snow part of the changes. So if someone tries to tell you that the coastal NW has already experienced major effects due to global warming, you might question their information.   And if someone says that a stable or increasing snowpack the past few decades proves global warming is nonsense...I would not trust their information either.  

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