Steven's Pass Melt Out

On Saturday, Steven's Pass had its "melt out", which is defined as the first day of the summer when less than two inches of snow water equivalent (SWE) was left on the ground.

It was the 8th earliest melt out in the last 36 years.  The average melt-out date the last 35 year is June 2, so it is about 1.5 weeks early.   Folks care about the melt out date because it is an integrated measure of the depth of the snow pack and the degree of spring warmth, and both of those are expected to be influenced by global warming.  Increased levels of CO2 should result in warming that will result in less build up of mountain snowpack in the winter and a quicker melting in the spring of what snow does accumulate.

Last year (2015) was a profound example of warming causing a reduction in snowpack and a very early melt off date (the earliest on record!).    Some folks are saying that there is trend towards poorer snowpacks and earlier melt-outs, and that that this is an indication that we are already experienced human-caused global warming.   But is it true?

Mark Albright, past Washington State climatologist, has plotted up the Steven's Pass melt-dates from 1981-2015 (see below).  The annual melt-out dates are shown by the blue dots, the mean over the period by the horizontal gray line, and the 5-year running mean by the purple line.   There is no evidence of a long-term trend for earlier melt-out dates.  In fact, just the opposite....melt out dates are trending later (which implies cooling or greater snowpacks or both).  Last year (2015) was an outlier, although two other years came close.

So there doesn't appear to be any global warming signal producing earlier snow melt offs in our region.

To drive this point home further, here are the mean melt-out dates for recent decades (again, thanks to Mark Albright).  It appears that the melt-out dates are getting progressively later, just the OPPOSITE of what we would expect global warming would do.

1980s: 30 May
1990s: 1 June
2000s: 2 June
2010s: 4 June (thru 2016)

This small delay in the melt out is consistent with other independent measures of snow content in the Cascades, such as the April 1 snowpack amount, also show little trend.

One or two bad years are not an indicator of a long-term trend and the evidence, as shown above, suggests minimal decadal trends of snow in the Cascades.