Sunday, March 26, 2017

Peak Snowpack Time

Historically, the snowpack over the Pacific Northwest mountains peaks right about now--the last days of March to first week in April--something that is illustrated by the figure below (a figure from Amar Andalkar's wonderful skiing the Cascade volcanoes site).

This year the regional mountain snowpack surged in early March, but has stagnated the last week or so because of warmer weather, something illustrated by the snowpack numbers at the Olallie Meadows SNOTEL site near Snoqualmie Pass (dark blue is this year's snow water equvalent, SW), light blue is normal.

Why does our snowpack hit its maximum around April 1, a time when the sun is getting quite strong (equivalent to mid-September)?

Before we talk about that, here are the latest snowpack numbers (percent of normal) around the West.  Virtually all the West is well above normal for SWE (total amount of water in the snowpack), with California's Sierra Nevada being crazy high.

As noted by Mark Albright, past state climatologist, with 720 inches of snowfall through 23 March, Mt Baker Ski Area has recorded its snowiest winter since the big snow years of 2011-12 with 808 inches and 2010-11 with 857 inches.  This is going to be a  long ski season for the Northwest.  Enough snow that Washington DOT is delaying its clearing of North Cascades Highway (SR20);   according to WA DOT it may be the latest opening since 1974.  This WSDOT photo of SR 20 near Liberty Bell mountain shows some of the challenges, including several avalanche chutes.

So why does Cascade snowpack peak around April 1?   It is all about temperature.  Since our weather systems come off the Pacific, it is good to look at the vertical sounding at Qullayute, on the NW WA coast.  Below are the climatologies of temperature there for three levels (925 hPa--around 2500 ft, 850 hPa--around 5000 ft, and 700 hPa--around 10,000 ft).  Those levels pretty much bracket the Northwest high terrain.  You will notice that they have a similar characteristic:   temperatures aloft don't start warming until mid-April.  I talked about that in a previous blog---the atmosphere has a lot of thermal inertia, which means it takes a while for the increasing warming at the surface to influence the deeper atmosphere.   So with temperatures remain cool and precipitation still hitting our region, snow accumulation can continue into early April.

And there is another issue, snow is highly reflective, so a lot of the sun over the mountains is reflected to space rather warm the surface.    This is an issue regarding our regional impacts of global warming.  As the earth warms, our mountain snowpack will lessen, which will allow more solar radiation to be absorbed, which causes more warming and thus melted snow.   A positive feedback for destroying snow and warming our region.

Those effects will become profound later in the century, but so far there have been only minimal losses of Cascade snowpack.     Larry Schick of the US Army Corps of Engineers, also known as the Grand Poobah of NW Powder, sent me some snow statistics of major regional ski areas provided by Tony Crocker (his best snow web site has lots of good material).  Both the Pacific Northwest and California ski areas show little trend (black line) through 2013.

And an analysis of snow water equivalent (SWE) of over 200 SNOTEL sites around the NW through 2016 by Mark Albright suggests little trend over the past 30 years (see below)

Now before some folks get irritated with me, let me underline that this will all change by mid-century as greenhouse gases increases.   We have been "protected" by the slow to warm eastern Pacific. but eventually the radiative effects of increasing greenhouse gases will warm the lower atmosphere even here causing substantially reduce snowpack.

Finally, what about the next week?  The latest ECMWF snow forecast shows some additional snow at higher elevations across our region.  Enjoy.


sunsnow12 said...

In the area where Mt. Baker is located on the USDA map, snowpack is shown at 107%. Yet all of the other data - including WSDOT; multiple ski areas; independent articles; and now this post, seriously contradict it. I think people have every right to question the USDA numbers, particularly given their history (see: Drought Monitor)

And then this:

"Those effects will become profound later in the century, but so far there have been only minimal losses of Cascade snowpack." Really? Looking at the graphs you posted, there is zero evidence of any decline - in fact the trendline from Larry Schick is up for CA.

Since the days of Philip Mote and the firing of Mark Albright when he dared to disagree with the fear-inducing collapsing Cascade snowpack theme, the trendline is neutral or up. So now we should revise history to say those claims were never made? Mark Albright was never fired for disagreeing with it? From exactly 10 years ago:

The political pressure put on science to conform to this theme is disturbing. The science I once knew only cared about facts, not "people getting irritated." That you even have to write it speaks volumes, but it is exactly what the intimidation (like firing scientists who disagree) is supposed to do, right?

"(T)his will all change by mid-century." We've been hearing it for decades now, with the heavy inference - along with California being in a "permanent drought" - that it would start imminently. Go read the articles from 2015. Remember those Cliff, about our snowpack and precip and the "dire picture of what we can expect to happen next"? Then the opposite happened.

Just exactly what is truth anymore?

Alex said...

sunsnow12... there literally is an orthodoxy in climate science right now. You don't dare budge from the party line if you want to keep your job. If the boss says the snowpack is below normal, you go with that. Even though it's a lie. The Soviet Unionization of America has arrived.

Eli said...

I dunno, I read Cliff as showing zero intimidation there, more poking fun there at anybody who doesn't think he should talk about short-term non-effects.

If you have integrity concerns, go blog about them and welcome, but I don't think Cliff or this post are your problem. Check your lenses?

Unknown said...

I follow the regional snowpack as part of my job. There has been a significant snowmelt from the lower elevation snotel sites in the Clark Fork and Flathead basins over the past 10 days. So much so that the USGS gage at Newport Washington is recording new daily record streamflows. However, the higher elevation snotels in the mountains are still accumulating.

Unknown said...

I wonder if the SNOTEL sites are the appropriate places to look for an early climate change signal, since they are mostly located well above the winter winter freezing line. In fact, wouldn't the mean winter freezing line be the place to look for an early signal?

JeffB said...

It's too bad that the rare gem and scientifically motivated Dr. Cliff Mass still has to issue a caveat like this: "Now before some folks get irritated with me, let me underline that this will all change by mid-century as greenhouse gases increases. "

Don't forget to genuflect to the CAGW mob, lest your integrity be impugned and your reputation dragged through the mud. There's no room for dissent amongst those who are on the politically correct side of any issue in 2017, even science which should be immune to politics.

Ansel said...

Cliff, could you give us a legend for those three sets of graphs of temperature vs. month at three different altitudes? I can't make out what those seven curves represent. I presume three of them represent daily high, low, and average, but what are the other four? (I gather the zig-zag lines are for a specific time period... but I'm mainly interested in averages.)