Guest Post by Verity Jones

While the MSM is all hot under the collar about the Killer heat wave in the mid-East US, not a mention about the massive snow accumulation in the Western USA this year. It’s not just a few roads being late to open due to the excessive snow clearance effort (WUWT: here and here), the snowpack is way above average this year. Good news for water supply; bad news for riverside communities.

Just take a look at the extent of this – the Snotel map from 5th June below shows percent of normal snow-water equivalent. The measurements are mostly off the scale, which if you’ll note only goes up to 140% of normal. From the lack of blue and green dots, I’m taking it that the red ones are errors.

From mid-May there has been concern in many areas over the amount of snow and the potential for flooding, but instead of melting rapidly the snowpack has persisted, and even continued to accumulate. As of 9th June almost all states listed here (with the exception of Alaska, Arizona and New Mexico, which have much less than normal) are showing vast excesses of snow for the time of year. For example Utah:

And a different format depiction for Wyoming:

Below is yet another way of looking at it – here for the Upper Colorado (link: http://snowpack.water-data.com/uppercolorado/index.php), specifically the feed into Lake Powell. Now this really made me sit up. The levels were ticking along a bit above average until just after mid-April, then they began to rise, and rise, and rise. This says two possible things are happening – either more snow has been falling, and/or temperatures are just not rising enough to melt what is there. Either scenario says ‘cold’.

On 5th June:

“April 15th is the date of maximum snowpack and basinwide snowpack is currently 66.6% of the April 15th average

Snowpack is 277.9% of the June 5th average.”

Of course you just know that when the melt really does get going you just know that all that snow and the ensuing flooding will be blamed on CAGW.

This got me thinking – at what rate does snow melt? I mean we’ve got some truly gargantuan snow drifts in places – how likely is it that significant proportions of them will remain in places that have not retained snow in summer for years?

The last slide in this EPA presentation gives ranges for melt rate with a degree-day factor. The range seems to be 0.07-0.150 inches per day per degree F. These are estimates for a variety of conditions ranging from partially forested/shaded areas to open sun on a prairie. Although some are quite specific, they are still estimates. Now if we take the example of a 22ft drift in Colorado’s Rocky Mountain National Park (Road opens way late due to massive snow) and look up appropriate degree day figures for the region used with this range of melt rate, perhaps we can get an idea of the potential for residual snow pack at the end of the summer.

Using the U. S. degree-day mapping calculator (Coop, L. B. 2010. . Version 4.0. Oregon State University Integrated Plant Protection Center Web Site Publication E.10-04-1: http://uspest.org/cgi-bin/usmapmaker.pl), the following map is for Colorado, calculated between now and the end of September for a 32F base:

For the higher altitudes we have 1500-2600 degree days before we might expect reasonable additions if not accumulations of snow again, but, still using guestimates for the actual melt rate it seemed sensible to work with a range:

[Update: The table above was produced on the assumption that the melt rates referred to depth of snow. Having covered a lot more background reading on this today I think I should have read the melt rate as “inches SWE/day*F”. Current rates of melting from the NOAA summary table are 0.1-1.6 inches SWE/day. For a 22ft starting snowpack (estimated as 150 inches SWE) my back-of-envelope calculation suggests melt rates would need to be sustained at >1.25 inches SWE/day to remove this depth of snow by the end of September.]

This suggests to me that at higher altitudes there’ll be significant snow ‘left behind’ this year. Those white patches on the distant mountains will be a welcome return for many – cameras at the ready folks!

More than that though, what effect will this have on local/regional temperatures? There would be increased albedo in the mountains where the snow is retained, and potential for cold air drainage as well as depressed river temperatures from prolonged snowmelt over the summer. These effects might be small, and it is, after all, just one unusual year.

Although this is “just weather”, what if we start to have more ‘higher than average’ years now that the PDO has flipped to a cold phase? High pass road opening dates are well documented in Washington State and, having plotted these for the Chinook Pass and North Cascades Highway, I had previously speculated Is the PDO correlated to road openings?

With many analyses suggesting cooler times are on the way, this year may be exceptional in recent experience, but how many “just one year”s would it take for us to notice the effects?

(Updated from post http://diggingintheclay.wordpress.com/2011/06/10/where-snows-dont-melt/)