Thursday, February 20, 2014

Well that was a quick recovery!

Our blog posted on 2/6 hinted that changes were coming which would be conducive for snowfall across the Inland Northwest. While that prognostication proved true, we had no idea just how much snow was going to fall. Since February 7th the region has been pummeled by a relentless parade of storms. Just look at some of these snow totals below.

All of these locations have seen more than the normal amount of snowfall for February in the brief two-week period. Some locations much more. The hardest hit locations have been near the Cascades with most locations seeing 2-3x the monthly normal already. While the 100" that fell at Holden Village was not a record (117.2" fell in February 1999), there is still more snow expected through the remainder of the month. The record could also be attained at Plain (66.5" in 1937). The Lewiston number isn't a record either but it is the most amount of snow that has fallen during the month of February since 1985. Below is a picture of what the snow depth looked like in western Chelan County.

Buried pickup truck in western Chelan of Chelan County Sheriff Office. 
So how has this snow impacted what was nearly a record low snow pack earlier this winter. First lets take a look at some individual SNOTEL sites and then a broader scale map of the region. For those not familiar, a SNOTEL is a site, typically set in a remote mountain location which measures things such as temperature and snow depth. You can check this link for more details.  So here's the data from Harts Pass SNOTEL located in western Okanogan County at an elevation of 6490'. If we just look at the blue dotted line it suggests that since the 9th of February nearly 40" of snow has accumulated. While 40" is a good amount of snow it is a large underestimation since the snow undoubtedly compacted from the shear amount that's fallen. Since February 6th, nearly 8" of precipitation has fallen (red line). If we use a climatologically average snow to liquid ratio of 14:1 that would yield around 112 inches of snow.

Hart's Pass in western Chelan County. 
Now if we look at a different site, (Blewett Pass in Chelan County) in a different format we can compare how we stack up compared to normal conditions. The important lines to look at are the navy one which shows the snow water equivalent for the 2014 water year (October 2013-current) and the lavender line which show the median conditions. Notice the navy line almost went straight up over the past couple weeks, falling just shy of the median. That is an awfully swift recovery.

Blewett Pass SNOTEL 

Now lets zoom out a little and look at things from a regional perspective. Below is a look at the snow pack as of the middle of January. Notice the widespread yellow and orange shading over the Cascades and some reds over the Olympics and Oregon Cascades. This denoted near record dry conditions over much of the region.

Snow water equivalent as of 1/14/14

Now fast forward just over a month later and the recovery has been rather impressive. Most of the Washington Cascades have now nearly attained a normal water equivalent in the snow pack, while the Clearwater Mountains of north-central Idaho have actually exceeded normal. Meanwhile the mountains stretching from the Okanogan Highlands to extreme northern Idaho have generally kept pace since mid-January.

Snow Water Equivalent as of 2/20/14

So will this wet trend continue? If we look at some of the model prognostications the answer is a resounding yes. Below is a look at precipitation forecast using some ensemble model data and associating it with similar weather patterns from the past (termed an analog). This analog suggest that from now through the end of the month, up to another 1-2" of precipitation can be expected near the Cascades with just a little bit less for the Idaho Panhandle.

Precipitation analog through 4pm  2/26

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