* Written by Ryan Niemeyer
So far, the Upper Columbia has had a pretty solid start to the snow year. This is due to the dump of snow in early November and the series of snow storms over the last two weeks.
So let’s review the status of our snowpack. Before we do that, let’s overview how we monitor snow levels. Hydrologists use snow water equivalent to monitor snowpack. Snow water equivalent is the depth of water if all the snow was melted into liquid. Snow typically falls at about 10% of the density of liquid water, so a 10 inch snowfall would typically equal 1 inch snow water equivalent.
Over the last two months, some areas in the Upper Columbia – especially in the Okanogan subbasin – got much of the current snowpack in early November. For example, on Nov 7th and 8th, Salmon Meadows in Okanogan County received 2.6 inches of snow water equivalent. Currently Salmon Meadows snowpack is at 4.2 inches snow water equivalent, which is 91% above average. Conversely, many areas – especially in Chelan County – received most of their snowpack over the last two weeks. For example, Stevens Pass added 4.1 snow water equivalent from November 27th to December 1st. As of this writing Stevens Pass is 5% above average.
But there are pieces of bad or less positive news. First, parts of the Methow did not receive significant amounts of snow in early November or the last two weeks. At Rainy Pass for example, which is on the edge of the Methow watershed boundary, the snowpack is currently 38% below normal. And in the headwaters of the Methow, Harts Pass is currently 22% below normal.
The second piece of bad news is weather models predict a weakening of the La Niña conditions. As I have explained in previous blog posts, a strong La Niña means ocean temperatures in the Pacific Ocean along the equator are cooler than normal, which typically produces cool and wet winters in the Pacific Northwest. November had strong La Niña conditions and December likely will too. However the models predict a weakening of La Niña conditions which means lower chance of a cold and wet winter. La Niña conditions are not the only cause for excellent snowpack – so even with weak La Niña we could still have a good snow year. But the odds are lower that we will get a good snow year. And we are still very early in the winter. So keep doing your snow dance.