The NW has had a lackluster start to the water year. While this has resulted in fewer number of hours snow shoveling and associated wet weather nuisances, it is not a welcome blessing for our mountain snowpack and water resources. Bottom line is that we’ll be playing catchup again this winter.
The “D” word? The definition of drought is simply when water demand exceeds supply, thus the precise definition will be sectorally dependent. Talking about drought in the middle of winter is a bit like craving a Slurpee in the middle of a blizzard. However, the topic of drought (and maybe Slurpees) will become more important come spring. Whether we want to call it a drought or a dry spell, here are a few pieces of evidence:
- All but the northernmost counties in Idaho are on the federal natural disaster list due to the suboptimal growing conditions.
- Reservoir storage in the Upper Snake is running about 1/3 less than this time last year with some reservoir levels at their lowest in 10+ years.
- While we don’t usually qualify annual precipitation as Jan-Dec in the western US due to the distinct seasonality of supply-demand, precipitation for the 2013 calendar year set record lows across parts of the southern Idaho, much of southwestern Oregon and over 2/3rds of California.
Snow making was in effect in the aptly named Sun Valley and other locations in the NW due to the lack of snowfall. And as the Boise Weekly reported, ski resorts in McCall and Boise were doing the snow dance in hopes of getting traffic flows for the Holiday crowds.
Cold and dry
The cold start to December pretty much solidified that mean temperatures for December would be below normal. The combination of cold and dry conditions during winter are not unexpected. A vast majority of early-winters (Dec-Jan, here just for Idaho statewide averages) that have been cooler than normal have been drier than normal. Likewise, most of the wet Dec-Jan have been warmer than normal.
The culprit of the invasion of cold air across the region and much of the central US was a high amplitude wave that facilitated the movement of Continental Polar and Arctic air-masses that were chillin over north-central Canada southward mentioned in a previous post. The map below shows the anomaly in the jet-stream for December. Two features of note: (1) significant weakening of the jet across the Pacific that kept the storm track at bay, and (2) unusually strong flow from the north spilling down into the Northwest. Northerly flow brings in cold, but moisture starved air; whereas west and southwesterly flow brings with it ample moisture and mild conditions. This contrast is strongest in valley locations as generally dry conditions are associated with a quiescent weather regime that allows for inversions to set up shop.
As of January 1, Moscow, ID had recorded 15.3″ of snowfall (about 75% of normal of 20.7″, but close to the median) since October 1st, while the Aneroid Lake, OR SNOTEL station had 11.4″ of SWE, actually a bit over the normal for that station due to the 4+ inches of SWE on Oct 1st this year.