Midwinter Western US Reservoir Update

FastCast—Tuesday, Feb. 7 to Sunday, Feb. 13:

After a weak system brought some light rain and breezy conditions to Western Washington on Monday, a large high pressure ridge will develop and bring dry weather through at least Saturday. A slight chance of rain is possible on Sunday. Expect clouds in the mornings and some clearing from midmorning into the afternoons. Highs will be in the upper 40s to mid 50s, with lows in the mid 30s to low 40s. For those residents who are sensitive to high barometric pressure, expect high pressure (30.50”+) through early Thursday.

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As dry weather impacts most of the Western United States due to the La Niña pattern, it seems like a good time to look at reservoir levels across the West, with summer approaching.

Starting in Washington, the crucial Yakima River reservoir system is in very good shape, far above last year (green) and average (red). The reservoirs themselves are 50-80% full.

Add to this that most of the snowpack is still held in the mountains, and we are in good shape for the summer. 

The SNOTEL snowpack map for the Western United States is below, as of February 7th.

Most of the West is in decent shape, with 70-130% of normal, which is lower than we’d like to see for this time of winter. No area is over 150% of normal, except the Oregon coast range.The areas with the least snowpack are parts of Oregon and Nevada, eastern Wyoming, New Mexico, and parts of Arizona.

However, good snowpack does not ensure good reservoir situations, and the spring/summer snowmelt won't fill some of the incredibly depleted reservoirs in the Southwest. (All lake levels from US Lakes.info)

Below is the level for critical Lake Mead, on the border of Nevada and Arizona.

At a level of around 1,067 feet, Lake Mead remains near its lowest level ever recorded, where it has been since late July. If conditions don't significantly improve (i.e. 100+ feet added to the lake) more water cuts are possible during the upcoming summer.

In a similar situation is Lake Powell, created by Glen Canyon Dam and straddling the Arizona-Utah border. 

This summer and in the months since, Lake Powell's level has been around 3,530 feet, over 100 feet below "full", and consistently at a record low.

Lake Oroville, in Northern California, stopped generating hydroelectric power from August 2021 to early January 2022. Thankfully, some atmospheric rivers earlier this winter have helped water rapidly refill the lake...sort of.

It has "recovered" to 746 feet, which is 100 feet above its record low. However, it is still over 150 feet below full level, which it did briefly reach in 2017 (red line). 

So...what is ahead? The 3-month precipitation outlook from the NWS Climate Prediction Center is below.

The Pacific Northwest is in very good shape for summer water supply, with above normal levels now, a near-normal snowpack, and above average precipitation expected.

The situation is much more grim in the Southwest and California. Below average precipitation is expected over many areas that have reservoirs very far below normal. Even a near-normal snowpack won't replenish the reservoirs enough for summer.

Another summer of very low Southwest reservoirs seems likely.