Drought Relief For The Inland NW This Week

Last Wednesday, the United States Bureau of Reclamation (USBR), a government agency that oversees water resource management in the Western US and Great Plains, announced that they would close the main irrigational canal that draws from Upper Klamath Lake for the 2021 irrigation season. This canal, known as the “A” canal in the USBR-sponsored Klamath Project, is a pivotal source of water for irrigators during the irrigation season, which is typically from March 1 to November 30 for the Klamath Project.

The USBR has restricted water usage rights in the Klamath Basin before; there was a big controversy back in 2001 when the USBR announced on April 6 of that year that “no water (would) be available” to farms that normally receive water from Upper Klamath Lake. This announcement was due to severe drought and protections for struggling salmon runs and several suckers that are endemic to the Upper Klamath and Lost River Basins in Southern Oregon and Northern California, respectively, two of which (specifically, the Shortnose Sucker & Lost River Sucker) are endangered. Protestors unlawfully opened the water gates in July to allow water to flow through the irrigation canals, and on July 24th, the Secretary of the Interior announced that 70,000 – 75,000 acre-feet of water (15-20% of average) would be released from Upper Klamath Lake to assist farmers.

But 2021’s situation is far worse than 2001. Assuming protestors don’t open the water gates, this will be the first time in the Klamath Project’s 114-year history that no water will flow through the main irrigational canal from Upper Klamath Lake. And if that wasn’t bad enough, the USBR also announced on Wednesday that they would not provide “flushing flows” for salmon this year, which help outgoing juvenile salmon survive by cooling water temperatures. Right now, a deadly parasite that thrives in warmer temperatures is ravaging the outgoing juvenile Coho salmon population, with 97% of juvenile coho in a key portion of the river testing positive for the parasite according to Frankie Myers, the Vice Chairman of the Yurok Tribe. In other words, the 2021 outgoing coho salmon run for the Klamath is essentially toast. These flushing flows have been prohibited so that Upper Klamath Lake can have enough water to support the endangered suckers that live in the lake and as a precautionary measure for the 2022 irrigation season in case severe drought conditions persist.

The US Drought Monitor shows that these historic drought conditions are hardly confined to the Klamath River Basin. Pretty much the entire Western US, including the Willamette Valley, is in the midst of a “Severe” drought or worse. “Extreme” or “Exceptional” drought extends over much of California and the Desert SW, and many reservoirs (including Lake Mead, which is impounded by the Hoover Dam and is the largest reservoir in the US) are forecast to reach record-low levels this summer.

In addition to severe water shortages and mandatory rationing, the drought makes for a very favorable environment for wildfires to ignite and grow this summer, particularly in forested locations like the Cascades/Sierra Nevada or the Northern California/Southern Oregon Coast Range. The weather has a much larger impact on fires than the fire environment – for example, 2020’s fire season would have likely been near or slightly above-average if it hadn’t been for two record-breaking events – the mid-August lightning outbreak over and around the San Francisco Bay Area and the Labor Day Fires over Oregon and California, so our best hope for this fire season is that we don’t see a lot of thunderstorms or periods of strong, dry offshore flow. I will have a more detailed “2021 Fire Season Outlook” blog within the next week or so where I discuss this all in a little more depth.

But there is good news. Moderate-to-heavy rain is expected over much of the Pacific NW this week, primarily over and east of the Cascades. This rainfall will occur due to a deep upper-level trough dropping south from Canada and slowly moving over the Pacific Northwest, enhancing instability and providing the large-scale dynamic lift needed for the formation of clouds and precipitation. It’s nowhere near enough to put a sizable dent in the drought – any true drought progress will occur during the rainy season. But at this point, we oughta be thankful for every last raindrop we get.

The current infrared satellite/500mb height chart shows two “lobes” of this broader upper-level trough – one over Vancouver Island and one over Alberta.

At the surface, we can see some showers and lightning strikes with the leading cold front draped over Montana, Saskatchewan, and even NW Manitoba (this is a BIG system!). Closer to the “lobe” over Alberta, we can see an area of lighter, more stratiform precipitation. Unfortunately, radar coverage is sparse up in the Great White North, but we can still get the general picture here; this is a broad, cold system with plenty of precipitation and a few lightning strikes to go along with it.

Over the next 24 hours, the lobe over Alberta will weaken and rotate to the NE while the lobe over Vancouver Island will move south over Western Washington and Oregon. The image below shows the trough at 5pm Wednesday evening. The cold air aloft and comparatively warm air at the surface will support the development of afternoon/evening thundershowers, and the diffluent flow aloft to the east of the low-pressure center will provide the surface convergence and synoptic-scale lift to allow showers to form and tap into any additional instability at higher levels of the atmosphere.

Wednesday should start off dry, but by the early afternoon we should see increasing showers as the sun warms the surface and destabilizes the atmosphere, resulting in convection. There are marginal amounts of CAPE (convective available potential energy – a measure of instability) over Western WA/OR and much higher amounts over Western Wyoming. Compare the precipitation from 2pm – 5pm tomorrow & the CAPE at 5pm tomorrow and note how well the instability and precipitation align. The only exception is over portions of the Idaho Panhandle, where the precipitation will be caused by a favorable synoptic environment to the east of the upper-level low (i.e. convergence at the surface and divergence aloft, resulting in large-scale vertical motion conducive to cloud/precip formation).

And yes, there is a slight chance of thundershowers over Western WA/OR tomorrow, but with such marginal amounts of CAPE, such storms will be the anemic “one-strike wonder” types and shouldn’t be particularly eventful. However, they could be slow-movers and could drop some small hail due to how cold temperatures aloft are. Bottom line: check your radar app before heading out and about tomorrow; you don’t want to get caught under one of these slow-moving thundershowers!

This trough will gradually weaken and move inland Thursday through the weekend, but look at how much rain it is expected to drop over the Inland NW in the process! Most of the rain over Eastern OR will fall Thursday afternoon through Saturday afternoon and precipitation will tend to be heaviest in the afternoon/evening when the atmosphere destabilizes and showers form. By 5am Sunday, much of Central Oregon may see 0.75 – 1.5 inches of rain, though amounts may be highly variable between locales due to the convective nature of the precipitation.

Again – nowhere near enough to put a sizable dent in the drought situation, but an inch of rain is nothing to sneeze at. Or, as this farmer would say…

Have a wonderful rest of your week and do some rain dances!
Charlie