Stormy Weather To Continue For California

Since Christmas, the storm track has shifted south to California, bringing heavy rain and mountain snow to the Golden State. Parts of the Sierra Nevada have seen over 20 inches of liquid-equivalent precipitation, much of it in the form of snow.

The most recent tempest occurred on January 4th and 5th. The image below shows a massive, 958mb low pressure system over the Pacific Ocean on 1/4. Not every day that you see something like this on satellite!

Though this system was far enough offshore to keep extreme winds over the ocean waters, it brought 15-25 foot swells all the way to the Western US coast, along with several inches of rain to the California lowlands and several feet of mountain snow to the Sierra Nevada.

More rain is on the way for California. An even stronger system will impact the area on Monday/Tuesday, bringing lowland rain, mountain snow, and potentially damaging winds along the coast. Flooding, landslides, and widespread power outages should all be expected, with wind gusts up to 75 mph possible along exposed coastal locations. Although California may see a temporary break in the action later next week, models show a return to stormy weather for the weekend and beyond.

California Drought

Though the storms are causing quite a bit of disruption, they have been extraordinarily helpful for California’s drought situation. California’s drought has been improving in recent weeks, and though large amounts of the state still remain in “extreme” drought, these percentages should continue to decrease over the next few weeks. The Drought Monitor seems to have a large emphasis on long-term drought indices such as groundwater saturation, so I suspect California will continue to experience drought conditions even after this series of storms. However, these storms are wet enough to make a sizable dent in the drought.

They are also doing wonders for reservoir levels and high-elevation snowpack. Most California reservoirs are still below their seasonal averages, but they’ve improved dramatically in recent weeks and should continue to do so over at least the next 10 days.

Snowpack is near-normal in the Pacific Northwest but well above normal over California and the Intermountain West. Quite a reversal from what you’d normally expect in a La Nina winter, as these winters usually bring the Pacific Northwest above-average snowfall while leaving California drier and somewhat warmer than average.

What about Lake Mead and Lake Powell?

Lake Mead and Lake Powell have made headlines for their long-term downtrends and record lows in recent months. I’m not a hydrologist and am not familiar with the Colorado River System, but I am pessimistic that these storms will do much to help Lake Mead and Powell. First, the vast majority of precipitation is expected to stay west of the Sierra Nevada Crest and outside of the Colorado River Basin. The Euro model shows up to a foot of liquid precipitation over the next 10 days for parts of California while most of the Intermountain West sees 2 inches or less. Well-above-average for sure, but wholly inadequate to make much progress filling these reservoirs.

Second, these two reservoirs in particular seem to have a more structural long-term downtrend due to overusage of water supplies. Although California’s reservoirs can dip to extremely low levels during drought years, they can skyrocket back to record levels during rainy years. Lake Oroville is a perfect example of this… in 2014, boats were stranded in marinas due to extremely low water levels, yet in 2017, Oroville Dam nearly had a catastrophic failure when extreme precipitation filled up the reservoir and heavy spillway releases caused the main spillway to erode. Lake Mead, on the other hand, has been on a downtrend since the 1980s, and this doesn’t show any sign of letting up soon.

With an active storm track depressed south for the next 10 days, the Pacific Northwest should remain mild and gray without experiencing any major systems. Just the typical gray weather we all know and love.