Many locations across the Pacific NW have seen their driest start to spring on record. As of April 22, Portland has seen a paltry 1.64 inches of rain since March 1, which is more than 4 inches below-average. According to the US Drought Monitor, such a dry spring has allowed the moderate drought conditions that persisted earlier this winter over SW Oregon to intensify and expand northward through the Willamette Valley, and some parts of south-central Oregon are now experiencing an “exceptional drought,” the highest on the scale.
It’s not your imagination that it’s been a dry spring in NW Oregon & SW Washington. Lack of rain since March 1 is increasing concerns about drought and fire danger. #orwx #wawx #drought #pdxtst pic.twitter.com/evpuK6U7aq
— NWS Portland (@NWSPortland) April 16, 2021
La Nina years often have cool/wet springs, but there can be a significant amount of year-to-year variability within La Nina or El Nino years. Years like this show the uncertainty in seasonal forecasts, particularly precipitation forecasts. This is why I favor the Climate Prediction Center’s method of seasonal forecasting, where they will focus on the probability of temperatures and precipitation being near, below, or above average, as opposed to other seasonal forecasts that focus on a more specific, definitive outcome. There are definitely weather variables that will “tilt” the odds of temperatures or precipitation being above or below average, such as summertime soil moisture, the existence of a strong El Nino/La Nina in the tropical Pacific, and any “Blob” of anomalously warm/cool water off the West Coast. However, as this spring has shown, these factors only weight the dice, and their correlation with precipitation in particular is relatively weak. We still have much to learn about forecasting on seasonal time scales.
But as dry as we have been this spring, the drought situation is far more dire over California and the Desert Southwest. Lake Powell and Lake Mead, two reservoirs along the Colorado river, are expected to reach historically low levels in the upcoming months, and if current forecasts are correct, states dependent on the Colorado River will be forced to ration water.
Lake Mead water levels (as measured at Hoover Dam) are at their lowest for this time of the year since 2016. Water levels are expected to continue declining over the next several months to historically low levels. pic.twitter.com/HwVR5gmmri
— Charlie Phillips (@GeoduckChuck) April 23, 2021
Unfortunately, with such dry fuels throughout the West, long-range forecasts are calling for yet another more active-than-usual fire season for the Western US. California and Oregon in particular had extraordinarily active fire seasons last year, and the “Labor Day Fires” of September 2020 in Oregon were associated with extremely powerful, dry, and rare offshore winds that typically only affect the region once or twice a century. Thankfully, even if we don’t see much rain in May or June and drought conditions worsen, there is still hope that we could have a below-average fire season in the Pacific Northwest if the summertime pattern is dominated by cooler, moister onshore flow from the Pacific Ocean and we escape any major heat waves or thunderstorm outbreaks. Unfortunately, strong offshore flow and the notorious strong, dry “Diablo” and “Santa Ana” winds are far more common in California, and with drought conditions as bad as they are there, I think there’s a pretty good chance California will see above-average fire-activity this summer and autumn.
Hopefully the entire Western US will see some drought relief this summer, but even if the weather doesn’t cooperate, we can do a lot to conserve water and prevent forest fires. Be sure to always completely put out any campfires, obey burn bans, properly discard of cigarettes, and when fire danger is particularly high, keep vehicles off dry grass and avoid power equipment that creates sparks. And know that it is OK if your grass gets a little brown this summer! You’ll save a ton of water by watering it less frequently over the summer, and it’ll be as green as ever after the rains return this coming autumn.
Speaking of rain, we are FINALLY expected to get some liquid sunshine this weekend! Expect periods of rain & mountain snow Saturday with showers persisting Sunday. Both days will also be much cooler-than-average; Saturday should only reach the low/mid 50s, which will feel absolutely arctic after the unseasonably warm weather we’ve seen over the past two weeks. Long range forecasts show a few showers persisting next week, and I don’t see any heat waves through the rest of April.
Stoked for the rain this weekend! Rain will arrive Saturday morning and stick around through much of the day, and showers should persist on Sunday. Snow levels will be at 4500 feet this weekend, so expect a few flakes up by Government Camp and a few inches at Timberline Lodge! pic.twitter.com/B8kY3uDkav
— Charlie Phillips (@GeoduckChuck) April 23, 2021
Have a wonderful Friday and enjoy the cool/wet weather this weekend. 🙂
Charlie
