Early January 2020: Winter Drought Takes a Welcome Break
Happy New Year (and new decade) folks! It’s been a hectic month for me, with holiday work in retail and whatnot. Also there were some problems with the Weather Together site over Christmas time, so I was limited to posting on my Facebook page. I encourage all of you to check it out; generally I post “minor” weather updates on that page and save this blog for the deeper discussions.
Fortunately (or unfortunately) it’s been a very boring first half of winter in our corner of the Pacific Northwest, so I didn’t miss out on blogging about any important events. Some of you are probably thinking, “but winter started just 2 weeks ago!”. According to the “traditional” calendar industry, winter begins on December 21-22 and ends March 19-21, with the midpoint around February 3-4. But climatological reality along the West Coast tells a different story: the coldest quarter of the year is roughly one month earlier than that, from November 20-21 until February 19 or 20. That puts early January smack in the middle. Yes…we can sometimes get cold and snow in late February or even early March, as happened last year. But we can just as easily see a stretch of 55-60 degree temps in the period around Valentine’s Day, sometimes even earlier. The turning of winter to spring isn’t consistent from year-to-year, but February 20 seems to be a good average.
The Portland metro area saw a brief cold east wind episode during the Thanksgiving weekend, with a very brief wintry tease on the night of November 30. That is literally the ONLY weather “action” we’ve had the entire season thus far! The atmospheric river in mid-December ended up moving north instead, and inundating Western Washington while we just got “normal” wet weather.
December 2019 was slightly drier than normal at PDX; only 4.39″ of rain as opposed to the 30-year average of 5.49″. And this comes on the heels of a very dry October and November. Since the start of the fiscal water year on October 1 (and not counting these first few days of January), Portland has seen 7.42″ of total liquefied precip. Compare to the 30-year average of 14.11″, and it’s clear that the first half of our ‘wet season’ has been very dry. It’s the second driest Oct-Dec period since at least 1981 and the fourth driest in 80 years of records! Only 2013, 1978 & 1976 were drier at the airport.
Maps across the West show Oregon standing out as especially dry. We’ve been in the middle of the “split” between the northern and southern storm tracks, which is the main reason our weather has been so boring.
Wow…notice how Oregon really sticks out like a sorely dry thumb! Rainfall/snowfall since the beginning of the water year is more than 50% below normal in much of the state. But wetter than normal in the Desert Southwest due to the southern storm track. Also…the mild temps and high snow levels during December mean that our snowpack was WAY below normal as of December 31. Here are the SNOTEL maps, in PDF form, for Oregon & Washington snow departures:
(PDF’s credit: https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/products)
Both states are in sorry shape, but Oregon more so. Only the mountains of Arizona are significantly snowier than normal for the beginning of January.
But if you’re freaking out about a Northwest snow drought, there’s good news: We’re now transitioning into a cooler/wetter pattern beginning tomorrow Saturday, which should last for a week or more. That means frequent North Pacific storm systems, chilly lowland showers, and lots of snow for the Cascades – likely 2 to 4 feet over the next week above the passes!
Colder air in the upper atmosphere is indicative of an upper level trough; because cold air is denser than warm, it hugs the Earth’s surface more closely, and because of that there is less air pressure in the high levels of the atmosphere. (Surface pressure, on the other hand, doesn’t always follow the same script!). This trough in the upper atmosphere reasserts itself by next Wednesday:
This is going to allow chilly storms to slide down from the Gulf of Alaska, bringing the valley rain and heavy mountain snow. The WRF model is showing between 2 and 4 feet in the Oregon Cascades over the next 7 1/2 days; while the WA and BC Cascades should be even snowier!
So there you have it. Lots of showers these next 7-9 days, with plenty of snow in the mountains due to a chilly airmass. We might turn even colder toward the middle of the month, but it isn’t clear yet. In any case, the Cascade snowpack will finally get a chance to build, averting what would otherwise be serious trouble.
What’s less certain is whether there will be enough evening breaks in the cloud cover, to catch a glimpse of Orion & Betelgeuse these next few nights. More on THAT topic in a blog coming soon….
Enjoy the “classically” chilly and wet Northwest weather these next several days! -Karl