Brutal East Wind On Tuesday

This will be a quick post (spoiler alert: it’s not), as my work starts relatively early (4am!) and sleep is one of those things in life you don’t want to skimp on. But I felt obligated to at least give you a brief warning about the cold, windy weather on tap for tomorrow morning so that you don’t get goosebumps walking into work.

The Setup:

It’s pretty much unheard of to have an arctic outbreak in October, but with the right setup, one can occur. And such an outbreak is occurring right now. We have a very amplified pattern, where the upper-level flow has large north-south components due to large upper-level ridges/troughs. This is contrasted with zonal flow, where there is relatively little ridging/troughing and the flow comes from west to east.

In addition to the ginormous ridge over the Pacific and threatening trough surging south into the Intermountain West, there is an epic atmospheric river stretching all the way from the Hawaiian Islands to Southern Alaska. Incredible. It’s highly unusual for an atmospheric river to stretch so far north. Also – ARs were known as the “Pineapple Express” when they originate from Hawaii, but that feel out of favor a bit when a movie was made about a marijuana strain of the same name. Glad to see it is making a comeback!

But while the atmospheric river is fine and dandy, it’s the dark, forboding trough bearing down on the West that will bring us a highly unusual, early-season arctic outbreak. And lucky for us, the high-resolution UW WRF model shows the progression of this arctic air in stunning detail.

At 8pm this evening, cold air had engulfed Montana and was fast approaching the Portland metro area.

By 8 am Tuesday, the cold air has moved through Portland and all the way south into Central Nevada. This is a fast cold front. Additionally, an intense pressure gradient forms along the Sierra Nevada, sending another round of Diablo Winds into the region and worsening fire conditions there. I have never seen such a relentless series of Diablo and Santa Ana events – prayers to all those affected by the fires.

By 8 am Wednesday the arctic air – now a shadow of its previous self – has reached Northern Arizona and New Mexico. Diablo and Santa Ana Winds continue to roar.

And by 8pm Wednesday, the air moderates and Diablo winds die down (Santa Anas will persist through Thursday evening).

The East Wind:

Cold air is denser than warm air, and as a result, it is associated with higher surface pressure. This relationship is clearly illustrated in the temperature/pressure maps above. Because the pressure gradient force dictates that air flows from high to low pressure, high pressure inland results in strong offshore gradients. Ironically, the very arctic outbreaks that bring frigid air into the West bring extreme fire danger to California as extremely dry, cold, high-elevation air sinks along the slopes of the Sierras and other California mountain ranges and warms dramatically as a result.

In our neck of the woods, this cold air tends to collect in the Columbia Basin, where it forms a localized area of high pressure. It then races towards lower pressure over Western Washington/Oregon through gaps in the Cascades, and no gap is bigger than the Columbia River Gorge.

The Forecast:

Our first intense East Wind event of the season will begin around midnight. Unlike most events, this event will be not be confined to the Columbia River Gorge but will be widespread throughout the metro area. 

Winds will peak between 2 and 8 am, but strong winds will persist through the day, with widespread 20-30 mph gusts throughout the Portland/Vancouver metro areas and gusts to 50 mph atop the West Hills and at the most exposed locations of eastern Clark and Multnomah Counties, particularly along the I-205 corridor.  It’ll be cold too, with highs barely reaching 50! Be aware for the potential for isolated power outages due to this being the first moderate wind event of the season, as well as the fact that deciduous trees still have many of their leaves.

The East Wind will finally become more confined to the Columbia River Gorge Tuesday night, allowing temperatures to plummet into the mid 20s for calmer spots around the Portland metro area Wednesday morning with low 20s in outlying areas. Expect similar conditions Wednesday/ Thursday morning before we finally transition to a slightly warmer and much less windy regime by the end of the week with continued sunny skies.

Well, that was a bit longer than I planned. Such is the curse of the weather geek – I get too excited about a subject to keep it to a few paragraphs. Thanks for sticking with me the whole way through, and bundle up tomorrow!!!

Charlie

Featured image retrieved from condolux.net