Strong and gusty easterly wind returns Thursday
Just about ALL of the metro area will be much windier tomorrow...watch out for flying garbage cans! You can expect a few scattered power outages too...just a few.
Strong high pressure east of the Cascades plus a sharp temperature inversion (warmer air over cooler air in lowlands) led to a very strong easterly wind through the Gorge today. Peak gusts exceeded 90 mph at both Crown Point and Rooster Rock. Gusts over 70 mph rocked the town of Corbett too, at the high end up what is typically experienced at both locations in the cold season. A person standing “at the rail” on those south-facing steps at Vista House certainly would have recorded gusts in the 100-120 mph range today.
Most interesting is that the cross-Cascade pressure gradient (difference in pressure between Portland and The Dalles), only peaked around 9 millibars. I would have expected lower gusts with that gradient. The key is that we have a strong inversion overhead. It was 53 today at 7,000′ at the top of Magic Mile chairlift on Mt. Hood. In a perfectly mixed atmosphere (warm season), high temperatures should have been around 80 down here at sea level! But it’s not perfectly mixed because days are so short and the sun is in its very weak winter position in the sky. Cool air gets stuck in valleys and warm air moves in overhead. In this case that “squishes down” the fast flowing air moving through the Gorge. Think of it as a certain amount of fluid being forced through a small hose. Velocity increases. But that fast moving air spreads out quickly and slows down under a strong inversion once it leaves the Gorge. Much of the metro area just saw light breezes today
What changes tomorrow?
Wind in the Gorge should be LIGHTER tomorrow, but much stronger wind (than today) should spread across the entire metro area at the same time.
A surge of colder/drier air is moving down into the northern Rockies tonight. The edge of that airmass should arrive over northern Oregon by sunrise. This loop shows 850mb temps...the temperature in Celsius around the 5,000′ elevation. From right now to tomorrow at 7pm. Notice at that elevation temperatures drop 20-30 degrees in just 24 hours around Mt. Hood; a drastic change. Timberline should stay in the 20s, instead of around 50 today. The change isn’t as dramatic westside, but significantly cooler air arrives several thousand feet up over NW Oregon too.
That will do two things...increase the pressure gradient a bit across the Cascades (more wind), but the cooling overhead weakens the inversion. The combination of wind surging right over the Cascades (instead of just through the Gorge) and weaker inversion means that wind will spread out into many areas west of the Cascades. That “small hose” of air will be a “much larger hose”. Less wind IN the Gorge, but a lot more elsewhere. This is common...I’ve always noticed that when we get easterly wind everywhere in the metro area, it tends to be weaker than expected at Vista House. The highest resolution model available (WRF 1.33km) shows quite the drop in wind gusts from 10am today to 10am tomorrow around Crown Point. Notice the blue area (gusts 45+ kts) on today’s chart is gone tomorrow, replaced by widespread gusts 25-40 mph in the West Hills and east metro.
We will see how this works out, but it’s just something I’ve noticed over the years. Another way to look at it is the cross-section around the Crown Pt. area. Light wind overhead today, but strong easterly by midday tomorrow (around 2,000′). And weaker surface windspeed tomorrow compared to today
It’ll be interesting to see if we get a tighter gradient (10-11 millibars) tomorrow but weaker wind out there. We’ll see. Regardless, plan on a few power outages in the metro area, but another sunny day!
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