December 27th wind storm wrap-up

I was off on holiday/vacation the past 4 days. After a quick Christmas morning post on social media, I pretty much checked out through yesterday. During that time the thaw finished, downpours commenced, and we had a windstorm. This post is mainly just a recap. That way in the future when I look back this event I’ll see what happened meteorologically.

It was VERY tough to get rid of that cold air. Sure enough, models pushed the cold easterly flow out too quickly last Friday/Saturday and we warmed very slowly on Christmas Eve. That easterly flow continued, although above freezing, through Sunday and Monday. Some spots in the valley hit 60 or higher on Christmas Day in the southerly flow!

By the way, at this point we’re experiencing the coolest December since 2016. That’s a combination of consistently cooler temps and the 3 days of REALLY cold stuff! Still, Portland did not make it down into the teens this time. I think it’s been about 6 years since Portland has dipped below 20! There’s still a chance for another 6-7 weeks or so of course.

As for rain, what a soaker! Between 4-5″ rain in Portland during the 4 day period ending Tuesday the 27th

This rain played a large part in the destructive windstorm on Tuesday. I’ve always noticed our windstorms are more “productive” when we have soaked/saturated soil at the same time. On Tuesday morning, a well-forecast “bent back occlusion” moved inland across southern Washington and northern Oregon. Here’s the WRF-GFS surface forecast for 10am Tuesday, just 6 hours after model initialization time. A main 973mb low moving toward the northern tip of Washington, while a secondary trough or possibly closed surface low moving toward Astoria. Both were beginning to “fill” or weaken.

This is a sort of “double-barrel” low. Radar confirmed this DID occur, in fact the surface “trough” moving onto the coastline sure appeared to be a closed area of low pressure.

That low was weakening while moving inland. Here’s the 1pm forecast

Peak wind for many of us occurred around this time (Noon-2pm). as the weakening low passed by to the north of Portland, tightening pressure gradients. Then by 4pm, the dying low had passed over and east of the Cascades

At this point wind was peaking over the central/eastern Gorge, valleys around Mt. Hood, and north-central Oregon. This DID finally wipe out the last of the cold air as temperatures finally jumped into the 40s in Hood River and The Dalles.

The peak gust of 48 mph at PDX was the strongest southerly wind there in almost two years. We really didn’t have any windstorms (from the south) last winter. Just about all official gusts were in the 45-55 mph range in the lowlands. Here are metro gusts, note Troutdale’s gust is from the east as the storm approached.

Valley wind gusts

And then those strong west/southwest gusts in the Gorge and Hood River Valley

70-80 mph on the river? Must have been quite a sight to see the spray blowing across the water like a hurricane!

Unfortunately there were at least 3 incidents in which trees fell on highways, hitting vehicles and/or causing collisions which led to deaths. East of Seaside on US26, east of Government Camp on US26, and I-84 near Bonneville Dam.

One part of the storm that’s most surprising is the amount of damage and power outages; both seem to be well beyond what we would expect with 45-55 mph gusts (for most of lowlands). To me it appears the damage is more like what we’d see with gusts 55-65 mph. This has happened in the past, and will happen again. Extremely wet weather saturated soils, allowing trees to uproot more easily. Portland alone picked up over 4″ rain in 4 days

You can see the effect on outages. LOTS of us lost power; I was lucky and only out 14 hours. At this moment (10:30pm Thursday), 1,500 of you are still out of power according to PGE’s website. This storm was similar in scope to January 2021, but not as bad as the April 2017 windstorm.

So, lots of rain, then strong wind = plenty of falling trees. We were fortunate that surface low was weakening instead of strengthening as it moved onshore and through SW Washington. Some of Portland’s strong storms (much stronger than this one) have come from that setup.

That’s it for now, I see uneventful weather this weekend as 2022 rolls into 2023. No storms, cold, or snow over the next week as the jet stream aims mainly at California.