We’ve been expecting a nice, slow, relaxed weather week. And that still is the case for almost all of this week…but a brief windstorm MAY cause havoc Wednesday morning/midday. That’s the only time period we’re concerned about.
KEY POINTS
- There’s no need to panic yet, but keep a close eye on forecast the next 24 hours.
- Over the past 24 hours, some models have been pushing a low pressure center quickly up the coastline on Wednesday morning. That would be followed by a quick surge of southerly wind.
- This IS our classic southerly windstorm setup for the western valleys from Eugene to Longview. Not in the Gorge, Cascades, or east of the mountains.
- BUT, everything has to be “perfect” for this to occur. Models are disagreeing on whether it happens. A high-quality morning forecast model says “forget it”
- This will likely be an “all or nothing” event. Either we get a windstorm for 3 hours Wednesday morning/midday, OR within the next 24 hours, we’re able to cancel and say “nevermind…the low is heading east, continue with Christmas”.
- IF some of the stronger wind forecasts are correct, this would be a devastating wind storm in the Willamette Valley. We’ll hope that’s not the case. Some models are spitting out 60 -75 mph gusts! That’s major windstorm territory.
THE DETAILS
To get a big southerly windstorm in the valley, a deep area of low pressure has to move northward close to the coastline. I like to call that “The Danger Zone”. IF THE LOW MOVES INLAND OVER I-5 OR EAST, there’s no storm west of the Cascades. THE LOW MUST STAY OUT ALONG OR OFF THE COASTLINE to get a southerly surge of wind as it passes by. Do you see how everything has to be “just right” (or just wrong) to get a major windstorm here? The faster a low moves, the bigger a danger it becomes. That’s because of the air rushing in behind it.
The Danger Zone(kptv)
For 2 days, the ECMWF (Euro) model has been strengthening a surface low pressure center off the California coast, then shooting it straight north at an incredibly fast pace. We’re talking California border to Vancouver Island in less than 12 hours. Although the surface low hasn’t been forecast to be too deep (980 mb. or higher), the rapid movement and sudden pressure jump behind it would produce a devastating south wind event in the valley (and to a lesser extent along the coastline). That’s because of the north-south orientation of the valley.
BUT, for almost two days no other forecast model has shown this. Then, overnight, other models jumped on board. Check out the WRF-GFS forecast…gusts 60 kts in the valley, that’s 70+ mph wind gusts! That would produce widespread outages and downed trees.
WRF-GFS wind gust forecast(kptv)
The NAM-3KM (tends to over forecast wind gusts) went nuts too. Gusts 65-80 mph up/down the I-5 corridor.
Crazy NAM model(kptv)
Also notice how it’s not extreme along the coastline, and no big deal in Gorge, Cascades, or anywhere in Central/Eastern Oregon.
Our morning GRAF model looked like this; you can see the tight little low pressure circulation just off the coastline at 10 a.m. Wednesday:
GRAF forecast wind gusts(kptv)
That low is moving so fast, that at 1 p.m. the storm is long gone. It’s maybe 1-3 hours of strong wind.
1pm Wednesday(kptv)
SOME GOOD NEWS THIS MORNING
- The morning run of the Euro model has weakened the low and shifted it east, passing pretty much over the Cascades. With this setup? Nevermind, it’s just a breezy west/northwest wind as the low passes by. Christmas continues and we can forget about it.
- We use “ensembles” of models to get a better idea where a low pressure center might move and how deep it’ll be. The morning ensembles from the Euro have shifted the low quite a bit as well.
Here’s the overnight run…lots of low pressure centers offshore (BAD).
Overnight Euro low locations(kptv)
Then from this morning’s run…far more scattered and most of them east of I-5 (GOOD!). Almost none of the 50 members of the ensemble would produce a windstorm here. Ignore all of the ones centered over Mt. Rainier, that’s a terrain issue.
Euro low locations from AM run(kptv)
SUMMARY
There’s a decent chance we can “call this off” within the next 24 hours, but pay close attention! If we get a significant windstorm, it’ll mess up a lot of Christmas plans. For now we’re calling Wednesday a FIRST ALERT WEATHER DAY for the possibility of strong wind.
We get new model information about every six hours, so make sure you are following me on my Facebook page, and I’ll be on-air this evening at KPTV of course.
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