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Is it REALLY going to snow?

by Matt Zaffino

Bio | Email | Follow: @Zaffino

Posted on February 22, 2011 at 2:29 PM

Updated Wednesday, Oct 30 at 3:59 AM

That's the question I'm getting most often now. Hey I'm not holding out! What I tell viewers on air is what I REALLY think is going to happen! Could I be wrong? Yes. Portland snow forecasts as you probably know, are complex and tricky. Here are my latest thoughts.

Forecast pattern looks similar to what it looked like last night, with a couple minor differences.

We may get a little snow in the valley late Tuesday night or Wednesday morning before it turns to all rain below about 500 feet Wednesday afternoon. That's because with south to southwest winds it should warm up enough in afternoon to make it rain below 500 feet.

But as temperatures fall Wednesday night, we're still on track for all snow in the Portland area Wednesday night and Thursday. Check out the forecast map below: 


You see low pressure (the black circles with the "L" in the center) off the Washington coast. The blue color over Portland equates to a temperature at roughly 2500 feet of about 28°, which translates into a sea level temperature of about 37°. So it's still borderline for snow until later Wednesday night, but with colder air advecting (moving in) and decent precipitation rates, it should be enough to get snow down to the valley floor Wednesday night.

The storm off the Washington coast will slowly move south to the mouth of the Columbia River Wednesday night. As it does, colder air continues to overspread northern Oregon.

Here's the 3-hour snowfall map from 4 am Thursday to 7 am Thursday:

This model paints an inch over Portland proper for this 3-hour period, with more to the south, including on the beach. What I like about this is it shows the nature of the snowfall. There will probably bands of heavier snow, surrounded by lighter snow. So it may be, for example, that Yamhill County sees three inches over this time frame while Multnomah County only gets an inch. 

Thursday morning is probably going to be the worst of it for drivers. We're also looking at record low temperatures Friday and Saturday. The cold may end up having more of an impact for some folks than the snow. 

The second most common question I get is "will it shut down the city?"

That's up to all of us on how we handle the snow and where we decide, in true Portland fashion, to abandon our cars.

Stay tuned!

Matt Zaffino

Chief Meteorologist

KGW NewsChannel 8