Significant Winter Storm Headed For The Northwest

It was last Thursday morning when our forecast simulations lit up with snow plowing into Washington & Oregon. That night on the five o’clock news is when I started talking about the potential for something big around here. Since then, the forecasting tools we use have taken us on more twists and turns than a John Grisham novel.

A day and a half ago, it looked like we could get 14″ of snow in Portland from Wednesday-Friday. As of last night that number was more like 3-6″ with snow starting Tuesday afternoon and a much faster warm-up for all areas except near – and especially in – the Gorge. Twists. Turns. It’s the stuff our northwest winter storm forecasts are made of!

Winter Storm Forecast: Where We Stand As Of Sunday Afternoon

• we get increasingly cold, dry & breezy as the work week starts. Lows in the 20s, highs slightly above freezing most places
• snow in the metro area starts by the Tuesday evening commute, perhaps a little earlier
• accumulation by 11pm Tuesday: our KOIN forecast model keeps us at 1″ to 2″ in the metro with little or no accumulation for Salem & points south. But another forecast model gives us 2″ to 4″ of snow on the ground in the Portland metro and maybe a quick inch or so for the Salem area (see the colors on this chart). So we still need some fine tuning–there’s wiggle room in both directions!

 

Three important things about this forecast

1. The trend the forecast models developed over the weekend was to shift the main storm’s center of low pressure increasingly north of us. The more north it goes the faster the valley warms up, the shorter the snowfall and the less snow we accumulate. You get the picture.
2. But the freezing cold east wind remains a wild card here. And it’s such a small scale thing that our forecasting tools have trouble understanding exactly how it will impact us. Often it keeps parts of the metro area below freezing while the rest of the I-5 corridor is well into the 40s. This could happen again, perhaps giving some of us  freezing rain overnight Tuesday night into Wednesday morning. On paper, most of the metro area warms into the 40s sometime on Wednesday. We’ll see.
3. This event has “I-84 is closed” written all over it. Those of you in the Gorge could see 6-12″ of snow by Wednesday morning. Then, we could see pockets of freezing rain. Worst of all, our KOIN computer model gives you a serious ice storm from late Wednesday afternoon into Thursday morning. Right now, it looks like that’s from one end of the Gorge to the other.

I’ll post another update with any significant forecast changes by around 9p.m tonight. We can probably expect more twists and turns. John Grisham would be proud of the way the Northwest does winter!