Why Forecasting Willamette Valley Snow Is So Difficult

If I listed all the reasons, this post would be in the Guinness Book of World Records for being the longest ever.

So, how about the short version?

And it starts like this.

Do you remember December 2008?

A 50 year cold snap helped produce a 40 year snow event in the Portland-Vancouver metro area. This picture is from my brother & sister-in-law’s back patio that epic December week. 18″ of snow on a table in Milwaukie, Oregon? I still can’t believe it.

But it was one of the few times in my 15 years of forecasting here that the snow forecast was so clear-cut: arctic air is here. Big, moist storms come in. Bing0! Big snow.

Snow In The Willamette Valley Is Almost Always A Borderline Situation

• Often, there’s plenty of moisture around – but temperatures are just barely too warm or just barely cold enough for snow. I have to pick which one.
• Other times it’s totally cold enough for snow – but the amount of moisture headed in is marginal. Time to pick again.
• In the case of this week, including today, any snow comes from almost impossible to time showers or bands of showers moving in. And we only know an hour or two ahead of time where these showers are actually headed. In the mid-west, you’d be able to track those showers on radar all day before they got to you. 
• If those showers last long enough or get heavy enough, that brings the snow level to the valley floor for a bit. This will happen part of the time.
• If those showers are light or don’t last very long, it’s mainly snow in the hills with rain on the valley floor. This will also happen part of the time.
• Looking ahead to Friday – some forecast simulations are predicting morning snow showers for our beach cities to start the day.

If the disturbance creating these moves west 100 miles, the coast will see nothing. If the disturbance moves east 100 miles, the Willamette Valley gets morning snow again. I’m watching and will make a choice this evening!

So, do you see what I have to work with here when trying to predict snow in the Northwest?

This is exactly why I joke with people about my real job description: “All I have to do is outguess God!” Definitely easier said than done.