Mild Winter So Far, But Colder With Snow Close to Sea Level Ahead

January 17, 2021

9:30pm Sunday…

Here we are in mid-January, halfway through meteorological winter (December-February). We’ve had ONE significant weather event during that time west of the Cascades; the wind and rain storm earlier last week. It has been a very mild winter as well. By the way, I just confirmed the peak gust at PDX was 50 mph during the last minute of January 12th (11:59pm).

December 1st through January 16th has been the WARMEST 1ST HALF OF WINTER ON RECORD IN PORTLAND! You like that big red font? This comes with one big caveat. Portland has grown tremendously and we have an “urban heat island” now. It’s most noticeable at night. A lot more people live here compared to 60 years ago. That means even if the climate was not warming (it is), we would be seeing Portland’s average temperature rising due to that effect alone. But check out Redmond (little/no urban influence there). It’s the warmest since 1951! And Olympia has seen the 3rd warmest after 1951 & 1981. Going back 100 years, Salem has seen its 5th warmest first half of winter. My point is that yes, it has been a very mild winter…so far.

Snowpack is well below normal, running about 60-80% of average in the Cascades. Yet 2018, 2012, & 2011 La Nina years saw similar or lower snowpack at this point around Government Camp. Many of these years we play “catch-up” with snowpack in February/March. We’ll see.

Of course weatherwise it’s been a very slow winter (again) for forecasters but we think that will be changing as we head into a colder weather pattern. And yes, we may be flirting with low-elevation snow at some point in the next 10 days.

Quick Summary

  1. The next 7 days will be much drier than average, it’s possible we don’t seen any rain until NEXT Sunday
  2. There’s no sign of an “arctic blast pipe-buster” for at least the next 10 days. That is a big shot of cold air from Canada; think lows in teens or lower and highs around 30 or below. I don’t see that happening.
  3. Beginning next Sunday, expect a cold & wet weather pattern with heavy Cascade snowfall
  4. Beginning next Sunday, we may see our first widespread foothill and Coast Range snow plus there may be more beyond that. This winter, sticking snow below 2,000′ has been rare. That will change for the final week of January. If you live between 1,000′ and 2,000′, you can expect to see snow more regularly beginning next Sunday.
  5. AT THIS POINT, we do not have (sticking) snow in our forecast (for lowlands) through at least next Sunday. That’s because we don’t see a setup that would drag sticking snow all the way down to the valley floor, or sea level. But it may be close to sea level at some point in the 7-10 day range. Keep a close eye on that Sunday-Tuesday forecast NEXT week.

What’s Changing?

We have a strong upper-level ridge right over us and it’s staying put through Wednesday. This is the flow of air up around 18,000′ (500mb). I’ve annotated the ridge with a yellow line. This is Tuesday

By Thursday, a cold upper-level trough is dropping down the back side of the ridge as it backs off to the west.

But it appears just about all moisture will remain offshore, so we’re going with just a few light showers (rain) Thursday evening. Weather geeks will remember that THIS was going to be the big system that would drop south and bring in arctic air at the end of the week. That was on some models maybe 5-7 days ago. Now it’s just a weak ripple in the northwesterly flow. Then by Monday the 25th, a much deeper & colder trough is moving into the Pacific Northwest

This one is preceded by a stronger cold front and plenty of moisture next Sunday. Depending on the exact track of surface low pressure, this setup CAN bring snow to sea level. I’ve got two thoughts on that. First, neither the GFS or ECMWF models at this moment retain enough cold offshore flow to bring widespread sticking snow to the valley floor. That’s because the low is coming in from the northwest. Second, the air isn’t that cold to begin with and we’re quickly going to onshore (mild) flow. That’s almost always a snow killer. That system next Sunday reminds me of several during the 2007-2008 winter that brought abundant snow to Detroit, the Gorge, Coast Range, and the Cascade foothills. But not quite cold enough for lowest elevations to get in on the snow action. 850mb temperatures are forecast to be around -5 to -6…again, not quite cold enough for a big snow event in the metro area next Sunday. I think the ECMWF rain/snow forecast shows the situation well for Sunday night

Beyond that, the upper-ridging wants to move even farther west of us, allowing a cold trough to set up over the Gulf of Alaska and send cold waves of moisture our way. A quick animation of those upper-level heights from next Monday the 25th to Monday February 1st (a full week), shows the progression westward, along with the coldest air

The final image tells me a lot.

It says that beyond about day 10, we’re into a classic La Nina pattern that’s wet and cool. Tons of mountain snow, but not much chance for it in the lowlands. This will likely be the first big week of mountain snow this winter, maybe like the middle of last January?

Check out the ECMWF ensemble forecasts for snow. About 1/3 to 1/2 produce “sleddable” snow in the Portland metro area sometime in the next 2 weeks. I think that might be generous considering what I’m seeing right now.

You can see model forecasts of high temperature (usually a few degrees low) dip to a minimum early NEXT week and then rise again as we get more systems off the mild Pacific. This is the GFS.

One more thing that gives me confidence that we’re not headed into a major cold/snowy spell…the 850mb ensemble charts. Excellent agreement through the next 7-9 days, then a rise (warming). Almost no members below -7 through the next two weeks. This is just the ECMWF, but GFS is similar.

This wasn’t the case 5-7 days ago. As we get closer to a change, models come together most of the time and this is a good example.

That’s it for now. Of course even without a “major cold/snowy spell”, we can get an event where part of the lowlands get snow and that may not show up until just a few days ahead of time. I’ll be working regular shifts for the next 3-4 weeks as we wrap up this “winter”. We should still be having some fun even if no widespread snowstorm shows up in the valleys.

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Chief Meteorologist Mark Nelsen