Will it snow in Portland this coming Monday or Tuesday? Sure, maybe in the air, but it’ll be far tougher to get more than a dusting down to the valley floor. My thinking hasn’t changed much the past two days because models have been doing a very good job with the evolution of the weather pattern over the next week. The end result is a cold upper-level trough descending on the Western USA
A strong cold front moves through the region the 1st half of Sunday. Behind it, the snow level (the lowest level in the atmosphere in which snow sticks) drops to around 1,500′ the rest of the day Sunday. So the Coast Range passes may see some snow come and go during the day, and of course the Hoodland corridor from Brightwood to Rhododendron should see some snow too. Models haven’t been showing temperatures cold enough for sticking snow lower than that Sunday, so I’m quite confident with this first part of the forecast. We’ll see showers off/on Sunday with a few flake possibly mixed in at times here in the lowest elevations. Temperatures hover in the low-mid 40s.
It gets more interesting Sunday night and Monday as cooler air continues pouring in. By Monday morning, any decent showers should be able to drop a dusting down to around 1,000. I’m pretty confident that if you live above 1,000′ you could wake up to at least a light coating of snow. Here in the city it’s more likely we’ll just have scattered showers milling about Monday morning with any of them containing snow too. Temps remain ABOVE freezing through the day Monday below 1,500′. The ECMWF and the GEM both show onshore low-level flow and a mixing southerly wind continuing through Monday AM. That generally kills the lowest elevation snow chances pretty well. But not always, see the next sentence.
The one item I’m watching closely is the possibility of a more organized band of showers and/or surface low pressure center passing by Monday morning/midday. THAT is the one thing that can drag the snow level lower in this pattern, and has in the past. The GFS depiction of snowfall pretty much agrees with my general this assessment, showing any real snow staying out of the lowest elevations:
Just so we’re all on the same page. This setup with cold showers streaming onshore Sunday night through Monday is not our “big snow/ice storm” pattern. The big snowstorm almost always happens when cold & dry air is in place (usually via cold easterly wind out of the Gorge) and THEN moisture returns overhead.
Speaking of that, it appears we go pretty much dry Tuesday and at least part of Wednesday as drier and colder Canadian air fills in from the north. We should finally have a widespread frost and some chilly daytime highs only around 40 degrees both days.
Models are then in relatively good agreement that a strong system pushes inland later Wednesday and Wednesday night to end our little mini “cold spell”. The ECMWF (and to a lesser extent the GFS) imply this could start as snow even in parts of the valley, and for sure in the Columbia River Gorge. I’m feeling somewhat confident that some sort of snow/ice “event” is on the way for the Gorge later Wednesday through Thursday. I’ll be watching this closely as well because, as mentioned above, this kind of setup (with the cold air in place) can cause quite a bit more havoc with transportation through the Gorge and possibly in the metro area. I noticed 28 of the 51 the ECMWF ensemble members show 2″ or more snow in Portland by next Thursday, lending a bit of confidence.
By the way, don’t forget one of my favorite websites…almost always right on! http://isitsnowinginpdx.com/
Just for the Christmas season, the blog snowflakes are turned on as well…enjoy. The astute reader will notice the angle of the snowfall will change as you move the cursor…that’ll kill some work time for you.
Chief Meteorologist Mark Nelsen