Addressing Next Week’s Snow Rumors

I love the convenience of modern technology. I love how I can pay 10 bucks a month for a music streaming service instead of hauling around a bunch of cassette tapes, I love how I can chat with my brother across different continents, and I love being able to blog about weather, nature, and life and share it with you all. And I even love the myriad of weather apps out there – even though they are automated forecasts, don’t capture all the idiosyncrasies of our climate, and can be misleading in the long-range, they do an extraordinarily good job all things considered.

But there are always several times a year when the dreaded “snowflake” icon shows up in the extended forecasts. One of those occurrences was Wednesday evening, and from the moment I walked in the office Thursday morning, I was playing damage control and trying to downplay the potential for any snow over the next 10 days. While I’d be lying if I said there was no chance of snow, our chances, unfortunately, look pretty darn slim, though the Southern Willamette Valley could potentially (one of a meteorologist’s favorite words) see some snow on Tuesday or Wednesday.

Weekend forecast: 

We’ll have a pleasant enough weekend, with mostly sunny skies this afternoon and increasing clouds this evening.

We should see a few showers early Sunday as a weakening front pushes through the area.

While this front won’t bring much precipitation, it will usher in chillier temperatures with moderate/strong onshore flow. The freezing level over Mt. Hood should drop from around 10,000′ this afternoon to 4,000′ Sunday afternoon after the frontal passage. After the morning precipitation, we should see partly cloudy skies Sunday afternoon, but a few more showers may sneak into the area Sunday night ahead of another system slated for Monday.

Next week:

Monday

Our real pattern change begins Monday as a deep upper-level-trough sags south and brings much cooler-than-average temperatures to the entire Western US. With a big ridge offshore and trough inland, we’ll have cool, unstable northwesterly flow aloft, and the aforementioned Monday system will create plenty of showers over the area.

This is a great pattern for mountain snow, but unfortunately for lowland snow lovers, the air is not quite cool enough for sea-level-snow. An ideal pattern would be closer to the one below, with a more amplified ridge over the Pacific with a favorable “tilt” – i.e. the ridge extends NNE into Alaska/the Yukon, allowing cold north or northeasterly flow instead of chilly northwesterly flow – and a sharp trough just to the south of the area bringing both precipitation and a reinforcing shot of cold northeasterly winds.

BTW, yesterday was the 9th anniversary of that event, which brought a surprise 2-5 inches to Seattle (most was expected to go south) and resulted in this viral video of cars and buses sliding down an icy street in Seattle’s Capitol Hill neighborhood. It remains my second-favorite Seattle snow event after the epic thundersnow of 12/18/2008, which was the first event to really thrust me into the spotlight as my high school’s resident weather geek.

Tuesday-Wednesday

Tuesday-Wednesday is our best shot at seeing any lowland snow, but it still looks very unlikely at this point. As the chart above shows, we will see a more “textbook” pattern as the ridge offshore amplifiess and begins to “tilt” into Alaska, but the trough over our area is too deep, with Southern Oregon/Northern Californa seeing a system while Seattle and Portland remain high and dry.

However, the American/European ensembles (a suite of models with slightly different initial conditions/physics schemes) show a wide variety of solutions, with some taking this low further north and giving Portland a bit of snow. Additionally, models have been trending northward with this low, and many solutions show it as a fairly intense system with a central pressure below 980mb. The University of Washington WRF model offered a nice view this morning, showing an intensifying ~979 mb low headed towards the California/Oregon border. While this is too far south to bring any snow to the Portland metro area, it would bring heavy snow to the extreme Southern Willamette Valley and extremely strong, ‘Deadliest Catch worthy’ northerly winds offshore.

Thanksgiving Weekend and Beyond: Dry, Sunny, and Chilly

Any sort of snow chances end for Turkey Day and Black Friday (or “Consumerism Day,” as I like to call it) as the trough digs further south towards Southern California. We’ll see sunny skies with highs near 40 and lows in the upper 20s, and the typical places near the Columbia River Gorge will see a biting East Wind as a cold pool with surface high pressure establishes itself over the Columbia Basin.

By next week, it looks like we’ll unfortunately transition back to a boring, highly amplified pattern with a ridge over the Intermountain West and a deep upper-level low over the Pacific. This type of pattern is known as a “blocking pattern,” as it shields the afflicted area from any storms associated with the prevailing westerly, zonal flow. In the winter, such a pattern often results in inversions/fog (especially in the Columbia Basin) and depressed weather geeks anxiously waiting for a pattern change. I wish I could give better news, but it looks like this pattern will stay with us through the first week of December and potentially beyond. Us weather geeks just can’t catch a break from this boring weather!

Summary:

We’ll see chilly and wet weather on Monday with snow above 2,000-3,000 feet. We have a very slight chance of lowland snow on Tuesday/Wednesday as a deep upper-level trough moves over the region and gives us a shot of colder air, but any precipitation is currently expected to be well to our south, and even if future model runs move it northward, the airmass over our region isn’t particularly frigid and it would still be a longshot to get accumulating snow at sea-level. We’ll dry out for Thanksgiving weekend with sunny skies, below-average temps, and a chilly east wind, and the following week looks like yet another unseasonably calm and boring week as a blocking pattern sets up off the West Coast and inversions form over the area, giving am fog to the I-5 corridor and potentially leaving the Columbia Basin perpetually foggy.

Have a wonderful Thanksgiving weekend, and be careful if traveling over the passes this Monday or Tuesday – you will most likely encounter some snow!

Charlie