Thursday Morning Update

Good morning everybody! Snow just started falling in Portland a few minutes ago (around 9:37 for my neighborhood). The flakes are very dry and light and are getting blown this way and that by strong easterly gusts through the Columbia River Gorge.

Speaking of gusts, let’s take a look at what Crown Point is doing this morning.

We’ve had multiple gusts over 70 mph, with a peak gust off 78 mph at 5:36 this morning. Things are picking up here in Portland too, with a gust of 45 mph at 9:25 this morning.  Crown Point gets northerly winds due to the local topography there, but look at how consistently the winds have been blowing from the east at the Portland Airport, which is just south of the Columbia River.Things are far less windy up north in Seattle, but the foothills are getting some very strong gusts. Enumclaw is currently gusting to 55 mph, and Snoqualmie is currently gusting to 48. Joe Richards in North Bend reports 40-50 mph gusts for the past 12 hours!

As I mentioned last night, the reason we are seeing such strong winds is because there is a large east/west pressure gradient across the Cascades. Air flows from high pressure to low pressure, and when there are large barriers blocking its path (such as the Cascades), it finds its way through gaps and accelerates at the exit regions of these gaps.

The Troutdale-Dalles (TTD-DLS) pressure gradient is currently -9.7 hPa, meaning the pressure at Troutdale is 9.7 hPa lower than the pressure at the Dalles. According to some local Portland meteorologists (thank you Mark Nelsen and Rob Grimes), our “major” events generally require a gradient between -12 and -14 hPa, and none of them have ever seen it reach -15 hPa. I can’t even imagine what Crown Point would be like then!

Taking a look at current radar imagery, you can see that precipitation is just spreading into SW Washington right now. This precipitation is very light and is more of a “tease” than anything else. Heavier snow is currently south by Salem and is working its way northward. My friend Tessa Harvey in Salem sent me these pictures below and reports that the snow is making her want to ski “so bad.” Though I’d wait for a slightly larger base to accumulate before practicing my pizzas and french fries, such a scene certainly conjures up dreams of skiing through the streets.

Right now, it appears as though Tess and her friends in Salem will see an hour or two more of snow before switching over to rain. Temperatures there are currently right on the cusp of freezing, so any freezing rain will be short-lived. Portland and areas closer to the Gorge will be insulated from the warming aloft by strong easterly Gorge flow, but they too will eventually transition over to a mix of sleet, freezing rain, and eventually regular rain as the night goes on. I will keep an eye on some of the surface and upper air observations and give you updates throughout the day with more specific timing for this changeover, but at the moment it appears as though the change will occur in the midday hours for places away from the gorge and further west and the evening hours for places closer to the Gorge and further east. Areas like Hood River may stay as snow throughout the entire event and could see up to 10 inches, while Portland and the surrounding areas will likely see amounts in the 2-4 inch range.

Seattle is dry now, but we will likely see flakes start to fall around 10 pm this evening, give or take a couple hours. We’ll likely skip the whole freezing rain deal as the cold air is less entrenched here, and we should see several hours of snow before switching to rain Friday morning.

Thanks for reading the blog, and remember to follow WeatherTogether on Facebook and Twitter for all the latest updates throughout the storm. Oh, and next week could be cold too, but let’s get through this storm first. 🙂

Have a nice day!
Charlie