I just got back from a weekend vacation at my uncle’s place in Pacific City, Oregon, but how I wish I could stay just one more night! Why, you may ask? The first significant windstorm of the 2017-2018 storm season is predicted to bring fierce winds to the coast Monday with 20-30 foot waves. Thankfully for a weather nerd like me, Portland is still predicted to get a pretty substantial blow today.
There’s nothing that warms my heart quite like the smörgåsbord of warnings and advisories that come with storms like these.
There are a couple of things that make this windstorm unique compared to other windstorms I’ve experienced recently in the Pacific Northwest. First, there was a ton of lightning associated with the cold front of this windstorm. I can’t ever recall hearing reports of more than a couple of flashes of lightning with windstorms in the past. According to the Portland NWS, we were averaging 100 strikes per hour at around 5 pm this evening. It sure looks like it based on the distribution of strikes below.
Additionally, this low is what we call a “double-barrel low,” as another, secondary low pressure center will form as the low deepens. This will stall its SSW-NNE trajectory and redirect it ENE towards Southern Vancouver Island, bringing the “bent-back-occlusion,” the occluded front that wraps around the center of low pressure, directly into the SW Oregon/NW Washington coast. Bent-back-occlusions are infamous for being the region with the strongest winds in an extratropical cyclone, and Monday’s will live up to the bill, with 50-knot sustained southwesterlies sending 20-30 foot waves into the shores of NW Oregon and SW Washington. The low will make landfall near Southern Vancouver Island as a highly degraded 990 hPa cyclone around 2 pm today, but the bent-back-occlusion will extend far enough south to bring advisory level winds to places throughout the northern Willamette Valley and Puget Sound Lowlands.
The animation below from the 00Z 11/13/2017 WRF shows the predicted path of the low from 5 pm PST 11/12 to 8 pm PST 11/13. Notice how the low slows its northward trajectory at the beginning and remains stationary while continuing to deepen from 9pm to 12 am, after which it begins to travel east.
Let’s start by taking a look at the current water vapor satellite imagery. The imagery doesn’t look all that impressive – the well-defined “dry slot” near the center that existed a couple of hours ago is no more, and it is impossible to determine the center of low pressure just from looking at this image. However, the storm is still deepening, and you can see a large bent-back-occlusion extending eastward from the storm’s center, which I believe is currently located around 46 degrees north and near or just east of 130 degrees west.
The storm is now close enough to land that we can get some observations from buoys offshore. Buoy 46002 at 42.612N, 130.537W (approximately 275 nautical miles west of Coos Bay, Oregon) saw increasing winds with the approach of the system’s powerful cold front, which likely passed through at around 5:10 pm due to the sudden drop in temperature and transition from SSW to SW winds compared to the 5 pm observation. After a relative lull in winds immediately following the cold frontal passage, even stronger WSW winds coincided with the post-frontal pressure rise. Now, winds are finally weakening as pressure rising rates decrease. The peak gust of 52.4 knots (60 mph) occurred at 630 pm from the WSW and was associated with the strong post-frontal pressure rise.
The WRF did a nice job modeling this immediate decrease in winds along the storm’s trailing cold front. I haven’t studied this feature before when monitoring strong extratropical cyclones in the Pacific Northwest, but I will definitely start paying more attention to it. Fronts are the defining feature/features of midlatitude cyclones.
Now that we’ve taken a look at what’s happening out over the ocean, let’s take things back to the North American continent. We’ll start by looking at the current gusts around the region.
So far, the highest gusts are at Marys Peak (71 mph), Cape Blanco (66 mph), Gold Beach (52 mph in town, 67 mph at the Flynn Prarie RAWS station just outside the city at approximately 1,500 feet), and Quail Prairie Lookout (53 mph). With the exception of Gold Beach, these stations are all coastal headlands or mountains and are very exposed, so that is why they are experiencing such strong winds. Winds are increasing along the central Oregon Coast, with many coastal communities now recording gusts in the 30s. Most inland locations have light winds.
The radar image below shows the storm tracking north towards the Pacific Northwest, with a large rain shield (don’t know if that’s an official meteorological term) off the Washington Coast and a cold front stretching all the way to 100 miles or so off of Cape Mendocino, California.
By the time you’ve read this, the cold front will have already made landfall along the coast. Portland should see an hour or two of moderate-heavy rain rates shortly after midnight, with Seattle experiencing similar rain rates a few hours later. In the meantime, pressure will drop, seas will build, and wind will increase as strong southwesterlies filter into the region behind the cold front.
The real fun begins around mid-morning today, as the aforementioned storm’s “bent-back-occlusion” swings through the area and delivers extremely strong winds to the Washington/North-Central Oregon Coasts. If the model below is to be believed, today will be a fantastic day to go storm-watching at Cape Disappointment.
You can see the bent-back occlusion in the model image below, which plots outgoing infrared radiation and simulates an infrared satellite image. It’s interesting how such a dilapidated-looking storm can deliver such powerful winds, and it’s all due to that bent-back occlusion.
After the coast gets absolutely hammered for 3-4 hours (likely starting between 9-11 AM), the bent-back occlusion will move inland and they’ll begin to calm down. Portland should have a brief (1-2 hour) period of advisory-level winds midday as the bent-back occlusion comes through, while Seattle’s window of highest winds will begin a few hours later and last between 2-3 hours. As we’ve experienced with recent windstorms, even advisory-level winds can cause massive power outages and tragic deaths due to falling trees, so please don’t let the “advisory” terminology give you a sense of security. For more on windstorm preparedness, click here.
Total rainfall amounts from this system will substantial but nothing out of the ordinary – a couple of inches in the mountains and up to an inch in the lowlands, with most places seeing less. Snow levels will drop precipitously after the cold front moves through tonight, and the Northern Oregon and Washington Cascades could see a foot of snow above 5,000 feet from now through early Tuesday morning. With snow levels near 4,000 feet, Snoqualmie Pass will unfortunately likely be a rain/snow mix, but snow levels will lower below 3,000 feet later in the week, and even Snoqualmie Pass should be able to get some snow.
I plan on doing a post-storm writeup on this blog and may do a more in depth writeup on The Storm King if this storm proves worthy and I have the time. I’d love to have some of your pictures from this storm for a review blog, so if you have any that you’d be willing to share, please send them to me at email@example.com.
Thank you and stay safe,