Windstorms

A Review of the Bomb Cyclone & Quick Look Ahead

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The “bomb cyclone” is here, and wow, does it look impressive on satellite! This looks like something you’d see in the Gulf of Alaska, not the Pacific NW.

The storm dropped to approximately 942 mb, setting an all-time record for lowest pressure measured off the Pacific NW coast. It passed directly over buoy 46005, approximately 300 nautical miles (345 statue miles) west of Aberdeen, and the buoy recorded a minimum pressure of 942.43mb, or 27.83” Hg.

Gusts at the buoy also topped out at 67 mph – not as strong as you’d see in a hurricane, but still very impressive. The *relatively* weak gusts near the center of the storm can be explained by the sheer size of the cyclone and how steep pressure gradients were distributed over a wide area. Take a look at the modeled pressure chart from WeatherTogether’s model page below.

According to UW professor Cliff Mass, the previous record low pressure for a storm off our coast was 950 mb, set during the November 14, 1981 windstorm, one of the strongest windstorms to hit the Pacific Northwest on record. The main reason why this storm was so much weaker despite having a lower pressure is because it is much further offshore.

Nevertheless, the storm has caused quite a bit of damage – more than I was expecting. In the morning, we saw easterly winds pick up in the Cascade foothills due to increasing offshore gradients ahead of the storm, particularly in the “usual suspects” downwind of the Cascade passes like Enumclaw (Stampede Gap) and North Bend (Snoqualmie Pass/I-90). This is due to strong offshore pressure gradients as the storm lay due west of the Puget Sound area. Forecast models did a good job with wind speed, with winds gusting up to 30-45 mph in most locations, but with this being the first good blow of the season and the winds being from an unusual direction, the there was an unusually large amount of damage for the amount of wind over the area.

The below video shows the winds near North Bend around 8am this morning. Even as gusts were reaching the mid 40s in the foothills, Sea-Tac was only gusting to 20 at 8am, showing how localized these strong gusts were to the eastern Puget Sound lowlands.

The power outage map from PSE reflects this well. Notice how there were nearly no outages this morning west of Lake Washington, but once you got east of I-405, outages picked up substantially. Enumclaw and North Bend were hit hard, with the Lake Sammamish area also seeing a sizable blow.


In the afternoon, a strong squall bringing lightning, very heavy rain, and gusty southerly winds brought another round of outages to Western Washington and Western Oregon, with most outages again being primarily located east of I-205. The bands of showers rotating inland from this storm were associated with quite a bit of low-level shear and some instability and were pretty robust, with the Portland NWS office issuing a few severe thunderstorm warnings for the PDX metro for storms with winds gusting to 60 mph and penny-sized hail. Salem saw a wind gust of 57 mph and briefly lost power during the event.

Radar at 1:29 pm 10/24/2021, showing a powerful squall line passing through the Willamette Valley and Puget Sound

The Portland office has also been issuing “special marine warnings” this evening warning of the potential for waterspouts/weak tornadoes due additional showers moving inland, many of which are weakly rotating due to the low-level shear.

Radar this Credit: UW Atmospheric Sciences

Tragically, a falling tree killed two people falling tree took the life of two people on Preston Fall City Road this afternoon, just east of Issaquah. One of my friends I know through the online weather community told me he’d driven on that road many times before and that the cottonwoods along the road looked compromised, so they could have toppled relatively easily under these gusts. It’s so heartbreaking to hear these stories, and unfortunately, it is not unusual for even minor Pacific Northwest windstorms to have fatalities from trees falling on cars or directly onto people.

Forecast:

This event is not over!!! We are seeing a break in the action now, but the wind and rain will pick up again overnight and into Monday as this behemoth of a storm meanders towards Central Vancouver Island and weakens in the process. The strongest winds will be over the Northern Interior tomorrow and not the eastern Puget Sound Lowlands, like they were today. The chart below shows the current watches/warnings/advisories over Western WA… High Wind Warnings are in effect until 6pm Monday for the Washington Coast and 6am Tuesday for the Northern Interior.

Credit: NWS

Showers should arrive in the morning and increase in intensity through the afternoon/evening as the low approaches Vancouver Island. I’m not expecting much lightning/hail with these showers and they shouldn’t pack the 50+ mph wind gusts that they did today in some locations, but they’ll still definitely be heavy showers by Pacific NW standards. You don’t want to get caught under one of these unprepared!

3hr precipitation ending 2pm Monday 10/25/2021
Credit: UW

By 2pm tomorrow, the low will have weakened to the mid 970s, but it is in a much more favorable location for areas north of Everett to see strong, SSE winds. The rest of Puget Sound will be gusty, but I’m not expecting the same sort of damage we saw today.

Sea-level-pressure at 2pm Monday 10/25/2021
Credit: UW

I imagine the peak winds for areas north of Everett will probably be from noon – midnight Monday, and the power outages should incrementally pile up over the Northern Interior during that time. Tuesday should feature frequent showers but decreasing winds, and a strong but much more “typical” storm should come through Wednesday night into Thursday, bringing heavy rain and some wind along the coast.

And finally, before I sign off for the night – I thought I’d share a link of the 29th annual Oregon AMS winter weather conference, which was hosted virtually and recorded this year. The winter weather conference happens every October and features a bunch of meteorologists that give their thoughts on the upcoming winter, and this was my first year giving a presentation! I’ve embedded the presentation below, feel free to give it a view if you’re curious about our winter weather outlook. And the Oregon AMS is always looking for new members, so if you’d like to join, click here to get yourself set up with a membership! It’s a measly 10 bucks a year and you get so much for your money… wonderful guest speakers, conferences/dinners, and of course, a great community to meet like-minded Pacific Northwest weather geeks.

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