Bomb cyclone flexes muscle offshore but we’re spared this time

Weather Blog

PORTLAND, Ore. (KOIN) —  We’re enjoying a very benign start to Thursday morning in Portland with partly to mostly cloudy skies and out-the-door temperatures in the low 50s.

After a day with rain Wednesday, it’s nice to have a break Thursday morning. Ok, did we jinx it? All this talk about pleasant weather, surely there must be something brewing.

Look out over the eastern Pacific and you’ll see a large rotating comma. This burbling brew is what we call a bomb cyclone — a.k.a. bombogenesis — a.k.a. an extratropical cyclone.

Image credit: CIRA RAMMB

Bombogenesis, a popular term used by meteorologists, occurs when a midlatitude cyclone rapidly intensifies, dropping at least 24 millibars over 24 hours. A millibar measures atmospheric pressure. This can happen when a cold air mass collides with a warm air mass, such as air over warm ocean waters. The formation of this rapidly strengthening weather system is a process called bombogenesis, which creates what is known as a bomb cyclone.

NOAA. What is Bombogenesis? National Ocean Service website, https://oceanservice.noaa.gov/facts/bombogenesis.html, 02/26/21.

Don’t be fooled by this lumbering low, it’s already creating hurricane-force winds hundreds of miles offshore. Just one day ago, it was half the strength it is now. I’m not the only night-owl meteorologist with eyes wide open, jaw to the floor. Read this snippet from the National Weather Service PQR discussion:

Water vapor satellite imagery over the past 12-24 hours shows one of the most impressive cyclogenesis events in recent history off the Pacific Northwest coast. WPC surface analysis places the main surface low pressure at 953mb near 136W and 47N when at this time yesterday it was near 1000mb.

https://www.wrh.noaa.gov/total_forecast/getprod.php?new&prod=XXXAFDPQR&wfo=pqr

Forecast

Luckily for us, the wolf in sheep’s clothing is not advancing towards us and will be tracking to the north. Rain is expected over Portland and the valley by 2 or 3 p.m. as the cold front arrives, and then gusts may reach 20-30 mph for the afternoon. 

The strongest wind gusts along the south-central Oregon coast may start as early as 8 a.m. and continue through the afternoon. The strongest gusts up to 60 mph should remain south of Florence.

Peak gusts for the northern Oregon coast near Tillamook/Cannon Beach may experience gusts up to 35-40 mph from 11 a.m. to 3 p.m. roughly. There is a chance for thunderstorms at the coast this afternoon and evening. 

Alerts:

High Wind Warning south-central Oregon coast 

Wind Advisory – Medford area

Gale Warning for coastal waters

Storm Warning 60-250 nm offshore

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