The Portland NWS issued a “Special Weather Statement” at 4pm warning of the potential for “cold core funnel clouds” this afternoon. But what is a “cold core funnel cloud,” you might ask??
Special Weather Statement National Weather Service Portland OR 400 PM PDT Tue Jun 16 2020 ORZ006>008-170100- Greater Portland Metro Area-Central Willamette Valley- South Willamette Valley- Including the cities of Hillsboro, Portland, Wilsonville, Oregon City, Gresham, Troutdale, Salem, McMinnville, Woodburn, Stayton, Dallas, Eugene, Springfield, Corvallis, Albany, and Lebanon 400 PM PDT Tue Jun 16 2020 ...COLD CORE FUNNELS POSSIBLE LATE THIS AFTERNOON... Isolated thunderstorms are developing in the Willamette Valley this afternoon, and the environment is favorable for cold core funnels. These funnel clouds do not usually touch the ground. However...if they do touch the ground they are dangerous and can be damaging. We have seen rotation in some of the showers this afternoon on the National Weather Service Doppler Radar. Please safely keep an eye on the sky and pass on any reports, photos, or videos of funnel clouds you may have. $$
Well, these funnel clouds are called “cold core” to distinguish them from the much stronger “warm core” funnel clouds and tornadoes in supercell thunderstorms. A supercell thunderstorm is defined by the existence of a mesocyclone – a deep, warm, rotating updraft – and the surface extension of this rotating updraft is – you guessed it – a tornado.
The vast majority of our storms lack any sort of organization whatsoever and we almost never supercell thunderstorms, though they are not unheard of west of the Cascades. However, we can still get strong, localized vortices that develop within a shower itself, and these can briefly touch down as a weak tornado. This is exactly what happened in Damascus on Saturday evening.
All of this funnel cloud talk is courtesy of a deep upper-level trough coming through the Pacific NW and combining with daytime heating to create a few short-lived thundershowers over region. The Portland NWS notes that they have seen some rotation some of the stronger showers, and their forecast discussion also notes the existence of some low-level wind shear. Even a weak tornado is pretty unlikely from this setup… they are rare beasts for the Pacific NW. Still, I would not be surprised if there was a funnel cloud sighting.
Credit: College of Dupage
Funnel cloud or no funnel cloud, these showers will give brief periods of heavy rain, small hail, and even a few strikes of lightning, so don’t get caught unprepared outside! Showers should decrease more dramatically by 8pm tonight.
