First December Tornado Watch in the Historical Record. NOAA has issued a Tornado Watch, valid for portions of southern Minnesota, until 8pm. Watches and warnings may be issued farther north, possibly including the MSP metro area.
And just like that, instant spring: 50s - even a few 60s over southern Minnesota this afternoon. Between the rain and the quick-thaw I've never seen snow melt so rapidly. Any sunshine will energize the atmosphere, and a small, compact storm approaching this evening will set off a squall line of strong to severe thunderstorms capable of wind damage, especially south and east of the Twin Cities.
Future Radar. NOAA's 3km HRRR model brings a line of strong to severe T-storms into the metro area by 7 pm this evening.
How can this happen with snow on the ground. Potentially record warmth, coupled with high water levels (for December) and strong dynamics aloft (powerful, twisting winds called "wind shear" capable of causing T-storms to spin like a top). It's the spinning T-storms that Doppler radar picks up, and I suspect there will be severe storm and possibly even tornado warnings for parts of southern Minnesota and southwest Wisconsin by the evening hours. Surreal.
A few headlines and things to watch:
- These storms will move at 60-75 mph, which adds to the wind damage potential and leaves less time for warning. If a warning is issued head for cover immediately. You may not have the typical 10-13 minutes to get to the basement.
- Most of us will not experience severe weather, but the farther south you live from the Twin Cities the greater the odds of wind damage. Most of this will be straight-line wind damage with wind speeds as high as 100 mph, but a few isolated tornadoes can't be ruled out.
- This is historic. There has never been a reported tornado in Minnesota during the month of December. We aren't thinking about severe storms or certainly tornadoes 10 days before Christmas. Text or call a friend who may be in the path of these storms later today.
- Sustained winds may surpass 60 mph for a time tonight as much colder air pushes back into Minnesota. Few of us will experience wind damage from severe T-storms, but all of us will hear the howling of the wind overnight. By daybreak temperatures will be in the mid-20s, so any wet roads and puddles will be icy. Expect a slow AM commute tomorrow morning.
A Surreal Bullseye for Any Month - Especially December. NOAA SPC has a "moderate risk" of severe weather for much of southeastern Minnesota with a slight risk extending into the Twin Cities. A moderate risk usually means tornadoes and fairly extensive straight-line wind damage. I would think twice about evening plans.
A Slushy Finish. Cold air on the backside of tonight's wild storm will turn the rain to snow with a few inches over central Minnesota, possibly plowable 4-8" amounts from near Alexandria to Walker and the Arrowhead. Something for the entire family today. (ECMWF forecast snowfall by midday tomorrow courtesy of weatherbell.com)
Live long enough and you'll see (almost) everything...
No time to weigh in on whether this is another climate signal. It is highly unusual, historic, and we can talk about how a warmer climate may have flavored this outbreak at a later date. For now what is top of mind is a potential for damage and injuries related to severe thunderstorms this evening. As far as the atmosphere is concerned it is mid-May. Take it easy out there, keep situational awareness, and once these storms fire and track into Minnesota consider calling or texting friends, colleagues and family members who may be in the path of these severe storms.
Be safe out there...
