Powerful storm system moving toward Minnesota: Here’s what to expect across the state

[MUSIC PLAYING] CATHY WURZER: Getting back to the severe weather that's forecasted to roll into Minnesota this afternoon and evening. It's been raining somewhere in Minnesota pretty much all day, but soon those could be turning into severe thunderstorms. Much of Minnesota is also under a flood watch from the international to the Iowa border. We have a lot at play here, so to break it all down is MPR Meteorologist Sven Sundgaard. Hey, Sven.

SVEN SUNDGAARD: Hey, Cathy.

CATHY WURZER: OK, we have round two in terms of rainfall, and it was actually pretty significant rain last night.

SVEN SUNDGAARD: Yeah, so Hayfield, where spotters saw that brief tornado, over 3 inches of rain fell there. That was one of the highest amounts, but there was a lot of 1 to 3 inch reports. Roseville even saw a little more than 2 inches and had some hail reports in southeastern Minnesota yesterday evening, too.

But the whole point of all that is the ground is saturated across most of the eastern half of the state, so that's why we have a flood watch in addition to the severe weather that we're worried about. And kind of ongoing showers. As you mentioned, right now, the rain is falling up 94 around Annandale, St. Cloud. We've got some showers out towards Granite Falls, Olivia, and up around Duluth as well.

And a pile of dying showers in southeastern Minnesota is producing some 40 to 45 mile per hour wind gusts. Not severe thunderstorms but just kind of you can imagine the outflow of those showers sort of breathing out from those showers. So for the Rochester area, they do have a special weather statement down there for the southeastern part of the state for some gusty winds here over the next couple of hours unrelated to the severe potential that we have coming.

CATHY WURZER: Well, let me ask you about the severe potential because we had the rain overnight. We've had some rain here this morning into the lunch hour. Has that taken any starch out of the atmosphere, or are we still looking at a potential severe outbreak?

SVEN SUNDGAARD: Yeah, usually in a typical severe weather situation when we're sitting here at this time of the day looking at cloudy skies and temperatures in the 60s, you think this is not going to happen, but this is a very dynamic, unusually powerful storm system for this late in the season. It's already clearing out rapidly across southern Minnesota. Temperatures are jumping into the 70s. If you've been outside at all today, you know it's already muggy. Our dew point is 61 degrees, and it's going to be even more humid. Dew points in the low 70s are going to push into southeastern Minnesota.

And so this system is drawing in its own warm, humid air to destabilize things as it is. So we've got a deepening surface low. It's right near Omaha right now where there's already a tornado watch from Sioux Falls down towards Omaha, including Lincoln, Nebraska. No watches yet as far as severe watches for Minnesota just yet, but they are watching that area because it's near that surface low where the storms are already popping right now that we expect those to continue to fill in, and that's all going to rapidly move northeast with that surface low, which will pass right over southern Minnesota and the Twin Cities here this evening, combined with some intense winds aloft.

You go up about 18,000 feet. Winds are roaring at about 100 miles an hour here this afternoon. That is unusually strong for the middle of the atmosphere. Even 4,000 feet up, winds are going to be going 60 to 70 miles an hour. So that produces what we call shear, that horizontal rotation of the air you can imagine. And then when thunderstorms get going with enough instability, those updrafts can rotate that vertical, and that's how we get these strong thunderstorms that we're expecting later today.

Storm Prediction Center has a moderate risk for us, level four out of five for the far southeastern part of the state, but they did adjust that a little bit north here in their update just about 20 minutes ago. So this includes Rochester and Winona now in that moderate risk, level four out of five. Enhanced slight risk for Albert Lea, Owatonna, Red Wing, Rochester, right through the southeastern suburbs of the Twin Cities. And then the Twin Cities metro proper included in a slight risk that is down towards Worthington and Mankato as well.

It looks like the prime time for severe storms is going to be in the 3:00 to 8:00 PM time frame, but we're already seeing these storms develop to the southwest. So this isn't a situation where we're waiting for them to develop late in the afternoon. They're already developing to the southwest and then will be moving into this very unstable air mass that's pushing out ahead of it into southern Minnesota.

CATHY WURZER: Because we have so much wind, are you anticipating spend any straight-line winds, bow echoes, anything like that?

SVEN SUNDGAARD: That is also possible with any of these storms because what we're going to see initially is these supercells develop, which produce the potential tornadoes and their own downburst winds. But then those will form into a line that can produce those bow echoes, which can produce those straight-line winds. Storm Prediction Center is talking about 70 to 90 mile per hour wind gusts in some of those bow echoes, so that is a distinct possibility as well for southeastern Minnesota, all of pretty much Iowa into southwestern Wisconsin and western Illinois as well.

They've got a 10% probability area for southeastern Minnesota into eastern Iowa of EF2 or greater tornadoes. So this is quite the setup here, that these are potentially going to be long-track supercells that could be more intense than normal. Typically in Minnesota, we see tornadoes develop. They're weak, and they're short lived. There's a potential for some of those stronger ones here later today.

CATHY WURZER: Wow. You rarely hear that, actually, up here. We've had kind of a slow start to the severe weather season too, and now obviously today is the big day.

SVEN SUNDGAARD: Yeah, Minnesota-- I was looking, and my preliminary estimate is that this is the least active start to our season in 21 years. We've only had a handful of hail and wind reports.

Now, what's interesting about that is nationally, it's the third most active to date. So it's been going in the Plains. We've been hearing about all the weather in Nebraska, Oklahoma, of course. And so time will tell if this is all marching north, but it's definitely been a slow start for us, and May is one of our peak months. May and June should be the peak of some of our severe weather in at least southern Minnesota

CATHY WURZER: So you painted kind of a concerning picture of some of the storms that could bubble up. You mentioned the flood potential, and we're not talking about flash floods, right? We're talking about just saturated ground. And how much are we thinking could fall out of some of these storms?

SVEN SUNDGAARD: Yeah, so the flooding situation, it's kind of both. We have that flash flood potential because some of the more intense storms could easily drop 3, 4 inches of rainfall. So if you're near some low-lying areas or you have maybe some creeks running nearby, those can go up pretty quickly. But then we're also talking about if we get this widespread 1 to 3 inches of rain, which looks likely across much of eastern Minnesota, we'll have to watch the river levels because those will slowly rise heading into the holiday weekend.

So yeah, it's kind of both. The immediate concern is some of that flash flooding this evening and overnight, but then longer term in the next several days, what will the rivers do? And, of course, that's all going to depend upon how much water falls where on top of the Mississippi, Saint Croix, Red River, some of those watersheds that are important.

CATHY WURZER: Wow. You go kind of weather whiplash. You go from drought to flooding. Wow. It looks like there's more rain on Friday?

SVEN SUNDGAARD: More rain on Friday. Let's hope that that's not as big. It doesn't look like a severe weather outbreak, of course, which is better in terms of seeing less of that intense rainfall, so that's the good news.

The other piece of good news heading into the holiday weekend, it looked kind of unsettled. It's increasingly looking likely that Saturday, Sunday should be mostly dry for most of the state, maybe a little cooler, low 70s to 60s, but maybe less in terms of unsettled weather. Maybe some thunderstorms on Memorial Day in southwestern Minnesota, but the weekend forecast, at least, is looking better.

CATHY WURZER: Well, that's positive. All right, Sven, I think you're going to be busy today. Thank you so much.

SVEN SUNDGAARD: You're very welcome.

CATHY WURZER: We've been talking to our Meteorologist Sven Sundgaard. Of course, our Chief Meteorologist Paul Huttner will be keeping an eye on things as well. He's going to join Tom Crann later this afternoon, All Things Considered, on air and online.