A Severe Weather Outbreak That's Potentially A Record-Breaker

 SPEAKERS

Jim du Bois, Kenny Blumenfeld

Jim du Bois  00:00

Damaging weather likely in parts of Minnesota this afternoon and evening. This is Way Over Our Heads. It's a weather and climate podcast. I'm Jim du Bois. Kenny Blumenfeld's a climatologist. Kenny, this is the stuff that makes history. This system that's on its way has everything.

Kenny Blumenfeld  00:19

It does. It's kind of unbelievable. Let's just talk real quickly for listeners, kind of give them an overview. It's Wednesday, December 15. We're talking in the morning. There's obviously some uncertainty, but there's also some certainty. So basically, we have a powerful storm system moving in, one of those big low pressure systems. It is likely to produce severe thunderstorms and possibly tornadoes in Minnesota. Even if it doesn't produce tornadoes, the chance for very strong winds with those thunderstorms is pretty high. This is especially true over southern and eastern Minnesota, basically, south and east of a line from say Worthington to the Twin Cities, you know, including New Ulm and everything southeast of there. The greatest risk running from you know, Mankato and Albert Lee and Rochester over to Red Wing. So that's one threat. So, unprecedented risk for severe weather, including tornadoes. And we usually don't discuss specific products from, you know, the Storm Prediction Center, because these things move and change during the day. But as of this morning, there is a moderate risk for severe weather from the Storm Prediction Center. And Jim, we, you know, have not had that happen in Minnesota in November, let alone December. So, even if we don't get the tornadoes, and, you know, maybe the thunderstorms underachieve a little bit, just the potential is something we have not seen in December before. So that's one piece. Another piece is, even if we don't get the storms, the one real certainty here is that there are going to be very strong regional scale winds that follow the temperature boundary this afternoon and evening. And so, there's a pocket of very strong winds with gusts up above 50 miles an hour. And in some cases exceeding 65, 70, maybe even 75 miles an hour are going to come out of Iowa, and they're going to pass into many of those same areas in Minnesota. Greatest risk is in the southern and southeastern part of the state. But the risk does extend farther up into, you know, central and southern Minnesota, including the Twin Cities. Much of the area's in a high wind warning, which is a step up from a wind advisory. And again, between the severe weather and the wind potential, there's a decent chance of some power outages, trees coming down and some damage, at least scattered or an isolated to scattered fashion across Minnesota. I would not expect, you know, that everyone's gonna have property damage or anything like that. But the chance for things breaking somewhere is quite high. And it's even higher, to be honest, if you look in the southern couple tiers of counties in Minnesota, you know, along  and south of I-90, and into Iowa and into parts of southwestern Wisconsin, so major regional weather event. And then not to be outdone, some of this, at least the thunderstorm activity is going to be riding in on and also produced by some really unusually warm and unstable air. Temperatures into the 60s are quite likely in at least far southern Minnesota. And up in the Twin Cities, you know, temperatures getting into the 50s and possibly touching 60 degrees. You know, this is all on the table. And with that, dew point temperatures rising into the 50s. And some of the models actually have dew point temperatures in the upper 50s. Which this will just obliterate our old dew point records for, say the Twin Cities where we have not recorded a 50 degree dew point anytime between I think it's December 5 And February 20. So, this would be an expansion of the you know, kind of 50 degree dew point season. If we do indeed get an hourly dew point reading 50 degrees or higher. We also haven't had a 60 degree reading, it's roughly the same basically from early December to mid February, there has not been a 60 degree reading in the Twin Cities. So, if we happen to do that, which is possible, then that would be another record. So, kind of unprecedented in three ways. We haven't had severe weather potential this time of year. We haven't had this kind of warmth and humidity. Even if that warmth and humidity doesn't make it into the Twin Cities, there are going to be records broken in other parts of the state, southern and eastern Minnesota.

Jim du Bois  04:48

Well in terms of the biggest threats today, obviously we have the possibility of tornadoes. We have the likelihood of extremely strong winds associated with the thunderstorms. And we should mention that there are two really separate wind events associated with this storm, the first being associated with the thunderstorms, the intense downdrafts, the fact that these storms are going to be moving, what, 60, 70 miles per hour, which is pretty incredible. And that will be the first wind threat, then we have a wind threat after that, which is related to the intense low pressure. And that's going to be a more sustained event, correct? Almost a derecho? Can we use the D word here, or is that more associated with the thunderstorms?

Kenny Blumenfeld  05:31

Yeah. Good questions, Jim. Yeah, so the derecho that the Weather Service was discussing in their morning discussion would be associated with the thunderstorms. Those are thunderstorm-related winds, they kind of progress through an area. You know, at least looking at some of the short term, high resolution weather models, they do show a derecho tracking from northeastern Nebraska and eastern Nebraska through Western and Northern Iowa into southern Minnesota and into western Wisconsin. If that actually happens, I don't know. But that would be associated with the thunderstorms. And you brought up a really good point, there's two different wind risks. So if you think of why thunderstorms produce winds, it's because air rushes out from the top of the thunderstorm, and then it hits the ground and fans out. And so that air that comes out of the top of the thunderstorm has the momentum of that downward acceleration. But it also brings with it some of the momentum that's transferred from the winds that are blowing higher up in the storm. These storms won't be particularly tall, they probably only be 20 or 25,000 feet, but the winds up there are over 100 miles an hour. And so that momentum will get transferred down. And then, you know, come down with that with the downdraft and hit the ground. And there's a lot of cold dry air behind these storms, so there's plenty of fuel for that sinking air into each storm. That's one piece. The other thing is then whatever speed the storm moves at, those winds just kind of move along with it. So if the storms are moving 60 miles an hour, you're pretty likely, almost guaranteed to have winds, if they're coming out of the storm, exceeding 60 miles an hour. So there's a lot pointing to the potential for at least as short but very intense burst of destructive winds with this kind of arc of thunderstorms that's going to sweep across Minnesota, between, oh, probably three or 4pm in the southwest, and maybe seven or 8pm in the east central and southeastern parts of the state. And then as you mentioned, the second wind event is with this powerhouse low pressure system. Now that low pressure system is going to pass probably through, you know, maybe the St Cloud area up towards Duluth. And there's going to be a very tight pressure gradient. This is probably the strongest low pressure system that we've had in Minnesota in, you know, maybe a decade. There was a really, a much more intense one actually in 2010. And we do get storm low pressure down just below 980 millibars, every, every couple years, but this one looks like it's going to bottom out in the lower or middle 970s in terms of millibars. And that would be about as low as we've had in, you know, maybe at least six or seven years and maybe a decade. That kind of storm can produce very strong winds, and also has these other features that actually get integrated vertically through the system that can actually enhance wind in these little pockets. So, that's going to be a more prolonged wind event that comes in basically after the storms pass through, the storms will probably be a little bit scattered, and they won't be particularly long-lasting at any one place. Sometime after they pass, there'll be a much longer push of gusty winds, maybe several hours. And at the peak of those you could have winds that are just as strong as the thunderstorm winds. So, you could have gusts exceeding 60 miles an hour, maybe even 70 miles an hour in some places. And this, this will happen on and off. This is the most likely outcome of all these things that this will happen almost certainly on and off for at least a few hours. And then even once the winds subside a little bit from that peak, it's still going to be a gusty and kind of blustery time as we get into Thursday. Just, I think the real wind damage potential comes first from the thunderstorms and then second from this larger aerial push of winds that will mostly be occurring in the late evening and overnight hours.

Jim du Bois  09:35

And then we see a dramatic drop in temperature, correct?

Kenny Blumenfeld  09:40

Yeah, the temperatures are going to drop you know somewhere between 25 and 40 degrees depending on where you are and exactly how warm it gets. (If) temperatures hit forecast levels in the Twin Cities and southern Minnesota, then the temperatures will probably drop even more than 40 degrees within a, you know, only about a 12 to 24 hour period. Now funny though, Jim, temperature dropping 40 degrees might only get us down to about normal.

Jim du Bois  10:08

Wow. It kind of puts it in perspective, doesn't it, about how record setting all of this is?

Kenny Blumenfeld  10:15

Yeah. So it's really the potential for multiple records. And we should, you know, talk about the tornadoes, you know, tornadoes are very hard to predict. And it's not clear if these storms will produce them. But with storms moving at 60 miles an hour, any tornado will come up very quickly. The National Weather Service has been urging people to just, you know, stay alert, and you know, know where to get your weather warnings and be up to date about them. Because, you know, 60 miles an hour is a mile a minute which means if a tornado is headed towards you and is seven miles away, it's gonna be on you in seven minutes. That's not a lot of time, you know, to get out of its way or get down into the basement. So, you know, there's a lot of potential today, a lot could happen, and people should probably be aware. This is one of the, boy, I suppose, Jim, forecasters could be really hanging their heads tomorrow if this thing under achieves because I'd say the messaging is going out on all channels that this is one of the most dangerous weather systems that a lot of forecasters have seen in their careers. So, it's unlike those summertime systems because this one has strong winds aloft that you find, especially in the winter season, even though we don't have the same level of heat and humidity that you get in the summertime, there's just an awful lot to work with. And (the) storm is producing a lot of potential in terms of, you know, not just the temperature and humidity, but the winds and severe weather. I should also, we should also mention, Jim, that on the other side of this, I mean not to be sneezed that the same system, which is really going to wind up is going to produce some winter weather in northwestern and western Minnesota. And you know, basically the northwestern half of the state is going to be on the cooler side of this system. And you know, right now the forecast office in Grand Forks is calling for, you know, a few inches of snow in parts in northwestern through north central Minnesota, but the winds will be very strong. And these could actually produce blizzard conditions in open country. So, if you are driving east or south out of the Twin Cities area today, just be careful late afternoon through evening for the chances for severe weather, and also those damaging winds. And then if you're heading northwest, if you're driving through northwestern Minnesota overnight, you got to watch out for, you know, whiteout conditions. There's not enough time for this system to produce dramatically heavy snow, but it's got a lot going for it. And for a short amount of time, the snow could come down at pretty high rates and be driven by you know, 40 and 50 mile an hour winds.

Jim du Bois  13:02

Well, Kenny, as you mentioned, it's very important to stay weather aware today. Stay tuned to local media, however you get your weather information. If you have a NOAA Weather Radio, make sure that's all set so it will go off in the event of any warnings that are issued. And we should also point out that at least in the Twin Cities and other parts of Minnesota, a lot of this activity is going to occur after the sun has set. So, if people are relying on looking out the window and seeing an approaching system, that may not be possible, given the fact it's going to be dark out.

Kenny Blumenfeld  13:34

Yeah, that's a great point. Thanks for bringing that up. This is such a bizarre setup. Most of the high resolution models that we use to try and understand, you know, when things are really going to kick off, they don't actually, don't actually show the storms beginning in Nebraska and southeast South Dakota and maybe far western Iowa until three or 4pm. That's kind of when things get kicked off. And well, what time's the sun go down here, Jim?

Jim du Bois  14:01

About 4:30 now, thereabouts?

Kenny Blumenfeld  14:02

Yeah, well, you know, before five across the region in any case, and it gets dark pretty quickly after that. So you're right, very good point. A lot of this risk is going to occur, you know, after darkness has fallen. So what a strange system not only do we have the potential for way out of season severe weather, but this could be happening at night. So, a lot of this is gonna, and the strong winds are almost entirely going to be occurring, those strong regional winds will occur almost entirely at night here in Minnesota.

Jim du Bois  14:38

Well, everybody stay safe. Keep an eye on the weather. Kenny, we will connect after this has all transpired and probably have a lot to talk about in terms of how this system actually plays out.

Kenny Blumenfeld  14:49

I think so. Everyone should honestly, especially if you are in that high wind warning, secure loose objects, secure anything that could become projectile or anything that you don't want damaged. Also, you know, high profile vehicles and other high profile objects are really going to struggle against some of those strongest winds, even if you don't get the thunderstorm, so those regional winds are going to be tough. And they're going to be coming out of the southwest later this afternoon. So, if that helps you ,if you're driving down I-94, that could be very difficult because you'd be basically, the wind would be perpendicular to your vehicle. So this will be something to pay careful attention to for sure.

Jim du Bois  15:35

Well, Kenny, thanks a lot for all of your insights on this. We'll check in with you again soon. This is Way Over Our Heads. It's a weather and climate podcast. I'm Jim du Bois. Kenny Blumenfeld's a climatologist. Stay weather aware today. Stay safe