Good morning! In this post, we’ll be taking a look at some interesting weather features across the Contiguous United States coming up this week.
This discussion is mostly going to be related to severe weather threats in the Ohio Valley and Great Lakes today and tomorrow, and my thoughts on severe weather potential.
This is the 500 mb temperature and wind map for this afternoon, and the heat ridge is very strong right now. The lines represent 500 mb height, and show the high pressure ridge centered over New Mexico, with warm upper-air temperatures across much of the South.
A pretty unusual thing to notice is the pocket of colder temperatures in North Dakota. This is called a cold-core low pressure system, and this is quite a strong cold core system considering that we’re in the summer.
Usually, we don’t see temperatures this cold in the summer, with 500 mb temperatures falling to around -15C.
This difference of temperature over a short distance is going to help strengthen the jet stream, leading to strong upper level support across the Midwest for some potential severe weather.
And looking at the SPC outlook for today, we can see that there is potential for some severe weather across portions of Minnesota, Wisconsin, and Michigan.
For this type of system, it isn’t best to look at raw model data, since models usually miss these MCS type systems. Rather, it’s better to recognize that the environment will be supportive of severe weather and ignore the future radar maps. The “forcing”, or method of triggering storms to form, is rather weak for this system, which makes it hard to tell what’s going to happen in advance.
The main threat is damaging winds for this area. The temperatures are pretty high, leading to lower humidity. This means that the bases of the clouds are higher than normal, stopping tornadoes from forming. One or two might form but it’s very unlikely.
Advancing this forward 24 hours, the system is still pretty cold at 500 mb. Not quite as strong, so the jet stream is going to be a bit weaker than today, but still should be strong enough to support organized severe weather on top of the heat and humidity-creating large instability values for storms to use as fuel.
In fact, tomorrow looks more concerning to me, so I’m going to go a bit more in depth.
Above is the SPC outlook for tomorrow, but this may have changed between last night and this morning. I am personally concerned for areas in Central Indiana, as well as the rest of the slight risk area, and I expect the SPC to extend that slight risk further West.
First of all, instability looks to be pretty intense across a large portion of Indiana, which will act as strong fuel for thunderstorms developing along a cold front. The NAM 3km from yesterday afternoon indicates a large swath of 3000-4000 J/Kg of CAPE, which is to say, quite a lot. This is enough energy for severe storms, and they may be quite energetic at that level of instability.
Really, for severe weather, we want values around 1,500 or higher during the summer, so this certainly meets that criteria.
Shear, which is required for organized severe weather, is not very high, but should be sufficient. Most models are indicating around 30-40 knots of shear in the lowest 6 km, which is just around the threshold for severe storms.
Where these two overlap, we have to be very wary of severe weather. This system has stronger forcing, and storms are appearing on future weather models.
These storms are moving over the area with high instability and decent shear, so they are likely to have damaging winds and produce organized severe weather.
The most concerning thing, however, is that there will probably be some tornado threat with this system in Central Indiana and Ohio.
This is a box-averaged sounding, or Skew-T diagram, for portions of Central Indiana, and I’ll run through the checklist as we see what might happen with some of the stronger storms. Box averaged soundings are good, so that we don’t just see the worst case scenario, but get a better idea of what the whole environment looks like.
Looking at the top right diagram, called the hodograph, there is a good amount of turning in the red section, which indicates winds are turning in the low levels. This sounding indicates 175 units of 0-1 km Storm-Relative Helicity, which can be used to assess tornado threat. 175 is not off the charts, but tells us that we probably will have a tornado threat. Values of 200 or greater in the lowest 1 km are generally favorable for tornado development, if other factors are in place.
This sounding screams “straight-line winds”, so what is most likely to happen is a squall line developing, and moving into the Southern Great Lakes, and producing isolated tornadoes. The tornado threat isn’t super high, but is definitely present.
If any isolated supercells form along the front, there is definitely a tornado threat extending as far North as Southern Michigan. If you do live in these areas, I encourage you to look at official forecasts from the Storm Prediction Center and the National Weather Service.
Elsewhere across the country, a much quieter, hotter pattern will set up across the Southern United States.
Looking at the high temperatures forecast for today, a huge swath of the Southern US is forecast to see high temps above 110F, with some areas in the Red River Valley expected to see temperatures of 115F.
This ridge is going to stay put over the next week, and it’s forecast to slide further East to encompass most of the Southeast and Midwest.
Moving on ahead to Friday, you can see how the temperatures slide to the East, as portions of the Midwest, especially Missouri, Oklahoma, and Kansas, are set to hit the century mark as well.
Really, the entire Southern half of the US is forecast to see above average temperatures over the next week or two. In my Coastal zone forecast, I discussed with greater detail about the high heat and how it’s forecast to stay for some time, so I would refer back to that for more information about the extreme heat.
