Saturday: High Risk Coming?

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By Scott Roberts

You may wonder why you’ve not heard much about the setup tomorrow here. We do have a pattern of not talking about things much if we don’t believe it is a big risk day, but that’s not the case here. I’ll be up-front: I’m getting as storm saturated as I suspect many are. With the previous high-risk day busting so badly in Kansas, I was cautious early on for fear of getting lured in again. And it still could fail to be a big day.

But especially given the holiday weekend and so many of us planning outdoor activities, I can’t let it slide by any longer — because tomorrow has all the markings of being a truly BIG DEAL.

 

I’ve spent a good amount of time this afternoon discussing this with several people, Matt and Brad included. From my looking at the models, all the signals are there. Yes, there is some uncertainty in the computer models. But a number of people who are much better forecasters than I (most of them meteorologists, which I am not) are setting aside some of that uncertainty.

I’m about to do something I have never done before, and that’s lift nearly the complete posting of another (Non-NWS) member of the weather enterprise. Paul Bouchereau is a meteorologist I’ve only been following for the past year or so, but I have found him to be extremely knowledgeable and not at all prone to hype — a diametric opposite of most of the (current and former) broadcast meteorologists in the Oklahoma City market.

Bottom line: Paul and I see this the same way, and I find Paul trustworthy. I only edit his words to take out a couple of tangents.

This is a very serious situation for Kansas and Oklahoma. Some of the most unstable air ever to reach the area will be seen. Dynamicswise, the upper wind energy is impressive but not overly powerful. IOW instability will drive this outbreak. We will be dealing with long track significant tornadoes and very large hail, Softvall in some cases,

Jet Stream… [The approaching upper-level system is called] a jet streak. They are totally different from shortwaves because we can now determine what sectors of the wind max will cause a problem. The left entrance quadrant and right exit quadrant produce huge amounts of lift. Its that left entrance quad that will cause the problems on Saturday. Notice how the Black Oval directly correlates with SPC’s Moderate Risk. This jet streak also draws in moisture from the gulf when it shifts surface winds to the SE.

Sounding.... This is a classic large hail/tornado sounding. From the Jet Stream we know we have shear. We can visualize it here. Directional shear is the change of wind direction with height. One thing I did not see from the previous chart was the 100kt wind just above that jet streak at 300mb. Extreme winds like this does two things. Once the updrafts start they need to be evacuated out the top of the storm. A 100kt wind does this very effectively. We see this evacuation in the form of an anvil. Next you have to visulize this. Winds at the ground are 20kts and 100kts at 300mb. visualize the differential wind speed with height. A theoretical rotor now exists that gets bent up by an updraft. One end becomes a mesocyclone the other end the outflow.

We have/Had an inversion, Red Arrow, When we say a CAP is broken in this case its because the rising air parcel is warmer than the air in the inversion. The white dashed line is a rising air parcels temp. Look at the distance between the red temperature profile and the white dashed line. The area described between the two is CAPE, Convective Available Potential Energy, IOW a meadure of instability. So when the air parcel hits this layer it then rises violently. From the wind profile we also knowits violently rotating. This is why we forecast tornadoes. The hail part comes in from tat spike to the left which means there is a dry layer. But this layer actually increase the creation of hail by producing evaporat\ive cooling that freezes more water vapor on already large hail stones.

CAPE... Anything over 2000J is considered extreme. In Oklahoma CAPE will peak at 5000. This isn’t gasoline on a fire, this is nitromethane!! Even with the wind energy, this is the main reason why the models are calling for some very violent weather.

Forecast Radar….

Saturday 9pm…. One thing thats painfully obvious is, the models are not as convinced as the humans that the CAP will break. This model is a convectively sensitive model, meaning it has a tendency to over forecast thunderstorms. Meanwhile the major models GFS EURO and HRRR really do not have much activity at all. The GFS does have a stray thunderstorm in southern Oklahoma. As we get closer to initiation it will become obvious who is right.

Paul Bouchereau, Posting to OK Weather Private Group, Friday May 24, 2024

I have duplicated his graphics except I’ve shifted the target area to Kansas.

Jet Stream

Saturday night 10pm CDT

Of particular note here is the bubble of 90 knot wind just west of the 573 west of Wichita. That indicates ~100 mph wind at an altitude of 19,000 feet (give or take 3 miles above the surface, which is at ~1500 feet MSL there).

Sounding

I have highlighted the same features Paul talks about with appropriate color arrows.

Also of note (green rounded box) is that the LCL (Lifted Condensation Level) and LFC (Level of Free Convection) are right on top of one another. AND they are less than 1KM from the ground. This means 2 things: the air parcel can lift from the ground (LFC) into the base of the storm (LCL) which means it can tap into the CAPE. It also means LCL (the visible base of the storms) will be running just above 3,000 feet off the surface. Low bases are a factor we look for in tornadic storms.

I’m also going to share a part of the graphic Paul didn’t share. Here is the shole forecast sounding and hodograph image:

Look first at the upper right hand of the image. If you have heard (perhaps in NWS or SPC discussions) the term “sickle-shaped hodograph,” this is nearly what one looks like. Imagine you’re looking from the top of the storm down, as you’d view it on a map. The red arc corresponds to the lowest 10,000 feet or so of the atmosphere, and the strong curve indicates the rotation with height which will sustain a mesocyclone.

There are a bunch of numerical values for the various parameters show, but let me put it in the words of SPC this afternoon:

The end result will be a rare combination of instability and shear across the Moderate Risk area, with potential for particularly strong tornadoes, wind, and extreme hail.
SPC Day 2 Outlook issued mid-day today.

CAPE

As Paul said, we start paying attention when CAPE goes over 2000 this time of year. While not as off the charts as he mentions for Oklahoma, the forecast values are nearly double the “where it gets interesting” amount.

Forecast Radar

The usual cautions apply — don’t take this literally, it will vary somewhat.

Bottom Line

All the usual advice applies:

  • Underground is the best shelter. If that’s not an option, move as low as you can go, as close to the middle of the building, as many walls as possible between you and the outside.
  • At the lake? Pack up and head for safety when you see these storms growing well to the west in the late afternoon/early evening hours, don’t let them get close before you take action.

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