So I’ve gotten a lot of requests to do a morning forecast routine walkthrough and I honestly don’t know how I’d even do that. The reason is my routine isn’t a routine and I don’t even have a set number of items I look at. Some days I look at every possible value, some days I only need to look at one or two things to chase effectively.
So instead of lying and going through a routine that doesn’t exist, I’m going to spend a bit of time going over my ten favorite things to look at for hunting supercells and tornadoes on the Plains. These may be applicable in other areas, but I’m focusing mainly on the Plains since its what I forecast and chase.
So with that said…let’s dive, right in.
Reflectivity + UH
This is the obvious one. Key with Reflectivity + UH is to never take it literally but take it seriously — especially averaged out over multiple runs. This is a skill you have to really work at, as you have to have an open mind to possibility and know how to blend solutions together.
You also have to take into account the limitations of models today. They won’t 100% model the atmosphere perfectly because they don’t have 1:1 resolution. So when looking at reflectivity charts, you can’t take them literally as they literally aren’t showing you a perfect representation of the atmosphere. What they do show is pretty good, and you should take it serious.
Finally, the updraft helicity swaths you see on reflectivity are a recent trend amongst chasers and I can get behind their usage in at least determining storm mode. I’m not sold on extreme updraft helicity meaning tornadoes, as that method has failed a lot, but if there are clearly defined streaks consistently over the same areas over multiple runs, that at least signifies local supercell potential is higher.
I also look at model reflectivity maps mentally as a collection of 100 mile bubbles. By that I mean I know that if I’m in the area of a storm and its within 100 miles of me to the west, I can be on it quickly. So if there’s a clustering of solutions with supercells in a specific area I tend to let radar and satellite do the rest and just keep things more general. One day we’ll have a consistent way to tell right down to the county where storms go but today isn’t that day.
Dewpoint + Wind Barbs
Dewpoints are one of the most important ingredients for severe storms on the Plains. I’m going to treat this as if you are completely clueless on what constitutes good dews on the Plains.
For the lower plains (the area from C NE down to N Texas) anything above 65 is considered pretty good. 70s are excellent. 60 to 65 is workable but not ideal and anything below 60 you have to have a lot of caveats to make work.
For the higher plains (think the Texas Panhandle up through Wyoming) you don’t need as much moisture to have greatness. Generally anything above 60 is considered really good and 55-60 is pretty solid if the shear is in place and its not too hot of a day. 50-55 is conditionally workable dependent upon a few other factors and generally I get much less interested below 50.
These are the winds in the middle levels of the atmosphere. If you want good, vented updrafts you want to ensure you have 500mb flow at 30-35 knots depending on the environmental conditions otherwise. Anything over 40 is ideal, with my excitement peaking about 55-60mph. Anything above that and we start to see storm movement speeds get unworkable. Ideal direction is west to west southwest.
Want big tornadoes? Then you need south to southeast 850mb winds at 30 knots or higher. The biggest tornado days on the Plains happens with S-SE 850mb winds at 40 knots or higher. If they’re present I get really excited about tornado potential during a day.
The 700mb temperature is a key metric to determining cap strength on the Plains and also how much existing storms may struggle to realize their full potential. The general rule on 700mb temps is that anything over 12 degrees celsius is a pretty stout cap. 10-12 degrees is workable and perhaps ideal, as if you get temps too cool at 700mb you could get too many storms. As a caveat, There are other ways to measure cap strength that are more effective when all are used together — but I tend to worry about the 700 layer a lot and given I’m limiting myself to 10 model charts this is going to have to do. However, we are going to have a full video on the cap soon.
I’ve talked about CAPE in multiple other videos. Check those out on our channel by just searching through for CAPE. This is a measurement of instability in the atmosphere, and I personally favor MLCAPE over all others because its more representative of what a storm is actually ingesting parcel wise. There have been multiple times I’ve seen storms in a 6000 SBCAPE environment act like 2000 CAPE storms because MLCAPE was actually down in that range. As with the rest of the values, let’s pretend that none of what I just said made sense.
Anything over 1000 MLCAPE is conditionally favorable for severe weather. I’ve seen plenty of tornadoes in low cape, high shear environments which tend to cluster around the 1000 MLCAPE to 1500 MLCAPE line. CAPE is not a measurement of if storms will form. Or put another way, CAPE doesn’t determine if your engine actually works — it just is the amount of fuel you can use if the engine can actually start.
2000 MLCAPE or higher is pretty supportive of big severe weather, with more extreme readings of 3000 and 4000 MLCAPE offering more potent environments which require less shear to make skinny things happen. As a general rule, the less cape you have the more shear you are going to need to get a storm to produce tornadoes and vice versa. If you have extreme cape, sometimes very weak shear can become very interesting in a hurry.
When it comes to tornadoes, you have to know if cloud bases are going to be low enough to make them happen. For instance, in an environment with extreme wind shear and MLCAPE at 3000 — if your LCL heights are at 2500 then you are almost certainly not going to get tornadoes (but expect some amazingly well structured high based supercells).
LCL Heights are another indicy which I think there’s a happy medium with heights at 1000m-1500m. Anything above 1500m becomes a bit harder to get tornadoes and anything above 2000m basically saying tornadoes are unlikely. Tornadoes are more likely with LCLs below 1000m but the chasing may not be as good. Typically low LCL environments are going to be characterized by faster moving, moderate instability or lower storms. While there’s something to be said about being guaranteed a tornado, these storms typically don’t look as good for the camera and are usually a bit tougher to chase since you’ll have to be closer to see the cloud bases of storms.
This stands for Storm Relative Helicity. Looking for tornadoes, I tend to favor shear over instability in my depth chart. The first shear Parameter I look at is 0-1km SRH. Anything over 100 on 0-1km SRH is considered favorable for tornadic supercells. Anything above 100 is good with increasingly good environments as you go up from there. There are no clear cut offs when it comes to SRH though, so if all other factors appear favorable and 0-1km SRH is 80…I wouldn’t give up hope just yet.
I look at the overall shear of an environment as well to determine if supercells are possible or not by looking at the 0-6km shear value chart. This measures the change in wind from the surface to 6km up in the atmosphere — and the more shear you have the more organized storms are going to tend to be.
For 0-6km shear, anything above 30kts I consider solid for supercells, with my preferences of anything 35kts to 40kts and over. The biggest tornado days see Bulk Shear in the 40+ range typically, with the average being closer to 50kts.
Lastly, I like this parameter a lot for determining if the environment is indeed highly supportive of supercells. If you have already checked off all of the boxes above, you do know this to be the case — but this is a final shortcut solution to kind of digging into the atmosphere and perhaps seeing where all of these ingredients line up in a single map.
Supercell composite takes into account Effective Storm-Relative Helicity, MUCAPE, and the effective Bulk Wind Difference. Or more simply, two shear values and one instability value.
There aren’t huge cut offs to when significant tornado events are more likely with supercell composite parameters but just generally the bigger the value the more likely big supercells are to happen. For instance, a supercell composite of 11 signifies an environment more supportive of severe weather than 3. But this is largely dependent upon storm mode processes that you’d need to be paying attention to.
So phew, that was a lot. There are of course many other options to look at when it comes to forecasting. I only gave 10 so do me a favor, let me know if there’s anything I didn’t list you’d favor more in the comments. We’re all about sharing information here. Also be sure to check us out on social media at the links on the site, you should hit that subscribe button too in the video!
We’ll see ya next time.