Our 10 favorite graphics for forecasting supercells and tornadoes is the closest we can get to actually giving a morning routine walkthrough when it comes to forecasting severe weather. This almost 13 minute video will walk through all 10, what to look for, and how we use them to forecast supercells and tornadoes.
1)Reflectivity + updraft helicity
The key to these is to never take them literally, but do take them seriously. This is especially true when you average multiple runs out over time.
2)Dewpoints (w/wind barbs)
Dewpoints are one of the most important charts you will come across in storm chasing. No moisture? No storms. For the lower plains, look for values of 65+ for good quality moisture. For the high plains, 55+ tends to work well.
Mid-level flow is hugely determinative of storm type and storm motion. The happy medium for big time storms but not screaming motion is that 40-50kt range here.
The low level jet (aka the 850mb chart) is a huge deal for tornadoes. Weak 850s (think 20kt or lower) are not very conducive for tornadoes. Look for 850mb flow at 30kt+ for the big time stuff.
There are a lot of ways to determine the strength of inhibition on the Plains — but 700mb temps are as good as any. Anything over 12c at this level means storms are going to struggle.
There are a few ways to measure instability. We prefer MLCAPE as the best overall metric if we had to pick one and we are. Anything over 1000 j/kg is plenty for big storms, but obviously the higher the better here. Anything over 4000 j/kg is considered extreme instability.
These signify the storm base heights. The lower the number, the better your chances of seeing a tornado. Lower cloud bases mean storms are certainly more capable of producing tornadoes. Anything below 1500m is living pretty right.
8)0-1km Storm relative helicity
This is a measure of low level wind shear. Anything over 100 is more favorable for tornado formation. This isn’t a hard and fast rule, but it is a good guideline to work with.
Bulk shear at 0-6km tends to be pretty descriptive of storm type. When looking for supercell formation, you want 0-6km shear at or above 30 knots at a minimum. Bigger tornado days typically feature 0-6km bulk shear of 40kt+.
Supercell composite is a good, averaged way to look at the setup holistically. This parameter takes some of the above ingredients into account and can be a good way to quickly assess a setup to start your forecast.
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