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Severe Weather Parameter Thresholds 

If you are interested in keeping up with the information we follow during a severe weather

event, the Storm Prediction Center (SPC) has created a top-notch mesoanalysis page for

the public to use. Click here for the page specifically for the southeast U.S.  The following

are thresholds for typical parameters we look at to try and make a decision whether the

environment is conducive to producing severe weather.  Remember, no one parameter

being met means severe weather will rear its ugly head.  Multiple parameters need to

be met, especially when it comes to the perfect balance between instability and shear. 

We'll start there (click on the title of each for definitions):

 

 

CAPE
(Convective Available
Potential Energy)

0 Stable
0-1000 Marginally Unstable
1000-2500 Moderately Unstable
2500-3500 Very Unstable
> 3500 Extremely Unstable

Shear Parameters
(The following are good to follow for
potential supercell formation)

Bulk Shear (Effective) 25-40 kts
0-6 km Bulk Shear 40-50 kts
0-8 km Bulk Shear Greater than 50 kts
0-3 km SR Helicity 250 m^2/s^2 or more
0-1 km SR Helicity 100 m^2/s^2 or more

 

After weighing the balance between instability and shear, there are a number of other parameters

to analyze for thunderstorm/supercell potential: 

 

 

Parameter Low Chance Moderate Chance High Chance
Lifted Index 0 to -3 -3 to -6 Less than -6
Convective Inhibitions 150 to 200 15 to 150 Less than 15
0-1 EHI 1.0 - 1.9 2.0 - 2.9 Greater than 3
LCL Height 1250 - 1499 m 1000 - 1249 m Less than 1000 m
LFC Height 2000 - 2499 m 1500 - 1999 m Less than 1500 m
Lapse Rates 5.5 - 6.0 C/km 6.0 - 7.5 C/km Greater than 7.5 C/km
Total Totals 40 to 44 45 to 49 50 +
K Index Less than 30 30 to 39 40 +