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 +