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Modified Jefferson Index calculator

 

 

Enter the 850 hPa ThetaW (°C)
Enter the 500 hPa temperature (°C)
Enter the 700 hPa dewpoint depression (°C)
The Modified Jefferson Index is

 

MJI    >27        thunderstorms likely in polar air mass.
MJI    >30        significant showers with thunderstorm.
 

The Jefferson Index is best used for air mass thunderstorms (no dynamical triggering mechanism)

 

Formula used: MJI = 1,6*Tw850 - T500 - 0,5*D700 - 8

Note: dewpoint depression = difference between temperature and dewpoint (in this case at 700 hPa)
 

 

Note: Java script must be enabled