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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