Boltek Lightning/2000 - Manual (Page 240)

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3. IC and CG lightning in a ratio of 1-1 to 4-1 and –CG
and +CG in a ratio of 10-1 – this is a normal storm
cell
4. Heavy IC lightning and minimal –CG lightning, ratio
of IC to CG lightning is 6-1 to 20-1, the ratio of –CG
to +CG is about 1-1, and the IC rate approaches 40
to 50 flashes a minute – this storm cell is borderline
supercell
5. Very high IC lightning and moderate +CG, there may
be little or no –CG lightning, the IC rate in this cell is
well over 50 flashes a minute and 5 to 7 +CG strokes
a minute, but in some cases the +CG rate may also
be zero – this is a supercell storm
In borderline supercell and supercell storms there is another
lightning anomaly that indicates that related severe cell activity
is about to start or has already started. This is the lightning
jump. This is an increase over a short interval (5 minutes) in
the total flash rate (all types of lightning) of 50 to 100 flashes
per minute for the five minute period. If this is followed by a
decrease to previous high levels then several types of severe
events have occurred or are about to occur: a microburst,
large hail, or a tornado. In the absence of IC stroke
information (storm at long range) significant pulsing in the –
CG or +CG flash rates can be used with less precision in
place of the lightning jump.
Another indicator is if a supercell storm that was producing
mostly +CG lightning switches to mainly –CG lightning.
This polarity reversal is another indicator that the basic
nature of the cell has changed and may indicate that a severe
weather event has occurred or will occur.
It should be noted that the ratios in stroke types/polarities
and flash rates will be affected by the terrain below the storm,
mountains vs. flat plains, the type of interface between dry
and moist air, as well as the season, summer vs. winter.