Expected Effects of Global Warming on Thunderstorm Frequency and Severity

Meteorologists and climate scientists interested in how global warming have conclusions about the impact warming will have on thunderstorm frequency and severity.   Thunderstorm frequency (related to the slope of the environmental lapse rate) is not expected to change, but the severity of thunderstorms is expected to increase.  The latter is related to the expected increase in the amount of water vapor in the boundary layer.

Since global warming is expected to affect all levels of the troposphere equally, then the slope of the environmental lapse rate will be the same.  However, if this warming in lower levels is matched by an increase in actual mixing ratios (more water vapor and higher dew points), then the CAPE would be expected to increase dramatically.  For the case shown, the LCL and LFC for all three scenarios are the same;  a cloud base would be found at the ground and the soundings are absolutely unstable.  However, the CAPE for the warmest case would be extremely large.

CAPE is a measure of the vertical acceleration due to buoyancy.  Since hail size and downdraft wind strength are directly proportional to CAPE, average hail diameters would increase and so would the strength of the downdraft winds.  A greater percentage of hail stones would meet the definition of severe hail, perhaps giant hail, and the number of cases with straight line winds greater than 57 mph would increase

 

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Fig. 1:  Skew-T/log p diagram with an initial sounding (far left) and then two soundings progressively associated with increasing mean temperatures due to Global Warming.  Note that the environmental lapse rate,  (ĘT/Ęz)e, is identical in all three cases.  Fig. 1 is duplicated in larger format at the end of the Homework.