A new study just out in Science suggests that we will have an increase in lightning strikes of about 12 percent for every degree C of global warming. That could add up. From the abstract:
Lightning plays an important role in atmospheric chemistry and in the initiation of wildfires, but the impact of global warming on lightning rates is poorly constrained. Here we propose that the lightning flash rate is proportional to the convective available potential energy (CAPE) times the precipitation rate. Using observations, the product of CAPE and precipitation explains 77% of the variance in the time series of total cloud-to-ground lightning flashes over the contiguous United States (CONUS). Storms convert CAPE times precipitated water mass to discharged lightning energy with an efficiency of 1%. When this proxy is applied to 11 climate models, CONUS lightning strikes are predicted to increase 12 ± 5% per degree Celsius of global warming and about 50% over this century.
This is the paper:
Projected increase in lightning strikes in the United States due to global warming. David M. Romps, Jacob T. Seeley, David Vollaro, and John Molinari. Science 14 November 2014: 346 (6211), 851-854. [DOI:10.1126/science.1259100]
How does lightning rate correlate with hailstone formation, any idea? I'd guess that higher convection energy means
-- more potential nuclei for hailstone formation are carried up high, maybe more hailstones forming, and
-- more lift available, so possibly more up and down cycles before hailstones get heavy enough to fall out.
As I recall, convective cycling is what builds up the size of hailstones.
"...explains 77% of the variance..."
Variance is real and part of the purest science (for you science deniers : it's called mathematics).
To be clear: if you have observational data, you don't need to apply them to any models (data is real, it's really not that difficult, just basic graduate science like science deniers say).