Use of vertically integrated ice in WRF-based forecasts of lightning threat

Previously reported methods of forecasting lightning threat using fields of

graupel flux from WRF simulations are extended to include the simulated field

of vertically integrated ice within storms. Although the ice integral shows

less temporal variability than graupel flux, it provides more areal coverage,

and can thus be used to create a lightning forecast that better matches the

areal coverage of the lightning threat found in observations of flash extent

density. A blended lightning forecast threat can be constructed that retains

much of the desirable temporal sensitivity of the graupel flux method, while

also incorporating the coverage benefits of the ice integral method. The

graupel flux and ice integral fields contributing to the blended forecast

are calibrated against observed lightning flash origin density data, based

on Lightning Mapping Array observations from a series of case studies chosen

to cover a wide range of flash rate conditions. Linear curve fits that pass

through the origin are found to be statistically robust for the calibration

procedures.