|Tornado||STP ≥ 1|
|Hail||MUCAPE ≥ 1000 J/kg, Eff. Shear ≥ 20 kt|
|Wind||MUCAPE ≥ 250 J/kg, Eff. Shear ≥ 20 kt|
The probability of at least one cloud-to-ground (CG) lightning strike within 12 miles (20 km) of a point over the 4-hour forecast period is determined by:
[0.6 * P(4 km Refl > 40 dBZ) + 0.4 * P(4-hr precip > 0.08 in.) + 0.1 * P(MU LI < -1)]
The forecast probabilities are calibrated to be statistically reliable based on CG lightning strikes recorded by the National Lightning Detection Network in 2017-2019.
Conceptually, PMM (probability-matched mean) is a variation of the ensemble mean with the original ensemble amplitude restored. At each grid point, the ensemble mean value is replaced with a value from the full distribution of individual member forecasts whose rank matches the point's rank within the ensemble mean distribution. See Ebert (2001, MWR) for more details.
LPMM (localized PMM) is a new technique from Clark (2017, WAF) wherein the PMM calculation is restricted to grid points inside some radius of influence, preventing precipitation in geographically distant areas from influencing the local value. On this site, we use r=110 km.
RF probs (random forest threshold exceedance probabilities) report the probability (PQPF) that the mean 24-h precipitation totals over the surrounding 20-km x 20-km area will exceed the given threshold (currently 0.1-, 0.5-, 1-, or 3-in.). The PQPFs are created using one random forest (RF) for each threshold. Inputs to the RFs include latitude and longitude as well as daily mean HREF ensemble mean forecast values of: temperature and dewpoint temperature at four atmospheric levels, 1-km above-ground-level reflectivity, surface-based CAPE and CIN, PWAT, hourly maximum wind components, 2-5 km updraft helicity, and forecast precipitation. These RF-based PQPFs perform best for the lower precipitation thresholds, which have the greatest climatological frequency.
NAM Nest members do not output hourly-minimum 2-5 km UH or hourly-maximum 0-3 km UH, so those fields are not plotted.
HRW NMMB members do not output hourly-minimum 2-5 km UH, so that field is not plotted.
HRW ARW and HRW NSSL members output all required fields, so plots for those members are complete.