# Probability of Severe Hail (POSH) - Probability of Severe Hail (POSH) - Warning Decision Training Division (WDTD)

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## Products Guide

# Probability of Severe Hail (POSH)

## Short Description

The probability of 0.75-inch diameter hail occurring.

## Subproducts

None

## Primary Users

NWS WFO

## Input Sources

Vertical temperature profile from the current operational NCEP/EMC mesoscale model (i.e., the RAP as of 2014).

## Resolution

Spatial Resolution: 0.01^{o} Latitude (~1.11 km) x 0.01^{o} Longitude (~1.01 km at 25^{o}N and 0.73 km at 49^{o}N)

Temporal Resolution: 2 minutes

## Product Creation

A linear correlation of the height of the melting level and Severe Hail Index (SHI) was produced by looking at a number of storm cases (Witt et al. 1998):

,

where WT (J m^{-1} s^{-1}) is the warning threshold and H_{o} (km) is the melting level measured above radar level (ARL). If WT < 20 J m^{-1} s^{-1}, then WT is set to 20 J m^{-1} s^{-1}.

The severe hail probability function is given by:

,

where POSH is the Probability of Severe Hail (%). POSH values < 0% are set to 0%, and POSH values > 100% are set to 100%. Despite the continuous nature of POSH, actual algorithm output probabilities are rounded off to the nearest 10%, to avoid conveying an unrealistic degree of precision. Note when SHI = WT, POSH = 50%.

## Technical Details

Latest Update: MRMS Version 10

## References

Witt, A., M. D. Eilts, G. J. Stumpf, J. T. Johnson, E. D. Mitchell, and K. W. Thomas, 1998: An enhanced hail detection algorithm for the WSR-88D. *Wea. Forecasting*, **13,** 286-303.