Severe weather index

Since the 2012 season, I am working with a few other people on an automated way to create severe weather warnings. The warning levels are roughly the same as the levels in the Estofex forecasts, however, there are a few differences.

The main difference is, that the Estofex forecasts are done "by hand" by experienced meteorologists. This is pretty much always more precise than a fully automatic forecast. Additionally, there are a few parameters which I didn't incorporate into our severe weather calculation yet, such as precipitation or non-convective storms. Because of that and yet insufficient empirical data, our severe weather forecast maps are to be treated as highly experimental and should under no circumstances be used as any kind of authoritative information! However, so far, the forecasts turned out pretty good.

This is the currect structure of the severe weather levels:

Thunderstorm

This level means, that there is about a 50% probability of thunderstorms occuring in the designated area.

Conditions

CAPE 255-0hPa >= 500J/kg and best 4 layer lifted index <= -2

Level 1

This level means that there is about a 5% chance of a severe thunderstorm, large hail or a tornado in the designated area.

Conditions

  • CAPE 255-0hPa >= 500J/kg, low level shear >= 10m/s, deep layer shear >= 10m/s and 3km storm relative helicity >= 100m²/s²
  • OR large hail probability (NCEP/SPC formula) >= 30%
  • OR surface based supercell composite parameter >= 3.5
  • OR surface based significant tornado parameter >= 1.2

Level 2

This level means that there is about a 15% chance of a severe thunderstorm, large hail or a tornado in the designated area.

Conditions

  • CAPE 255-0hPa >= 1000J/kg, low level shear >= 15m/s, deep layer shear >= 20m/s and 3km storm relative helicity >= 150m²/s²
  • OR large hail probability (NCEP/SPC formula) >= 99%
  • OR surface based supercell composite parameter >= 7.5
  • OR surface based significant tornado parameter >= 2.5

Level 3

This level means that there is about a 15% chance of an extremely severe thunderstorm or a tornado in the designated area.

Conditions

  • CAPE 255-0hPa >= 2000J/kg, low level shear >= 20m/s, deep layer shear >= 25m/s and 3km storm relative helicity >= 200m²/s²
  • OR surface based supercell composite parameter >= 15
  • OR surface based significant tornado parameter >= 5