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Europe TS Risk


3 main ingredients + a secondary for severe storms:


- InstabilityConditional, Potential, Latent

- LiftLow level convergence, Frontal, Orographic, Dynamic/upper level divergence

Moisture: Sources, Location

- Wind shear: Updraft tilt (speed), Rotating updraft (directional)


Colours refer to ingredients section below:

Instability, Lift, MoistureWind shear

Thunderstorm Probability + Thompson Index

Thompson Index Criteria: Potential + Severity


< 20: Weak Potential for TS

20 to 30: Moderate Potential for TS

30 to 40: Strong Potential for TS

40 to 50: Very Strong TS of thunderstorms

> 50: Extreme Potential of thunderstorms


From 35 upwards, potential of severe TS

Severe TS: Different countries = different criteria


United Kingdom:

  • Any force tornado

  • 20 mm (0.79 in) min size hail

  • 89 km/h (55 mph) min wind speed

  • "Conducive to flash flooding" rainfall rate


extremely severe convective weather phenomena:

  • A tornado of class F2 or stronger

  • At least 5.0 cm hail size

  • Wind gusts with a speed of at least 33 m/s (about 119 km/h or 65 knots)


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