Assertion: thunderstorm | /r/CapableOf | develop in cooler polar air masses
Facets:
value: especially
type: MANNER
value: with a strong jet stream
type: CAUSE
Source sentences:
text: In Europe, the mini-supercell, or low-topped supercell, is very common, especially when showers and thunderstorms develop in cooler polar air masses with a strong jet stream above, especially in the left exit-region of a jetstreak.