Even in the presence of factors thermodynamic favorable, an updraft appears only when unstable air near the ground is pushed to the free convection. In the case of a uniform air mass movement and without the warming alone can suffice, but in general, there are triggers that will allow to concentrate the storm activity:
- Local inversion can reduce or even completely disappear if a jet stream altitude passes in the sector because inside the jet stream, particularly high winds, blowing several hundred kilometers per hour, moving in the direction of flow by forcing the air downwards in front of them and sucking up the air behind. This phenomenon of suction bottom, if strong enough, can dissipate a reversal and promote the formation of thunderstorms or intensification of storms in progress.
- The same thing can happen with a jet stream of low-level but in this case, it is the convergence of mass to the left of the jet which forces air stacked up like a pot that is pressed at its base .
- Local effects such as the ascent forced air along a slope by large-scale weather or sea breezes that bring moist air to an unstable area.
- The passage of a cold front , where cold, dense air advances in a warmer region, making their way under the hot air lifting.
In general, we identify areas of severe thunderstorms by analyzing the thermodynamic potential of the air and the position where the maximum dynamic trigger mass is obtained.