Question

What upper-air patterns would support a forecast for severe thunderstorms or tornadoes?

Answer 1

Extreme instability caused by high differential temperatures between two air masses(cold and warm) , combined with high humidity at the surface and very dry condition.

For example:

Most tornadoes are found in the Great Plains of USA– an ideal environment for the formation of severe thunderstorms. In this area, storms are caused when dry cold air moving south from Canada meets warm moist air traveling north from the Gulf of Mexico.

They make fronts in upper in environment like warm front or cold front, then occluded front according to the activness of warm or cold air ,or both .

Heat releases from this process suitable for forming jet stream in upper atmosphere layer or troposphere.