The passage is an occluded front and trowal brings a change back to polar air-mass weather.

这一段的锢囚锋和高空暖舌带来与极地空气团天气相反的变化。

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"It's a subtropical air mass, " Pedram Javaheri, and can spark thunderstorms as it collides with a cooler front coming over from Texas.

CNN: More rain for flooded parts of Louisiana

In a warm front, a mass of relatively warm air pushes against a block of cooler air and is forced to flow up over it.

BBC: Turbulence ahead: Flight heads into storm's heart