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    US in the Heart of Second Severe Weather Season

    By By Heather Buchman, Meteorologist
    November 06, 2011, 1:44:11 AM EST

    While spring is by far the most active time of the year for severe weather and tornadoes, there is a second severe weather season that develops in the fall.

    Most often, this second severe weather season spans late October into early November, affecting the South Central and southeastern U.S. However, severe events can also periodically affect areas farther north as well.


    590x393_11031715_two-severe-weather-seasons


    The driver for this second season is the jet stream, an area of strong winds high above the ground that divides cold air to its north from warm, moist air to its south.

    The jet stream acts to support strong upward development of thunderstorms and also creates wind shear, a necessary ingredient for severe thunderstorm development.

    Wind shear is a change in wind speed and/or direction with height above the ground. When winds change direction with height, they can cause thunderstorms to rotate and produce tornadoes.


    400x266_11031716_jetstreamnov


    In the fall, the jet stream starts to become stronger as temperature differences across the United States become greater. This happens as cold air from Canada starts to spread southward into the northern tier of the U.S. and clashes with warm, relatively humid air still in place across the southern tier.

    The result is the development of severe thunderstorm and tornado outbreaks.

    The right ingredients for a severe weather outbreak, including the risk of tornadoes, are expected to come together over the southern U.S. next week. AccuWeather.com Expert Senior Meteorologist Alex Sosnowski has the details on this potential.

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