As convective SIGMETs morph into G-AIRMETs for airframe ice, pilots flying in the Southeastern U.S., including the southern Appalachians, should expect a marked change from summertime weather as the upper-air pattern amplifies, the fall colors wane, and the cold season approaches. October and November are what meteorologists call transition months as the jet stream migrates south out of Canada. With each passing month during the winter, the increasing upper-level flow reaches well into the Deep South. The freezing level transitions from the lower flight levels in September to near the surface by the early part of December over a large portion of the northern tier of states-as forecast discussions are dominated by uncertainty about the precipitation type that will reach the surface.
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