Mississippi River Valley Effects

Because the Mississippi River Valley leads from the Great Plains to the Gulf, it provides a natural way for migratory pressure systems to enter the coastal regions. Outbreaks of cP air are frequent during the winter with occasional cA air reaching the coastal area. During the spring and fall, diffused and modified mP air masses are generally the rule. Most frontal systems that affect the local area must have a deep upper-level trough of sufficient magnitude to force the Polar Jet deep into the Four Corners region of the southwestern U.S. or central Texas. If this troughing is followed by a cA air mass, freezing temperatures can be expected locally.
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