A classic winter weather situation is brewing for this weekend. This time of year the Arctic air masses that come out of Canada are cold and dry, thus relatively dense. The dense air hugs the ground, making the high pressure system shallow, which disconnects it from the steering winds of the jet stream. When that happens the Arctic air struggles to get over the Appalachians. Instead it sinks southward across the Great Plains and into the Gulf of Mexico. On occasion the cold air will cross the Gulf, pass through the Isthmus of Tehuantepec (you do remember it's strategic importance to the Gadsden Purchase, right?) and reach the Pacific. As the cold air funnels through the gap in the Sierra Madre it creates a violent breeze snickeringly known to juvenile meteorologists as a tehuantepecer. more ›