Resumen
Several cases of the synoptic situation associated with intense frosts, which has affected the plantations of coffee and citrus in eastern and nourtheastern Mexico, are analyzed, these events also damaged citrus and vegetables in Texas, Lousiana and Florida. the origin and evolution of the anticyclonic circulations associated with the polar air mass, are traced. these originate during a blocking situation of the westerlies in the Northeastern Pacific with a confluence zone close to Alaska, and an intense cyclogenesis in the northeast of United States. the major cold air outbreak over the east, northeast and Central Mexican Plateau is observed when an anticyclone associated with the polar air covers southeastern United States, Gulf of Mexico and the easthern Mexico.