The norther has its source within the cold polar air masses forming within the Rocky Mountain region and along their eastern slopes. During the winter half of the year, when the days are short and the sun remains low on the horizon at high latitudes, cold air forms and accumulates within a high pressure system stretching from Alaska southeastward into the United States. Portions of this cold air mass, or the entire system, break out regularly and are carried southward and southeastward by the upper winds down the gently sloping planes and Mississippi Valley and out over the warm Gulf of Mexico waters. During a typical winter, as many as 30 such cold outbreaks reach the Gulf coast. The majority of these cold outbreaks, spilling out over the Gulf, produce winds only in the 15-25 knot range, but about 10 or so have strong enough winds to cause gales with maybe 5 of these being vigorous enough to cause whole gale winds.
Winds reaching hurricane force in a norther within the Gulf or Caribbean areas are rare.
The number of northers are the severity of these winds vary considerably from year to year depending on the pattern of the general circulation of the atmosphere. During winters with a persistent strong upper level ridge over the Rocky Mountains and a deep trough over the eastern half of the country, cold polar air forms in generous quantities in Alaska and western Canada and is swept at regular intervals deep into the southern United States and out over the Gulf. The cold air outbreak, with the cold front as the leading edge, is easy to follow southward and southeastward down across Canada and the United States. A norther can therefore be predicted with a good degree of accuracy. The development of an extratropical cyclone, as a wave on the cold front over the Gulf of Mexico or the southeastern United States, helps accelerate the cold air mass farther southward well out over the northwestern Caribbean Sea where the northerly winds merge into the normal northeast trades.