The most severe freezes the last 60 years are listed from most severe to least: December 1989, January 1962,December 1983, February 1951 in Texas, December 1962, January 1985. The January 1962 freeze is almost as severe as 1989 with similar durations of low temperatures but the low temperatures in 1989 were lower. The January 1985 freeze was not very severe compared to the others because the low temperatures were much higher in the citrus belt. In 1962 there were two severe freezes the same year similar to the back to back freezes in Florida in December 1983 and January 1985. The January 1985 freeze was more severe east and not very severe in south Texas. A very very cold air mass blew over Texas in January 1962 but the coldest air stayed north of the Rio Grande valley and was not very damaging.

If you grow citrus north beware of the high frequency of really really severe freezes like those listed above. In the really super severe freezes temperatures can remain below freezing for more than 24 hours with lows well below 20F. I was looking at the weather history for Mobile,AL at weatherundergound and in 1951 the temperature declined all day on February 1 with temperature 17F at 11 PM and a continued plunge all the way to 14F near sunrise. The total durations below 18F was more than 12 hours for the night of February 1 and the morning of February 2. The low February 3 was even lower at 11F! This was a February freeze which is not very common in the last 50 years. It seems most of the severe freezes are between mid December and early February. Most of them have occurred in December and January. What is really impressive though with some freezes is the incredibly long durations of very low temperatures!

The latitutudes between 22N and 30N in North America are much colder than these same latitudes in all areas in both nothern and southern hemisphere. The low temperuture in San Antonio in 1989 was 0F. I cannot find such a low temperature on the same latitude in Asia, Africa, South America or Austrailia. North America is indeed a polar continent. There are many places where mangos will grow at 29 latitude but not in North America!

Just think ,if there were a east west mountion range in Canada to block the coldest air, severe freezes would not occur so far south.

I saw a weather surface chart of the massive arctic air mass that caused the 1983 freeze event. The pressure at the center of the high was 1064mb and it extended from the Canadian arctic coast to the Gulf of Mexico. It covered over 90% of the United States December 24 with temperatures as low as -64F in some locations! A low temperature of -7F was recorded in Philadelphia and many record lows were set on December 25. In this freeze event some locations set all time low temperatures for the month of December.