Alabama Landscapes
Weather and Climate
Controls on Alabama's
Weather and Climate
Alabama's climate is controlled by several factors, chiefly the Gulf of
Mexico, the Polar Jet Stream, and the season. With respect to the last of
these factors, the seasons can be divided into two: summer proper and
the rest of the year.
Fall-Winter-Spring.
From September to December average monthly temperatures drop by about 5o
F per month throughout the state. Cooling of the surface at night is
responsible for most of this drop as the earth cools down under clear
skies. Eighty degree days with warm and moist southerly winds are often
followed by fifty degree days with cold northerlies to northwesterlies
In December, January and February more cold and dry air masses force
their way south from Canada, bringing cold, dry and clear conditions
(Figure CL4).
Variation is the norm, with several cold clear days followed by a warm
one or two. For example the average high
and low temperatures in Birmingham on New Year's day are 52oF and 32oF,
but high temperatures have reached 78oF (1952) and lows 11oF (1977).
The variability is the result of the passage of fronts
through the state. 
Figure CL4. Sources of the main air masses that affect Alabama in the fall-winter-spring season. A: Arctic air mass, cP: continental polar air mass, mT: maritime tropic air mass.
Wave cyclones often cause severe weather. Tornadoes occur during this season
Summer: In summer, the Jet Stream
generally stays north, and Alabama's weather is controlled by warm
and moist air from the Gulf of Mexico, aided and abetted by a
subtropical High pressure cell (called the Bermuda high) that parks
itself off the east coast (Figure CL5). This high blocks the easterly movement of air
masses from the Rockies.
Figure CL5. Factors influencing Alabama's summer.
Hurricanes occur during the summer and fall
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