Cyclical Barometric Pressure


I have a question regarding barometric pressure:  Do changes in pressure follow any rhythm (seasonal, annual)?  


Assuming that we are focusing on Louisiana and the Gulf Coast region . . .  (I believe that the following would be true for just about every location, but I have not investigated the data on a national or international scale) . . .

Typically, expect monthly/seasonal average pressures to be higher in the "cooler" months (winter) . . . and lower in the "warm" months (summer).  For south Louisiana, peak average monthly pressures typically can be expected in January & February (say, ~30.10-30.20 millibars at SLP), with lowest average monthly pressures ranging from June to September (~29.95-29.85 mb, the actual month for each and every site varies a bit as a function of "average statistics".)

The diurnal (daily) average pressure rhythm - highest in the early morning, lowest in the mid/late afternoon - tends to be of nearly the same magnitude/range as the annual cycle.

Why (for the annual & daily cycles) you may ask?

Because, all other things held "constant", surface pressures tend to fall as surface temperatures increase.  Heating of the surface air makes it "lighter" . . .

Jay Grymes
Chief Meteorologist
WAFB Storm Team