Right on Time: Autumn in Iowa

gfs_slp_180mToday’s raining and dreary day perfectly matches the season that just arrived a few days ago.  Fall is here, and Mother Nature is sure making it feel like it.  Temperatures are below normal and are not expected to rise too much until mid week.  It’s a good indicator that colder weather is not far off.  The graphic to the left illustrates this perfectly.

You can see a large cold dome reaching the US east of Iowa just over a week from now.  This is a sign that the frigid weather well to our north is beginning to make its way back into the lower 48.  This not only leads to a gradual shift in the climate here in Iowa, but also can renew the threat for severe weather.

Some call it the “second season.”  But whatever you call it, it should never come unexpected.  The bottom line is a lot of severe weather in the early spring is produced by the classic clash of the air masses.  As winter turns to spring, large areas of cold and warm air battle it out over the Midwest.

Well in the fall, the same thing happens, only the winner is reversed.  Cold air returns and takes over the land conquered by a warm air mass during the summer.  All of this means a second spike in severe weather.

Generally that increase happens south of Iowa, but it can produce dangerous weather here very later in the year.  You only need to go back as far as 2005, when a deadly tornado struck the central Iowa town of Woodward on November 12, yes, November.  Severe weather likely will stay away from Iowa for a while, but as the warm air tries to breathe its last gasp over the Upper Midwest, don’t be surprised to hear of thunderstorm and tornado warnings around the time you’re starting to think about Turkey.

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