May 1, 2012

Dry season not over (but "rain year" is done!)

Finally, after a long dry spell, stormy weather has returned.

Could it be at the same time the "rain year" is also done?

Summer style clouds like these are still weeks away,
But could it be that a new rain year has already begun?


According to my calculations, yes.

South Florida’s rain year runs from May 1st to April 30th. That means that from this point forward any rain we gets counts toward our new rain, not the previous one, which officially goes in the books as shown in the bar chart above.


Miami led the way with over 60 inches of rain. Lake Okeechobee recorded the least. But that’s nothing new. It always does. The primary reason is that its large body of water disrupts the upward-flowing convectional wind currents that bring the bulk of the summer rain to the rest of the peninsula.

The wet season accounted for 80 percent of the south Florida’s annual rain total.


Why sum annual rain across (not within) calendar years?

That way we can plot consecutive wet and dry seasons one on top of the other on the same graph. If we went by the calendar year we’d have parts of two different dry seasons in the same graph.

The above bar chart shows wet and dry season rainfall totals for select basins across south Florida.  The recent four day deluge along the southeast coast pushed Miami above sixty inches for the year.  The calendar year starts in the middle of the dry season, thus for meteorologic correctness, it makes more sense to sum the annual rainfall total from May to April  to include back to back wet and dry seasons.

To confuse matters even worse, this year’s dry season still isn’t done.

A couple weeks remain before the true summer showers begin. Until then, whatever rain does fall will be counted towards the new "May 2011 to April 2012" Rain Year.


Nobody said splitting rain drops in the swamp would be easy!

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