Published: 2010-09-16 16:34:00
Updated: 2010-09-16 16:41:00
Posted September 16, 2010
By Nate Johnson
We're halfway through September, but we don't exactly have a lot of rainfall to show for it. Through the 15th, we have recorded a scant 0.13" of rainfall this month, below the record-driest September on record. Back in 1985, we only picked up 0.23" of rain that September. If we stay dry through the end of this month — a distinct possibility, given the dry upper level pattern we have going right now — we could set a new "driest September" record.
I want to talk about "normal" rainfall for a bit. Our normal rainfall is re-calculated every ten years. Statisticians and climatologists look at the previous thirty years' worth of data. The last time this adjustment took place was in 2001, so our normal highs, lows, and rainfall numbers are based on the period of record from 1971-2000. Based on that period of record, our normal September rainfall is 4.26", making it the second wettest month of the year.
However, you may recall that the 1990s included a couple of very wet Septembers due to Hurricanes Fran (1996) and Floyd (1999). Each hurricane helped bump the September rainfall in their respective years to astronomical numbers: 16.65" in 1996 and 21.97" in 1999. Looking at a graph of September rainfall numbers since 1971, you can see that these two years are clearly outliers. Take those two years out of the equation, and our would-be-normal September rainfall drops to 3.19". That would put it on the dry side, making it the fifth driest (or eighth wettest) month in a "normal" year.
I highlight this for a few reasons:
Bottom line: It's dry out there, and while a dry September isn't all that odd, it is troubling when it follows the kind of hot and dry summer we have endured this year. If we don't get some consistent, widespread rainfall in the coming weeks, we will likely head into one of the drier times of our year riding dry or moderate drought conditions, if not worse.