September has arrived! Here's a look at September climatology in the TN Valley.
Before we move ahead to the new month, we always like to look back at rainfall stats across the area from the previous month. For the Northwest Alabama Regional Airport in Muscle Shoals, the location of our region's climate records reporting station, rainfall was still slightly below average for August. We measured 2.55 inches of rain for the month, 1.22 inches below average. That puts us a little shy of 2 inches below average for the year so far.
Having said that, those Muscle Shoals stats are misleading when looking at the area as a whole. Many areas of western Colbert through much of Lauderdale Counties of Alabama, into a large part of southern middle Tennessee, saw anywhere from 4 to 7 inches of rain for the month. Several of our personal rain gauges across Florence, AL alone recorded over 6 inches of rain for the month. That puts many areas well above average in terms of rainfall for the month of August, and in some cases, double what we typically see. That is reflected in today's update to the drought monitor, which still shows dry conditions... and even drought conditions in places... but there has been significant improvement. With the on and off wet pattern expected ahead, we expect more drought improvement to come.
So, let's move ahead to September. Climatologically speaking, September is when things begin changing in the Tennessee Valley. This is the first day of "meteorological fall", with astronomical fall (the true autumn equinox) happening on September 22nd. We group the meteorological seasons slightly differently to make climatology records easier to track. We begin seeing a downhill trend in the average temperatures this month, normally speaking. The average high for the overall month of September is 85 degrees, and this is the start of when the average high slips below 90, even on the 1st of the month. By the end of the month, we're talking about an average high under 80! We all know it can still get hot in September though. Our monthly record is 108 degrees, set back in 1925! And while we average a low of 62 for the overall month, it can occasionally get chilly at night too. Our record monthly low is 36 degrees, set in 1901! September is one of our driest months in the Tennessee Valley, with normal rainfall averaging around 3.72 inches. Thunderstorms and the occasional tropical system can give us WELL above that though.
September is the heart of the Atlantic hurricane season, with the actual peak of it occurring on September 10th. The entire Atlantic basin is usually open for business this time of year, with both "home grown" systems and the long-track systems rolling off the African coast both being possible. While strict climatology does show that the absolute most likely area to see a system is off the East Coast in the open Atlantic, this is the time of year when tropical storms and hurricanes are climatologically most likely to strike the United States, and September can bring some violent hurricanes at times. Fortunately, we don't see any signs of that happening in the immediate future!
While we can still get the occasional severe thunderstorm warning for summer type pulse storms with gusty winds or small hail, the good news is that September is statistically the least active month of the year for tornadoes in north Alabama and middle Tennessee. Just about the only time you have a tornado threat here in September is in association with a landfalling tropical system. In my 28 years of forecasting weather here, I have only seen one mid-latitude (a low pressure system with a cold front) type of severe weather threat with tornadoes in the area in September. That date was September 22, 2006. The brunt of the event was from Arkansas to Illinois, but a few supercells formed on the warm front in north central Alabama that afternoon, and there were a few tornadoes, including an F2 tornado in Blount County, AL. Never say never to anything, but that type of ordeal is VERY RARE here in September. However, it won't be long until tornado activity statistically picks up, especially as we head toward November...