October getting ready to arrive. What is "normal" for October weather in the TN Valley?
Today marks the last day of September, a month that has flown by. In the weather department, September is often one of our driest months in the Tennessee Valley. We have been a few tenths of an inch above normal at the weather reporting/climate observation station at the Northwest Alabama Regional Airport in Muscle Shoals, and this does not count rain that has fallen there this afternoon. This puts us not far from being 10 inches above normal in rainfall for the year so far. So, with October beginning tomorrow, what can we usually expect out of the weather in the Tennessee Valley?
October is often when the transition to cooler weather really starts kicking in across the Tennessee Valley. By the start of the month, our average daytime high is below 80 degrees, and it is below 70 degrees by Halloween. Our average morning lows are in the mid 50s to start the month and in the mid 40s as we head out of the end of October toward November. It can still get hot this time of year though, as 2019 showed us, with a record high of 100 degrees. We can also occasionally see frosts and freezes as we head into the month, with the record low for October being 23 degrees set in 1917 on Halloween of that year. We've had below freezing temperatures on record over the years as soon as October 3rd.
Based on 1981-2010 climate records, October normally averages as the second driest month across the Tennessee Valley (with August coming in 1st and September being 3rd driest) with an average of only 3.43 inches of rain. Heavy thunderstorm or heavy rain events and even an occasional tropical system can sometimes dump much more precipitation than that though. We normally do not think accumulating snow this early either, but we have occasionally seen snow flurries as early as late October, even as recently as a couple of years ago. Once we get temperatures down into the 30s, the weather can do some funny things, regardless of what is considered "average" or "normal" for the time of year.
Although, as 2019 and 2020 showed us, we can still occasionally get a tropical system or two to target the northern Gulf Coast in October or later, the increasingly frequent cold frontal passages often start shifting the main activity to the south and east. Tropical development in October is most likely either off the East Coast or in the Caribbean, with the most favored tracks being out of the Caribbean and either into the Bahamas or across the Florida peninsula, and a secondary favored track off the Southeast coast toward the Canadian Maritimes or the open North Atlantic. We can also occasionally still get systems develop off the Cape Verde Islands, but those are much more likely to recurve before having a chance to affect the United States.
As we head into October and the cooler months in general, we also begin our gradual but steady slide into the fall severe weather season. Tornadoes remain possible all twelve months of the year, but tornadoes outside of tropical storms and hurricanes are most favorable in a long period beginning in October and going through the end of May or early June. Within that extended period, there are a couple of peaks. The primary peak being in the spring months of March, April, and May; with a secondary peak in the fall, especially around November. Although October isn't the heart of the fall severe weather season, we can occasionally get severe weather and tornado threats... and these can include even Moderate and High Risk days. 2001 and 2010 are two such examples with Moderate and High Risk days in Tennessee and Alabama during the month of October. As we head deeper into the fall and winter months, some of these severe weather threats CAN be associated with violent, long-tracked, upper-end type tornadoes, just like we can sometimes see in the heart of spring.