If you like crisp fall weather, with frost on the pumpkins and sweater weather while leaves are still clinging to the trees, you’re likely to be bitterly disappointed by the weather that appears to be in store for the weeks ahead. October is setting up to be a very warm month, not only in Tennessee but across the entire eastern United States.
Let’s get a little technical. This is going to be a non-scientific, nutshell explanation of the setup, but if that nevertheless causes your eyes to glaze over, skip to the next section.
This map, which is an output from the GFS computer model, shows the setup that will develop to our west, and it’s an ugly one if you like cool, crisp fall weather in the east. This is a depiction of what the model expects the pattern to look like by Oct. 12. There’s no particular reason for choosing that date; I just pulled one frame out from this morning’s run of the model.
The first thing to notice is the strong area of low pressure in the Gulf of Alaska. This part of the world is famous for its persistent, stubborn weather systems that sorta get stuck in place because of the greater steering pattern over the region. The second thing is the area of high pressure off the coast of Alaska, which is going to be equally stubborn. And the third thing, which isn’t as easy to depict on this map, is the lowered atmospheric heights over the West Coast region.
This is a setup that screams cool, wet weather across the Pacific Northwest, and hot weather for just about everyone east of the Rocky Mountains. Now here’s the translation, from the same time on the same model, depicting the temperature anomalies at the 850mb pressure level (which is about 5,000 ft. above the surface).
That’s an ugly picture for October.
What does it mean for us?
This setup that is evolving in the Pacific means that most of the eastern U.S. is likely to be bathed in warmth for at least a few weeks — or as long as the pattern persists.
Our normal temperature for this time of the year (early October) is highs in the mid 70s and lows in the mid 40s. By the middle of the month, that drops to highs in the upper 60s to near 70, and lows in the lower 40s.
Our high temperatures for much of this week will be slightly below normal, simply because of all the clouds and rain that will be around. But we’ll rebound to above-normal temperatures by the weekend, and that looks to be the general pattern as we move into the middle of the month. It’s hard to say exactly how warm we’ll be, but high temperatures around 80 (or a little above) will probably be more common than high temperatures in the 60s for much of October.
Here’s the forecast from the National Weather Service’s Climate Prediction Center, for Days 8-14. It’s an ugly temperature outlook.
And here’s the outlook for the month of October as a whole, which is nearly as bad:
Best guess scenarios
The last very warm October we had here in East Tennessee was in 2016, which was one of the warmest Octobers on record in Oneida. But it was warm for a different reason, and can’t really be used as a predictor for what’s to come.
The last time we had an overall atmospheric setup that most closely resembles what we’re going to see this month was 2007. That was also a very warm month in East Tennessee, with a temperature reading as high as 89° on Oct. 8. There were several cold fronts that provided big cooldowns that month (something we may not see for at least the next couple of weeks), but the overall temperature for the month still wound up being about four degrees above normal.
An about-face in November?
Some long-range modeling data suggests that we’ll see a major change in November, going from what is essentially a late summer temperature pattern to what is more like an early winter temperature pattern. We’ll see in the weeks ahead how the pattern evolves and whether a temperature crash grows more likely for some time in November.
The bottom line
Warmer-than-average temperatures will be with us for at least the next couple of weeks, and likely beyond, as a pattern sets up that typically leads to warm-to-hot Octobers across the eastern U.S. This will extend the growing season and impact the fall foliage season. A flip to a cooler-than-average temperature pattern could occur after we move into November.