Smile Politely

C-U Monthly Weather Review: September 2021

We’re well into the second month of climatological fall and if the slowly changing leaves weren’t sign enough, the recent gloomy weather and daily rain showers should be setting the vibe for you. Even with the cooler, rainy weather, we’re still running about 10 to 15 degrees warmer than average this week, a warm trend that goes all the way back to September.

When we look back at September ’21 in Champaign-Urbana, we get a month that came in quite a bit warmer than average, and a little drier than average. The monthly mean temperature was 70.3 degrees, 3.1 degrees warmer than average. Total precipitation for the month came in at 3.11″, about a quarter of an inch below the September average of 3.37″.

Out of 30 days, 19 were “warmer than average” with seven days in the last half of the month being over 10 degrees warmer than the daily average. That meant a lot of days with afternoon high temperatures in the upper 80s and lower 90s, with a 91 degree high temperature on the 19th being the monthly hot-spot.

The first sharp cold front of the season did bring an injection of crisp fall air on the 22nd, sending high temperatures into the 60s with our first overnight lows in the 40s on the 23rd and 24th. The cooler pattern didn’t stick however, and we were back in the upper 80s and 90s by the end of the month closing with three straight days with temperatures more than 10 degrees warmer than average.

While we came close to touching the monthly average for precipitation, rainy days were relatively few and far between. We saw rain on seven of 30 days in September, with 1.11″ falling on September 8th making it the rainiest day of the month. A little over 1.5″ of rain also accompanied the sharp cold frontal passage over a two day span September 21-22.

Where are we headed for the rest of the fall season? October is already off to a warmer start, even with recent gloomy, rainy conditions.

A large-scale pattern change is going to take place across North America as we head into mid-month, but the sensible impacts may not be all that different here in Central Illinois.

For now, all signs point toward mild temperatures continuing unimpeded through the next 7-10 days. Even with mild conditions continuing, shower and storm chances should return to the forecast after a dry weekend ahead.

At least one, but potentially several large storm systems are expected to sweep across the Central U.S. through mid-month. We’ll likely be on the breezy and warm side of the storm track, with chances for scattered showers and thunderstorms every few days. Depending on the storm track, this could even mean a severe weather day or two locally in the second and third week of October. Midwestern severe weather outbreaks in October aren’t necessarily commonplace, but they’re not rare either as we transition seasons and the jet stream sinks back into our neck of the woods.

Where the pattern goes in late-October remains a bit of a mystery. There are a handful of reliable long-range weather models that argue for warmer conditions lingering into late-month, but it’s been my gut, along with others, that we’ll become more vulnerable to shots of cold air in the Midwest by the last half of the month.

Still, I think we’re looking at an October 2021 that closes warmer than average overall in Champaign-Urbana, and a near average month with respect to precipitation. The pattern will offer up multiple chances for showers and thunderstorms, and there’s certainly a world where we could end up with several soaking rains that send us above average, but for now we’ll play the average. I simply think if the precipitation forecast is going to bust, it will bust high. Put me down for very high confidence with respect to the warm October idea though.

All in all, while there may be frustration around the shortage of sweater-weather, I think we’re looking at a great month to make some final outdoor memories in 2021!

Andrew operates Chambana Weather, where he publishes daily weather information for Champaign-Urbana and surrounding communities. He also serves as Senior Meteorologist with Nutrien Ag Solutions at Research Park, focused on domestic and international weather and its impact on agriculture.

Champaign-Urbana monthly climate statistics are courtesy of the Illinois State Water Survey.

Top photo by Andrew Pritchard.

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