September sizzle getting underway; extended warm spell coming

Data pix.


A streak of sub 80-degree days ended Monday when the temperature reached 84° in Indianapolis. After five straight days in the 70s our weather is taking a turn.

Temperatures and humidity jumped on southeast breezes and even warmer weather is in the works this upcoming work week.


Our young September has been slow out of the gate in the sunshine department. September ranks third annually as the sunniest month, tying June at 65% possible sunshine. It was nice to see the brighter skies following the rather cloudy Sunday. To date we've only had 48% the possible sunshine. Sunny weather is definitely in the forecast moving forward as a new pattern takes hold.


As first forecast last week, the jet stream pattern is changing and evolving into a typical summer pattern. Interestingly, it is possible that it will hold for the next two weeks.

The main branch of the jet stream will migrate north and run from west to east along the U.S./Canadian border - typical of the summer months. This will allow a late season dome of heat to expand and become better established, anchored over the southeast U.S. Off the overnight computer projections, the length of the warm pattern is eye-catching - meaning the warm pattern could last a full two weeks with only small pullbacks from time to time.

The upcoming work week will include afternoon high temperatures at or above 90-degrees through Friday with a heat index around 95-degrees starting Tuesday. Only moderate relief is expected behind a passing cold front Friday evening as we enter the weekend.

With lowered temperatures and humidity, this upcoming weekend is still expected to remain above normal. However temperatures will climb again to near 90° next week. Below I'm posting the upper air pattern forecast for Wednesday and then again next Monday. Note the warm colors over the eastern U.S. This is where the atmosphere (heights) are the largest or thickest. This is a region where the atmosphere is expanding and where sinking air compresses and heats up. This machine forecast leads to high confidence that temperatures are going to be well above normal into next week and possibly beyond. Summer isn't done yet.

We average three 90-degree days in September and each of the last six September's have produced at least one day. Last year there were eight 90° days in Indianapolis.

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