After an unusually cool and wet summer, Indiana might very well see a return to more normal conditions as autumn sets in.
Temperatures are expected to rebound to near-normal and then normal for the rest of September and develop into a warmer-than-normal trend for October, according to the Indiana State Climate Office, based at Purdue University. Precipitation should be about normal in October.
The relative warm-up would be the result of a “positive” Arctic Oscillation that is expected to keep cooler air out of the region and a jet stream that is likely to shift more east to west than north to south.
The outlook is “a broad climatology of expectations,” said Dev Niyogi, state climatologist.
“This appears to be a season where we will have to keep a close eye to see how things are evolving every month, with no major drivers dominating our seasonal outlook,” he said.
From now to the end of October in the far northern counties, daily high temperatures normally fall from 70 degrees Fahrenheit to 55 and lows from 50 to 40. In extreme southwest Indiana, the highs normally cool from 78 degrees to 64 and the lows from 54 to 42.
Total October precipitation normally ranges between 1.7 and 1.9 inches across the state. October usually is one of the driest months of the year in Indiana.
With autumn’s return, attention shifts to the question of when Indiana will have its first frost. The average earliest first-frost dates are more than three weeks away.
For most of Indiana, the first killing freeze of 28 degrees Fahrenheit or lower typically has occurred during of period of Oct. 23-29. Scattered portions of the state, mostly in some of the central and northern counties, have had their first frost Oct. 17-23.
Most southern counties have experienced their first frost Oct. 29 to Nov. 17.
A map of Indiana’s average first-frost dates is available here.