Autumn climate outlook for Indiana

Monday, September 21, 2020

Meteorological Autumn has begun, with the autumnal equinox following later this month. The National Weather Service and Climate Prediction Center have released its fall advisory data, and Indiana receives a little guidance from this data.

Nationally, we prepare for the probable onset of La Nina. The El Nino Southern Oscillation (ENSO) is showing a propensity for some amount of time where the average temperature in a portion of the equatorial Pacific Ocean will be more than half a degree Celsius below average. This relative chill near the equator affects weather patterns in the Pacific Northwest and Southeastern U.S. in very predictable ways.

In particular, those two regions become wetter than normal with a corresponding dry pattern in the Southwestern U.S. This effect arises as the oceanic waters affect the location and activity of the jet stream. For temperatures, these interactions produce a warmer than average experience for the Southwest and drier areas, with the effects of climate change being valued in putting the entire contiguous U.S. into some level of confidence for above average temperatures.

In Indiana, we see the benefit or harm of above average temperature predictions, but a La Nina event in the autumn does not lend confidence to any particular precipitation regime.

“The challenge is Indiana’s location well inland from the ocean coastlines that tend to see bigger impacts from La Nina events,” according to Dr. Beth Hall, Indiana state climatologist.

Indiana could have greater than average rainfall, average rainfall or below average rainfall. Where La Nina events do creep into Indiana predictions comes later, as winter comes, the jet stream shifts a bit, and the entire state trends a little warmer and wetter.

There are two climate regimes in Indiana, however, the snowy north and the temperate south, according the Koppen-Geiger climate classification system. Warmer, wetter temperatures in the north may mean more snow for the Michiana area, while warm and wet for the south means less chance of snow and more rain. However, the likelihood of La Nina conditions persisting through the winter at this time is 55 percent, according to the Climate Prediction Center. In fact, the chance of La Nina forming during the autumn is currently only 60 percent, adding another level of uncertainty to the forecasts.

To summarize, Autumn in Indiana is predicted to be warmer than average with some confidence, while no confidence exists in precipitation patterns.

If La Nina forms and persists into the winter months, confidence in warmer, wetter than average conditions will increase for our state. Dr. Hall adds that this uncertainty from rather weak ENSO phase outlooks makes seasonal predictions difficult this far in advance. Even the dates of the first hard freeze event (less than or equal to 28 degrees Fahrenheit) show no significant preference during La Nina, Neutral or El Nino years.

If La Nina does not form and the autumn and winter turn to ENSO-neutral conditions, the cycling of the other climatic oscillations will have more influence over local weather. The Arctic Oscillation, North Atlantic Oscillation, and Pacific-North American Pattern can actually interfere with the ENSO trends we expect when those oscillations are strong enough. None of those oscillations tend to have the staying power of ENSO, however, as they tend to look at the time scale of weeks rather than seasons. For more information on climate outlooks, contact the Indiana State Climate Office at 765-494-8060.

Visit www.extension.purdue.edu/putnam or contact the local Purdue Extension Office at 653-8411 for more information regarding this week’s column topic or to RSVP for upcoming events. It is always best to call first to assure items are ready when you arrive and to RSVP for programs. While many publications are free, some do have a fee.

Upcoming Events:

Sept. 22, 29 – Steps in September, Big Walnut Sports Park, 9 a.m.

Sept. 28 – ServSafe Food Managers exam – limited space , 9 a.m.-noon. Register at: https://purdue.edu/servsafe/workshops.

Oct. 5 – Virtual Master Gardener Roundtable, 6:30-8 p.m. Register at https://tinyurl.com/MGRT2020.

Oct. 20 – Morning Ag Mixer, 9a.m. Join at: http://bit.ly/MorningAgMixer.

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