May Outlook


Colder air continues to be likely through April.

A high pressure ridge keeps hold over the west which allows cold Canadian air to flow into the Miami Valley.

There are hints that the ridge may finally break down allowing warmer temperatures to return to the Miami Valley.

Right now the Climate Prediction Center’s early outlook for May keeps equal chances for above or below temperatures and rainfall for the month.

The good news is normal temperatures continue to climb a degree about every three days. May will start with a normal high around 67 degrees and end with a normal high of 76 degrees. The normal low starts at 47 degrees and ends at 56 degrees.

May is a very important month for the growing season. Last year we saw measurable rainfall 19 of the 31 days. The fields were too wet to plant. Ohio saw a poor corn and soybean crop.

Sam Custer is the Interim Assistant Director for Ohio State University Extension, Agriculture and Natural Resources. He also works locally as the Darke County Ag Educator.

He said farmers are hoping to avoid cold rain while they are planting. Highs in the 60s raise soil temperatures. Soil temperatures need to be at 50 degrees two inches deep for three days in a row.

“If soil conditions are right moisture wise we will see farmers planting a significant number of acres this week,” Custer said.

Custer said farmers are hoping for an inch of rain a week after planting with lows in the mid 50s. The warmest days need to be around 75 or 80 degrees.

2018 was a good year according to Custer.

“Almost everything was planted the first week of May,” Custer said, “and then we had ideal conditions after that for May and June. Farmers had some of the best yields ever in 2018.”

One of the patterns the Climate Prediction Center looks at to make monthly outlooks is the El Nino Southern Oscillation.

ENSO is determined by measuring Sea surface temperatures at the equator in the Pacific Ocean.

Right now temperatures are neutral meaning there is not a large enough anomaly to be considered above or below normal.

Neutral conditions were present in 2018. The average temperature was above normal for the month and rainfall was around three inches. The only difference is 2018 was a neutral year following La Nino. 2020 is following El Nino.

Other neutral years following El Nino include 2005, 1995, 1993, 1984, 1970, 1978, 1967, 1960, and 1952.

All but one of these years saw temperatures about or just below normal. In 1970 the average temperature was 3 degrees above normal.

Neutral years following a La Nina trend warmer in May than neutral years following El Nino.

El Nino was present during the 2019 May that resulted in flooding across northwest Ohio.

The Climate Prediction Center also looks at several other patterns to determine the forecast, but ENSO tends to be one of the stronger influences. Looking at trends from past years help determine outlooks, but is not an exact forecast. There are exceptions to the patterns.

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