NWS predicts cool, wet May in most of Upper Midwest

If the National Weather Service's new May forecast becomes reality, the Upper Midwest's already-slow planting pace will slow even more.

The NWS Climate Prediction Center's May forecast, issued today, calls for below-average temperatures and above-average moisture in most of the region. The exceptions are northern Minnesota and extreme northeast North Dakota, where equal chances of below-average, average and above-average moisture are forecast.

So far, planting delays aren't particularly worrisome, says Joel Ransom, North Dakota State University Extension agronomist for small grains and corn.

But further delays, which appear inevitable if the new forecast is accurate, would cause many fields to be planted later than normal.

"Late planting is not a good thing. Yields generally are better when crops are planted earlier," Ramsom says.

The biggest immediate concern is the excess moisture that has made many fields too wet to plant, he says.

"The main thing we need to worry about is getting rid of some of this moisture, and that's largely driven by heat."

Cool weather in May, particularly if accompanied by more precipitation, would keep many fields too wet to plant.

A cool May also would further slow warming of fields that already are colder than usual. Late-April soil temperatures across most of the Upper Midwest ranged from the high 30s to the low and mid 40s, according to information from the North Dakota Climate Office, Minnesota Department of Agriculture and South Dakota Office of Climatology.

A soil temperature of at least 50 degrees is particularly important. Upper Midwest farmers generally don't plant corn when the soil is colder than that.

Falling soil temperatures

Cold air temperatures late in April even caused soil temperatures in many areas to drop. A few examples:

•The soil temperature in Jasper, in southwest Minnesota, fell from 49 degrees on April 26 to 46 degrees on April 29.

•In Sidney, in east-central Montana, the soil temperature fell from 50 degrees on April 26 to 40 degrees on April 29.

• In Britton, in north-central South Dakota, the soil temperature fell from 44 degrees on April 26 to 42 degrees on April 29.

•In Rolla, in north-central North Dakota, the soil temperature fell from 44 degrees on April 26 to 42 degrees on April 29.

Once the soil is thawed, soil temperatures respond relatively quickly to changes, both up and down, in air temperature, experts say.

So, even normal air temperatures in May would warm soil rapidly. But the new NWS forecast indicates that might not happen right away.

Connecting wet, cold

The NWS had been predicting that much of the Upper Midwest would be cool and wet in May.

But the new forecast issued today calls for cool, wet conditions to encompass even more of the Upper Midwest than what the NWS predicted previously, says Laura Edwards, South Dakota State University Extension climate field specialist.

The region's excess soil moisture goes hand-in-hand with the National Weather Service forecast for a cool, wet May, says Adnan Akyuz, North Dakota State Climatologist

"It's been wet. That's part of the problem," he says.

As spring arrives, the sun sends more solar radiation to this part of the country," Akyuz says. When the soil is dry, much of the solar radiation is used to warm the atmosphere. When the soil is wet, as it is now, more of the solar radiation is used to evaporate moisture, leaving less to warm the atmosphere.

As soil moisture evaporates into the atmosphere, more clouds are formed, prolonging cold, wet conditions, what Akyuz calls "positive feedback."

"The Climate Prediction Center knows about that dynamic. They're aware of how wet the soil is. That's a factor in the May forecast," he says.

Keep an eye on El Nino

Forecasters also are watching El Nino, a complex weather pattern that results from variations in water temperatures in the Pacific Ocean. El Nino can contribute to cooler, wetter weather in the Upper Midwest during the growing season.

Conditions are trending rapidly toward El Nino, although it hasn't been declared officially yet, Edwards says.

Even if it continues to develop, El Nino's impact on the Upper Midwest won't be seen until mid or late summer, she says.