Warmer-than-usual spell to linger through early summer

Iowa's seven-month warm spell is likely to continue at least through early summer, meteorologists say.

Average temperatures in Iowa, with one minor exception, have been warmer than normal for each of the past seven months - a condition at least partly attributable to El Nino holding sway.

Warmer than normal winter and spring weather is typical in Iowa during a strong El Nino, State Climatologist Harry Hillaker said. That effect should continue as long as the El Nino remains in force, he said.

Historical tendencies indicate that summer temperatures during an El Nino will be above normal 70 percent of the time, Hillaker said. 'Those are high odds in meteorological terms,” he said.

El Nino - Spanish for little boy - is characterized by periodic huge pools of warm water in the tropical Pacific. Both El Nino and its opposite, La Nina, affect the position of the jet streams, which in turn affect the track and intensity of storms.

Sea-surface water temperatures in the region from October through December were 2.3 degrees Celsius above average, according to the National Oceanic and Atmospheric Administration's Climate Prediction Center. That departure, the agency said, ties the peak anomaly measured during the 1997-1998 El Nino, the strongest since record keeping began in 1950.

While El Nino remains in force, it is weakening, according to NOAA. A transition to neutral conditions is likely by the early summer, with close to a 50 percent chance for La Nina to develop by fall, NOAA said.

'It looks like the El Nino will continue at least into June or July,” said Elwynn Taylor, an agricultural meteorologist at Iowa State University who has long studied the effects of El Ninos and La Ninas on crop production.

In an El Nino growing season, he said, there is a 70 percent chance that corn and soybean yields will be above the trend line.

'It's the other way around in a La Nina - a 70 percent chance of being below the trend line,” he said.

Iowa Agriculture Secretary Bill Northey said Friday that the persistent warmth may help farmers plant crops earlier than usual this spring.

As of Thursday, the 4-inch soil temperature in Linn and surrounding counties was 48 degrees, up from 43 degrees a few days earlier.

'Iowa farmers typically start planting corn when the soil temperature hits 50 degrees as long as soil conditions are right and the forecast is favorable,” Northey said.

The warm weather and lack of snow cover likely hastened the northward migration of waterfowl this spring, which may help lower the odds for another outbreak of bird flu, Northey said.

Last year the disease resulted in the deaths in Iowa of more than 30 million hens and 1.5 million turkeys and an economic loss of more than $1 billion.

'Last year the migrating birds stayed here longer waiting for snow to clear up north, which increased the opportunity to transmit the virus to domestic poultry,” Northey said.

As of April 1 last year, Northey said bird flu outbreaks had already been reported in Minnesota and Missouri, with Iowa's first outbreak confirmed April 13.

So far this year, there have been no confirmations, he said.

Statewide since September, variations from normal temperatures all have been positive with the exception of January, which was 0.2 degree cooler than normal.

December exceeded normal by the greatest margin, 10.1 degrees, but positive margins were also substantial in March (6.3 degrees), November (5.3 degrees), September (5.2 degrees) and February (4.1 degrees).

Positive margins were recorded during all seven months in Cedar Rapids, Iowa City and Dubuque.

The recently completed month of March was 6.3 degrees warmer than normal, but that variance may not have seemed exceptional to the many Iowans who remember March 2012, which was 15.2 degrees warmer than normal - the highest positive monthly departure ever recorded in Iowa.

Statewide precipitation was well above normal in the last four months of 2015, but it has been slightly below normal in the first three months of this year.

'Right now we have plenty of moisture in the soil - all it can hold,” ISU's Taylor said. 'That could be a disadvantage at planting time unless we get a window of good weather to dry it out.”