It’s ‘a go!’ All signs are pointing to a change in the climate pattern for this fall, and winter too, due to El Niño — formally called El Niño Southern Oscillation, or ENSO.
“Looking at the latest 30-day and 90-day maps generated (for this autumn 2018, and issued Aug. 16) from the Climate Prediction Center, it appears we’re witnessing the incorporation of an El Niño event into the outlooks,” said Allen Dutcher, associate state climatologist, Nebraska State Climate Office, Lincoln, Neb. “During the past four weeks, there’s been a subtle shift toward a wetter pattern across the southern Plains, while the northern Plains has slipped towards the dry side.
“If typical El Niño conditions develop in earnest this fall, I’d expect the southern Plains, the southeast, and eastern seaboard to tilt toward the wet side, especially during the second half of the three-month forecast period.”
Dutcher noted the dryness in the Pacific Northwest is already spreading across the northern Plains, which does typically experience warmer and drier weather during these events.
Current projections are for a weak event, possibly making it to the threshold of a moderate event.
“We typically see a relaxation of the northern jet, while the southern jet becomes stronger,” he said.
A Kansas meteorologist with the National Weather Service concurred that the official September/October/November outlook favors warmer than average temperatures and wetter than average precipitation during this period.
“I think the paragraph (from the CPC) that sums up the current outlook is: ‘During the autumn and winter 2018-19, the temperature and precipitation outlooks are consistent with the elevated probability of El Niño development and its impacts. Temperature outlooks for winter 2018-2019 were modified over parts of the central plains and southwest regions to represent (moderation of probabilities for) above normal temperatures by a potential shift of the jet stream and storm tracks southward, due to the impacts of a potential El Niño. Areas of probable above-normal precipitation in late winter 2018-2019 and early spring 2019 outlooks were expanded westward into southern California, representing impacts of the potential shift in the storm track due to El Niño,” relayed Chad Omitt, warning coordination meteorologist for the National Weather Service in Topeka, Kan. “However, I’ll caution that long-term forecasts in late summer early autumn are notoriously difficult to make given the weak relationship between EL Niño/La Niña and overall weather patterns this time of year.”
An El Niño event is expected to gradually develop across the Pacific into October/November, but Omitt said there’s much uncertainty about how strong it may become.
“If this were to become a moderate or strong El Niño, it could help favor better odds for wetter conditions across at least some parts of Kansas,” he said.
Although El Niño conditions frequently favor higher than normal precipitation in the Plains, delayed onset may result in less impact during the fall.
“Note, this outlook (the warmer than normal temperature forecast) is the average of the three-month period, and doesn’t eliminate the possibility of colder-than-normal conditions during the period,” said Mary Knapp, assistant state climatologist at Kansas State University, Department of Agronomy, Manhattan, Kan. “The precipitation outlook is driven mainly by the sea-surface temperature and constructed analog models. Keep in mind, the skill with both outlook products is weakest with neutral ocean temperatures, and doesn’t account for individual events such as a heavy rainfall event.
“Warmer than normal temperatures would increase the opportunity for late-planted spring crops to mature before the first frost, but could increase evaporative demand and have flowering/grain-fill occur under less favorable conditions than normal.”
Harvest may be a bit of a challenge from Interstate 80 southward in the western corn belt with the return of moisture.
“The northern Plains is a crap shoot, to be perfectly honest,” Dutcher said. “Although a dry trend would be expected, heavy moisture through mid-July means some soil moisture carryover which could cause excessive wet surface conditions until/if the typical El Niño develops across the northern Plains. If this happens, I’d expect the first half of fall to have the highest risk of crop harvest delays.”
As Omitt put it, “We should begin to have an idea of how strong this El Niño event will become by late October into November.”