Most weather signs are pointing to an El Nino weather pattern this fall and winter
August 31, 2018
With all signs highlighting a switch, from the La Nina to the forecast El Nino (formally called El Nino Southern Oscillation or ENSO) climate pattern for this fall 2018, and winter too, meteorologists and climatologists expect to have a better idea of how strong this El Nino event will become by late October into November.
"Looking at the latest 30-day and 90-day maps generated (for this Autumn 2018 which the Climate Prediction Center issued Aug. 16, 2018) it appears we're witnessing the incorporation of an El Nino event into the outlooks," said Allen Dutcher, associate state climatologist, Nebraska State Climate Office-Lincoln. "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."
Wet Conditions Southern third of U.S.:
"If typical El Nino 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 said. He noted the dryness in the Pacific Northwest is already spreading across the northern Plains, which typically experiences warmer and drier weather during these events.
“Looking at the latest 30-day and 90-day maps generated, it appears we’re witnessing the incorporation of an El Nino event into the outlooks,”
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"The general concept of El Nino's influence on the continental U.S. has its strongest impact during the winter, but those influences can extend to the fall and spring period depending on the strength and longevity of the event," Dutcher said. 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."
The official CPC statement:
A meteorologist with the National Weather Service said the official September/October/November outlook favors warmer than average temperatures and wetter than average precipitation for the central Plains southwestward, 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 Nino 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 Nino. areas of probably above-normal precipitation in late winter 2018-2019 and early spring 2019 outlooks were expanded westward into southren California, representing impacts of the potential shift in the storm track due to El Nino," according to Chad Omitt, warning coordination meteorologist, National Weather Service-Topeka, Kan. "However, I will caution that long-term forecasts in late summer early autumn are notoriously difficult to make given the weak relationship between EL Nino/La Nina and overall weather patterns this time of year," he said.
An El Nino event is expected to gradually develop across the Pacific into October/November, however Omitt said, there's much uncertainty about how strong it may become. "If this were to become a moderate or strong El Nino, it could help favor better odds for wetter conditions across at least some parts of Kansas."
Regarding the Colorado perspective, although there had been a 50 percent of a forecast El Nino, now the current forecast is a 60 percent chance of El Niño development in the fall and a 70 percent chance of an El Niño during the winter.
"It's important to note the key differences between a La Niña winter (what we had last year) and an El Niño winter (what we should have this winter). In a nutshell, we (in Colorado) flip from the wetter-to-north/drier-to-south setup (which we did see last winter) to a drier-to-north/wetter-to-south setup," said Becky Bolinger, Ph.D., assistant state climatologist, Colorado Climate Center-Colorado State University Department. Atmospheric Science.
The CPC's outlook for September/October/November shows the entire Colorado area has an increased likelihood of above average temperatures, and the southwest has a slightly increased likelihood of above wetter than average conditions, as does Florida and surrounding areas. The Pacific Northwest has a slightly increased likelihood of being drier than average. "This is very in line with a classic winter El Niño pattern," Bolinger said.
The real key here is the exact placement of the jet stream. "We know we can expect wetter conditions to the south, but how far north that extends, and how much that will impact your region of interest, is uncertain at this time, which is why most of the region shows equal chances (EC) of above, near, or below normal precipitation on the CPC outlook. The further north you go though, the less likely they are to be wetter than average (looking at Wyoming in particular) I would say that an El Niño in the forecast does provide a little bit more hope for relief for the southern areas that have been in drought for a while," Bolinger said.
The recent (Aug. 16) outlook probability forecasts are showing a good chance of above normal temperatures in all of Wyoming for the September through November period.
"The chances of this occurring increase as one goes from northeast Wyoming to far southwestern Wyoming where the odds of above normal temperature are better than 50 percent," said Tony Bergantino, deputy director; Water Resources Data System — Wyoming State Climate Office and Wyoming CoCoRaHS State Coordinator.
Meanwhile, the situation is not as cut and dried for precipitation, with the southwestern part of Wyoming seeing better chances for above normal precipitation. "The chances diminish as you go north and east. The signal for most of the northeast half of the state is unclear," Bergantino said, which results in (EC) also known as having equal chances for either: above normal, or below normal or normal precipitation.
"Note, this outlook (the warmer than normal temperature forecast) is the average of the three-month period, and doesn't eliminate the possibility of a cool end to the season, or vice versa. 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," said Mary Knapp, assistant state climatologist, located at Kansas State University, Department of Agronomy, Manhattan.
For Kansas and Nebraska:
"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," Knapp said.
Considering that El Ninos also increase Eastern Pacific tropical activity, above normal moisture depicted in the southwest 90-day outlooks suggest the monsoon (the wind pattern seasonal reversal beginning at the 'Four Corners' region of Colorado/New Mexico/Arizona/Utah) will continue to be aggressive and likely that several tropical systems will move up the Baja Peninsula, shunting moisture into the southwestern desert region," Dutcher said, adding, "I wouldn't be surprised to see this moisture feed be entrained into the southern jet and the moisture then shunted eastward into the southern Plains, enhancing precipitation chances."
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. Although a dry trend would be expected, heavy moisture through mid-July likely means some soil moisture carryover that could cause excessive wet surface conditions until/if the typical El Nino develops across the northern Plains. If this happens," Dutcher said, "I'd expect the first half of fall to have the highest risk of crop harvest delays."
New trending climate product:
One interesting product that Bolinger has been directing people to, is an experimental product put out by National Oceanic and Atmosphereic Association's Earth Systems Research Laboratory. They have a page showing the "Risk of Seasonal Climate Extremes" related to ENSO conditions. "So, select El Niño, and pick for the September-November time period. In a nutshell, most of Colorado shows an increased risk of wet extremes and a decreased risk of dry extremes during an El Niño fall. What can this mean? Hopefully that drought is very unlikely to intensify during the fall and actually has the chance of weakening in severity," said Bolinger, adding, "Fingers crossed. The risk page can be found here: https://www.esrl.noaa.gov/psd/enso/climaterisks/.
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— Hadachek is freelance writer who lives on a farm with her husband in north central Kansas and is also a meteorologist and storm chaser. She can be reached at firstname.lastname@example.org.