Retired UNL climatologist says forecast models have repeatedly underestimated the duration of the heat wave
Lincoln’s blast of late-summer heat is expected to peak this weekend, but retired University of Nebraska-Lincoln climatologist Dr. Ken Dewey says the more troubling part of the forecast is how long the unusually warm weather may persist.
Dr. Ken Dewey (@kdewey1unl)/X
During an appearance on Drive Time Lincoln with Jack Mitchell, Dewey said temperatures could remain above normal through the middle of September—or longer if forecast models continue to underestimate the strength of the heat wave.
“It originally showed this as a three- or four-day heat wave, then about a one-week heat wave,” Dewey said. “And then the 70s are gone.”
Dewey said forecast temperatures that had previously been in the 80s were revised upward into the 90s. As of his Thursday interview, the outlook called for highs near 97 degrees Friday and Saturday, followed by 93 Sunday, 94 on Labor Day, 96 Tuesday and 94 Wednesday.
The projected highs then ease only slightly—to the lower 90s late next week.
“This heat wave surprised the computer models and the forecasters and has lengthened from a seven-day event up to almost a two-week event,” Dewey said.
Hot Conditions for Nebraska Football Fans
Saturday’s heat will coincide with an 11 a.m. Nebraska football kickoff in Lincoln. Dewey said the earlier starting time is preferable to an afternoon game, but fans will still be sitting in direct sunlight as temperatures climb from the upper 80s into the lower 90s during the game.
“If it’s not windy, it’s going to be very, very hot just sitting in that sun the entire day,” Dewey said. “Fortunately, it’s a little bit earlier. An 11 o’clock kickoff is good.”
The highest temperature of the day is expected after the game, but Dewey said that will provide little relief for fans inside the stadium.
He advised those attending to arrive prepared for prolonged exposure to the sun and heat.
A Gradual Cooldown—Eventually
Dewey said the current forecast does show some easing by the middle of September, although temperatures would initially remain well above seasonal averages.
“Finally, Sunday the 13th, 88, which is still way above normal. It should be down in the lower 80s,” Dewey said. “Monday the 14th, 87. Tuesday the 15th, 83—a gradual easing back.”
Longer-range projections continued to show above-normal temperatures through at least September 17 at the time of Dewey’s interview.
“If we go all the way out to the 17th of September, that’s almost three weeks into the month, and the temperatures still are remaining above normal,” Dewey said.
He said some projected temperatures were running 15 to 16 degrees above normal. Lincoln’s normal high was approximately 84 degrees in early September and will fall to around 75 by the end of the month. The normal low at the end of September is approximately 48 degrees.
Dewey stressed that 90-degree weather in early September is not unprecedented. He said the historical probability of reaching 90 early in the month is close to 40 percent. By late September, however, the probability drops to only about three to five percent.
“The climate tells us this has to end,” Dewey said. “Will this heat ever stop? Not for a while.”
August Was Cooler During the Day
The September heat follows an August that was relatively mild by daytime-temperature standards.
Dewey said Lincoln went 17 consecutive days without reaching 90 degrees. The city recorded only eight 90-degree days during August, compared with a typical total of 11 or 12.
“During the day, the highs averaged below normal in August,” Dewey said. “So, it was a cooler-than-normal August, which is making this that much more uncomfortable.”
Overnight temperatures were warmer than normal, however, because of persistent humidity. Dewey explained that moisture in the atmosphere makes it more difficult for temperatures to fall after sunset.
The lack of wind has also made the current heat feel more oppressive. Dewey said Lincoln has not experienced the frequent strong winds or violent thunderstorms normally associated with weather on the Plains.
“We haven’t had any violent thunderstorms for weeks and weeks,” Dewey said. “We haven’t had any windstorms. We just have not had weather that you expect out here on the Plains.”
Dewey said the reduced wind can be documented, although comparable long-term humidity records are not available.
Rain Helped Erase Earlier Deficit
Despite the current dry and hot conditions, Dewey characterized the overall summer as relatively favorable for Lincoln.
Rain during June and July reduced the need for lawn irrigation and erased a precipitation deficit that had placed Lincoln on pace for one of its driest years on record. Dewey said the city moved from that deficit to approximately two inches above normal precipitation.
“We escaped summer,” Dewey said, noting that Lincoln exceeded 100 degrees only a couple of times.
The sudden September heat represents a reversal of the usual seasonal pattern.
“We had August in August, which was really September,” Dewey said. “And now we’re getting August.”
Dewey said Lincoln will eventually need additional rainfall, but he did not see a significant chance until after the weekend.
Will Lincoln Get a Real Fall?
Mitchell asked Dewey whether eastern Nebraska could miss out on an extended period of comfortable autumn weather, much as spring appeared to shift quickly from cold to summerlike conditions.
Dewey said he hopes temperatures decline steadily and allow for a traditional fall, including changing leaves. However, Nebraska weather sometimes changes seasons abruptly.
“I’m hoping for a gradual slide into fall,” Dewey said. “But Nebraska doesn’t fool around. Sometimes the season switch just goes on-off.”
A strong, cold and windy system late in September could knock leaves from trees before they reach peak color. Dewey said that possibility remains speculative, but it illustrates how quickly the state can transition from one season to another.
For now, Dewey said there is no clear sign of a sharp break in the heat.
“I would like this forecast to go wrong and suddenly for it to start getting cooler,” Dewey said, “but there’s no sign of that.”
Dewey continues to maintain the Lincoln Weather website in retirement. Local climate data, weather graphs and a link for submitting questions are available at lincolnweather.unl.edu.