It’s not your imagination — Michigan’s fall weather has been warmer than normal.
Meteorologists say September temperatures were 1.3 F above normal and the area received 2.28 inches of precipitation or 71% of the normal amount. Temperatures also jumped globally last month, beating the previous September record by 0.5 C, a change that Zeke Hausfather at the Berkeley Earth climate data project called “gobsmackingly bananas.”
Detroit conditions reflect a long-term warming trend for fall weather, with average September temperatures rising by 4.2 F since 1970, according to science organization Climate Central data. Lauren Casey, a meteorologist with Climate Central, said the fall season has warmed by 3.5 F overall during that period. Human-caused climate change is the ultimate cause of this heating.
The El Niño weather pattern that tends to produce warmer temperatures in the Upper Midwest also influences the current weather. And now an “omega block,” an expansive region of high pressure that stalls over an area, is sitting above the region. This has led to temperatures as high as 87 F in the Upper Peninsula’s Negaunee Township and temperatures in the mid-90s in Minnesota.
El Niño is influenced by climate change because it draws on heat in the Pacific Ocean, much of it derived from human-caused warming. It’s less clear if omega-blocking patterns have become more common as the planet heats up, although some research suggests that the size of these blocking events could increase.
These strong and stagnant areas of high pressure, associated with high-altitude wind patterns shaped like the Greek letter omega, may also be called “heat domes.” Beneath heat domes, hot air becomes trapped over a region for days or weeks, events that scientists say are becoming more frequent and intense with climate change. As in Greece this summer, the low-pressure areas on opposite sides of these blocks can produce persistent storms and flooding.
Casey said Michigan’s warm fall weather is a sign that action is needed at the local, national, and international levels to rein in emissions and “bend down the curve” of increasingly high temperatures.
“So long as we continue to emit carbon into the atmosphere by burning fossil fuels, we’re going to continue to heat things up,” Casey said.
Casey added that omega-block events can potentially trap heat and wildfire smoke. And warmer falls could lengthen allergy seasons and lead to higher energy bills for those using air conditioning.
In Detroit, the urban heat island effect – the heating that occurs in urban areas where buildings and pavement absorb and re-emit heat – amplifies high temperatures. Limited green space and tree cover worsen heat islands, and some urban areas see as much as 20 F degrees of additional warming. A previous analysis by Climate Central found that 86% of neighborhoods in Detroit and many inner-ring suburbs experienced 8 F degrees of warming or more from the heat island effect.
Heat can also help produce drought conditions, which research shows can lead to more heating.
Researchers believe this may occur because there isn’t enough moisture to evaporate heat. Fortunately, most of Michigan isn’t experiencing the extreme dryness that has impacted neighboring states, leaving much of Indiana, Ohio, Illinois, and Wisconsin dealing with drought or abnormal dryness.
Casey says that the cool air coming off the Great Lakes in Michigan can mitigate some of the high temperatures that other Midwestern states might experience during an omega block pattern.
Michigan’s warm fall weather is expected to dissipate by the end of the week as rain and cooler temperatures return to Detroit. But the National Oceanic and Atmospheric Administration predicts the city will continue to see above-average temperatures throughout the month of October.
NOAA’s one-month and three-month outlooks also show most of Michigan with above-average chances for warmer and drier conditions. This aligns with what might be expected during an El Niño winter when the polar jet stream shifts northward and the Upper Midwest experiences warmer and drier conditions. And Michigan’s warm fall weather could continue into the spring.
NOAA predicts there is a more than 95% chance El Niño continues through March 2024.