A wave of summerlike weather is upon us, and, as soils warm, soon the 17-year cicadas will emerge in astonishing numbers throughout the D.C. area.
Because it is so warm, do not be surprised to see a few early bloomers this week as well.
Once they come out of the ground, the cicadas should stick around for about a month before laying their eggs and dying off.
How we made our forecast
Forecasting cicada emergence is a lot like predicting peak bloom for the cherry blossoms. Cicadas and cherry blossoms peak based on the season and the temperature. Based on historical data, we generally know when a peak should occur, but the dates can vary by days or weeks, depending upon the weather.
“The cue for the cicada nymphs (immatures) to emerge from the ground is 64°F about 8” down in the soil,” Paula Shrewsbury, a professor in the entomology department at the University of Maryland, wrote in an email. “A warm rain will often trigger an emergence.”
Much as the peak cherry-blossom bloom depends heavily on temperatures in March, the weather in April and early May will speed or slow the outburst of cicadas. We have had some chilly weather in past weeks, but a significant warm-up this week will help soil temperatures rise.
According to Daniel Gruner, also a professor in U-Md.’s entomology department, current soil temperatures range from the 50s to low 60s in the region. Students in his ecology class have been taking measurements since March.
“We have several sites that are approaching 64F, while others are stuck in the low to mid-50s,” he wrote in an email.
The soil temperature is often a reflection of the air temperature averaged over the previous three days, according to the website Cicada Safari. With highs in the 80s and lows in the 60s predicted through Thursday, soil temperatures should reach or surpass the critical 64-degree threshold in some areas.
“We should start with a trickle this week in some areas as the weather gets hot towards mid-week,” Gruner said. “I do not know if it will be the tipping point for the region or if we’ll need to wait a bit longer.”
Shrewsbury wrote that the first adult cicada of Brood X already emerged on April 19 in Towson. “The April 19th adult was early and we will likely see more of these,” she said.
If the warm weather this week does not trigger many cicadas, another shot of warmth early next week may do the trick. After cooler temperatures between Friday and Sunday, temperatures will be off to the races again early next week, predicted to surge above 80.
Our forecast for a noticeable emergence of cicadas next week is based on the cumulative effect of this week’s and next week’s warm weather. We anticipate cicadas will become apparent in large numbers in about two weeks as a third period of warmer-than-normal weather is suggested by computer models around May 10.
Because temperatures can vary a great deal between the southeast and northwest parts of our region, how soon you see cicadas will depend on where you live.
“I would predict that in the more southeast counties where Brood X occurs in MD, cicadas may emerge a matter of days (not likely weeks), earlier than counties in the north west where elevations are higher and temperatures tend to be cooler,” Shrewsbury wrote.
Dan Mozgai, who operates Cicada Mania and has contributed to studies on the insects, agreed that areas south and east of the District will see cicadas first. He expects the bugs to explode in the time frame from May 9 to 23.
For historical context, Brood II cicadas, most prevalent southwest of Washington, began to emerge in large numbers in 2013 on May 12 in Prince William County. That April was slightly warmer than the present but did not have the same late-month burst of warmth as this year. Moreover, highs in the first week of May were mostly in the 60s. It did not hit 80 degrees until May 10 and 11, and cicadas exploded right after that.
In 2013, the cicadas peaked during the last two weeks of May, and they were still numerous and active into the first week of June. By July, they were gone.
Looking back at the last Brood X cicada emergence, in 2004, photo records show they were at peak numbers in Fairfax County during mid-to-late May. That year had volatile temperatures in late April and early May, and the cicadas awaited more sustained warmth that arrived in the middle of the month.
If the cicadas start to emerge in large numbers next week and peak not long after, it will be on the early side and in keeping with what we might expect to see happen more frequently in the future as temperatures rise.
“With climate change and a warming world we would predict there to be a trend towards earlier emergence,” Shrewsbury wrote. “Gene Kritsky (College of Mount St. Joseph in Cincinnati) who studies cicada emergence data found that in Ohio the mass cicada emergence occurs an average of two weeks earlier than it did prior to 1950.”
This cicada forecast is experimental and the first time Capital Weather Gang has undertaken such an endeavor. It is certainly possible the cicadas will peak earlier or later than we are predicting. As these bugs appear only every 17 years, limited historical data is available to calibrate this forecast.