Late April and the start of May offered a flash of summer, but warm weather has now retreated and may not return until the second half of the month. This may keep the much-anticipated outburst of cicadas at bay for at least one to two more weeks.

An unusually chilly weather pattern, not unlike what Europe has experienced for weeks, has just begun to settle over the eastern United States.

High temperatures most afternoons over the next seven to 10 days are not predicted to exceed the 60s, while nighttime lows will frequently dip into the 40s to near 50. The daily average temperatures, hovering in the 50s, will chill soils and probably keep most cicadas underground.

Cicada emergence is tied to soil temperatures at or above 64 degrees. They flirted with that threshold in recent days, and cicada sightings trickled in on our social media feeds. But the cicada swarm will probably await more sustained warmth.

Our first-ever cicada forecast, issued last week, called for a cicada explosion next week, between May 10 and 12. However, as the weather forecast has trended substantially cooler, our inclination is to push back a cicada “peak bloom” period about a week, to between May 18 and 20.

How cold?

Between now and mid-May, average highs in Washington rise from the low 70s to the mid-70s. But we’re generally expecting highs about five to 10 degrees below these averages.

Low temperatures will tend to dip to near 50 in the District and the 40s in our cooler outlying areas, which is also between five and 10 degrees below average.

Computer model forecasts call for milder weather to arrive between May 15 and 17, with near normal temperatures in the mid- to upper 70s. Assuming this warmth is sustained, it should be enough to raise soil temperatures to that 64-degree threshold for cicada emergence.

“The models are trying to warm the pattern the week of the 17th,” said Capital Weather Gang contributor Matt Rogers, who specializes in long-range forecasting. “That seems reasonable right now, although we’re not sure about the durability of it.”

Rogers said there’s some chance the cool weather pattern will last longer than models are indicating, which could hold back the cicadas further, possibly delaying a mass emergence until late May.

The chilly air mass over Washington is overtaking much of the eastern two-thirds of the United States, from the northern Rockies to northern Florida. It will have the beneficial effect of lowering prospects for severe thunderstorms and tornadoes in the Plains and South. However, the weather pattern will focus unusually hot and dry conditions in the Southwest and California, intensifying a severe drought.

The D.C. area and much of the eastern United States also experienced cooler-than-normal conditions last May, and sustained warmth didn’t arrive until the final third of the month. In Washington, it was the coolest May in 15 years.

As we noted in our initial cicada prediction, this type of insect forecasting is experimental. Because the Brood X periodical cicadas appear only every 17 years, we lack the historical data needed to finely calibrate our predictions. If the current cool period lasts longer than expected, it wouldn’t surprise us to need to revise our forecast one more time and for the cicada explosion to hold off until late May.