A Warm Fall Could Extend Mosquito Season, Threat of Mosquito-bourne Illnesses

The threat of the mosquito-bourne illnesses West Nile Virus and Eastern Equine Encephalitis have caused many communities in western Massachusetts to limit evening outdoor activities until the first hard frost. But that hard frost could come later than usual this year.

Michael Rawlins, manager of the Climate System Research Center at UMass Amherst, says because of general warming patterns in the northeast, current prediction models call for warmer than average temperatures through October and November. If temperatures stay warm he says, that could delay the first hard frost by one or two weeks, which would extend the mosquito season.

“That said, weather variability plays a large role. We could easily have a really cold snap that lasts a day or two that would give us that hard freeze, and then the mosquitos are basically done.”

Rawlins says mosquito season has already been longer than usual this year due to the abnormally warm spring. He says though precipitation has been fairly average so far this year, a spike in rainfall could produce even more mosquitos.

“If we were to get a lot of rain over a period of a week or so, let’s say two to three inches, and the ground gets really wet, a lot of standing water, that may allow a lot more mosquito larvae to hatch and create even more of a problem.”

The state Department of Public Health has raised the risk-level for mosquito-bourne illnesses to “critical” in five communities in western Massachusetts. They are Athol, Belchertown, Chicopee, Orange, and Royalston. Many other communities, including Springfield, Holyoke, Northampton, Amherst, and Pittsfield have a “high” risk level for the viruses.