The temperature dropped into the upper 20s in places like East Aurora, Delevan, Randolph and Olean this morning, according to the state's new Mesonet system.
That's cold enough for a hard freeze.
It could happen again tonight in southern Erie and Wyoming counties, forecasters warn.
A freeze warning is posted for southern Erie and Wyoming counties from 11 p.m. until 9 a.m. Wednesday.
Temperatures are forecast to dip below the freezing mark into the lower-30s. That could damage tender vegetation, forecasters warned.
Meanwhile, in northern Erie, Niagara, Orleans, Genesee and Chautauqua counties, a frost advisory is posted.
The thermometer is expected to dip into the mid-30s overnight, according to the forecast.
It dipped to 34 degrees at the Buffalo Niagara International Airport about 6 a.m. Tuesday.
May 9 has only been colder four times in Buffalo since World War II, most recently in 1983, weather service data shows.
The average overnight temperature in Buffalo for this time of year is 45 degrees.