The first frost and possible freeze of the season were predicted for Monday night.

North and west of the metro a hard freeze, meaning temperatures dropping into the 20s, was expected to bring an end to the growing season and damage tender vegetation, the National Weather Service said.

The arrival of the chilly air comes right on schedule. The second week of October is the average date of the first freeze in the metro area, said Jim Taggart of the National Weather Service in Chanhassen.

Cold air that was pooled above Canada over the past week slid south and east into Minnesota during the day Monday, pushing the dew points into the low 30s and upper 20s. Cloud cover was forecast to dissipate in the overnight hours, setting the stage for frost in the metro area and a freeze outside the urban core, Taggart said.

"That's not unusual for October," said Kenny Blumenfeld with the state climatology office, noting that the urban heat island may keep temperatures above 32 in Minneapolis and St. Paul.

Overall, October has been wetter and warmer than normal, Blumenfeld said. High temperatures for the month have averaged 66 degrees, and low temperatures have averaged 51 degrees.

The coldest night since May could give trees holding onto their green leaves "a jolt if they are not turning color yet," Blumenfeld said.

Even with a lower sun angle and more darkness than daylight, the warm October will continue. After highs in the 50s Monday, temperatures will moderate into the 60s by midweek as a southerly wind flow returns

"This is not going to last long," Taggart said.

Tim Harlow