The cycle of freezing and thawing this week with the snow melting has put the Miami Valley on alert for invisible black ice on roadways and ice hazards on sidewalks.

The danger begins in the late evening when temperatures fall below freezing and continues until temperatures rise during the next day, said Dan Hawblitzel, a meteorologist with the National Weather Service in Wilmington.

That cycle will continue all week, he noted. Wednesday morning, temperatures dropped as low as 27, Hawblitzel said.

"With the melting snow, any water on the road that refreezes will cause black ice conditions," Hawblitzel said. "We had a lot of reports of slick spots. Those spots of black ice can creep up on you."

Fog will also plague motorists as the snow evaporates in the next week.

Miami Valley Hospital reported a sharp increase in injuries Wednesday morning after overnight freezing temperatures turned local roads into skating rinks.

Spokeswoman Nancy Thickel said the emergency room was extremely busy with everything from fractured wrists to sprained ankles. One physician saw 20 patients from 9 a.m. to noon, half of them injured from falls.