ROCHESTER, N.Y. — Believe it or not, Wednesday is the "nicest" day of the week when it comes to temperatures.

It's only going to get colder from here, with wind chills as low as 10 to 25 degrees below zero Thursday. Not the actual temperature reading, but wind chill temperatures, and the lower the wind chill, the less time that can be spent outside safely. Doctors say when outdoors, covering exposed skin is a priority.

Frostbite and hypothermia can occur within 15 to 30 minutes when wind chills are near minus 25. When the wind chill dips that low, school districts start paying careful attention and 25 below zero is usually the cutoff for cancelling school.

"It is a tough decision. It is a very important decision," said Dr. Michael Mendoza, Monroe County Commissioner of Public Health. "On one hand we want to balance the safety of our students, staff and teachers and on the other hand we have kids to teach and all the consequences that come with keeping kids home from school, so it is a tough decision. We are here to help the districts anyway we can, but really it is up to them to make the call."

Most districts have specific closing guidelines, for example the Rochester City School District says it considers things like if the wind chill will remain at 20 below for an extended amount of time and whether there is blowing snow causing hazardous sidewalk or road conditions.