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It’s furnace time in southwest Ohio. Here’s what you should know.

Published: Tuesday, October 15, 2019 @ 1:00 AM

It wasn’t more than a week ago that many of us were complaining about the heat, but that conversation has shifted quickly as temperatures plummeted to more typical levels and below.

>> Here are tips to keep your pumpkin fresh until Halloween

Just this past weekend temperatures fell to the 30s in spots with some areas of patchy frost.

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Frost is not uncommon this time of year. According to the National Weather Service in Wilmington, most of southwest Ohio on average sees its first frost mid to late October. Dayton and Cincinnati’s average first 32 degree or lower temperature reading falls around Oct. 22.

Temperature reading may vary depending on topography, urban and rural settings and the placement of recording instruments. Official temperature readings are taken at about 5 feet above ground level, but ground-level temperatures can be lower as colder air may pool closer to the surface.

Other than topography, there are many atmospheric ingredients that can lead to frost.

  • Clear skies lead to radiational cooling at night. Daytime heat acquired during the day can easily radiates back to space on a clear night causing temperatures to drop dramatically.
  • Calm and light winds also play a major role in frost development. The lack of winds prevent stirring of the atmosphere, which allows a thin layer of super-cooled temperatures to develop at the surface and these can be up to 10 degrees cooler than 4 to 5 feet above the ground.
  • Low temperatures, with some moisture, dropping close to the dew point can promote ice crystal development.
  • Local topography, as discussed above, can determine whether or not frost forms. Cold air settles in valleys, therefore frost is more likely in these regions. You may also notice frost forming in areas blocked by any breeze that may be present.

If temperatures are low enough it can be considered a “hard freeze.” A “light freeze” or “light frost” refers to temperatures that are just a few degrees below freezing for a few hours. A “hard frost” or “hard freeze,” also known as a “killing freeze,” refers to temperatures that drop further, below 28 degrees. That’s cold enough for it to kill the top growth of most perennials and root crops.

>> Live Doppler 7 Interactive Radar

Sunny days and cool nights are perfect for vibrant fall foliage. But a hard freeze is not what you want, because those types of temperatures could accelerate when trees shed their leaves.

As always, you can stay updated on the forecast and whether or not it will be a frosty night on or on WHIO-TV channel 7 every day.