Fall is in full swing here across the Tri-State. We have had a very nice stretch of dry and seasonal air over the last few weeks, but a stronger cold blast moves in as we head into the end of the week and that could bring a surprise for some of you: FROST.
You may be saying to yourself, "this seems a bit early doesn't it?" and if you are, that would be correct. Over our last 30 years (1992-2021) our average first frost is around October 15. If you narrow that time down to just 10 years (2012-2021) that moves a little later to October 20. However, this is not the earliest we have ever seen a frost, far from it actually. The earliest frost on record goes back to September 21 in 1962. For perspective, last year our first frost was November 2.
There are a few ingredients we look for when forecasting frost. You need a clear to mostly clear sky, calm to light winds (usually less than 5 mph) and cold temperatures. In fact, for frost to form, the temperature needs to be at freezing at the grounds surface, but that doesn't mean the actual air temperature reading will be 32°. The clear skies allow for any of the warmer air and radiation to escape, or mix, into our upper atmosphere. As that happens, the air coolest to the Earth's surface cools the quickest. That means we can have a shallow layer of freezing or subfreezing air right along the shallowest levels of the Earth, meanwhile the temperature that is read on your thermometer could be as high as 36°. That is usually the threshold when it comes to frost.
So, will we see it? Well, of the two days I think that Sunday looks the most promising, but Saturday morning will still have a chance at frost for areas outside of the city. Temperatures will likely range from 33° to 37° for most communities outside of town. However, the urban heat island effect of Cincinnati should limit the Greater Cincinnati Metro from receiving frost.
Temperatures Sunday are expected to be slightly cooler by a degree or two, but that should be enough to lead to better frost formation. Lows could get closer to freezing Sunday morning. The one thing that could limit that is a better chance for cloud cover and slightly higher winds Sunday morning.
Now would be a good time to bring some of your sensitive plants and vegetation inside if possible, if not you will definitely want to cover these up before you go to bed both Friday and Saturday nights.
