Why the 30s in late spring may be harmful


While our average lows this time are year are in the upper 40s, it’s not unusual to see the 30s for overnight and morning temperatures this time of year (late May). But since the growing season has started already, we’ll now wanna look after those tender flowers and vegetables you may have already planted.

A frost advisory gets issued when frost is possible… that happens when the temperature drops to between 33° and 36° for more than an hour. Frost forms under clear skies with calm winds. This allows moisture in the air to go straight from a vapor to a solid… that’s the frost.

Sometimes a Frost Advisory is issued even when we may not see frost… but the temperatures are cold enough to cause damage to plants. It’s all about the impacts. So the best way to think about this is if you have a Frost Advisory issued for your area, assume your plants can be harmed.

A Freeze Warning happens when the temperatures drop to 32° and below for longer than an hour. You start getting into the “killing freeze” territory when temperatures drop to the mid-20s. Some hearty plants may survive brief freezing. If you’re unsure, cover them or bring them inside anyways.

Here’s a map of our average last freeze (below)… as you can see, most of the state sees the last freeze date anywhere from May 11th through the 20th.

But we have seen freezing temperatures much later than this… here are some of the dates of the latest times the temperature has dropped to 32° or colder around the state. (below)

The current temperature we see on our phones comes from a gauge inside a box (typically at the airport) to keep it from being tainted by the environment…and that’s above ground. It’s not unusual for the temperature to be a few degrees cooler on the ground next to your plants.

For more Weather Whys topics: https://www.kxnet.com/weather/weather-whys/

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