At 3 a.m. Sunday, the National Weather Service issued an updated freeze warning in effect from 2 a.m. to 9 a.m. Monday for Delaware and Philadelphia counties.

The weather service describes: “Temperatures as high as 33 degrees will lead to frost formation.”

“Frost could damage sensitive outdoor vegetation. Sensitive outdoor plants can be killed if left uncovered,” the weather service says. “Take action now to protect tender plants from the cold.”

Freeze notice – that’s what it means

Frost advisories are issued from May through October (but may be extended if necessary) when temperatures, winds, and sky cover are favorable for frost development. This is most likely to happen when the temperature is 36 degrees or less. In some cases, the frost is severe enough to end the growing season and is then referred to as a “killing frost.”

According to the weather service, if a frost advisory is issued for your area, cover sensitive plants before sunset so they can help retain heat near the plants, or move plants indoors for the night if possible.

Advance Local Weather Alerts is a service provided by United Robots that uses machine learning to compile the latest data from the National Weather Service.