Frost in Southeast Louisiana this weekend? Here’s why it’s not a guarantee

NEW ORLEANS (WVUE) - It’s that time of year again when we have to protect our gardens and plants from frost.

The typical first frost on the north shore falls from early to mid-November, and along the lake in late November. It’s typically also in late November for coastal Mississippi, the river parishes, and inland areas of Terrebonne and Lafourche parishes. Everywhere else, including the New Orleans metro, is in early to mid-December.

So it’s no surprise that this upcoming weekend, on November 14th, the morning lows could be cold enough for frost on the north shore. But here’s the thing - there’s one key ingredient that might be missing for frost to actually form, and that’s very light wind.

Frost needs a specific recipe to develop. You need air temperatures around 33 to 38 degrees, very light wind, and clear skies.

Here’s how it works: frost forms when heat is released into the atmosphere from the earth at night, cooling the ground enough to freeze dew. If the air temperature is 36 degrees, an object sitting on the ground - like a car, house, or blade of grass - can actually be several degrees colder, around 32 degrees. In fact, it’s easier for ambient objects to cool faster than the air around them.

That temperature difference allows any moisture or dew to freeze, creating that layer of frost we see on our windshields and lawns.

The wind is really the wild card here. For frost to form, the wind needs to be incredibly light. According to the National Weather Service, wind typically needs to be less than 8 mph. Anything stronger than that, and frost has a hard time forming.

A clear sky also plays a big role because it allows heat to escape more rapidly into the atmosphere, making it easier for temperatures to drop.

This weekend will be cool because a strong cold front is sweeping through on Thursday. Temperatures will plunge starting Friday and continue to drop through Friday night into early Saturday morning.

We’re expecting mainly clear skies with lows in the mid to upper 30s, with some isolated spots in the low 30s. But here’s what matters for the frost potential: the placement of a surface high-pressure system will determine whether we end up with calm winds or 10 mph winds. If we’re close to the center of that high, it will keep the winds virtually calm, allowing for frost to form. If we’re farther away, the winds could pick up and work against frost development.

A 10 mph wind may not be strong to us, but to frost, it deters growth.

Regardless, if we do see frost this weekend, it would not be unusual, and it’s pretty seasonal for this time of year.

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