First frost of the season expected Sunday

Published 1:44 pm Saturday, November 13, 2021

By Skip Rigney

A frosty Sunday morning is likely thanks to clear skies, calm wind, and the coldest air mass we have seen so far this autumn in south Mississippi.

A weak cool front moved through late Thursday afternoon. Showers ahead of the front on Thursday morning brought the first rain to Pearl River County in two weeks. However, most locations received less than one-quarter inch, and about one-fifth of the county didn’t receive any rain at all.

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The humidity in the air behind Thursday’s front was lower, but the air was not much cooler. That made for a pleasant Friday with temperatures climbing into the lower 70s in the afternoon.

But, a much stronger secondary cold front was already sweeping southward across the Great Plains, and by Friday evening the leading edge of cold air was entering Mississippi. The humidity was so low in the air brought by Thursday’s that the second, stronger cold front couldn’t kick off any showers as it approached the area.

By the time you read this on Saturday, the strong cold front will be far to our south and east. A dome of surface high pressure will be enveloping most of the south-central and southeast United States. Temperatures today (Saturday) will only reach the low 60s, making this our coldest day since March 19th.

Tonight, much of the energy the earth absorbed from today’s bright sunlight will be lost to space.

That’s because there will be no clouds and very little moisture in the air to act as a blanket. Solid objects, including the ground and things near the ground, will cool down faster than the air.

Light winds can mix down some of the air in warmer layers above the surface, but with winds expected to die down to calm, conditions should be optimal for what meteorologists call radiational cooling.

So, we can expect that early Sunday morning, as the air temperature at the official observation height several feet above the ground falls into the middle 30s, the temperature of solid objects near ground level will be even colder allowing frost to form on grass, some plants, and objects like automobile windshields.

The last time that temperatures dipped into the middle 30s in Pearl River County was on April 3rd, and some locations in the county have not been that cold since March 8th.

The core of the cold air mass will move off pretty quickly to the east on Sunday. The air over us will warm up under the influence of sunshine and warming conditions in the upper levels of the atmosphere. Sunday’s high temperatures are forecast to reach the middle to upper 60s. Sunday night will be chilly, but no frost is expected since air temperatures are expected to only fall to around 40 degrees.

Temperatures will moderate to near or slightly above the historical averages for mid-November for the work week with highs in the 70s and lows in the 40s and 50s.

Skies will be mostly fair, as moisture will be very slow to return to the region. Even though there’s a slight chance of showers beginning Thursday, it’s possible we could have yet another week with little or no rain.

All in all, after a chilly start, this should be a week of very enjoyable fall weather.