As South Carolina prepares to head into the final month of meteorological fall, colder nights are expected to set the stage for the first frost and possibly a light freeze for northwestern portions of the state.
Typically, the first frost in the Palmetto State occurs in late October, especially in the higher terrain of the Upstate and along the North Carolina border. Areas farther south and along the coast usually experience their first frost or freeze several weeks later, due to the moderation caused by the warm Atlantic Ocean.
While frosty mornings might not look like they have much of an impact, they can have significant ramifications for gardeners, farmers and even travelers.
A significant frost or freeze event can bring an end to the growing season and damage sensitive plants if precautions aren't taken.
National Weather Service offices have several products they can use to notify the public when temperatures are expected to drop near or below freezing.
The first of these cold-weather alerts is a Frost Advisory, which is issued when conditions are favorable for frost formation and is often depicted in light blue on weather maps.
Frost can develop when both the air temperature and dew point reach the same level - near the freezing point - which means the air is saturated.
It’s important to note that the official temperature readings are taken several feet above the ground, which means a thermometer can show 34, 35 or even 36 degrees, and frost can still form because the cool air is nearer to the ground.
Wind conditions must also be calm to prevent mixing and warming air from reaching the surface.
Frost is common during the fall months, when there is still enough moisture around to allow ice crystals to form on surfaces such as roofs and plants.
A Freeze Watch is issued when forecasters expect at least a 50% chance that temperatures will fall to 32 degrees or lower within the next 48 hours.
Typically, the alert includes advice for farmers and pet owners to avoid any potential problems from the cold weather.
Once confidence increases that temperatures will reach or fall below 32 degrees, NWS meteorologists will upgrade the watch to a Freeze Warning.
The term “Hard Freeze Warning” was previously used to describe conditions when temperatures were expected to drop to or below 28 degrees for several hours, but in recent years, the agency has abandoned the alert and now includes those conditions under the broader Freeze Warning category.
The average number of freezing days per year varies significantly across the state, with communities east of Interstate 95 averaging around 20 freezing days each year, while areas of the Upstate, including Greenville and Spartanburg, seeing more than 40 days with freezing temperatures.
Once a widespread freeze occurs - generally during November - NWS offices will stop issuing frost and freeze alerts for the winter season. The agency says this is because the growing season is officially considered to be over, with no new agricultural production.
If no widespread freeze has occurred by Dec. 1, the alerts are automatically suspended until the start of the next growing season, which is considered to begin on March 1.