Will southwestern Illinois get frost this weekend? Here’s what forecasters expect

Southwestern Illinois residents should prepare for potential frost from Saturday night to Monday morning, according to the latest forecast from the National Weather Service St. Louis office.

Compared to season averages, it’s a bit late in the spring to be getting frost. The NWS provides data going back more than 20 years for average first and last frost dates, typical temperatures, normal precipitation and more.

Here’s what you can expect in a typical southwestern Illinois and St. Louis area spring, with data from the NWS and a prediction from the Farmers’ Almanac.

When is the average last frost in Belleville?

The average last frost date in the Belleville area is April 10, according to NWS Service St. Louis office data from 2000 to 2022. The earliest date of the last potential frost during the time period was March 19, and the latest was April 29. Some years had incomplete data.

In St. Louis, the average last frost date is April 2 and the typical first frost date is Nov. 2. The earliest date of the last potential frost in St. Louis from 2000 to 2022 was March 9, while the latest was April 22.

The first and last frost dates are defined as days where the temperature was 32 degrees or lower.

Those looking to protect their outdoor plants from frost should consider loosely draping sheets or medium-weight fabric over their plants, the Old Farmers’ Almanac says. Plastic should not be used as a cover.

Typical spring temperatures near Belleville

While April still sees average low temperatures in the mid-40s, May usually brings a significant warm-up. Here are the average temperatures in Belleville in April and May, according to NWS:

Belleville in April:

• Average minimum temperature: 46 degrees

• Average maximum temperature: 70.6 degrees

• Average overall temperature: 58.3 degrees

• Total normal precipitation: 4.9 inches

Belleville in May:

• Average minimum temperature: 56.3 degrees

• Average maximum temperature: 79.1 degrees

• Average overall temperature: 67.7 degrees

• Total normal precipitation: 5.05 inches

St. Louis in April:

• Average minimum temperature: 47 degrees

• Average maximum temperature: 68 degrees

• Average overall temperature: 57.5 degrees

• Total normal precipitation: 4.73 inches

St. Louis in May:

• Average minimum temperature: 57.9 degrees

• Average maximum temperature: 77.1 degrees

• Average overall temperature: 67.5 degrees

• Total normal precipitation: 4.82 inches

Farmers’ Almanac spring predictions

Temperatures will be slow to warm this spring, according to the Farmers’ Almanac’s Spring 2023 Weather Forecast.

“Overall, we see a wet and cool season for most places, with spring taking its sweet time to arrive,” the almanac’s prediction reads.

The almanac forecasts a cool, “very stormy” spring in Illinois and a “coolish” season in Missouri with above normal precipitation.

It makes predictions based on a mysterious formula that considers factors such as planetary positioning, sunspot activity and tidal action of the moon.

“The only person who knows the exact formula is the Farmers’ Almanac weather prognosticator who goes by the pseudonym of Caleb Weatherbee,” the organization’s website says. “To protect this proprietary formula, the editors of the Farmers’ Almanac prefer to keep both Caleb’s true identity and the formula a closely guarded brand secret.”

The Farmers’ Almanac has provided extended forecasts since 1818, according to its website.