BLOOMINGTON — There is a theory that it can be too cold to snow and when the temperature drops below zero and struggles to reach double digits in the afternoon, the threat of snow is low.
This is not entirely true, said Daryl Onton, a meteorologist with the National Weather Service in Lincoln.
“As temperatures get bitterly cold, there can be a limit to the amount of moisture the atmosphere can hold,” he said. “It certainly decreases, but it can still snow at very cold temperatures.”
As evidence, the NWS has issued a winter weather advisory from noon Friday until midnight for portions of Central Illinois, mainly along and north of Interstate 74 and including McLean, Woodford and Tazewell counties. An advisory means periods of snow will cause travel difficulties.
The NWS forecasts 2 to 5 inches in the region with the heaviest snowfall between noon and 6 p.m.
Snow began falling in downtown Bloomington around 11 a.m.
Motorists are urged to be prepared for snow-covered and slick roads and limited visibility, and to use caution while driving, particularly during the Friday evening commute.
When temperatures decrease, the maximum capacity of water vapor that can be in the air also decreases. So, the colder it gets, the less water vapor there will be in the air. When the temperatures drop into the single digits or below zero, heavy, wet snow is unlikely, according to the NWS.
Temperatures often rise as a weather system moves through an area, which is expected to be the case on Friday that includes the possibility of 2 to 4 inches of new snow falling in Bloomington-Normal in the afternoon or evening.
Temperatures are expected to warm up slightly, but the high could still only reach 18 degrees, Onton said; even colder temperatures will return on Saturday.
“It doesn’t appear that we are going to break the freezing mark for at least another week,” he said. And the 4 inches of snow that fell on Christmas Eve hasn't melted.
On Saturday, the high is expected to be only 8 degrees and the overnight lows will be around minus 4 degrees. Sunday’s high will be around 10 degrees and the New Year starts with a high of around 11 degrees, said NWS.
Tuesday’s high will be around 11 degrees and on Wednesday, the high will be about 17 degrees.
“This cold snap is going to ebb and flow and those overnight lows will drop below zero,” Onton said. “As far as reaching 32 degrees, it’s not in our forecast at this point.”
The last time the temperature was above freezing in Bloomington-Normal was Dec. 23 when it was 36 degrees.