McHenry County residents can expect a relatively mild-weathered Saturday before an arctic cold front hits sometime Sunday afternoon.
Unseasonably low temperatures have swept through the county during the past few weeks, but record-breaking high and low temperatures are projected for Monday and Tuesday, a meteorologist with the National Weather Service in Romeoville said Friday.
The NWS predicts a high of
42 degrees with a low of 31 degrees Saturday. On Sunday, the high is forecast to hit 39 degrees with the cold front moving in sometime in the afternoon, meteorologist Jake Petr said.
The low Sunday is expected to be
21 degrees, and 1 to 3 inches of snow could accumulate at night, Petr said.
“Monday, we will probably be in the uppers 20s,” he said. “Tuesday, the highs will barely be in the mid-20s. We could see some record-breaking low-high temperatures Monday and especially Tuesday.”
The lowest temperatures predicted for this time of year range from
8 degrees Nov. 12, 1986, to 28 degrees Nov. 11, 1984, and Nov. 12, 1995, Petr said.
Cloud cover Monday could prevent the temperatures from dropping even further, Petr said.
“When you have snow on [the] ground and clear skies, it can really drop the temperature,” he said. “If there is cloud cover, it can insulate the heat radiating from the earth and keeps the temperature warmer. If the clouds aren’t there, then that heat releases into the atmosphere.”
Petr said it is too soon to say whether the unseasonably cold weather will continue through the rest of the fall and winter.
“The main thing causing this is the pattern with the jet stream,” he said.
Jet streams are bands of strong wind in the upper levels of the atmosphere. They typically blow from west to east, but occasionally shift to travel north to south. Jet streams follow the boundaries between hot and cold air, which are most pronounced in both the northern and southern hemisphere winters, according to the service.
“The jet stream is farther north toward Alaska,” Petr said. “It’s dipping down to the south and angling northwest to southeast across the U.S., allowing shots of cold air into the area.”
It’s likely not cold enough to see any warming centers open in McHenry County quite yet, however, said Bob Leracz, a preparedness planner with McHenry County’s Emergency Management Agency.
“Usually it has been when the lows are 15 below [zero] or worse,” Leracz said. “In the last five years, the only time we considered it was this past year, when it reached 25 below zero.
“People in McHenry County don’t utilize warming or cooling centers very much. Last year, when it was 25 below zero, we had less than five people one night across seven or eight open centers.”