A relatively warm December in the Stateline will give way to a big cooldown just in time for Christmas, which may deliver single digit temperatures to the Rockford area for the first time this season.
Through Friday, 17 of December’s 19 days thus far saw temperatures at or above the daily normal. This stretch has featured two days with record heat: Rockford saw the warmest December 9th on record with a high of 55° and the 10th tied with two other years for the warmest recorded daily high having hit 57°. Temperatures are forecast to remain above normal through the middle of next week before a big drop in temperature is expected to welcome in the holiday weekend.
Early next week, our jet stream is forecast to build a sizeable ridge over the northwest United States. A sizable trough is forecast to follow, however. Both are expected to deepen as they move further inland through Monday and Tuesday. As the ridge moves over the Midwest, significant warm air advection will take place in the middle and upper levels of the atmosphere above the Stateline while strong southerly winds flowing into an approaching storm system will pull a warm air mass northward down at the surface. As a result, temperatures are forecast to reach the 40’s on Monday, Tuesday, and Wednesday. However, the storm’s likely strong cold front will be moving in overnight between Wednesday and Thursday. Strong northwesterly winds will immediately begin pulling frigid air into the Stateline and the previously mentioned trough will be doing the same above the surface. This should keep highs in the lower 20’s, possibly even the teens in several spots, on Christmas Eve. Low temperatures on Christmas Eve are forecast to drop into the single digits which would be the first time the thermometer hits single digits this season. Meanwhile, wind chills early Friday morning could potentially dip below zero. This cool pattern will last through Christmas Day with only a slight bump in temperatures expected. This does not look to stick around long, however, with temperatures expected to be back up to normal by the weekend.
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