After two relatively balmy days with highs in the 40s, winter has returned to the Chicago area and the Midwest. The mild Pacific air has been replaced with cold arctic air from northern Canada. The upper flow has switched to the northwest bringing down the cold air. Nothing unusual though as this week is climatologically the coldest week of the year. Next week we actually begin the long climb to peak summer readings in July.
The last two days in the Chicago metro area were certainly mild. The high hit 43 on Friday and 47 on Saturday, or 12 to 16 degrees above the normal high of 31. However, at noon Sunday we are sitting at readings over the metro area only around 20, or roughly a 25 degree cool down from 24 hours earlier. Last night the cold air moved in on gusty winds of 50 to 55 mph over land, higher along the lakeshore. Just as a point of comparison, the record lows for those two days were -21 and -23 respectively.
The highs both Monday and Tuesday will only be around 10 degrees. The coldest night will be Monday night with lows from 0 to 5 in the city and around -5 in the outlying areas. The graphic shows the overnight lows forecast by the GFS model. With a lack of snow cover over or near the metro area it is really difficult to get much colder than those temperatures. NWS Chicago has a real nice article on their site describing the connection between subzero lows and snow cover. Adding to the lack of snow cover is the fact the polar vortex will still be up over Canada.
While the next few days will be cold, certainly nothing compared to what has occurred in the past at this time of year, so not too bad. By Wednesday afternoon the surface high will be to our east so highs will jump back to the 15 to 20 range. By Thursday highs will rise into the 20s. It is Thursday night we may finally see some accumulating snow. Low pressure will be moving to the south of the area. If we accumulate one inch of snow, it will be the first time this winter and end our record streak of latest one inch snowfall. To be determined.
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