So far this winter there has been no real arctic plunge of air over the country. Temperatures have been consistently no worse than near normal, with most days above normal. So far since the start of meteorological winter on December 1, this is the 11th warmest winter for Chicago. The long term average for the first six weeks of winter is 27.5°, so far this winter the average has been 33.8.
The mild spell has limited time to run, at least for a while. For the rest of the week highs in the metro area will bounce around from around 30 to 40 as a series of low pressure systems move to our north. This would be above normal as the normal high is now 31. Little if any precipitation is expected with maybe some flurries along a cold front. The drought continues. The Chicago snow records for longest streak without one inch snowfall (325 days), and latest in season, will continue to grow.
The temperature change will happen over the weekend as the upper level flow undergoes a major shift. The graphic shows the upper level flow valid Monday evening as forecast by the ECMWF. For the first time this winter a flow all the way from the arctic will be over the center of the nation. Highs in Chicago for the first few days of the week will only be in the teens with overnight lows around zero. The temperatures would be even colder if we had a snow cover. The bare ground will moderate the air somewhat. In those areas of the Midwest with snow cover, lows will drop well below zero.
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