The first true blast of arctic air this winter is over the center of the nation. This morning saw the first widespread readings of zero or below. With so much bare ground over the central US, the readings were not as cold as they would have been with a snowcover. A map can be found here with the northern US lows. One has to go up to northern Wisconsin and Minnesota to find any really bitter cold. The really brual stuff was up in Canada where there is a much larger snowpack.
For the Chicago metro area, overnight lows were generally around zero over the city, and zero to 5 below most outlying areas. Mundelein took low honors with a -7. Even the perennially cool spot of the Sugar Grove airport for the Aurora reading only reached -2. Considering what has been experienced locally in the past at this time of year, no big deal. The graphic from the NWS shows some of the Illinois and metro area overnight lows as of 7:00 a.m.
For the Chicago metro area temperatures will already begin to moderate tonight. Overnight lows will be from 2-5 degrees warmer than last night as clouds and maybe even a few flurries move in late. For Wednesday and Thursday the high will be near 20. Late Thursday night into Friday morning may see some light fluffy snow as an upper level disturbance of Pacific origin moves overhead. Moisture will be very limited so any accumulation will be limited.
The big news is that by Sunday the upper level flow will have become more zonal (west to east) and the jet stream will have moved back north. This combo will allow warmer Pacific air to move over the center of the nation. Highs on Sunday will warm to around 30 and into the 30s next week. Sunday night into Monday will see rain and/or snow as the warm air moves in.
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