After a relatively quite weather week over the Midwest, things are about to become more interesting. Two storm systems will be crossing the Midwest and the Chicago metro area this week. The first will bring in a quick surge of mild air and be almost all rain. The second will move into a cold air mass behind the first system and be mostly snow.
For the Chicago metro area we are about to be on the temperature roller coaster. After a chilly couple of days with the high Saturday only 20, the temperature on Monday will jump into the middle 40s on strong south winds off the Gulf. Once the system passes Monday night, highs for Tuesday will only be around 20 and the low 20s Wednesday.
With highs in the 40s on Monday, the precipitation that comes in late in the afternoon will be rain, ending around midnight Monday night. There may be a brief flip over to snow flurries before all the precipitation ends. Due to the fast movement of the system, rainfall is expected to only average less than 1/4 of an inch over the metro area. A little more extreme east sections.
The more moisture laden system will be the one that comes through late Thursday into Friday. Snow will move into the metro area from the southwest late Thursday With the main part of the upper system moving well west of Chicago, along with the surface low, we will just see some "warm advection" (warm air moving over cold air) snow. This usually is good for a few inches, but nothing real heavy. That will be well away from the area. With the low expected to move and weaken over extreme northwest Illinois Friday, the Friday highs will actually jump into the middle 30s to melt some of the new snow. The graphic shows the ECMWF model forecast valid Friday morning.
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