Thought I would use Chicago as a good example of the wild temperature swing we are about to see across the heartland of the US over the next 72 hours.

While a howlling Pacific flow warms the majority of the country with unseasonably mild air with many rising Wed and Thursday to between 15-25, locally 30F above normal, it’s the cold building north of the border which is worth watching closely.

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Snowpack across the Lower 48 is down to 7% following the 31% a mere week ago, blame that zonal, Pacific flow and even the still-early time of year for the erosion of the snowcover. Locked down cold normally doesn’t arrive till next month.

So, how warm is it likely to get? Back on Saturday I posted on facebook and twitter that Chicago could go into the 60s on Thanksgiving, according to WGN’s Tom Skilling, they’re going for a 64° high which would be warmest since 1966 when a high of 69 was recorded.

While that’s impressive, what’s more impressive is the fact that temperatures the next day (Friday) are to crash as an arctic front sweeps through and may bring snow showers to the area. Friday night appears to drop into the 20s with a strong NW wind which will make it feel closer 20. On Saturday, the high may fail to hit freezing and Saturday night into Sunday may see the city’s first teens of the season.

Early next week (Mon-Tues) may see the first measurable snowfall of the season as a system rides up the eastern flank of the cold air (SE of Chicago), the rain-snowline will be close but if the cold air is positioned right, along with the system, then a few inches may accummulate.

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