Today is a pretty nice day across much of the country, with mild to warm temperatures in most spots from coast to coast. Enjoy it while it lasts, though, because cold Arctic air is likely to spill down from Canada next week, plunging temperatures 10 to 20 degrees below normal.
A low pressure system will develop over the Plains early next week, gathering strength as it moves northeast towards the Great Lakes and Ontario over the following couple of days. A strong cold front associated with the low will drag cold air from Canada south into the United States by midweek.
Both the GFS (American) and ECWMF (European) models show both high and low temperatures behind the cold front coming in 10 to 20 (or more) degrees below average for this time of the year. The above animation shows temperature anomalies from this morning's run of the GFS model, beginning this afternoon and ending next Friday night.
How cold could temperatures get? The National Weather Service in Chicago is predicting the city's high temperature to only reach 39°F on Tuesday. The latest GFS model suggests that high temperatures could have a hard time making it out of the 30s and 40s across much of the country east of the Rockies from Wednesday through the weekend.
It's worth noting that parts of New England close to the Canadian border from New York to Maine could see some accumulating snowfall this week. Winter Storm Watches are in effect in northern Maine at this hour for 6-12 inches of snow. More snow could fall in border states from Washington to Michigan over the next week or so, especially in the Upper Midwest. Exact amounts to be determined closer to the event, but a measurable accumulation is possible.