Most of the time when you see a post here on The Vane, it’s about some horrible weather event somewhere that killed lots of people and destroyed most of their belongings. I have good news for once! We’re about to have an exceptionally nice weekend across the eastern United States, featuring crisp temperatures and mostly clear skies. Such a universally nice weekend is rare, so enjoy it while you can.

A scalpel-sharp trough in the jet stream—one that models suggest will stretch from far northern Canada down to the Gulf of Mexico—is taking shape at this hour, and it will bring a big change in the pattern for most of us who live east of the Rocky Mountains. The cold front that serves as the leading edge of the Canadian invasion is already draped across the Upper Midwest, and it will steadily make its way southeast over the next three days.

The strong cold front crashing into warm, humid air to its east will fire off some thunderstorms—some of which could be severe along the Mid-Atlantic coast on Saturday, according to the SPC—but many of us need the rain anyway, and the reward behind the storms will be worth the 30-minute hassle.

The end result here is abnormally cool temperatures and drier air than many of us have seen since early last spring. The graphics below show surface temperature anomalies, in degrees Celsius, as predicted by this morning’s run of the GFS model.

Here’s 18z Saturday, which is 2:00 PM EDT/1:00 PM CDT:

...and the same time on Sunday:

...and for Monday:

Brr! Well, sort of. It will definitely feel chilly to those of us used to nothing but the crushing finger of heat and humidity for months on end, and folks up in the far north (near the border) will have to wear jackets for the next couple of mornings. Lows in the 30s will cover the northern Plains and Upper Midwest through Saturday, and a few spots in northeastern Minnesota could dip into the upper 20s.

Here are the forecast high temperatures for Friday, Saturday, and Sunday (according to The Weather Channel) for select big(gish) cities affected by the cool-down, compared to the average high temperature in each city.

Chicago is expecting a high temperature in the low 60s on Saturday, which is 15°F below average for this point in September. Even Mobile, Alabama, down along the northern Gulf Coast, will get in on the coolfest, with high temperatures seven degrees below average and humidity levels practically unheard of in mid-September. The NWS predicts a dew point of 50°F (!!!!) in Mobile on Sunday afternoon. That kind of dry air nirvana usually doesn’t make its way down that far until mid- to late-October.

The Canadian invasion will largely stay in interior parts of the eastern United States, with the nicest rock-bottom temperatures staying west of cities like New York and Boston (sorry!). Still, many of us will experience temperatures at or slightly below average through Monday before the chill peters out and a ridge brings in more warm weather.

This cool pattern will shift late next week, with temperatures ticking back above average for most of the country east of the Rockies, while the West Coast dives back into cooler (and for some, possibly wetter!) weather.

Fall is nothing but the dying gasps of summer and the first breaths of an eager winter duking it out for dominance, and the result is two or three seasons’ worth of weather occurring all at once. The roller coaster is just beginning. Enjoy the nice weather while it lasts.

[Model Images: Tropical Tidbits | High Temp Forecasts: weather dot com | Chart/Forecast Map: author]

Email: dennis.mersereau@gawker.com | Twitter: @wxdam

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