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Among New Yorkers,Watch Secret Sessions Online there's a dark hypothesis about fall weather in the city, which is that there's only one "perfect" fall day with crisp sunshine and cool temperatures. For that single day, the city's harsh climate, with torrid heat in the summer and frigid cold and wintry mix events in the winter, is forgiven.

But after that day, which typically occurs in mid-to-late October, the weather turns dreary and cold. And then comes the wintry mix.

Well, that perfect day has come and gone, and the frigid air is knocking at the city's doorstep, poised to rush in overnight this Thursday, and really make itself known by Friday morning and into the first part of the weekend.

This Arctic blast means business. The frigid air mass first entered the lower 48 states on Wednesday, and on Thursday morning, air temperatures were in the single digits Fahrenheit in Minnesota, and below zero Fahrenheit in North Dakota.

By Friday morning, wind chill readings in New York City and Boston will be in the teens Fahrenheit, the coldest they've been so far this season.

Then on Friday night, overnight low temperatures in New York may hold in the low-20s Fahrenheit in the city, while parts of the Hudson Valley could see lows in the teens. Numerous record lows could be tied or broken on Friday night in the Mid-Atlantic and Northeast, according to the National Weather Service (NWS).

A hard freeze is also forecast in Boston as well as Philadelphia and Washington, D.C.

The cold will come as an especially harsh shock since the East Coast has experienced an unusually mild fall, so far at least.

According to the Washington Post's Capital Weather Gang blog, there's a chance that some record low temperatures could be set or tied on Friday night. For example, if National Airport reaches 26 degrees or lower Saturday morning, "it would rank among the top 10 coldest temperatures so early in the season in recorded history."

The Arctic blast is likely to trigger lake effect snow squalls across the Great Lakes, as cold, dry air blows across comparatively mild waters, picking up moisture along the way and dumping it in the form of narrow bands of heavy snow across parts of upstate New York, Ohio, Pennsylvania, and Michigan, among other areas.

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Fortunately for the Northeast and Mid-Atlantic states, the cold blast will be short-lived, with temperatures moderating back toward the seasonal average by early next week. However, after that, there are signs that cold air could return with more staying power.

Some computer model guidance is hinting at the development of a weather pattern in the North Atlantic that would favor cold and stormy conditions along the East Coast, potentially even leading to a snowy Thanksgiving for some. However, other models are less bullish on this scenario, instead showing a milder-than-average finish to November in the East.