It’s another day of bone-chilling cold for millions, with temperatures 15 to 20 degrees below average for a massive swath of the United States. Record lows and brutal wind chills will make trick-or-treating seem like a polar plunge in many cities, after a week punctuated by toppled low temperature records.

The cold air mass, shunted south, thanks to a massive Alaskan ridge and downstream dip or trough in the jet stream, will continue to shift east — and moderate some — swallowing much of the Gulf Coast and the Eastern Seaboard this weekend. Signs point to it being part of a larger, long-lasting cool pattern that the contiguous United States could face for several weeks.

The low hit 8 degrees Thursday morning in Denver, surprisingly several degrees above what was forecast. It has snowed there for each of the past five days. Now up to 12.5 inches for the month, this stands as Denver’s greatest October snow in at least a decade.

Denver will climb into the “balmy” lower 40s Thursday afternoon, one of many cities in the Intermountain West where people will be trick-or-treating in the winter gear.

Salt Lake City fell to 19 degrees Thursday morning, while Idaho City, Idaho, dropped to 13. These are lows that would be 10 degrees or more below average even in January. Salt Lake City also recorded its all-time lowest October temperature on record early Wednesday at 14 degrees; records there date to 1874.

The anomalous cold is even bleeding west into California. Sacramento hit 39 degrees, coming within a degree of its daily record low Thursday morning. San Diego had its second-coldest October temperature on record, at 44 degrees.

It’s all thanks to a wonky jet stream pattern — one that’s surging north with exceptional warmth over Alaska, diving south thereafter and shunting the cool air with it.

At the moment, the Lower 48 is nestled in the most unusually cold air in the world — in terms of its departure from average. Almost everywhere else is running above average.

Despite the chilly weather that remains, the High Plains and Rockies have it better off now than they did earlier this week, when the center of Arctic high pressure had parked over them.

Temperatures hit minus-45 Wednesday morning at Peters Sink, an elevated valley in northwestern Utah known for its cold-air draining and radiational cooling. Since the 1990s, scientists have been studying the bizarre dynamics behind the extreme and hyper-localized cold pocket, which is often a few hundred feet across. While that temperature appears to be the October low temperature record across the Lower 48, it won’t go into the books as such, as the reading doesn’t come from an official National Weather Service climate site.

The core of the cold has since sauntered east, with the Plains and Mississippi Valley next in line for the worst of its icy kiss. Kansas City, Mo., started its day at 28 degrees Wednesday, with nearly an inch of snowfall. Its high temperature was 35 degrees on Tuesday and Wednesday, and it hasn’t hit 40 since 4 a.m. Monday.

Thursday could be close, but if the airport doesn’t reach 40 degrees, it would probably end up with a 100-plus-hour cold streak — its longest such October stretch on record.

In Chicago, it was snowing on Halloween. The National Weather Service isn’t forecasting the temperature to make it above 40 degrees until Sunday. The Windy City’s average high this time of year? 56.

Meanwhile, areas to the east of the impending cold front are toasty — but won’t be for long! Imagine working in Chattanooga, Tenn. The temperature at 9 a.m. Thursday as folks headed into the office was 73 degrees. By 5 p.m., it will be closer to 47. Tullahoma, Tenn., dropped from 70 degrees at 6:15 a.m. to 57 degrees at 6:35 a.m. Two hours later, they had plummeted to 45 degrees with strong northwesterly winds, and should sit at 38 degrees by close of business Thursday.

Murfreesboro also fell 13 degrees in 20 minutes, while Nashville dropped 15 degrees in an hour.

The abrupt cold front has a very sharp gradient — 30 degrees or more in a little over 100 miles.

After storms push through the East on Thursday, the cold will sag south, covering the Eastern Seaboard and even the Gulf Coast for a time. New Orleans can expect a Halloween evening in the lower 50s, dropping to 44 degrees overnight, while Mid-Atlantic spots like Washington, Philadelphia and Baltimore will be 20 degrees cooler Friday than Thursday.