Temperature difference from normal over Lower 48 states at 2 a.m. Eastern time on Wednesday. (WeatherBell.com)

A powerful blast of preseason winter is surging south over the western United States, bringing a swath of record-low temperatures and a premature dash of snow to some. That mass of Arctic chill is set to swing east, engulfing most of the Lower 48 states by Friday, but not before adding a headache to Halloween plans from the Intermountain West to the Appalachians.

Dozens of low-temperature records have been set in the Intermountain West since Monday thanks to this exceptional surge of frigid air.

We begin in Denver, where Tuesday’s temperature failed to top 18 degrees, tying the mark for the coldest October high recorded. Meanwhile, 6.6 inches of snow fell Tuesday, inching the city’s October total to nearly a foot. The flakes were tapering off west to east on Wednesday morning.


An animated forecast shows the cold front heralding the impending Arctic air surging east late this week. (PivotalWeather.com)

In Salt Lake City, the mercury fell to 14 degrees at 3:37 a.m. Thursday, going into the books as the coldest temperature recorded there in October. According to the National Weather Service, record-keeping there dates to 1874.

Peter Sinks, an elevated valley location near the Utah-Idaho border known for its extreme cold-pooling and radiational cooling, fell to a mind-boggling minus-45.5 degrees Wednesday morning. While Peter Sinks is not an official climate station, there is no record of any colder temperature in the Lower 48 states during October.


Wondering where this cold air mass came from? Try the Arctic! (NOAA)

Was it a legitimate reading? Probably. Acting like a large hole for cold to slosh downhill into, Peter Sinks frequently features an extremely localized temperature anomaly. How localized? On Monday, when its temperature fell to minus-35 degrees, a thermometer located 250 feet higher a half-mile away remained above zero the entire time.

Here are other notable records that were set Wednesday morning:

  • Grand Junction, Colo., fell to 13 degrees, its lowest October temperature on record.
  • Bozeman, Mont., and Casper, Wyo., recorded their lowest October temperatures on Tuesday and Wednesday morning, falling to minus-14 and minus-8 degrees, respectively.
  • Boulder set a daily record low of 3 degrees.

Low temperature records and near-low temperature records as of 8 a.m. Eastern time on Wednesday. (CoolWx.com)

The cold is a reflection of an extreme jet-stream pattern, while feeding this frigid air into the Mountain West, simultaneously directing a surge of record warmth into Alaska. Anchorage’s low temperature of 47 degrees on Tuesday was the warmest on record for the date by 8 degrees, and its high of 54 broke the previous record of 52.

The intensity of the cold over the Intermountain West, while historic in some areas, is a large departure from the weather across most of the Northern Hemisphere and the planet, which is generally warmer than historical averages.


Temperature differences from normal over the planet on Wednesday, as simulated by the American (GFS) model. (University of Maine Climate Reanalyzer)

Looking ahead

More records will probably be set across the Rockies through Thursday, particularly where winds go calm.

In Denver, clear skies and a freshly fallen snowpack will foster radiative cooling once the sun sets, allowing morning lows Thursday to plummet to near zero, potentially its coldest October temperature in 100 years. The mercury will rebound to just below 40 degrees by Thursday afternoon.

Meanwhile, the cold will march east, thrusting the Plains into its icy grips. Kansas City has been below 40 degrees since 4 a.m. Monday, and after some wintry mix Wednesday, may not hit 40 again until Friday! That potential 100-hour streak below 40 could be their coldest such October stretch on record.

In Chicago, Thursday’s evening commute could be treacherous as the cold oozes into the region late in the day. After a morning high in the upper 30s with periodic rain or snowflakes, the temperature will fall to below freezing around dinner time. That, combined with standing water from overnight rain late Wednesday, may allow for pockets of black ice to easily form.


Heavy rain will move from the Tennessee and Ohio valleys into the Northeast and Mid-Atlantic ahead of the incoming shot of Arctic air. (PivotalWeather.com)

By Friday, while the intensity of the cold will ease, even the Gulf Coast and Eastern Seaboard will see a switch to chilly weather. Highs will hover only in the 50s from Friday through the weekend in places like Washington, Philadelphia and New York, while Bostonians get to enjoy one more warm — albeit wet — day on Friday. Before then, the powerful cold front could spur some severe weather across the interior Mid-Atlantic, especially near the Blue Ridge Mountains. A “convective fine line” of low-topped but gusty thunderstorms may probably form, posing the risk of 50 mph-plus winds and even a low chance of an isolated spin-up tornado.

Even in New Orleans, the National Weather Service is calling for a high of 59 on Friday! The first day of November will certainly be evocative of the impending winter. Lows overnight will drop into the 40s.

The cold largely looks to relent a bit into the early and middle portions of next week before additional chilly shots punctuate the majority of November.