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What do you wear when you encounter every season within a 12-
hour window?

Residents of Denver enjoyed a beautiful Wednesday afternoon with
temperatures in the lower to middle 80s. During the evening
commute, a cold front swung through, bringing strong northerly
winds and plummeting temperatures to freezing. Just eight hours
after setting the record high for the day, it was snowing.
Denver also set a record low by midnight.

“That’s our largest one-day temperature change in October on
record,” said Russell Danielson, a meteorologist at the National
Weather Service in Boulder. “We tell people around here to dress
in layers, because sometimes you get summer and winter in the
same day.”

[Tumultuous weather pattern triggers historic snowstorm in
Plains, Nor’easter and western windstorm]

That chalks up to a 54-degree temperature drop within one day.
It also marks a 40-degree plummet in four hours, the mercury
diving from 81 degrees to 41 between 4 and 8 p.m. As the winds
switched around from the north, gusts up to 55 miles per hour
heralded the bone-chilling front’s arrival.

Temperatures were continuing to fall on Thursday, the National
Weather Service forecasting a low of 14 degrees into Friday
morning. “The record low is 22 degrees, set back in 1946. We
should shatter that record.”

Denver's temperature has dropped to 20°, officially making this
the city's largest October temperature drop on record.

It's a 63° drop from 3pm yesterday, when Denver's temperature
was 83°.#COwx pic.twitter.com/9C3a1vMQ8f

— Chris Bianchi (@BianchiWeather) October 10, 2019
How strong can these cold fronts be?
Cold fronts on the High Plains are notorious for their dramatic
and capricious shifts. The dry climate makes it easier for
enormous fluctuations to occur, while the lack of water bodies
or obstacles means that air masses of the opposite extreme can
battle it out over relatively short distances. It’s not unusual
for the temperature to fall 30 degrees or more behind a fall or
winter cold front.

“Our biggest temperature difference in a singled day was 66
degrees on Jan. 25, 1872,” Danielson said. “We had a high of 46
and a low of minus-20.”

On occasion, it’s possible to get both a drop and a leap,
sometimes with multiple iterations, in the same day. That’s most
common if a stationary front stalls, wobbling back and forth.
These stationary fronts can also develop a very sharp gradient.

On Jan. 20, 1943, a stationary front got hung up in the Black
Hills of South Dakota. The thermometer registered minus-4 at
7:32 a.m. Two minutes later, it had spiked nearly 50 degrees to
a comfortable 45. Temperatures continued rising during until the
midmorning, hitting 54 degrees before a drop to minus-4 27
minutes later. The temperature swings were reportedly so
dramatic that motorists’ windshields cracked, the temperature
fluctuations stressing the glass driving from a warm pocket to a
cold one.


A vigorous cold front plowed through Denver on Wednesday.
(Weatherbell.com)
Wild temperature swings of the past decade in Denver
Feb. 24, 2014: In two hours, the temperature jumped from 26
degrees to 57 degrees in the midafternoon. The temperature
stayed at 63 degrees until 10:30 p.m. By midnight, it had fallen
to 29.
Jan. 5, 2015: 27.9-degree jump, from 12 degrees to nearly 40
degrees in one hour. The same day featured a 15-degree drop in
one hour, thanks to a stalled stationary front. After a morning
low of minus-4, the thermometer stood at 55 degrees just before
midnight, marking the largest one-day temperature swing of past
decade. Wednesday’s cold front just missed the mark.
Dec. 9, 2016: 11 degrees at 3 p.m., 53 degrees at 8 p.m.
Dec. 27, 2017: 2 degrees at 2 p.m., 45 degrees by 6 p.m. Two
days later, on Dec. 29, the temperature swung from 63 at 8 p.m.
to 30 degrees by midnight. The next morning’s low was 9 degrees.
It’s worth noting that Wednesday’s temperature drop of 40
degrees appears to be the largest four-hour drop in temperature
in Denver in at least the past decade. A four-hour temperature
change of 40 degrees or more occurs on average once every two
years.

Where is the cold front now?
The cold front has sailed well past the Colorado Rockies and has
a history of producing record-shattering cold to the northwest
in Montana. Great Falls tumbled to zero Thursday morning, its
lowest October temperature ever recorded.

Here is a preliminary look at some of the cold records that were
set this morning. #mtwx pic.twitter.com/VhMQUQntGH

— NWS Great Falls (@NWSGreatFalls) October 10, 2019
Denver will drop into the teens by Friday morning; if
temperatures were to hit 7 degrees overnight, they would snag
their largest two-day temperature swing. The current record of a
76-degree leap from December of 2008 stands.

The cold front showed up on satellite imagery over Oklahoma and
the southern Texas Panhandle on Thursday morning, an “undular
bore” marking the shock felt in the atmosphere. The encroaching
cool, dense air was significant enough to send out a ripple-like
wave ahead of it, triggering at its leading edge a roll cloud
with a few oscillations behind.

Meanwhile, look at this "undular bore" rippling through
southwest #Oklahoma after having just cruised through the Texas
panhandle. ??

This is associated with the cold front that will knock
temperatures back into the 60s this afternoon, w/poss. severe
weather to the east. pic.twitter.com/neSuXM8o4o

— Matthew Cappucci (@MatthewCappucci) October 10, 2019
By Thursday afternoon, the front had plowed through western
Oklahoma, plunging some spots into the upper 30s and lower 40s
while southeastern Oklahoma enjoyed a summery afternoon in the
middle 80s. Kenton, a town in the Oklahoma Panhandle, was 45
degrees cooler Thursday afternoon than Wednesday. Kenton hit 87
yesterday.


Temperatures across Oklahoma mid-afternoon Thursday spanned a
range of more than 40 degrees. Can you find the cold front?
(Oklahoma Mesonet)
The front will continue to march east, losing its steam as it
approaches the Mississippi Valley. And if you’re in Denver, good
news! Next week will feature highs around 70.

WEATHER: Heavy snowfall in Denver, Colorado: Yesterday: 77
degrees Fahrenheit, today: 21 #COwx pic.twitter.com/5iwfTaxRxL

— BNL NEWS (@BreakingNLive) October 10, 2019

https://www.washingtonpost.com/weather/2019/10/10/denver-hit- degrees-wednesday-afternoon-eight-hours-later-it-was-snowing/
 

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