Denver, Colorado, experienced a historic drop in temperatures Wednesday afternoon as the country braces for a “bomb cyclone” sweeping a large portion of the United States.

The winter storm system is expected to bring freezing temperatures to widespread portions of the U.S, spanning as south as Texas and Florida in the days leading up to Christmas:

An update from the National Weather Service’s Weather Prediction Center warns of a “powerful winter storm” which is expected to “produce a multitude of weather hazards across the central and eastern United States through the end of the week.”

This includes what the NWS describes as “bitter cold and life-threatening wind chills” in various areas of the U.S, including the northern Plains, which will “surge southward” and “swing towards the East Coast” by the end of the week. 

The warning adds that some areas  — The Intermountain West and northern High Plains  — have seen temperatures drop 25-35 degrees within a matter of hours.

Per the NWS:

This, combined with sustained winds of 20 – 30 mph and higher wind gusts of up to 60 mph, have and will continue to lead to wind chills as low as minus 40 degrees across a large swath of the Intermountain West and northern/central Plains, with more localized areas of minus 50 to minus 70 possible through the end of the week. Wind chills of this magnitude can cause frostbite in less than 5 minutes if precautions are not taken, with hypothermia and death also possible from prolonged exposure to the cold.

Denver is among areas that has seen a rapid drop in temperature on Wednesday, dropping from the lower 50s to just 5 degrees in a matter of hours. Temperatures dropped 37 degrees in a one hour time span. 

Per AccuWeather:

Denver was in the lower 50s Wednesday afternoon before the weather changed in a potentially historic way. Temperatures dropped rapidly between 3:53 p.m. and 4:35 p.m. local time, going from 42 degrees Fahrenheit to 5 degrees. According to preliminary data taken from Denver International Airport, the observed 37-degree temperature fall would be the largest one-hour drop in the station’s history. The previous biggest one-hour drop was from 41 degrees to 6 degrees in the afternoon of January 27, 2007.

Temperatures, at the time of this report, were expected to drop to minus 16 in the city, resulting in a 68 degree plunge in less than a day:

Hundreds of flights have been grounded as a result of the winter weather.

The winter storm comes over two months after October’s cold snap, which saw over 100 million Americans under frost or freeze watches or warnings.