Photo: Projected Wind Chills for the Continental United States for Wednesday, January 30 at 12z from the NAM model. (Courtesy of PivotalWeather.com)
In the North Pole, the polar vortex is usually found as a strong upper-level low pressure that is confined to that area. Under the current circumstances, warm air has made its way into that area which weakens the vortex, causing a split into multiple vortices that can travel away from its natural location. Due to this phenomenon, the polar vortex is slated to move into the United States overnight and into the morning of Wednesday, January 30th.
There are many discussions explaining the extreme cold temperatures with comparisons to previous events. A similar cold air outbreak occurred in the region on January 5, 2014 which set records for cities over Illinois, Wisconsin and Minnesota. The current event is being referred to as a “generation spanning event” by local news stations, likely because of the comparisons from the previous generation that experienced an event like this in 1985. Specifically, the coldest temperature ever recorded in Chicago at the O’hare International Airport station was -27℉ back on January 20, 1985 (from NWS Chicago). Other stations in the Northern Illinois region that day may have actually been colder than that!
Along with the discussion of historic cold temperatures, must be a talk about equally historic wind chill values. The next graphic from the Golden Gate Weather Services (https://www.ggweather.com/windchill.htm) demonstrates the difference of wind chill calculations from past and present.
Photo: (1) “New” Wind Chill Chart (2001-Present), (2) “Old” Wind-Chill Chart (Past-2001) (Courtesy of Golden Gate Weather Services)
Popular social media outlets are comparing the severe wind chill event from 1985 in Chicago being record-breaking with wind chills in the 70 to 80 degree below-zero range, to the event that is occurring tomorrow, the 30th of January.
What makes this interesting is that in November 2001, National Weather Service determined a more elaborate formula to calculate wind chill that is deemed more accurate, and may better reflect reality. Using the above graphics with an example, prior to 2001, a -20 degree Fahrenheit temperature reading with 35 mph wind speed was suggested to feel like -82℉. Today, with the new calculation and the same variables, that would feel like -55℉.
Regardless of comparison, it will certainly be dangerously and historically cold tomorrow (1/30) and the proper precautions are necessary to remain safe.
Photo: A comparison of the new wind chill formula vs. the old Formula. (Courtesy of 1728.org)
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© 2019 Meteorologist Jason Maska