|Above: Chilly snow-covered Illinois as seen on February 1, 2019, by the MODIS instrument on NASA's Aqua satellite. The previous morning, Mt. Carroll, Illinois, set a new all-time state cold record of -38°F.|
The remarkable “polar vortex” cold blast that froze the Midwest U.S. during late January and early February set a new all-time cold record for the state of Illinois, a NOAA-led team concluded on Wednesday. The -38°F temperature recorded on January 31, 2019, at Mount Carroll, Illinois, has been officially confirmed as the all-time state cold record, beating the previous record of -36°F set Jan. 5, 1999 in Congerville. Mt. Carroll is about 130 miles west-northwest of downtown Chicago, near the Mississippi River in northwest Illinois.
According to the final report from the State Climate Extremes Committee (SCEC), the record low at Mt. Carroll was consistent with the overall meteorological setup, featuring clear skies, light winds and snow cover, that typically produces extreme low temperatures in winter. They noted the location of the Mt. Carroll instrumentation sits in an area of relatively low elevation on the city's west side near Carroll Creek. Cold air drains and settles into such low-lying areas on nights with light winds, since cold air is more dense than warm air.
Figure 1. The Mt. Carroll, Illinois COOP station. Instrumentation is a standard Cotton Region shelter with two glass thermometers, alcohol in glass for minimum temperatures and mercury in glass for maximum temperatures. Bill Zink was the observer and has been serving for one year. The time of observation was 7:15 am CST, January 31, 2019. Image credit: Quad Cities WFO.
Seven other locations near Mt. Carroll also reported lows of -30°F or colder that morning, effectively eliminating the possibility that the Mt. Carroll reading was a result of instrument failure. The National Weather Service in Davenport, Iowa, which serves northwest Illinois, confirmed the instrumentation was in good working order and that proper procedures were followed. Daily temperature observations have been taken in Mt. Carroll since 1897.
All-time state temperature records are very hard to beat. The extreme heat associated with the Dust Bowl years of the 1930s generated almost half of the all-time state highs that exist today. Interestingly, that decade also produced more of the currently standing all-time record lows than any other decade.
Since 2000, there have been just two new all-time state cold records set: in 2011 in Oklahoma (-31°F at Nowata on Feb. 10) and in 2009 in Maine (-50°F on Jan. 16 on the Big Black River near Saint-Pamphile, Quebec). One all-time state heat record has been set since 2000 (113°F at Columbia University of South Carolina on June 29, 2012) and one has been tied (120°F near Fort Pierre, South Dakota, on July 15, 2006, a record first set in 1936). An excellent recap of Oklahoma's impressive state record low of 2011 appeared in the Bulletin of the American Meteorological Society.
The SCEC has not yet launched an evaluation of the low temperatures reported at several astronomical observing centers atop Hawaii's Mauna Kea during a February cold outbreak, some of which may have matched or exceeded the state's official all-time low.
|Figure 2. Decade of first occurrence for the official all-time record lows (left) and highs (right) for each of the 50 U.S. states. Note that in 2006, South Dakota tied its all-time heat record first set in 1936. Data based on the list maintained by the NOAA/NCEI State Climate Extremes Committee.|
All-time state highs and lows and climate change
Because they depend so much on very particular local configurations of events, and because they are so few in number, all-time state highs and lows are a poor index of long-term climate change. A much better climate-change index is the number of daily record highs and lows. Because thousands of daily highs and lows occur every year in the United States, there is more statistical power in any conclusions one might draw from them. Since the 1970s, there's been a clear trend toward more daily record highs and fewer daily record lows, as shown by independent meteorologist Guy Walton and others.
As of Thursday, NOAA's Daily Weather Records site showed that the last 365 days had seen 18,633 daily record highs but just 11,313 daily record lows. These trends extend to rural areas where the urban heat-island effect is not a factor, as it can be in large cities.
Despite the all-time record cold in far northern Illinois on January 31, the state of Illinois ended up having a warmer-than-average winter, as detailed in our previous post.
Jon Erdman of weather.com and Bob Henson contributed to this post.