Extreme Heat Proves Relentless in Central States

By Andrew Freedman

While much of the country has had a brief respite from the extreme heat and humidity that has marked the summer of 2012, in the nation's heartland — including key agricultural areas from Nebraska to Illinois — the heat has proven relentless. When the temperature soared to 105°F at 3:00 pm central time, St. Louis tied its all-time record for the most days in a single year with high temperatures of 105°F or greater. The existing record of 10 such days was set in 1934.

High temperature forecast for Tuesday, July 24, showing the area of extreme heat in the central states. Click on the image for a larger version. Credit: NOAA.

Through July 21, St. Louis and Columbia, Mo., had each set a record for the warmest year-to-date, beating a record established in 1921. The National Weather Service said that by October, the records for the maximum number of days with a high temperature of 90°F or greater, and 95°F or greater, “will also likely be threatened at all three of our official climate locations.”

Further west, it is possible that North Platte, Neb., will wind up with its second-longest streak of consecutive 100°F days, with nine such days if temperatures reach the century mark through Wednesday.

North Platte, which sits along I-80 in the western part of the state, had already seen 16 days this year with temperatures of 100°F or higher as of July 23, including 12 100-degree days in July alone. The all-time record is 29 such days, set during the Dust Bowl year of 1936. Omaha has had its fourth-longest streak of consecutive days with high temperatures of 95°F or greater, and has hit 100°F or higher five times this month. The high temperature on both July 22 and 23 was 105°F, which were record daily highs. Omaha normally averages just two 100-degree days during July. 

During the July 17-to-23 period, 866 daily high temperature records were set or tied across the country, along with 716 warm overnight low temperature records. Of these, 14 of the high temperature records were monthly records, and eight were all-time high temperature records. So far this year, warm temperature records have been outpacing cold records by a ratio of about 7-to-1. The ratio is even more lopsided, at closer to 9-to-1, when looking only at record daily highs compared to record daily lows. (Track record-breaking temperatures using Climate Central's Record Tracker.)

In recent years there have been many more warm temperature records set or tied in the U.S. compared to cold temperature records, part of a longer-term trend. Credit: Climate Central.

As the climate has warmed during the past several decades, there has been a growing imbalance between record daily high temperatures in the contiguous U.S. and record daily lows. So in the coming decades, we may see more and more of these record-breaking temperatures in cities across the U.S. A study published in 2009 found that rather than a 1-to-1 ratio, as would be expected if the climate were not warming, the ratio has been closer to 2-to-1 in favor of warm temperature records during the past decade (2000-2009). This finding cannot be explained by natural climate variability alone, the study found, and is instead consistent with global warming.

The heat in the Central states is compounding drought concerns, as one of the worst droughts in U.S. history has intensified during recent weeks due to the combination of record warmth and well below-average rainfall.

Further north, though, some beneficial rain is falling in a zone from Minnesota through northern Illinois, Michigan and Ohio. A frontal boundary marking the dividing line between cooler and less humid air to the north, and the extreme heat to the south, has already sparked one round of severe thunderstorms on Tuesday. A long-lasting, fast-moving complex of thunderstorms producing widespread damaging winds (similar to but not quite meeting the official criteria of a “derecho”) — tore through the Chicago area, knocking out power to as many as 175,000 people.

More severe weather is expected during the week, but most of the rain from these thunderstorms is likely to fall to the north of the areas most heavily affected by the drought.