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Extremely Hot Days to Double in Missouri


Days Above 95The number of extremely hot days will approximately double across parts of Missouri by mid-century, according to a simulation by the National Oceanic and Atmospheric Administration (NOAA).

Click on graph for larger view.

The first graphic at right shows three charts from the report. The bottom left shows the current number of days above 95°, the bottom right shows the predicted number by mid-century, and the top shows the change between the other two.

By mid-century, a small region of Missouri along the Kansas/Oklahoma border is simulated to average as many as 70-80 days above 95° each year. The western part of the state is simulated to average 60-70 days above 95°, while most of the rest of the state is simulated to average 50-60 days above 95°.

A single hot day is one thing, but the length of a heat wave is very important in determining its overall effect. The second graphic at right shows the largest number of consecutive days with high temperatures above 95°. Heat Wave LengthIn an average year, the length of the longest heat wave is simulated to increase by 16-20 days in the Bootheel, 12-16 days across southern Missouri, 8-12 days across mid-Missouri, and 4-8 days across northern Missouri. Some regions are simulated to have as many as 25-35 consecutive days with temperatures above 95°.

Click on graph for larger view.

These predictions involve temperatures for an average year. That means that cool years will be less hot, but it also means that hot years will be even hotter.

How much would it vary year to year? The report simulations don’t say. However, a “back of the envelope” estimate can be constructed from temperature data maintained by local weather service forecast offices. The table below shows the number of days above 90° and 100° for 1874-2011 in St. Louis:

# of Days Above 90° # of Days Above 100°
Mean 42 1
Third Quartile 51 4
Maximum 79 37
Variation (Max – Mean) 37 36

For temperatures above 90°, the maximum count differed from the mean by 37 days, and for temperatures above 100° by 36. Combine this data with the simulations in the NOAA report and it suggests that during the hottest years, much of the state could have 86-96 days above 95°, while the part along the Oklahoma-Kansas border might have as many as 106-116.

The report calls its results “simulations,” not “predictions.” The reasons are complex, and I recommend reading the report if you want to fully understand. For our purposes today, let us simply say that the language indicates the large amount of uncertainty involved in all climate projections. If certain assumptions are followed, best current knowledge suggests that temperatures will be as simulated. But there is no certainty that the assumptions will be followed. The next post contains a discussion of this uncertainty.

Finally, it should be noted that the simulations in this report used as their starting point the climate models that were created for the IPCC Fourth Assessment Report. Those models are now more than 5 years old. New models are being used for the IPCC Fifth Assessment Report. A draft of that report is available, but the final report is not scheduled for release until early 2014.


National Oceanic and Atmospheric Administration (2013). NOAA Technical Report NESDIS 142-4. Regional Climate Trends and Scenarios for the U.S. National Climate Assessment. Part 3. http://www.nesdis.noaa.gov/technical_reports/142_Climate_Scenarios.html. This report is one of several regional reports used to create a new National Climate Assessment report scheduled for publication in early 2014.

Ranked Occurance of Temperatures >= 90 and 100 Degrees 1984-present. National Weather Service St. Louis Forecast Office.
St. Louis National Weather Service Forecast Office >> Local Climate >> Local Data/Records >> Monthly and Seasonal Data for STL (since 1874) >> Ranked Occurrence of Temperatures >= 90 and 100 Degrees 1894 -present. http://www.crh.noaa.gov/lsx/?n=cli_archive.

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