Period of Records
It has been obvious to everyone across the Central and Eastern United States for the past couple of weeks that it has been hot, on occasions oppressively hot. After a series of storms across the Midwest to the East Coast that left hundreds of thousands to millions without power for days the heat was likely unbearable. Dozens of deaths have been contributed to this heat wave that has obviously been described as record-breaking. Perhaps some have even titled it as the ‘worst-ever’. News stories across the nation have been using the numbers courtesy of NCDC and NOAA to describe just how hot it has been, with over 23,000 daily high temperature records broken this year through July 5. However, there is an important caveat to remember and that is a variable known as period of record. The period of record indicates how long that station has been in operation, and NCDC requires a station to have a period of record (POR) of at least 30 years to be included in their records database. But, do these stations with only 30-50 years of data skew the records?
In my opinion, yes. Sure there have been record-setting temperatures in the recent decades for stations that date back to 1900, but on the same token some of the hottest summers’ occurred during the 1950s and 1930s. For an example, take a look at Kansas City who period of record dates back to 1889, here are the top 10 warmest summers:
Only one of those (1980) have occurred within the past 58 years! This will be an important factor when I dig into some numbers below. But first, another detail that can skew these record numbers. The NCDC records database is based upon the exact station, for example Kansas City International Airport is the current official observation station for Kansas City. While records from the local NWS climate report date back to 1889, the NCDC records database only goes back 39 years for Kansas City as that is the time in which the airport become an observation station. This is the case in many areas where the official observing station has switched locations and taken on an new identifier, the period of record in the NCDC database does not incorporate an entire record such as one you would find in a local climate report. The NCDC records database indicated that in June 2012 that Kansas City International Airport had 5 daily record high temperatures. How many of those were actual records with the actual data that dates back to 1889? Zero!
Let’s dig into some of the data and numbers that you may have seen thrown around lately. In June 2012 there were 3,282 daily high temperature records either broken or tied across the United States. Those 3,282 records account for 1.9% of the records that were possible, in other words there were still 168,160 daily high temperature records that remained unbroken. While that may be significant, I don’t have the research done to conclude whether that 1.9% is indeed statistically significant or not. The main focus is the period of record, so of these 3,282 records how many of them had a period of record that reaches back through the 1930s? How many of them don’t even touch the 1950s?
Only 697 of the 3,282 came from a station with a period of record dating back at least 80 years; that is only 21.2% of the daily high temperature records that include the dust bowl era. Of those 3,282 there were a whopping 1,331 of them that were from a station with 50 years or less of records under their belt; that accounts for 40.5% of the daily high temperatures which don’t include the 1930s or even 1950s! One can’t say how many of those 1,331 records would have still been records if data was available through the 1930s, but one can reasonably presume that a majority probably would not make the cut. The same discrepancy can be found as you head into the first five day of July with daily high temperature records, with 1,570 either broken or tied of a possible 29,022. While that does equate to a solid 5.4% of daily high temperature records broken out of the possible only 324 (20.6%) have a period of record of at least 80 years. And once again, there are more stations that have a period of record of 50 years or less, 569 or 36.2% than those with the 80+ years of record.
In the end, I’m not saying the recent heat wave wasn’t really that hot or that it wasn’t record breaking. I’m simply informing you that you need to take into consideration other variable before spitting out raw numbers and a little research is always a good thing!