Hot, but compared to what?
Henry E. Temple, 80, of Baltimore, whose daughter describes him as "a big ol' weather geek from way back," believes there's a more accurate way to compare temperatures for two time periods than the one used by the National Weather Service. Here's his question:
"When comparing the same two calendar time periods from different years to determine which was the hotter time period, I believe that the area under the sawtooth of highs and lows starting from a baseline would yield a more accurate measurement than averaging high and low readings. I am curious as to your opinion on this assumption. Thank you. - Henry E. Temple, Baltimore City
I'm no mathematician, Mr. Temple, but I agree with you. Simply averaging the daily high and low, or the month's high and low, ignores the dimension of time.
For example, imagine a day during a prolonged heat wave. When the new day begins at midnight, the temperature at BWI is still 83 degrees. It remains way too hot all through the wee hours. Fans and air conditioners are running all night. And when the sun comes up, it only gets hotter. The mercury climbs quickly to 90 degrees by 9:30 a.m., and by 2 p.m. it's 100 degrees. The heat persists into the evening. (We've had days just like this in Baltimore; you can look it up.)
Then around 11 p.m., a cold front pushes into the region. Thunderstorms break out, rain cools the pavement and a new air mass replaces the hot air. Temperatures at BWI drop from 80 degrees at 11 p.m. to 65 degrees by the time the day expires at midnight. Average temperature for the date: 82.5 degrees (100 degrees + 65 degrees divided by 2= 82.5 degrees).
Now consider another scenario. Same heat wave. Same high temperature of 100 degrees at 2 p.m. But this time the cold front moves in at 2:30 p.m. instead of 11 p.m. By 4 p.m., the temperature has dropped to 70 degrees, and by 11:59 p.m., it's 65 degrees at the airport. Average temperature for the day is 82.5 degrees (100 degrees + 65 degrees divided by 2= 82.5 degrees).
On the weather service record books, and for all eternity, the days will look identical. The high was 100 degrees, the low 65 degrees, and the daily average temperature was 82.5 degrees. But arguably, for anyone who had to be outdoors in it, the first scenario produced a much "hotter" more miserable day than the second. There were more hours with higher temperatures. Perhaps we need a new term - maybe "degree-minutes," or "heat-hours."
It's not an alien concept to the science. For example, hurricane researchers have a measurement for hurricanes that captures the element of time. In addition to a storm's maximum wind speed, and the maximum category it attains on the Saffir-Simpson Scale of Hurricane Intensity, scientists record "storm days" (the number of days a storm spins at tropical storm strength); "hurricane days" (the number of days a storm packs hurricane-strength winds); and "intense hurricane days" (days at Category 3 or higher).
That capacity to include time in the measurements allows a more precise comparison of storms and storm seasons. A storm that blows hard enough and long enough to be a Category 1 hurricane for 8 days, is clearly more of a menace than a tropical storm that reaches hurricane strength for only one day. Yet both are remembered and recorded as Category 1 storms.
And you're right, Mr. Temple, the way to capture that element of time in the temperature data would be to measure the area under the daily temperature curve, above a standard baseline. Makes sense, but it also involves a more involved and sophisticated calculation. The weather service folks and their computers are surely capable of it. But as far as I'm aware, nobody does it. And implementing it would mean a break from the way things have always been done, and a break from more than a century of continuous, comparable data - a valuable resource. So, while such a measure could be added to the database, I suspect it would never replace the old system of simple averaging.
Good question. Thanks. Comments always welcome.