WRAL WeatherCenter Blog

Fishel: Fun with numbers at the RDU airport

Posted July 23

Some of you may have heard or read my rant about the seemingly unexplainable 5.4 degree temperature drop at the RDU Airport over a 15 minute period on Friday afternoon.

Yes, there was some Cirrus around (as well as rapidly developing cumulus clouds), and yes, there are these things called turbulent eddies that can cause temperature fluctuations both up and down. But over 5 degrees in 15 minutes a little over an hour past solar noon? Really?

These are the actual five minute temperature plots from both Friday and Saturday as well as plots of the five minute changes. And, for Friday, I have highlighted the period of time in question.

Fishel: Fun with numbers at the RDU airport

Fishel: Fun with numbers at the RDU airport

Fishel: Fun with numbers at the RDU airport

Fishel: Fun with numbers at the RDU airport

Notice that the actual temperature plots are not smooth, indicating the very real presence of these turbulent eddies. Now look at the five minute temperature change plots. Does it strike you that all the changes, both up and down, have a magnitude of either 1.8 degrees Fahrenheit or 3.6 degrees Fahrenheit? Never a 2.2 or 3.4?

Well, there's a reason for this as it turns out. Even though the data is measured in tenths of a degree Celsius, it is reported in whole degrees Celsius. So let's take a look at a 3.6 degrees Fahrenheit drop in five minutes. This equates to a 2.0 degrees Celsius drop.

Let's suppose that the actual temperature, measured in tenths of a degree Celsius, actually fell from 35.0 to 33.0 degrees Celsius. That would indeed equate to a 3.6 degrees Fahrenheit temperature drop (95.0 to 91.4).

But, now let's consider that in reality it dropped from 34.5 to 33.4 degrees Celsius and we just didn't know it because the data is reported in whole degrees Celsius. Then we would have a drop in degrees Fahrenheit from 94.10 to 92.12, or a 1.98 degrees Fahrenheit drop.

But, because of the use of whole degrees Celsius, we would still see it as a 3.6 degrees Fahrenheit drop because 34.5 degrees Celsius rounds to 35 degrees Celsius and 33.4 degrees Celsius rounds to 33 degrees Celsius. The bottom line is that, depending on the exact temperature readings (which we don't know except at the top of each hour), the magnitude of the five minute change could be overdone by a factor of almost two.

In this day and age, shouldn't we all be privy to the exact measurements as opposed to the rounded ones?

1 Comment

Please with your WRAL.com account to comment on this story. You also will need a Facebook account to comment.

Oldest First
View all
  • Brian Jarman Jul 23, 1:15 p.m.
    user avatar

    very interesting; and, Yes, we should be able to get the exact measurements. Is the rounding the result of out-dated equipment at RDU?