Community, Meteorology

Measuring Temperature

There was a meme out a while back, pointing out the differences between Fahrenheit, Celsius, and Kelvin.  Measuring was a challenge in those early days – heck, measuring was a challenge to me after I had completed college classes on the topic.  Somewhere in the Glen Lake Irrigation District files of “as built” projects, my blunder on the Tamboer Siphon may still be recorded – I carefully picked the best spot for an inlet structure, numbered it 0+00 and began surveying.  A couple weeks later, I realized that I needed shots further upstream and had to start using negative numbers to finish the project.  It was a solution, but not an elegant solution.  After the experience, I started at 10+00.  Less mockery occurs when your mistakes aren’t so obvious.

Anders Celsius made a similar blunder – he set the boiling point of water at 0 degrees and the freezing point at 100 degrees.  Then as he continued his studies, he found that the boiling point of water changes with elevation (atmospheric pressure) while the freezing point of water was independent of both latitude and atmospheric pressure.  After Celsius died, the Royal Swedish Academy of Sciences noted that Celsius’ successors had reversed the measurements.  It does make more sense to start measuring from something constant.

The amazing thing about the Fahrenheit scale is that it came first.  Without a consistent scale on the thermometer, the extra energy involved in shifting from water to ice (or vice versa) makes precise and accurate measurements somewhere between difficult and impossible.  Fahrenheit chose to set his zero at the point that the reaction between ice, water and ammonium chloride quit working.  Once he had that, and marked his thermometer, he could repeat his experiment and determine that he had a consistent zero, based on a chemical reaction.  His next line was assuming the human body temperature was 100 degrees.  Then he could measure the temperature of ice water.  A bit of refinement, and freezing became 32 degrees, body temperature 96 degrees, and individual degrees could be measured by cutting the difference in half – 32 to 16, 16 to 8, 8 to 4, 4 to 2, and in 5 steps Fahrenheit had the gradations on his thermometer.  In the US we still use his method, though the rest of the world uses the modification of the Celsius system.

William Thompson (Baron Kelvin) came up with the Kelvin scale in 1848 – where zero was based on his calculations of absolute zero.  Thompson’s calculations showed absolute zero at -273 degrees centigrade.  In the following century and a half, his calculations have been corrected to -273.15. 

All told, it’s kind of humbling to see what these folks could do in the 18th and 19th centuries, without calculators and computers.  Thermometers of sorts were invented long before – but developing a universal measuring scale was long in coming.

Community, Meteorology

The Weatherman Said

It looks like we’re into some near record or even record breaking high temperatures.  Kalispell’s record high was 105 degrees back in 1961.  I probably handled that by heading into the creek.  Still, that’s fairly gentle, compared to Glendive in 1893, or Medicine Lake in 1937 – both of which saw 117 degrees. 

As I look at the predictions for the next few days, my mind goes back to the concept of growing degree days, and then to the temperature limits on plant growth.  Corn, for example, doesn’t grow unless the temperature is at least 50 degrees, and anything over 86 is wasted.  Today’s heat isn’t much help for the sweet corn in the garden.  Wheat, as I recall handles temperatures up to 90 – but there isn’t much good to be said about 100+ degree weather for crops or people.  Alfalfa doesn’t notice the temperature until it tops 104.  (All of this is from memory, and the last time I taught the class was 35 years ago – I don’t believe that I’ve lost it since then, but checking the numbers won’t hurt my feelings)

The excess temperature has the spinach, broccoli, cauliflower, lettuce and similar leafy greens bolting – going into seed production early.  I’m not sure how the early heat is going to affect the tomatoes and peppers this early in their growth.

Still, I’ve been through the hottest day Montana could offer – I was manning a target so we could tie in two separate benchmarks on two separate mountains . . . the kind of job a monkey with passable radio discipline could handle.  I’d figured on waiting for the radio call to shift the target, then napping in the shade.  When I got to the only shade available, I saw a rattlesnake slide into a crack in the boulder I had planned to use as a back rest.  It was a shady, smooth boulder – and if I had gotten there 5 minutes later, I would have probably got the nap.  Instead, I stood in the sunlight.  There’s a word for fear of snakes.

A Science for Everyone, Meteorology


It’s not really that cold out, is it?

Are you asking the thermometer? To a chemist or a physicist, temperature is really just a measure of how fast the molecules that make up air are moving, how much energy they have.

To those of us more interested in what the thermometer says outside, temperature has more to do with the rate at which we exchange heat with the environment. At the same temperature, a metal spoon will feel hotter than a wooden one; The metal spoon, being metal and thus more conductive exchanges heat with us at a faster rate, and so feels hotter.

Cold works the same way. The faster we lose heat, the colder it feels, even if the reading on the thermometer hasn’t gone down any.

Windchill, then, has to do with the way wind changes the rate at which we exchange heat with the air around us, specifically the rate at which we lose heat.

It makes an obvious sort of sense. The more wind, the more particles of air move by us, the more opportunities for particles of air to get a little warmer and us to get a little colder. But it’s actually worse. Wind will strip away that nice little layer of air you’ve already exchanged some heat with. It’s slightly warmer (which means its taking slightly less of your heat) and keeping all that really cold air from touching your skin. Insulating. Wind strips away that insulating layer of air.

Windchill, while ostensibly a measure of how cold it feels, is really a measure of heat loss. At it turns out, your body cares far more about how cold it feels than how cold the thermometer reads. While your skin temperature isn’t going to drop below ambient temperature, your body will perceive things as colder than they are, and respond accordingly. Frostbite? Hypothermia? The symptoms of those are the result of the body responding to how cold it feels.

Thirty degrees and windy can’t actually drop your skin’s temperature below thirty, but it’ll feel colder, and that is enough to increase the risk of cold related injury such as frostbite. While the equations to calculate windchill vary a bit, windchill warnings are serious business.

It’s not really that cold out, is it? Not if you ask the thermometer. If you’re asking me, however…