Originally Posted by
Hypno Toad
Honestly, there's too much to unpack in this paragraph, but I'll be very clear: a glass of water in the shade (or at night) placed on a table (not on the ground) with not freeze until the air temp is below freezing.
Ever heard of a thing called “heat capacity”? Nearly everything has it. Air has it, water has it, the ground has it, the glass has it, and the table has it. Water happens to have bucket loads of it and can suck lots of it from the surroundings. A glass of water on a table will pull heat from the air, the glass, and the table. Isolated from the surrounding with air blowing over the water, the water would lose enough heat to evaporation to eventually freeze. But it has to be isolated from the surroundings. Your analogy is flawed.
The only time water freezes in the shade, with air temps above freezing, is ground temp, it has nothing to do with wind chill.
I beg to differ. As someone living in an area where we have very high winds, I’ve observed freezing water at air temperatures slightly above freezing on the shaded sides of building caused by the wind blowing across the water. Yes, it’s partly because of the
ground temperature but that doesn’t mean the water isn’t freezing.
If the ground is frozen, the thermal transfer will freeze water in direct contact the ground. In fact, this is why when I'm winter camping, I focus on a sleeping mat with a high R-value... it's not the winds, I'm in a tent, it's the ground temp. I feel like you understand this.
Can you
not see that adding just a little bit of wind with liquid water in contact with the ground can lower the temperature of the water below the freezing point of the water? Or are you saying that water doesn’t cool due to evaporation?
In other words: the air temp is the coldest it will get, no matter what the wind is doing. The wind will cool your exposed skin, or that glass of water, to the air temp faster than it would cool with still winds, but the lowest temp is always the air temp. And how much exposed skin do you have at temps below freezing?
You might want to go back and review what you just said. Why does the wind cool your exposed skin (or the glass of water)? The lowest temperature
isn’t the ambient temperature around you. The lowest temperature
on your skin is how much heat is lost due to the evaporation of the water. The amount of heat lost is going to be dependent on how much water is present.
Let’s look at this from a different perspective. During the summer, do you not feel cooling from the sweat evaporating from your skin? Is the lowest temperature you experience the temperature of the air around you? We sweat to lose heat through evaporation. It’s quite effective. Just because the temperature changes from hot to cold doesn’t mean that evaporative cooling goes away. We use “wind chill” to cool ourselves in the summer to avoid overheating. We don’t want to lose heat to evaporative cooling in the winter (aka wind chill) because we don’t have enough heat to lose.
You have said it and made my point earlier: wind chill is a thing, but not the headline the weather forecast ALWAYS makes it. Winter comfort is based on many factors, wind is part of the equation, but far down the list of things I think about when preparing for my daily winter ride and rarely factors into my clothing choices.
You know this isn’t all about
YOU. You (
and I) probably don’t need to pay much attention to the wind chill. I don’t know how many years you’ve been doing this, but I’ve been winter commuting for 40 years. I’ve got a system work out based on that experience. But other people may not have the same experience. Lots of people have very little experience with being outdoors at any time of the year and information about wind chill, even if flawed, is still useful. I agree that wind chill is delivered with a little bit too much drama but it’s still useful information for many.
On the other hand, I object to your spreading of incorrect information. The Slate article you posted and the other “journalist” you quoted contain very erroneous information. It took me less than 5 minutes to find the modern research paper that set the new standards and to find that the Slate article was not just wrong but insultingly so. The whole wind chill is only measured for short, fat people was journalistic malpractice. So was the similar quote from Collins. The least both could have done was to read the paper and/or contact the researchers before printing out false information and/or deciding that the scientists are stupid.
See post 21: .... once temps are around 20F/-7C, my wind blocking layers do not change ... even at temps down to -30F/-34C. One wind blocking layer is all you need, OTOH the layers of wool will increase as the mercury falls.
See post 14 for information about quality bike-specific winter wind-blocking kit. With a lifetime of winter activities in Minnesota cold, including thousands of miles of winter biking, I've found some great gear and brands I trust ... and found some that is worthless too.
In summation: dressing for the air temp in the winter should* take care of any wind chill factor. (see Bob Collins blog post) *[poor quality winter gear might fail this rule of thumb]
But you don’t “dress for the air temperature”. If you were sitting around doing nothing, increasing the wool layers would probably be enough. You wear the wind blocking layer
because of the heat loss caused by you moving through the wind. Would you go out and ride without that wind blocking layer? Probably not. Why do you use it? To block the wind from evaporating the water on your skin and causing you to loose heat. What was that definition of wind chill? Oh, here it is: “
Wind chill is the lowering of body temperature due to the passing flow of lower temperature air”.