Why does the cold feel cold?

Do you ever wonder why you feel miserable when it is 40 degrees and raining and yet you feel all right if it is 20 degrees and sunny?

On a cold wet day, say 40 degrees and raining, it can feel really cold. I grew up in the Seattle area, and I can remember playing outside on a rainy day in the winter. My hands were extremely cold and numb when I came inside. Some folks would even say it feels colder on a rainy, 40 degree day than it might on a 20 degree day with clear skies.

Humidity is playing a role here.

When it is raining, the relative humidity is 100 percent. Relative humidity is a measure of how much water vapor is in the air. If it is raining, that means there is more water vapor in the air than can be held, so some of it must come out as rain.

On a cold wet day, the larger amount of water vapor in the air has the capacity to absorb a lot of heat. Such as the heat from your body.

Water has a high "heat capacity." This is one of the reasons why it feels so cold on a wet day in the winter. As you go outside, your body releases heat into the air. With a lot of water vapor around, more heat can be transferred from your body to the air, and it happens faster. So you "feel" colder.

However, on a dry, 20 degree day, the heat transfer is slower, so you don't feel it as much. Your body also has more time to adjust. In fact, when it is dry out, your body will start to warm the air around it, and a layer of warmer air will begin to build up around you.

But there is a catch. What if it is windy on that dry, 20 degree day? Well, you can kiss that layer of warmer air goodbye. Meet the "wind chill." The wind chill works (much to our chagrin) by quickly removing that layer of somewhat warmer air around your body, produced by your own body heat.

In fact, wind chill is really the main factor in determining how cold it feels on a typical winter day. If it is perfectly calm, that layer of warmer air will surround your body, and it won't leave unless you make a move. But when a wind comes along and removes this layer, your body immediately senses the new cold air, and it feels much colder than it really is. Also, as the wind speed increases, the worse it gets, since your comfort layer is being stripped faster.

But I would hazard a guess that all of the above won't matter to you if it is -40 degrees outside. At that temperature, it doesn't make much of a difference what you do, it's just too cold in absolute terms. As the temperature drops, a point is reached where it begins to dominate how cold it feels. Fortunately, we don't live in Nome, Alaska, so the wind is really our main concern.

All three factors described above play a role in determining how cold it feels, but to varying amounts depending on conditions. Humidity is important, but only when it is not windy and not really too cold. Wind plays a dominant role at most temperatures and humidity levels. Once the temperature starts to get in to the single digits, and then goes negative, all bets are off. You need to get inside.

There is a fourth factor which is your own subjective interpretation of "cold." Each person will feel a different level of coldness. Subjectivity is an important factor in how we interpret our surroundings, but it is hard to measure and quantify.

However, we can measure absolute temperature, wind speed and relative humidity. And, again, of those three, the two most dominant factors are absolute temperature and wind speed. Humidity plays a role when comparing a wet 40 degree day to a dry 20 degree day, with no wind. This can explain why you might feel colder on a wet winter day as opposed to a dry one. But as soon as wind is part of the equation, things change quickly.

It makes one long for Hawaii.