Winter Cycling - Effect of sun radiation on temperature?

On cold days when the sun is bright, I notice it feels 10 degrees warmer than what weather.com reports. Even my bike computer records a higher temperature ( though usually 5 degrees warmer than weather.com ). On cloudy days, my bike computer and weather.com are exact. I realize this is due to sun radiation. Any other comments about this phenomena?

You do know that the posted temperature on weather channels, weather websites, etc. is shade temperature, right?

Of course your bike computer and weather.com have the same recording when it is cloudy because both are recording the shade temperature. And of course your bike computer will record a higher temperature when it is in direct sunlight. Go stand under a shady tree for a while, and see what your bike computer says then.

You do know that the posted temperature on weather channels, weather websites, etc. is shade temperature, right?


That is news to me. Is there some rule of thumb for how much the shade and sun temperature differ? I suppose it depends on time of day? Does it also depend on the season?

That is news to me. Is there some rule of thumb for how much the shade and sun temperature differ? I suppose it depends on time of day? Does it also depend on the season?

No, there's no rule of thumb for how much the shade and sun temperature differ ... it depends on a lot of things. But meteorologists record the shade temperature all year round, not just in the winter.

Here ... have a look at these articles:

http://www.usatoday.com/weather/resources/askjack/2006-08-21-shade-temperature_x.htm

http://www.bbc.co.uk/weather/weatherwise/activities/weatherstation/temp_what.shtml

http://meteorologyclimatology.suite101.com/article.cfm/weather_instruments_gauges

On cold days when the sun is bright, I notice it feels 10 degrees warmer than what weather.com reports. Even my bike computer records a higher temperature ( though usually 5 degrees warmer than weather.com ). On cloudy days, my bike computer and weather.com are exact. I realize this is due to sun radiation. Any other comments about this phenomena?

If the ground is not cold and frozen the effect of a bright sunny day is significant. Usually you can dress as if it were 10 degrees warmer than the air temperature indicates. However, when the ground is cold and frozen radiant heat loss to the ground seems to nullify most of the suns warmth. In this condition it's usually best to dress the same and just be a little warmer and prepared if the weather changes for the worst.

For the past year, I have compared conditions as reported by The Weather Network (http://www.theweathernetwork.com) and AccuWeather. (http://www.accuweather.com) WN uses traditional humidex and windchill. Accu uses a "feels like" which includes, among other things, sun exposure. So far I have found the "feels like" from AccuWeather to be much, much more accurate to what I "feel".

If the ground is not cold and frozen the effect of a bright sunny day is significant. Usually you can dress as if it were 10 degrees warmer than the air temperature indicates. However, when the ground is cold and frozen radiant heat loss to the ground seems to nullify most of the suns warmth. In this condition it's usually best to dress the same and just be a little warmer and prepared if the weather changes for the worst.

That's for sure. Riding when it's 45 degrees F in August or September is much warmer than riding in 45 degrees F in March, no matter what the actual air temp is, the ground and snow and water (lakes, streams) are "radiating" coldness.