Tired of being reminded it's 37 degrees outside?

[jeremym]

Originally Posted by Jordo

Don't you think 32* would be a better heads up?

Ice can form even if the outside ambient temperature is above 32 degrees Fahrenheit.

[stockguru]

Scientifically, at 37 degrees it is possible for snowfall. It is a bit cooler up by the clouds and allows snow to form. At 37, it is not warm enough for that snow to turn into rain on the way down.

Although at 37 degrees, it is likely there won't be much accumulation since the ground is too warm. Thus the snow melts on contact forming a wet slushy surface (black ice)

[Penguin]

Originally Posted by jeremym

Ice can form even if the outside ambient temperature is above 32 degrees Fahrenheit.

The temperature of the road surface can be several degrees different than the air temperature at the location of the temperature sensor, i.e., the temperature display is not the road surface temperature.

Hence the signs you see which say:



Even though I am sure the temperature displayed in the dash will not change on the bridge.

[Richard in NC]

Precisely! The wind blowing over and under the bridge caused a wind chill and can freeze water on the bridge surface when the actual air temp is > 32.

I'd bet if the wind is high enough, and the bridge long enough, it might drop a degree or 2.

Several years back in an E39 M5, I ran into a hail storm in May on a road out in the country. It lasted 10-15 minutes and there was no where I could go. The road became covered with hail marbles, was slick as heck, and the temp display dropped from 70 to 35!!! I got the ding. I finally managed to find an awning and pulled off the road under cover. The lot was so slick, I could barely make it back on the road after it passed. The end result was a $2000 Dent Wizard bill.
NationWide processed several 1000 claims that day!

[JCL]

Originally Posted by Richard in NC

Precisely! The wind blowing over and under the bridge caused a wind chill and can freeze water on the bridge surface when the actual air temp is > 32.

Wind chill isn't a real temperature; it isn't actually any colder than the ambient temperature. It is a virtual temperature that relates to how cold it feels on your skin. Cars and roads don't experience wind chill.

The 3C buffer simply allows for the risk that roads may be colder than ambient, and thus still have ice on them.

[LeMansX5]

Originally Posted by jdbretz

Not sure when BMW started doing it but my '89 325i had the alert too, it was just a little more primitive than the snowflake graphic.

Most new cars these days have this warning. I had a 2010 GM Equinox rental a while back which also had this warning.

[soldmystang]

Originally Posted by Richard in NC

Precisely! The wind blowing over and under the bridge caused a wind chill and can freeze water on the bridge surface when the actual air temp is > 32.

I'd bet if the wind is high enough, and the bridge long enough, it might drop a degree or 2.

Several years back in an E39 M5, I ran into a hail storm in May on a road out in the country. It lasted 10-15 minutes and there was no where I could go. The road became covered with hail marbles, was slick as heck, and the temp display dropped from 70 to 35!!! I got the ding. I finally managed to find an awning and pulled off the road under cover. The lot was so slick, I could barely make it back on the road after it passed. The end result was a $2000 Dent Wizard bill.
NationWide processed several 1000 claims that day!

we got that same storm in Raleigh also, not quite as severe but i had sleet in the yard. freaky.

i'd swear that today when i got the chime, the readout said "temp is 30"

[Penguin]

Originally Posted by Richard in NC

Precisely! The wind blowing over and under the bridge caused a wind chill and can freeze water on the bridge surface when the actual air temp is > 32.

No, it will not freeze above 32 if the bridge temperature is above 32, and the bridge temperature will not be 32 or below unless the air temperature hasn't been 32 or below. Heat will never flow from a lower temperature body to a higher temperature body no matter what the wind speed is.

[Penguin]

Originally Posted by JCL

The 3C buffer simply allows for the risk that roads may be colder than ambient, and thus still have ice on them.

Precisely.

[Richard in NC]

Originally Posted by Penguin

No, it will not freeze above 32 if the bridge temperature is above 32, and the bridge temperature will not be 32 or below unless the air temperature hasn't been 32 or below. Heat will never flow from a lower temperature body to a higher temperature body no matter what the wind speed is.

But if the temp was below 32 (over night) and the water on the bridge froze, the next morning, the air may be above 32 but the water on the bridge is still frozen.