Weather It Is (Frozen and Icy Roads)

Good Evening:

Subject: icy roads.

The temperatures have warmed a bit, but there is still plenty of snow in the higher elevations.

The snow radiates heat quite well, cooling, which then cools the overlying air.

Tonight we're predicting a couple of degrees above freezing.  So, why are roads freezing and why will there be wet patches that are really ice when we wake in the morning?

The reason is two fold: first, the surface cools more than the air temperature, and second, the dew point (or air humidity) is very low.  The dew point is the atmospheric temperature (varying according to pressure and humidity) below which water droplets begin to condense and dew can form.  For us, it means that water from the roads will evaporate, and when they do, they will use energy and cool the surface. Eventually, enough water molecules (yes, it is the combined efforts of many) evaporate that any standing water freezes.

I don't expect this too happen too early in the evening, but sometime in the dark of night, when most of us are already tucked in bed, icy patches will form, and the roads in these areas will become extremely dangerous to drive on, or even walk.

Now, here's the worst of it all: today was a bit warmer during the day than yesterday, so there is a lot of water on the roads.  Moreover, the sun is late to rise, so the ice will be late to melt.  Perhaps, those in high places we should consider to take the day off the already short day of school?

Looking ahead, temperatures will hold steady for a few days and then head sharply upwards mid-next week, before falling off. There is a 40% chance of rain to end the new year, with only a very small chance of any frozen precipitation.

Barry Lynn