Ross,
Water does not form ice crystals or begin to form ice until it reaches freezing point itself.
for an ice crystal to form, that ice crystal
has to be at zero degrees minimum.
When you talk about that in relation to the weather then it is a question of the local conditions.
Ever noticed how your windscreen will ice up but your side windows do not?
A reason for this is that while the windscreen is facing the sky, side windows are facing horizontally (obviously) so they are affected by radiated heat from whatever is about them.
The reason why during the winter, patches of shaded ground remain heavily frosted, and puddles still frozen, (apart from t he obvious fact they are not warmed from direct sunshine) is of course because the fround temperature is remaining low enough to stay below freezing.
This mostly happens through the months of January and February, after the shortest day has passed.
The reason?
The ground itself takes a long time to warm up and cool down, generally it takes until after the winter is very well advanced for the mean temperature of the ground to have fallen to the point where its temperature is low enough for long enough for the water to freeze up and stay frozen.
This is the reason why the coldest days of winter are January side of the shortest day and not the other side of it.
You get the flip side of this in the summer too.
The warmest weather always occur after the longest day, the ground has taken this long to absorb the energy from the sun, and to radiate it back out.
That may have drifted off topic a little, but this thread doesn't have real topic as such, so I don't feel too guilty
one of my teeth gritting frustrations with domestic customers is the fact that they all have different ideas as to what constitutes window cleaning weather.........or not>
It's not worth cleaning the windows, it's going to rain.
They don't need cleaning in the summer so much.
They need cleaning more often in the summer.
Its too cold to clean windows.
Its too hot to clean windows.
And don't you just hate it when they change there statement into a question? and add a 'Don't you think so?'
Time for work, I'm outta here.
Ian