Hills or plains better for observing?

[Stonius (Markus)]

Hi Y'all,

I had a rather disastrous night the other night where I tried to sneak off after an evening engagement for a little dark sky stargazing. Packed the car, was on the road by 10:30. I have a special spot I've observed at a number of times and it works rather well for me as I can turn up late at night and it doesnt bother anyone. I drove with the heater off, so the scopes stay closer to the ambient temperature, which was about 1 degree. As I got closer to my little spot patches of fog became so thick that I had to use my fog lights and drive 30km in an 80 zone just to avoid accidentally making skippy pancakes. Yet strangely, if I looked straight up, you could still see stars quite clearly. And it would come and go from a pea soup to a beautiful clear night in a matter of meters! Very strange. Hoping that my little spot would be elevated above all this I persevered, only to find when I was within *600m* of my destination the road had been closed. Ugh!

Long story short, I found myself in the bush with no reception wondering where the hell else I could go for a little stargazing where I would not draw the attention of local attack dogs, shotguns or even worse, light pollution.

My bad, I should have sorted out a B plan before I left, but to those weather gurus out there, do you happen to know whether this sort of thing is caused by moist ocean air (which would presumably have less of an effect further inland where the air is drier), or is it a factor of elevation causing condensation by orographic uplift (where a lower elevation would, presumably be better) or is it a matter of bushland trees retaining moisture that is released back to the atmosphere at night causing fog, in which case a cleared area, either on a hill or a plain would be best?

My knowledge on local weather is sadly lacking in this area.

Markus

[gary]

Hi Markus,

When you experienced patches of fog but it was a clear night as you
looked up on the drive out, that was no coincidence.

When the sky is clear, infrared radiation has a clear path from the ground
out into space and the ground cools. If there is moisture near the ground,
for example from moist soil or vegetation, then if the temperature
reaches the dew point, the water vapour in the air will condense and form
fog.

Being on top of a hill you can often delay the time it reaches you
because the valleys fill up with fog first.

A clear, dry area is the better place to avoid it.

[Stonius (Markus)]

Originally Posted by gary

Hi Markus,

When you experienced patches of fog but it was a clear night as you
looked up on the drive out, that was no coincidence.

When the sky is clear, infrared radiation has a clear path from the ground
out into space and the ground cools. If there is moisture near the ground,
for example from moist soil or vegetation, then if the temperature
reaches the dew point, the water vapour in the air will condense and form
fog.

Being on top of a hill you can often delay the time it reaches you
because the valleys fill up with fog first.

A clear, dry area is the better place to avoid it.

Thanks Gary, so vegetated areas are not good. Is it true that the air is going to be drier inland then? So for Melbourne you're best to head North rather than East or West?