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Thursday, January 13, 2011

Robertson's weather - extraordinarily ordinary.

Well, we are not having the floods of Queensland, although our location on top of the escarpment is equivalent to that of Toowoomba.
What we are getting is grey, misty skies. Sometimes raining, sometimes leaking watery sunlight through the clouds.

It is difficult to make Robertson's weather sound "romantic". The best I can say is that in Robertson we do "ordinary" weather "extraordinarily well".

This month, our rainfall has been consistent, but not dramatic. Rain, alternating with mist, drizzle, more mist, rain and fog.The rainfall so far this month has been: 0; 2; 0; 4; 0; 0.5; 0; 15; 7; 24; 24; 43; 1 (all in mm).

Unlike the Inuit people of Greenland (who according to Peter Hoeg, in "Miss Smilla's feeling for snow" ) have more than twenty different words for snow, we Robertson people do not, but we can go close for different words for fog. 

Well, actually we could if we were a more literate society (instead of a Potato-growing, Rugby League-obsessed community).

I measure the fog by the visibility factor - how far I can see through the fog.

There is a standard measure. Aircraft pilots have defined fog and mist as follows:
"Fog is visibility less than 1000 meters and mist, by definition, is visibility between 1000 and 5000 meters. Both have their origins in light suspended cloud droplets with a nearly 100% relative humidity and an abundance of condensation nuclei."
Are they kidding? 
That's not a real fog - not in Robertson, anyway.

Visibility reduced to 5 Kms approx (beyond Belmore Falls)

 I measure Real Robertson Fog in terms of 
those trees which are the furthest away which I can see from my back deck.
  • If the trees at the Cemetery (800 metres away) disappear, that is a light fog.
  • if the Power stanchion in the next paddock below my house, disappears, that is a medium fog, or more likely, a heavy rain cloud rolling in from Kangaroo Valley.
Visibility reduced to my back paddock - 200 metres.
Bright light, medium fog
  • If the trees in the lower paddock (100 metres away) disappear, that is a medium-thick fog.

Medium-thick Fog - today
  •   There is another complication - the depth of fog directly above me. In other words, is the fog really part of a dense cloud? If so, it dramatically lessens the available light. So I can have a bright fog, a dull fog, or a dark fog, depending not on the "density" of the fog itself, but the amount of light coming through the clouds above. Sometimes the light in a fog can be so bright as to almost cause "white out". Yet it can still be a thick fog.
  • Of course, there is yet another factor - I can have clear air (in my immediate vicinity)  but be looking at a wall of fog rolling up the valley. That is illustrated in the series of photos in the blog post from October 23, 2008.
  • If the furthest tree I can see is the Sassafras growing 30 metres from my house, then, and only then, do I rate that as a true thick Robertson fog.

I suggest you take note of the white road "dividing markers" kindly used on the main roads in the Robertson area by the RTA. Because we are an area known for experiencing fog, they are very strict in ensuring our roads are marked.

    RTA illustration
  • According to Table 4.1 in that document linked above, the white lines are 3 metres long, and spaced at 9 metre intervals.
  • If you can (just) see the next white line mark, you have a fog visibility factor measured at 12 metres. Two white lines, means you can see out to 24 metres. Either way, that is a serious fog and it is a definite road hazard.
  • If you are driving in such a fog, my advice would be: 
  1. Adjust your driving speed according to the conditions. 
  2. Slow down, 
  3. Put your head lights on (even in daylight). 
  4. Experienced local drivers use their hazard lights (blinkers).


mick said...

I feel like saying "I'll swap you some rain for some fog" but maybe the weather you know is the best/safest to keep :-) About some new language to describe your climatic conditions - maybe you could make a start by being creative with some multiple words - descriptive words strung together - like the German does?

Flabmeister said...


WRT the pilots definition I also thought that 1000m visibility was not really a fog. Then I thought about a landing speed of 200 kph. You cover 1000m in 18 seconds: not long to try to swerve a jet!

We often discuss, but rarely resolve, whether the heavy moisture in the air is fog or cloud. I'm not sure if there is a conceptual difference.

I hadn't realised there was a standard distance for the 'dashes' on the roads so thanks for that! Our local roads are unenhanced by centre lines (or indeed any lines). The main road does have a centre line, but as it is twisty it is usually solid in both directions.

Our weather in Carwoola seems much more humid than usual (for the time of year). I suspect the Maximum temperatures are lower (the winds are more Easterly) but the minimums are higher (clouds insulates against heat loss).


Denis Wilson said...

Hi Mick
I know we cannot compete on rain - not at the moment, anyway. Nor would I wish to.
Aaah, Germanic constructions: big-thick-cannotseemyhand fog?

Denis Wilson said...

Hi Martin.
You are right about the speed factor for planes. Visibility is very important for them.
Re the technical distinction between fog and cloud, I really am not sure.
I do know my summer day fogs are very different in formation to Canberra's cold, winter night fogs.
And some are a specific creation of the mountain edges to the escarpment. Those are called orographic clouds
. If you are in one of those, you are in a really thick fog.
Our normal summer fogs are much more generalised than that (in location). But one usually knows if you drive out of Robertson 5 Km you will drive out of the fog.
Down Macquarie Pass, you drop below the fog - then it looks like cloud above you.
So I guess there really is no difference.

Lake Tana said...

A good informative post. The pictures are really amazing and so also the whether of the locations.
Thanks for the post and enjoyed visiting it.

Anonymous said...

Hi Denis!

“Unlike the Inuit people of Greenland (who according to Peter Hoeg, in "Miss Smilla's feeling for snow" ) have more than twenty different words for snow, we Robertson people do not, but we can go close for different words for fog.”

Yes, especially the first rule is: do not eat yellow snow. ;-))
What name this may also contribute.

Here it is again much warmer. (+8 0C). The snow is almost gone (+ rain) and also with us is the high water, but not in the proportions as in Queensland or Brazil or last year in Pakistan.

Cheers Peter

Denis Wilson said...

Thanks Peter, for reminding us of "Yellow Snow".
Fortunately it doesn't apply to fog.
Glad your snow has almost gone now.

Mark Young said...

It never ceases to amaze me just how much people don't take it easy in fog or heavy rain conditions! What's a few extra minutes compared to having an accident?

Snail said...

Great tip about the road markings.

When the power went off here the other night, it took ages to be restored. The fog was so dense that the Ergon people couldn't locate the damage!

Denis Wilson said...

Hi Mark and Snail
Thanks both of you.
Fog driving is pretty scary, but surely common sense indicates the need to slow down?
Common Sense - an oxymoron?

Your power outage in the night and in a fog must make it hard for the Linesmen.
Glad it is back on again.