Weather forecasting out bush

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Weather forecasting out bush

Postby Clownfish » Thu 23 Apr, 2009 1:10 am

I've written this up for my personal bushwalking blog - any and all critiques, corrections and comments most welcome!

Red sky at night, sailor’s delight. Red sky at morning, sailor take warning.

Thus goes the old saying, and there’s a lot of truth in it. The sky can tell us a great deal about what the weather is going to get up to. Reading the weather is a skill that few of us possess these days, but one that walkers should try to acquire. After all, when you’re on the third day of a six-day trek, the only place you’re going to get a weather report is from the sky above you.

Of course, you should always try to get the most up-to-date forecasts possible before you leave, so you have some idea what to expect. However, with Tasmania's weather, expect the unexpected. Snow in midsummer is not unknown, on the Central Plateau. Weather can change drastically, in a very short time. Knowing a bit about what warning signs to look for can be very helpful, at the least.

Wind and most especially clouds are your most reliable indicators of the weather that you can expect in the coming hours and days.

Wind direction is very important, but its meaning is also very dependent on your locality. It is important to bear in mind that the information about wind direction here is strictly relevant to Tasmania.

South-Westerly winds mean colder, wetter air in Tasmania. Just how wet and how cold depends on the time of year, and exactly where in Tasmania you are.

Easterly and North-Easterly to South-Easterly winds are good news for North-West to South-West Tasmania, producing clear skies and mild days for the Western half of the island. For Eastern Tasmania, though, such winds bring cool and cloudy, and possibly wet weather to the East.

Persistent light Westerlies or windless conditions indicate a stable atmosphere, and no severe weather. Warm sunny days with smaller, puffy cumulus clouds or “mackerel skies” are likely to stay that way, and also into the next day. Clouds that break up or reduce near sunset herald a fine day to follow. Morning dew or frost is also a good sign, as is morning fog that burns off rapidly.

Clouds are a great indicator of approaching fronts and wind changes. If you can see two sets of clouds in the sky, one low and moving with the present wind direction, while the other is much higher and moving in a different direction, the upper set indicates the direction the change is coming from.

Wispy, cirrus “mare’s tails” high in the sky form in the direction the wind is blowing in the upper sky.

Rippled clouds also show wind direction, but contrary to what you might expect, the ripples form at right angles to the wind.

Cirrus clouds often show an approaching front. When cirrus thickens enough to cover most of the sky, it is known as cirrostratus, and a change is likely in about 24 hours. Halos around the sun or moon are associated with cirrostratus. Cirrostratus mean that rain or snow are likely in coming days.

If cirrostratus thickens further into altostratus, extensive rain or snow are on their way.

Image

Thickening and growing cumulus also means worsening weather. If you see the classic, anvil-shaped cumulonimbus thunderheads building, best to get to shelter soon!

Image

Low, dark, ragged and patchy nimbostratus clouds mean heavy rain is probably between hours or at most half a day away.

Large white cloud banks with a furry, diffuse top, approaching from the South or West, indicate a very cold change involving snow. Get to cover or lower elevations.

Image

So, what about the red sky at night?

Well, that depends on the exact colour red. A red sky at night means that the setting sun is sending its light through a high concentration of dust particles. A light, pinkish sky is generally a fairly good sign. This usually indicates high pressure and stable air coming in from the west. Basically good weather will follow. A deep fiery red, on the other hand, more likely indicates bad weather to come.

And a red sky at morning?

If the morning sky is red, it means high water content in the atmosphere. So, rain is on its way.

Sources:
Burroughs, Crowder, Robertson, Vallier-Talbot, Whitaker, 2008, Weather, The Five Mile Press
Leaman, D. E., 2001, Step into history in Tasmanian reserves, Leaman Geophysics
McManners, H, 1995, The Backpacker’s Handbook, HarperCollins
Last edited by Clownfish on Mon 27 Apr, 2009 12:33 pm, edited 1 time in total.
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Re: Weather forecasting out bush

Postby tasadam » Fri 24 Apr, 2009 9:58 am

A fantastic topic.
This topic shows areas of mobile phone coverage. I have in the past made phone calls to the Bureau of Meteorology from places such as Shelf Camp on Mt Anne, and on the range leading dowm from Frenchmans Cap to the Irenabyss.
They have always been very happy to take my call, and one of them once thanked me for calling him from the most "unusual, exotic location" (Perrins Bluff). It made his day - he is also a walker who was on Pelion West only a couple of weeks prior.

The black cockatoos come to the lowlands when the weather is going to be rough in the mountains.

It is possible to get a feel for what is happening longer-range if you know where to look.
I made my own weather page, just a heap of useful links.
Weather page
Useful ones include
Weatherzone 28 day rainfall forecast by region (click on areas on the map)
7 day numerical model and 4 day forecast chart and Colour enhanced infrared satellite loop and Weather chart of the Southern Hemisphere are all good to look at together and compare, get a feel for what's going on.
The more you use these links, the better a feel for what's going on you will get.
Certainly for a 7 day walk you should be able to get accurate info for the first 4 days, and usually a pretty good idea for the remainder. The further out you go from the forecast, the less reliable the forecast will be.

And if you are looking for a feel of local weather, compare the Colour enhanced infrared satellite loop with the 128km or the 512km composite radar loops and the hi res satellite images of Tasmania or Southeast Australia.
I'm hoping they one day replace the radar in NW Tas with one of those new hi res radars like they have in centres such as Melbourne.
It's worth reading more about the radar too.

One last bit of local advice. Don't plan a bushwalk on the weekends of Agfest, Launceston show, or Burnie show. These events are somehow tied in with the weather gods to guarantee rain. :roll:
Happy forecasting!
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Re: Weather forecasting out bush

Postby Clownfish » Fri 24 Apr, 2009 10:45 am

Thanks for the info about the black cockatoos - that sort of local folk knowledge is invaluable.

I was going to include the old bit of wisdom about cows lying down and huddling together when it's going to rain, but it didn't seem relevant to the sort of places most of us go.

Another unusual one is that certain species of ant (I forget which) gather grains of mica around their nests when a fire is coming, apparently it's something to do with reflecting radiant heat.

I've also been meaning to take that mobile topic and build it into some sort of interactive map. One of these days ...
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Re: Weather forecasting out bush

Postby Son of a Beach » Fri 24 Apr, 2009 10:49 am

Clownfish wrote:I was going to include the old bit of wisdom about cows lying down and huddling together when it's going to rain, but it didn't seem relevant to the sort of places most of us go.


Is still good for Lees Paddocks some weeks. :-)
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Re: Weather forecasting out bush

Postby Clownfish » Mon 27 Apr, 2009 1:02 pm

I took this sequence on the weekend, to show a typical front developing from the West:
Image

The sky early in the day had been characterised by extensive stratus clouds progressively clearing.

Frame 1 shows extensive cirrus forming high in the atmosphere. Notice how the tails of the cirrus show the wind direction of the developing front.

Frame 2 Within an hour or so, the cirrus had thickened into altostratus. It's obvious that rain is on the way! The cumulus at the bottom of the pic is the clearing remnants of the previous day's rain.

Frame 3: Sure enough, within another hour or so, the altostratus had descended and formed an ominous nimbostratus. Time to find shelter: Sure enough, the rain started within half an hour, and didn't let up all night.

This whole sequence took less than 3 hours to develop.
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Re: Weather forecasting out bush

Postby loric » Mon 27 Apr, 2009 1:56 pm

Cool topic.

If you guys use a GPS, most of them now can track barometric pressure.

If i'm unsure of the weather coming up (e.g. 4 days out and not able to pick up AM broadcast) i turn on the GPS in evening and log air pressure for a few hours overnight.

The pressure plots will tell you when a front is approaching/leaving etc.
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Re: Weather forecasting out bush

Postby abowen » Mon 27 Apr, 2009 2:58 pm

Clownfish,

Frame 1 shows extensive cirrus forming high in the atmosphere. Notice how the tails of the cirrus show the wind direction of the developing front.

Are the tails at the bottom of the picture or at the top? Or is the wind blowing towards the photographer or away? This is one that I often get confused about.
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Re: Weather forecasting out bush

Postby Clownfish » Mon 27 Apr, 2009 3:07 pm

loric, that's a good point. I had thought of barometers as a fairly exotic piece of equipment, but if they're equipped in GPSs, that makes them a little more common or garden.

abowen, the tails are at the bottom of the picture - the wind is blowing towards the photographer.
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Re: Weather forecasting out bush

Postby tasadam » Mon 27 Apr, 2009 3:19 pm

On the subject of weather, can you imagine being out bush and having to dodge these?
That's just mad.
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Re: Weather forecasting out bush

Postby sml_12 » Mon 27 Apr, 2009 3:52 pm

Sounds like that front came in pretty fast - or is that standard? What was the wind like on the day?? Can you judge how quickly you think you'll get the weather by the wind speed?

What would happen to the barometric pressure on a day like this?? Is that a stoopid question?

Thanks for keeping me posted!
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Re: Weather forecasting out bush

Postby Clownfish » Mon 27 Apr, 2009 4:24 pm

The wind, I don't recall being overly strong that day. Possibly it's because I spent most of the day safely inside, and our house is well sheltered by a massive hedge.

The problem with a front like that, is that it is developing quite high in the atmosphere, then drops lower as it forms, so you don't always get the same wind on the ground.

It did develop pretty fast, but then, it's not unusual to get ugly weather rolling in from the west like that.

As for barometric pressure, I'd say that it would be dropping pretty fast: If anyone can correct me on that, please do. I'm not as au fait with those sort of high-falutin' scientific thingys :wink: ; I'm more concentrating on the sort of naked-eye observations. But then, if GPS units are coming with built-in barometers these days, those sort of instrument readings would obviously be more common.
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Re: Weather forecasting out bush

Postby alliecat » Mon 27 Apr, 2009 5:21 pm

You can check out the BoM's records for that day. The pressure almost certainly dropped quite severely as that low came towards us. I think a barometer is a very useful instrument on extended trips for exactly that purpose. Sometimes you don't have a good view to the west (or even of the sky at all) so a dropping pressure might be the only warning you get.
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Re: Weather forecasting out bush

Postby Area54 » Tue 05 May, 2009 11:18 am

I've got a barometric altimeter built into a couple of watches - my Highgear and a titanium Tissot that I got for fathers day. These should be calibrated from a reference point at particular times of the day to enable accurate calculations - although the Highgear does have a trending display that is useful for tracking the natural ups and downs of barometric pressure, as well as a weather indicator. Makes me look hardcore at parties :lol:

But seriously I do use the functions quite a lot for very real purposes.

I also have a barometric altimeter built into the Garmin bike computer, but only for altimetric purposes, no weather data. Some other GPS models have trigonometric altimeters that base the altitude calcs on satelites, can be a bonus in some situations so the barometric pressure does not affect the altitude calcs.
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Re: Weather forecasting out bush

Postby loric » Tue 05 May, 2009 12:14 pm

If you're looking at the barometer functions on the widgets - get one where the widget can log the pressure data - otherwise you'll have to manually record the readings on a notepad and 'visualise' the trend.

I use a Garmin VistaC. I can simply turn it on and let the sucka log away (say whilst sleeping). In the morning i check the plot, see if it's tapering off or going bananas...

I only do this on walks longer than a week though. For trips up to say 3-4 days the BOM info is plenty sufficient.

As a side note - the Garmin VistaC also has a calculator for moons, tides etc. this is really handy if there's any night walking involved or tidal areas to cross.
It also has a calculator for parachuting drop points (which may possibly be useful if i get blown off fedda and want to know exactly where i'm going to hit the ground... LOL
Handy widgets these!
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Re: Weather forecasting out bush

Postby Dave Bremers » Wed 11 Nov, 2009 11:19 am

What does your gut say? Apparently the subconscious processes a lot of this stuff. A bit of weather knowledge (what kind of clouds indicate instability etc.) gives you the confidence to believe it. But DON'T go hiking expecting to "follow your gut". Come on. Just something to consider.
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