Bushwalk Australia

I'm thinking more about what gear I carry for what temperature I expect, as I often have the choice of heavy and safe, or light and risky. This goes for boots, sleeping bag, tent etc. I took my heavy sleeping bag the last few days, and stayed warm, but I'm wondering what the temperature actually was so I can make these decisions easier in the future.

I know there's a general rule along the lines of minus a degree for every hundred metres altitude, is this accurate ?

If it was forecast -4 in Maydena (300 masl) the last few nights, what was likely the temperature camping at Mt Field (1200 masl) ?

All I know is it was *&%$#! cold out.

I think 1C per 100m is correct for dry air.

Moist air, around .6C per 100m

http://www.cmmap.org/learn/clouds/lapseRate.html

its exacerbated by generally increasing windspeed he higher on a mountain range you are. i walk up a 100m hill nearby regularly, i can be toasty at the bottom, but at the top its freezing with the wind, the air temp isnt much lower...

The standard atmosphere defines -6.5°C/km as the lapse rate. It's meant to be a typical value. The actual lapse rate varies considerably during the day, seasonally, due to specific terrain and because of weather.

Take a look on BOM at the temperatures for Hobart (51m) and Mt. Wellington (1260m) on June 3rd. Using those two nearby locations you would calculate a lapse that varies from -4.9°C/km in the middle of the afternoon to an inverted +1.4°C/km in mid-morning. Inversions aren't uncommon.

Here's a table of suggested lapse rates for mountainous terrain for different months the year (from Seasonal and Synoptic Variations in Near-Surface Air Temperature Lapse Rates in a Mountainous Basin, JAMC, Jan 2008):



Note that the data that went into producing this table were from the northern hemisphere so you'll want to invert the values seasonally, e.g. Jan <--> July.

And take them with a grain of salt.

Awesome post Orion !

I think it's ok to assume it was at least -8, which gives me an idea that my heavy sleeping bag will handle nearly anything in Tassie.

2 degrees C per 1000' is the average I use at work, but I'm guessing most on bw.com no longer use feet!

Can be as high as 3 degrees C per 1000' in completely dry air.

As stated above, can actually be a reverse gradient in the event of a temperature inversion (such as early morning) but this is unlikely to be noticeable for a hiker who resides in the boundary layer air close to the Earth's surface.

South_Aussie_Hiker wrote:2 degrees C per 1000' is the average I use at work, but I'm guessing most on bw.com no longer use feet!

That's the same as 6.5°C/km... which is usually wrong in the mountains.

South_Aussie_Hiker wrote:As stated above, can actually be a reverse gradient in the event of a temperature inversion (such as early morning) but this is unlikely to be noticeable for a hiker who resides in the boundary layer air close to the Earth's surface.

I disagree. I think it's not at all uncommon for cold air to sink into the valleys at night rendering the surrounding higher terrain warmer. I experience that here (in California) frequently.

Falls Creek is a classical example of the summit being warmer than nearby valleys [ eg Pretty Valley in the Valley itself]
It's why mountain villages in Europe are often about a third of the way up a slope to avoid that pool of cold air

2 degrees/1000' is the average lapse rate in the troposphere, just because it is routinely different doesn't mean this figure is wrong - that's what an average is. If you look at the average earth surface temperature, the temperature of the isothermal layer at the tropopause, it equates to an average of 2 degrees per thousand feet. As I stated, it can vary depending on the moisture content of the air, and lots of other factors too such as season.

A temperature inversion does not require mountainous terrain, but it does help strengthen it if the cold air can be trapped. Camping in a valley with mountains on all or most sides will be a very different experience to at the bottom of a mountain where air is not trapped due subsidence. In this case, katabatic winds are likely to be more of a problem during night before sunrise.

To the OP:
Id recommend some reading on atmospheric stability, and perhaps invest in a cheap barometer for your walking. A large stationary high will lead to light prevailing winds, and stronger temperature inversions (similar to the conditions required for fog). I'd plan to camp a bit higher in conditions such as this. Low pressures cause atmospheric instability which will prohibit strong inversions, and also promote precipitation - so I'd be camping lower down.

Temp lapse theory is all well and good, but as Wayno said, from a safety and comfort point of view, probably a more important consideration is wind when at higher altitudes.

South_Aussie_Hiker wrote:2 degrees/1000' is the average lapse rate in the troposphere, just because it is routinely different doesn't mean this figure is wrong - that's what an average is.

I know what an average is. And right now the current temperature where I am is NOT equal to the average for the earth or the solar system or the universe. It's a different value, the answer to a different question.

In the context of the lapse rate, if you use the average tropospheric lapse rate to estimate a temperature at some elevation up slope from where you are you will often get the wrong answer.

South_Aussie_Hiker wrote:Id recommend some reading on atmospheric stability, and perhaps invest in a cheap barometer for your walking.

Thanks for the suggestion. My understanding of weather is very poor. Perhaps you can provide a short list for bedtime reading?

As for barometers -- I already own a number of them and do sometimes carry one or more. On 10 day walk last year I recorded over half a million barometric measurements.

Id recommend some reading on atmospheric stability, and perhaps invest in a cheap barometer for your walking.

Sorry if this wasn't clear, but this part of my post was directed at the OP.

South_Aussie_Hiker wrote:Sorry if this wasn't clear, but this part of my post was directed at the OP.

Oops! Reading failure on my part.

I really could use a suggestion for a good book on weather though.