how cold?

[jake11]

hi again

everyone says it gets cold at night in the desert. sure, but how cold?

i will be there in late september/early october and sleeping in a tent. i can't decide whether to take a sleeping bag. i am thinking that a woollen or synthetic blanket bought in a market (plus wearing some warm clothes if necessary) would be sufficient. what do you think?

thank you for any advice

paul

[ydv]

I was in Niger/Chad year ago about November. I've slept on the desert in Air Mountains and light sleeping bag together with warm blouse/sweater was ok.

I had bad experience with open truck rides overnight. It was so cold (mainly due to constant cool air flow) that putting everything I had was not enough (local guy in t-shirt next to me was not complaining although). It was really bad but good windstopper (I didn't have one) should do the job.

[Sam Rutherford]

Take a roll-mat - you lose more heat to the ground than to the air so you need to insulate beneath you. A woolly hat will also keep in a lot of heat.

Other than that, in a tent you should be fine.

Sam.


PS Rather than a tent, why don't you take a tarp - half the weight/cost and a fraction of the time to put up, ie during the day for a spot of shade whilst waiting for a lift?

[jondoe]

hi all!

What are the temperatures in desert,dayly hi and night low,in degrees celsius?
Not avrage temp's!

cheers!

[Sam Rutherford]

August, +42C at 2pm, +20C at dawn
January, +30 at 2pm, +5 at dawn

Ambient, no wind chill.

Up or down by 5C variation due to weather/wind direction etc....

Occasional extremes in excess of these figures. Altitude will reduce these temperatures by 1.5C per 1000ft (300m).

Sam.

[GWJ]

http://www-4.wetteronline.de/Algerien/Tamanrasset.htm

http://www-4.wetteronline.de/Niger/Agadez.htm

- click "Rückblick"
- choose "Tiefsttemperaturen"
- "September" and "2001"

Have a nice trip!

[Sam Rutherford]

Sula,

That's a great website!

Also disperses the 'it's too hot to live' argument against travelling in August...

Sam.

PS Also glad to see that my figures are not too far out!

[Col Campbell]

Sam not trying to be picky or anything, just for your future reference, temperature drops at 1.98 degs C for every 1000ft of altitude.

Col Campbell

[GWJ]

Sorry - I discovered only now: There is a english version!
http://www.weatheronline.co.uk/Algeria/Tamanrasset.htm
click on History - and the rest is easy!

[Sam Rutherford]

The Environmental Lapse Rate is taken as 1.98C per 1000ft.

Saturated ('SALR' is 1.5C per 1000ft), and more interestingly for the region in question, the DALR (Dry Adiabatic Lapse Rate) is 3C per 1000ft.

I remembered them being the other way around, we are looking at the DALR, thus 3C per 1000ft.

It's amazing what stuff (mostly) sticks during flight school!

Sam.

[Terry Davies]

With regard to high temperatures, temperature isn’t the whole story. Relative Humidity must be taken into account as well. As the Relative Humidity increases, the air surrounding your body is less able to absorb your sweat. This means that your body cooling becomes less effective.

In the US they use the Heat Index, which is the temperature that your body feels when heat and humidity are combined. The formula is about 40cm long, and there seems to be different versions of it.

At 35°C with 20% Relative Humidity, the Heat Index is 33, ie it feels like 33°C - cooler than it actually is. But with 80% Relative Humidity, the Heat Index climbs to 56.7 - past the danger point of 54°C where heatstroke becomes highly likely with continued exposure.

In the Sahara we have very low Relative Humidity, but as you move South things change. In August Nema has a maximum temperature of 36°C with a Relative Humidity of 59%, which gives it a Heat Index of 47.8. This would be classified as hazardous/dangerous in the US (Sunstroke, muscle cramps, and/or heat exhaustion likely. Heatstroke possible with prolonged exposure and/or physical activity.).

With regard to low temperature, again temperature isn’t the full story. You need to take the Wind Chill factor into account.

A good website with calculators for the Heat Index and Wind Chill factor can be found here: http://www.wrh.noaa.gov/Glasgow/calculator.shtml.

From personal experience I can tell you that I’ve woken up in the morning with frost on the outside of my tent. That was on New Year’s Day in the Saudi desert.

[kitmax]

Thank you, Terry for that invaluable information – you are the great researcher of this forum!
Just to confuse everyone, the ‘sleeping bag factor’ is worth mentioning; the more you weigh, the less thermal insulation a sleeping bag provides.
At around 13 stone I have been compelled to discard my down-filled 40’ – 0’C bag and adopt an 40’ to –5’ bag.
This has proved considerably more effective in keeping out the night chill. I’m a pyjama freak and wouldn’t consider going to bed wrapped in heavy sweaters, socks and hat!
While the desert temperature may not drop below –5’ C (except possibly in the Atlas or Hoggar or Tibesti regions) wind chill factors should, as Terry observes, be considered.
Sleep well…


------------------
Kitmax - Traveller
Desert Pictures at
http://www.kitmax.com/kitmax/kit03ph...velgallery.htm
homepage http://www.kitmax.com

[Col Campbell]

Well Sam you learn something every day, during my apprenticeship I had 1.98 drilled into me, I had just taken this figure for granted, thanks for enlightening me.
Thats the best part of these forums, when a few ideas start to get thrown around everyone usually learns something.

Col Campbell

[andrasz]

Is the 1.98 linear (for mountain altitudes), or rate varies with altitude ?

I was not aware of this figure, but had a perfect confirmation when we climbed Uweinat last november. Early afternoon high was around 30C in the valleys, yet on the peak it was only 22C at 1pm, perfectly matching the altitude diff of 4000 feet.

The coldest I ever experienced in the Eastern Sahara was 0C at dawn early december at the Gilf Kebir. Early/mid october it is unlikely to have anything below 8-10C, except at altitude.



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Happy Travels,
Andras

FJ Expeditions

[Sam Rutherford]

The rate doesn't change with altitude, except when changing from SALR through ELR to DALR as your altitude increases.

Clear??!!

Sam.