Elevation and Temperatures

[MJ Poore]

I live in a city that's 1700m above sea level, that being Johannesburg in South Africa. The only equivalent to this in the US is Denver which is 1600m above sea level. But here's the strange thing, Johannesburg is situated at about 27S, not far from the tropic of Capricorn. Yet in Johannesburg we have much cooler summers that Denver. The highest ever recorded summer temp in JHB is 35c, the average being around 27c. Yet Denver, despite being closer to the poles, can get much hotter than this. What's going on??

 

[Brian Emfinger]

putting it simply... Some of its adiabatic warming as air parcels pass over the rockies and begins descending into the plains. I bet there is more moisture in South Africa too since its distance is not so great from a moisture source as Denver. With the lower dews in summer Denver can get warmer easier while the higher moisture in Johannesburg will have a moderating effect.

 

[Willoughby Owen]

Denver is situated right next to the Rockies and air descends from there on most days when winds are light (correct me if i'm wrong...).

Mountainous states of the US heat up very quickly during Spring and warms the troposphere over North America considerably up to 200mb or so... I think 500mb temperatures of 5C are pretty common there over the CO Rockies in July/August. Add to that, hot dry southwesterlies out of the AZ and Mexican Sonoran Desert... and relatively humid southeasterlies from Kansas southwards, of which are very predominant from the southerly half sets up the right conditions for heat.

Johannesburg on the Highveld doesn't have a desert as arid as the Sonoran in the vicinity I don't believe and the lack of mountain ranges would prohibit any possible foehn winds on the lee side of the ranges (like Denver does and Jo'burg doesn't.)

In the troposphere during Summer... being ocean-dominated, the Southern Hemisphere is markedly cooler than the other half. So just another thing to consider.

I just checked this year's temperature data and Denver Intl. got to 38C and Johannesburg 31C which is a pretty impressive difference.

 

[MJ Poore]

Thanks for the answers.

I can see the oceans having an influence, surrounding either side of the sub continent. We're close to the Kalahari desert, about 400kms. But this doesnt seem to affect us.

With the dew points, it's normally only about 12c during summer. But very dry during winter. Dryness = cold around here.