[gavia1]

London is regularly 3-4° warmer than the towns and village that border the M25 ring road. You can genuinely feel the difference when you take a train into the city and vice versa.

[quickthrower2]

Is that allowing for the time difference between when you get on and get off the train affecting the temperature?

[gavia1]

Absolutely. If you so wish you can take the train at noon and get off at 12:30 where any temperature difference due to the sun should be minimal.

[majewsky]

Not terribly relevant to your point, but: Noon is actually a time in the day where it is still getting warmer. Temperature usually peaks around 16:00 or 17:00 in the summer.

Example: http://wetterstationen.meteomedia.de/?station=104870&wahl=vo... (the forecast diagram for my local weather station)

[onetimemanytime]

any idea why? The ground starts releasing accumulated energy or what?

[gavia1]

It probably reaches saturation at that time of day where it can no longer absorb anymore heat.

[lostmsu]

Because the sun is still heating faster, than heat dissipates at 17:00.