On Jul 19, 8:46*pm, Pete L wrote:
On 18 July, 19:14, Tudor Hughes wrote:

* * Have a look at this:

* * * * * * * * *http://weather.noaa.gov/weather/current/SAWH.html

Ushuaia (the most southerly town in the world) is on the the south
coast of Tierra del Fuego with mountains to the north. *This is a warm
airstream, but even so......
* * * * *There appears to be an error in the recent dewpoints, which I
think should be negative. *The whole thing may be an error but I don't
think so.
* * * * The July mean is 1°C and normal weather is wind and sleet.

Tudor Hughes, Warlingham, Surrey.

Guess you have seen what has happened since? Midnight last night
(19th) temp 15 dew pt -5 with NW wind now just 18 hours later -0.1
snowing and a 20kt SW'ly. Back to normal now!

Indeed it is - these things never last long. The clue was in
the Punta Arenas ascent which showed a huge inversion at about 3000
ft. The air from above the inversion must have been dragged down the
lee side of the mountains and probably only affected a small area. I
have been monitoring this part of the world (Ushuaia, Río Gallegos and
Punta Arenas) for some time and the first two of those are prone to
Föhn effects but the wind direction needs to be fairly precise. All
three are surprisingly (?) dry, Río Gallegos only receiving about 220
mm per year.

Tudor Hughes, Warlingham, Surrey.