Posted on: 2014-03-01 17:22:56 by KenR USA

isotherm 0C forecasts on MeteoFrance - strange?

In the last year or so, MeteoFrance started doing something I love – posting forecasts of the altitude of freezing temperature for different times of day for each mountain group and ski station. Problem I've discovered: The Isotherm 0 Centigrade altitudes for the ski stations often do not make sense to me.

Maybe I just don't get it. As I'm writing now, forecast for a ski station at about 1100m altitude shows a forecast for Dimanche - Soiree (Sunday - evening) of Temperature 1C/0C and Isotherm 0C altitude of 2000m.
Now to my non-weather-expert mind, if it's 0C at 2000m in evening, then it ought to be significantly warmer than 1C at 1100m altitude. (In early morning I could believe there's an inversion, but not likely in evening).

Another day last week at sunset in similar location w similar Isotherm 1800m forecast, I was actually there on location at sunset, and observed refreezing on the snow surface at 1300m and my car's thermometer at 1200m reported 1C.


... Another Isotherm forecast ...
From the "Bulletins d'estimation du risque d'avalanche" page for the same mountain area – also on the MeteoFrance website.
Isotherm for Dimanche Apres-midi (Sunday afternoon) forecast altitude 1000m.
(The MeteoFrance ski station forecast of Isotherm for Dimanche Apres-midi is 1500m.)

Maybe if I were a weather expert I'd know two different definitions of Isotherm 0C ?

Any ideas?