# Problem with FRZ ALT curves

• @TZ
Freezing altitude curves (isohypses) do not agree with the map.
It seems that the curves are "too smooth".

• @meteo-gr Hi! Yes, all isolines are smoothed.

• Maybe the smoothing factor should vary per layer. Thank you for suggestion!

• I adjusted the colors on the map, so the 900m to be "black"
and it is not in accordance with the 900m curve.

• Ok, I tested it, but it takes too long to compute, so we will not implement finer isolines now.

• @tz Hi, what is strange for me is the freezing altitude above mountains like the Alps. The map shows a freezing altitude close to 0m, when the local weather forecast indicates a freezing altitude of 2000m to 2300m at the same time. Does it mean that windy shows the distance from the ground and NOT the altitude of the isotherm 0°C?
Then I cannot display the freezing altitude in meter, but only in feet. Is it a bug?

• @idefix37
A possible explanation:
the model takes into account the surface temperature
(let say -13C on a location with altitude 2.000 m)
then computes frz alt by using normal lapse rate (6.5°C/km).
So, the result is frz alt = 0 m.
At noon, as the surface temp. rises to e.g. -7C , the frz alt rises to 1.000 m.

• @meteo-gr
I understand what you mean and may be you are right.
I have looked to iso 0ºC maps on other websites. Some show isolines and on the Alps the isolines are about 2000m because at the moment the temperature is very mild. Some other show colour range for the iso 0°C and, same, on the Alps, the colour corresponds to 2000m.
But on the map from ICON Europe, there is a cross hatched area over the highest parts of the Alps with the legend « Cross hatched area : iso 0°C < indicated value (iso 0°C under the ground of the model) ».
Isotherm 0°C SE of France - ICON Europe
How can we explain that? It could be the reason why on Windy the isotherm 0°C is at the moment at an altitude of 100 ft over the Mont Blanc when it should be at 6000 ft?

• @meteo-gr
I understand what you mean and may be you are right.
I have looked to iso 0ºC maps on other websites. Some show isolines and on the Alps the isolines are about 2000m because at the moment the temperature is very mild. Some other show colour range for the iso 0°C and, same, on the Alps, the colour corresponds to 2000m.
But on the map from ICON Europe, there is a cross hatched area over the highest parts of the Alps with the legend « Cross hatched area : iso 0°C < indicated value (iso 0°C under the ground of the model) ».

How can we explain that? It could be the reason why on Windy the isotherm 0°C is at the moment at an altitude of 100 ft over the Mont Blanc when it should be at 6000 ft?