Cloudbase & Meteograms
Can someone please help explain this? Between 3 and 6 cloud base reported as 3400 meters but the meteogram shows an awful lot of cloud low level. What are we to believe?
TZ Administrator last edited by
@Edgington Hi, this is probably because of different calculation of both values.
Cloud base is directly taken from ECMWF parameter called "ceiling". It is height (above model orography i.e. AGL) of cloud layer covering more than 50% of the sky. It estimates height where you can expect "significant clouds". Detailed description is here: https://confluence.ecmwf.int/display/FCST/43r1+new+parameters%3A+Ceiling
On the other side the grey meteogram is calculated from relative humidity. It can be explained as a distribution of water in the atmosphere. The height in the meteogram is in pressure levels. km/ft values are only rough estimation and they are AMSL. I admit that this can be confusing.
Possible explanation of the difference: There could be signigicant humidity (almost 100%), so there are drawn clouds in meteogram, but the cloud coverage according to ECMWF is less than 50%, so the ceiling is considered to be higher.
In such strange case it is better to look also in cloud maps, which can give you better overview. However, if the location is in the mountains then the values can be misleading, because model orography is very rough.
csabatatar Moderator Pilot last edited by
@tz In this case maybe it would be better to have "Ceiling" word despite of the currently used "Cloud base", if the data is ceiling data that Windy got directly from ECMWF. Because Cloud base means the first cloud layer that can be also lower extent than 50%, in aviation it can be written like FEW (1-2/8 octas) / SCT (3-4/8 octas), in the METARs at the airports we can find these informations. Regarding the Ceiling, it can be from BKN (5-7/8 octas) to OVC (8/8 octas) types, because these two are covers more than 50% of the sky, so either BKN or OVC is depicted in a METAR this will be a "Ceiling". And this difference between Cloud base and Ceiling is very important according to my opinion.
I think maybe in this case it would not be so confusing, if you would change its name to "Ceiling" on Windy Meteogram.
What do you think about that? @TZ @Korina @ivo