A difference between reference time and update time
Each model has a different update time and it could be confusing what connection does it have with the update time.
Here is the explanation:
- Reference time - is the time when a model starts a new forecast block.
It consists of:
Initialisation - data are entered into the model, this creates Initial conditions (initialisation time) and then model starts calculating conditions.
Assimilation - normalisation on data and assembling data for computation.
Computation - calculating the future atmospheric rates of change in time increments.
Data extraction - extracting data into regular forecast intervals.
Data storage - data are stored and written in accessible format.
Data postprocessing - special postprocessing routines
For example model ECMWF has an update interval 12 hours (or 6 hours interval for Premium users), that means the first reference time will be 00:00:00Z (Zulu time) and second one 12:00:00Z.
- Update time is time between the reference time and the actual update.
The whole process of data computation takes approximately from 8 to 9 hours.
So for ECMWF model the update times are 07:15:00Z and 19:15:00Z.
See the exact update times here - When and how often are the weather data updated?.
Where to find info about reference and update time:
Thanks Korina, a lot easier to understand now :-)
But, then it is something wrong by NEMS! When I look on it, comparing models, I see big time difference between reference and update data!(?)
Hello, please see this post about update times - https://community.windy.com/topic/3340/when-and-how-often-are-the-weather-data-updated. There is nothing wrong with NEMS model.
if you look on the "reference time" for NEMS, for example hier, https://www.windy.com/multimodel/44.107/15.326?44.108,14.248,8
you'll see for METEOBLUE (NEMS) :
Reference time: 2020-02-25
Or, I don't understand something?
Thanks! All is clear now! I supposed the forecast was fresh, the mistake was only in one place, concerning reference time...
One picture says more than 1000 words!
Mark_Marsh last edited by
Thanks, for share this article
Md Eyasin Ali last edited by
@Korina India & Bangladesh post see
@Md-Eyasin-Ali Hello, what kind of information are you looking for?
Md Eyasin Ali last edited by
@Korina Thanks for this post.
I'm interested in the GFS model in particular.
When a new grib file is released by the NOAA, how long does it take Windy to show it ? Is it pretty much instantaneous (a few minutes) or does it take longer ?
vsinceac last edited by
You have full info about currently selected model via "i" control (screenshot).
About GFS: it is computed every 6h by NCEP/NOAA, starting from 00h UTC. On NCEP/NOAA site, it is available about 3h40m after each runtime and it may take a while to download and ingest it on server side: 1 full grib2 file (all parameters/levels) for one date/time validity is about 500 MB in size...
@vsinceac Thanks a lot for your reply. When you say "it may take a while ..." do you have a rough estimate of how long that is ? Are we talking something like 1h or much less ?
Also, I'm curious about the file size that you mentioned, 500MB : do you know how big is the grib2 file, covering the whole 16day forecast ?
vsinceac last edited by vsinceac
There is no 1 grib file for all validities: each of them comes in a single, dedicated grib file. There are 209 grib files for each runtime, from f000 to f384, where the number is in hours related to runtime. From f000 to f120, validities are provided every 1h, then every 3h up to f384.
You can check e.g. this one (runtime today at 06hUTC, validity for 07hUTC, 515.1 GB, all params/levels): https://nomads.ncep.noaa.gov/cgi-bin/filter_gfs_0p25.pl?file=gfs.t06z.pgrb2.0p25.f001&dir=%2Fgfs.20211014/06/atmos.
Here you can select the day, the runtime, the forecast, then optionally only partial parameters/levels/coverage to download: https://nomads.ncep.noaa.gov/cgi-bin/filter_gfs_0p25.pl?
Download time of course depends on many factors:
- internet speed/latency/bandpass/etc. (it may be also regulated sometimes by NCEP/NOAA itself)
- one can download only part of available grids (parameter/level) in a grib2 file (size to download would be smaller)
- I don't know if Windy downloads all 209 validities (size to download would be smaller)
- full size of 209 grib2 files for a runtime is about 110 GB
- for an average download speed of 30 MB/s from NCEP/NOAA servers (which is not easy to obtain e.g. from Europe), you should download all grib files of a runtime in about 1h
Then I guess Windy servers spend also some time to ingest the downloaded grib2 files before being able to serve map data layers to client side.
@vsinceac Thanks a lot for such a thorough reply. Slowly, thanks to people like you, I understand more and more about the details of these weather updates.
FYI, my interest in the "precise" timing of Windy is because I play an e-sailing game (called Virtual Regatta) and it uses real world weather data (GFS model, only wind speed and direction).
So, for example, when the 00z file is released (@3h40 UTC), the game's weather starts to update (takes around 2h) and often, it is interesting to look at Windy but I wanted to know if what Windy shows is still the old (18z) data or already the new one (00z) and when/how it goes from one to the other.
Again, thanks for your reply.