500 mb height anomaly
Alex Henson | Premium last edited by
Not something that is necessary but Tropical tidbits has a 500mb height anomaly which can be pretty useful in predicting upcoming weather trends. A similar effect can be done by using the wind layer at 500mb heights and geopot height but the one on tropical tidbits adds a nice coloration too, sending a link for reference.
Any parameter (temperature, wind, 500hPa height…) shown as ´anomaly’ is a comparison of the current forecast with the the normal value at same day or week or month. The normal value is the mean value over the 30 last years. It could be less than 30 years, but this climate reference is averaged on a long period of time.
That would suppose that Windy store or get the data of the normal values of the considered parameter over all points of whole globe.
The weather services of each country computes generally this normal data, but to get a whole and global picture of the normal data, this is done by reanalysing the past climate.
ECWMF provides anomaly data using what they call climate models on a significant period of time.
Example with SST
For 500hPa heights it seems ECMWF only provides weekly anomaly: