Starting in May of 2022, Vaisala now offers our users a choice of weather data from either MERRA2, which is made by NASA, and ERA5 which is made by ECMWF.

The MERRA2 weather data source is what Vaisala has been using previously. Requesting MERRA2 as the weather source will keep your data files and data sources entirely consistent with what you have downloaded from us previously. The weather data that we provide with MERRA2 is

• wind speed
• wind direction
• air temperature
• air pressure
• total precipitable water vapor

The ERA5 weather data source is a new offering that we are excited to be providing our customers. When you select ERA5, you will receive more weather information. The weather data that we provide with ERA5 is

• wind speed
• wind direction
• air temperature
• air pressure
• total precipitable water vapor
• albedo
• total precipitation
• snowfall (precipitation as snow), as water equivalent (see note below)
• snow depth on the ground, as water equivalent

ERA5 Precipitation and Snow

Occasionally, the hourly values for precipitation as snow exceed the total precipitation in the same period by a small amount. This is expected and is an artifact of how the data is stored and transmitted from the source (ECMWF).

To reduce storage and bandwidth requirements, the source data is packed into GRIB messages in a way that introduces a small error. Total Precipitation and Snow are each stored independently from each other and have different packing errors. ECMWF has a good explanation of how they do GRIB packing for weather data here.