Why:
AirTemperatureData["LESA", DateObject[{2020, 1}], Mean]
and
AirTemperatureData["LESA", {DateObject[{2020, 1, 1}], DateObject[{2020, 1, 31}]}, Mean]
give different outputs?
Thank you
Guillermo
Try...
AirTemperatureData["LESA", {DateObject[{2020, 1, 1}], DateObject[{2020, 2, 1}]}, Mean]