As far as we know, there are no current weathers in GEFS-online.
But you have the wind! And the time simulation (But the sky doesn't turn anything)
Wind[]
The wind can be set in the options page in game, click "Weather"
First tick the box "Wind blows: ⬜"
Then you can select the wind speed (max. 60 kts)
and you can change the direction.
Time[]
The time can be set in the options page in game, click "Weather"
First tick the box "Enable time of day illumination: ⬜"
Then you can set the time, but DO remember that the time you set follows the Universal Time! (UTC)