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)
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.
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)