If we know in advance whether there will be heavy fog tomorrow. Where can I watch it?

The most authoritative and accurate thing is to go to the website of the Central Meteorological Observatory.

Meteorological disaster early warning

Weather reality

Strong convective weather forecast

1-3 days precipitation forecast

High temperature smoke forecast

Cooling, gale and dust forecast

typhoon

Typhoon real-time path display

These are all available. You can see them as long as you find your city.