Limpar vs. clarear vs. estiar
While limpar, clarear, and estiar can all describe the weather improving or calming down, they focus on different sensory aspects of the change: the disappearance of clouds, the increase in brightness, and the cessation of rain, respectively.
Limpar
A2This verb translates literally to to clean, and when applied to weather, it means the sky is becoming free of clouds, fog, or haze. It implies that the blue sky or the stars are becoming visible again after being covered.
O céu limpou completamente depois da tempestade.
(The sky cleared up completely after the storm.)
Espero que o tempo limpe para podermos ir à praia.
(I hope the weather clears up so we can go to the beach.)
A neblina limpou assim que o sol nasceu.
(The fog cleared as soon as the sun rose.)
Finalmente o horizonte limpou e conseguimos ver as montanhas.
(Finally the horizon cleared and we managed to see the mountains.)
Clarear
B1This verb is related to claro (light/bright) and means to brighten or to become lighter. In a weather context, it describes the moment when the dark, gloomy jagged clouds of a storm give way to light, or simply when the day begins to break.
Parece que o tempo vai clarear antes do meio-dia.
(It looks like the weather will brighten up before noon.)
O céu estava escuro, mas agora começou a clarear.
(The sky was dark, but now it has started to get lighter.)
Assim que a chuva passou, o dia clareou novamente.
(As soon as the rain passed, the day brightened up again.)
Esperamos clarear um pouco para sair de casa.
(We waited for it to get a bit brighter to leave the house.)
Estiar
B2This verb specifically refers to the action of the rain stopping or pausing. It does not necessarily mean the sky has turned blue or bright; it simply means water has ceased falling from the sky, sometimes only temporarily.
Vamos correr para o carro quando a chuva estiar.
(Let's run to the car when the rain lets up.)
Choveu a manhã toda, mas finalmente estiou.
(It rained all morning, but it finally stopped.)
Aproveitamos que o tempo estiou para passear com o cachorro.
(We took advantage of the rain stopping to walk the dog.)
Se não estiar logo, o jogo será cancelado.
(If the rain doesn't stop soon, the game will be canceled.)
Summary
To summarize the differences regarding weather: use limpar when the clouds go away and the sky becomes blue; use clarear when the darkness lifts and it becomes brighter; and use estiar specifically when the falling rain stops.