Is it necessary to fast the thirtieth day of Sha‘ban if the weather is cloudy and the crescent moon could not be sighted?

"Yawm al-Shakk" (Day of Doubt) is the last day of Sha'ban, concerning which there is doubt as to whether it is part of Ramadan. Fasting on it is forbidden due to the Prophet's (peace be upon him) saying: "Fast when you see it [the new moon] and break your fast when you see it, and if it is obscured from you, then complete the number of Sha'ban as thirty." And due to the saying of Ammar ibn Yasir: "Whoever fasts on the day concerning which there is doubt has disobeyed Abu al-Qasim (the Prophet, peace be upon him)." This has been used as evidence for the prohibition of fasting on this day, and this is the soundest of opinions. However, if the Imam commands fasting on it, one should break the fast secretly without showing it openly.