Base rate: an all-day fog in Istanbul in late spring almost never happens
Counted from Istanbul airport weather reports, 1996 to 2024: between April and October there was not one day with fog for most of the daytime. Any fog at all in the daytime: 0.2 percent of May days. For 25 May to 15 June (the modern calendar dates of the 1453 events) 0 all-day fogs in 593 days. Thunderstorms are common (10 percent of days from 20 May to 20 June); hail at the station is rare (1 day in 869).
How it connects
This clue from nature supports this hunch
The 1453 omens were made by the volcano base rate: such a fog almost never happens in late spring
This clue from nature is a clue for
The mystery eruption of 1452/53 and the omens at the fall of Constantinople
This clue from nature we read it in
Istanbul Ataturk airport (LTBA) weather reports 1996 to 2024, Iowa Environmental Mesonet archive
This clue from nature came from this step
Checked the Constantinople omens of May 1453 against the sky and the weather