These winds are very unlikely. The small area of damage they might produce would probably not be recognizable along with the mess produced by F4 and F5 wind that would surround the F6 winds. Missiles, such as cars and refrigerators would do serious secondary damage that could not be directly identified as F6 damage. If this level is ever acheived, evidence for it migh only be found in some manner of ground swirl pattern, for it may never be identifiable through engineering studies. Before a tornado hits, the wind may die down and the air may become very still.
Tornadoes generally occur near the trailing edge of a thunderstorm.
It is not uncommon to see clear, sunlit skies behind a tornado. It could be your basement or, if there is no basement, a center hallway, bathroom, or closet on the lowest floor. Keep this place uncluttered. If you are in a high-rise building, you may not have enough time to go to the lowest floor. Pick a place in a hallway in the center of the building.