Which type of precipitation is least likely to produce IFR weather?

Hail is least likely to produce Instrument Flight Rules (IFR) weather conditions because it typically occurs during severe thunderstorms, which are often accompanied by heavy rain, strong winds, and lightning rather than low visibility or low ceilings associated with IFR conditions. Hail is a solid form of precipitation that falls from cumulonimbus clouds, and while it can indicate turbulent weather, it doesn't necessarily lead to low visibility or low cloud ceilings.

In contrast, rain can lead to reduced visibility depending on its intensity and duration. Snow can accumulate and also cause low visibility, particularly in blizzard conditions, while fog, which consists of tiny water droplets suspended in the air, can drastically reduce visibility, making IFR conditions more likely. Therefore, hail, while it can be dangerous and indicative of severe weather, does not inherently create the same low visibility conditions as the other types of precipitation listed.