High clouds that appear in the form of mares' tails usually indicate what weather event?

High clouds that appear in the form of mares' tails are known as cirrus clouds. These wispy clouds often signal an approaching weather system, particularly a warm front. When mares' tails are observed, it typically indicates that moisture is being lifted into the upper atmosphere, leading to the development of clouds and precipitation as the warm, moist air rises over cooler air.

Furthermore, the formation of these high-altitude clouds usually precedes a change in weather, specifically suggesting that rain may occur within the next 24 to 36 hours as the warm front moves in. This makes option B the most accurate choice.

In contrast, the other options do not align with the characteristics associated with cirrus clouds. For instance, an approaching cold front would more likely lead to the formation of lower clouds and storms, rather than high clouds like cirrus. High pressure typically presents clear and stable weather conditions, which does not correlate with the presence of mares' tails. Lastly, while immediate thunderstorms can occur under certain conditions, cirrus clouds are generally a sign of a more gradual weather change rather than an indicator of imminent thunderstorms. Thus, the presence of high clouds such as mares' tails is most reliably linked to the approach of a warm front and the potential