What air temperature conditions would likely lead to the formation of ice pellets?

The formation of ice pellets, also known as sleet, primarily occurs under specific atmospheric conditions where warm air is situated above a layer of cold air. In this scenario, precipitation in the form of rain falls from the warm air aloft and passes through the colder layer beneath. As the raindrops descend, they encounter temperatures below freezing in the cold air layer, leading to their transformation from liquid to solid while still in transit. This process results in the formation of ice pellets upon reaching the ground.

In contrast, the other options do not align with the conditions necessary for ice pellet formation. Cold air from surface updrafts would not facilitate the warm-over-cold structure needed for this type of precipitation. Warm, stable air layers without cold air below would lead to a different precipitation type, such as rain, rather than ice pellets. Lastly, constant temperatures across different air masses do not create the necessary temperature gradient for the raindrops to freeze into ice pellets during their descent. Therefore, the presence of warm air aloft with colder air below is essential for the formation of ice pellets.