What type of precipitation may indicate freezing rain at a higher altitude?

Ice pellets, also known as sleet, are solid forms of precipitation that occur when raindrops freeze before reaching the ground. This type of precipitation forms in a specific atmospheric profile where warmer air is sandwiched between layers of cold air.

As precipitation falls through the warmer layer, it initially starts as rain. Upon entering the colder layer closer to the surface, it can freeze into ice pellets. If the surface temperature is at or below freezing, these ice pellets can indicate the potential for freezing rain conditions, given that the air at the surface is still cold enough for the rain to freeze upon contact with surfaces.

Snow, sleet, and rain are each associated with different atmospheric conditions. Snow typically forms in colder temperatures where the entire atmospheric column is below freezing, resulting in ice crystals that fall as snowflakes. Rain is simply liquid precipitation without the presence of ice pellets. Therefore, when considering the indication of freezing rain conditions at a higher altitude, ice pellets are the clearest indicator due to their unique formation process between temperature layers, contrasting with the purely liquid or solid forms of the other choices.