When should a train operator be particularly alert to guard against sliding wheels on a yard track?

A train operator should be particularly alert to guard against sliding wheels on a yard track at the beginning of a light rain because this is when conditions can become slippery due to the combination of dry tracks and freshly fallen rain. The moisture can cause the dust and accumulated debris on the track to become slick, leading to a higher likelihood of wheel slippage, especially when the locomotive is accelerating or negotiating turns.

While snow and extreme heat can create slippery conditions, they do not typically pose the same immediate risk of sliding as light rain on dry track. Snow requires accumulations to become hazardous, and extreme heat primarily affects the rails themselves rather than causing immediate traction issues for the wheels. During track switching, while care is needed, the primary risk factors differ from those presented by weather conditions. Therefore, the beginning of a light rain is particularly critical for train operators to exercise caution to prevent wheel slipping.