As ambient temperature drops, the cooling tower’s capacity for heat rejection actually skyrockets. A tower designed to cool 100°F water down to 85°F on a 95°F summer day can easily overcool that same water to 40°F or lower on a 20°F winter night. While this sounds like a performance gain, it leads to the "Ice Paradox": The better the tower performs thermally, the faster it self-destructs structurally.

Here it is, the line you should memorize and stencil onto the tower control panel:

Most operators assume that cold weather is a blessing for cooling. After all, if it’s freezing outside, the tower doesn’t have to work as hard to shed heat, right? This is the single most dangerous misconception in wet cooling tower management.

From the Cooling Tower Handbook, 4th Edition

Watch the fan exhaust. A healthy winter plume is wispy and dissipates quickly. A dangerous plume is thick, heavy, and drifts horizontally without rising. This indicates the water is entering the cold air basin at a temperature too low to melt the ice forming upstream.