Snow/ice detection

I have a spot on my front sidewalk where melting snow causes water to drip on the front step and sidewalk, where it promptly freezes and becomes a hazard. Salt/ice melt is useless because the dripping water washes it away.

I bought some heated mats designed for melting snow/ice from sidewalks and stairs, and they're plugged into a z-wave outlet. It's easy enough to turn the mats on/off through HA or Google Assistant, but I'd love to take it a step further and make it fully automatic.

Looking for ideas as to how to detect water/ice, or some other condition that would be suitable for triggering an automation to turn the mats on/off.

I've considered using predicted or measured precipitation from a weather entity, but this icing problem can occur on a sunny day when the snow on the roof is melting, but the sidewalk is below freezing.

Temperature alone doesn't seem like it would work, because if the air temp is cold enough, there's no snow melt, and thus nothing dripping onto the sidewalk.

Ideas?

UPDATE:

I've settled on the following automation, which seems to be doing what I want.

• if the temp is below 40, I cycle the mats on for an hour, off for an hour. This has kept any roof-melt from freezing on the sidewalk
• using OpenWeatherMap, if current or forecast condition is "snowy" or "snowy-rainy", I turn the mats on.
• every hour that the mats are on due to "snowy" or "snowy-rainy", I add an hour to a helper timer that is in a paused state
• if conditions change from "snowy" or "snowy-rainy", I unpause that timer. Once it expires, I turn off the mats.

We're under the gun for a record-breaking snowfall here tonight/tomorrow. Picked up about 5 inches overnight last night, and the front sidewalk is perfectly clear.