A lack of snow on a roof helped police in Leicester uncover what they called a "significant" cannabis factory.
Reports of suspicious behaviour led officers to look in Aylestone, where they noticed only one house in a street had no snow on the roof.
On Thursday, the Montrose Road property was raided and about 300 cannabis plants and a growing system were found.
Officers said the systems gave off a lot of heat and the lack of snow helped confirm suspicions about the house.
No-one was in the house. No arrests have so far been made but police said inquiries were at an early stage.
Pc Chris Gerrard said the house had been badly damaged by work to set up the cannabis factory.
He said: "The landlord has been left with a lot of clearing up to do.
"By closing this drugs factory we have disrupted a significant criminal enterprise, and stopped a large amount of drugs from reaching the streets of Leicester."