Melted snow can show up a drugs farm - or poor insulation
Snow melting prematurely on a roof could be a clue that the house is being used as a cannabis factory, police say.
Officers in Leicestershire are asking residents to look out for homes where roof-top snow has melted more quickly than on neighbouring buildings.
They said cannabis factories were equipped with high-level lighting, which generates a lot of heat, causing snow and ice to melt.
The force said it hoped to use the cold weather to find more factories.
Drug find arrests
On Wednesday officers discovered more than 100 plants at a house in John Nicholls Street, Hinckley.
They found a further 200 at Hinckley Road, Leicester Forest East, on the same day.
One man has been arrested in connection with the find at Leicester Forest East, and remains in custody pending further police inquiries.
No arrests have been made in connection with the other find, but police say inquiries are continuing.
Sgt Mel Thomas said: "This is another clue that members of the public should be aware of.
"If the snow has melted from a neighbour's house when everywhere else still has a covering, it could indicate that the house is being used for growing cannabis."