Can't the weather radar detect a tin roof nearby?

Yes, according to the weather radar detection network. Iron roof is a typical fixed ground object, which will reflect, scatter or absorb electromagnetic waves emitted or received by radar, thus causing fixed ground clutter. If the iron roof is close to the radar or located in an important area within the radar detection range, it will seriously affect the radar detection effect and data quality. So the weather radar detected that there could be no tin roof nearby.