I think the locals would be more efficient in forecasting weather, and external aids are not necessary. When we grow old, our joints would act as our radar. Before it rains, the joints would start to ache due to arthritis. The more severe the pain, the more serious is the rain.
These are my interpretation of the weather forecasting stone:
Stone is wet – Rain (It could also mean the kids are using it as target for practising their shooting skills with their water guns.)
Can’t see stone – Foggy (It is also true in USJ 11, Subang Jaya – this is where I live. Apparently, it is reported as one of the highest incidence of dengue fever. At times, when Subang Jaya Municipality does the fogging, it is really foggy. Not only the mosquitoes will suffocate and die, anyone who goes into the “cloud” would suffer the same fate. So, whenever the residents heard the sound of fogging machine drawing near in the evening, the residents would dash to close all windows and doors – that includes me – leaving the Aedes mosquitoes still in the house, if any, unscatched.)
Swinging stone – Windy (Runners could accidentally hit the stone, which is a prelude to “hitting the wall”.)
Stone jumping up & down – Earthquake (The dogs would jump and pull the stone thinking that it is the potato.)
Stone gone – Tornado (In local context, most likely, the stone is gone because someone has stolen it thinking that it is a magical stone that brings good luck.)