I would install the buienradar node in node-red.
You can get the values, run it through a change node with jsonata to average the data
example flow (requires this node to be installed)
[{"id":"7cba216f9bea0f5d","type":"buienradar","z":"f8b839d1b6352dff","name":"","station":"6215","interval":"60000","forecast":true,"x":314,"y":96,"wires":[["3f42dc5d8b3da22e","daf8e598e8677e04"]]},{"id":"3f42dc5d8b3da22e","type":"change","z":"f8b839d1b6352dff","name":"get average","rules":[{"t":"set","p":"payload","pt":"msg","to":"payload.$average(**.kansregen)","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":502,"y":96,"wires":[["0873602b9d3d8a09"]]},{"id":"7a52cd85ee1cfb8e","type":"debug","z":"f8b839d1b6352dff","name":"yes","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":786,"y":72,"wires":[]},{"id":"0873602b9d3d8a09","type":"switch","z":"f8b839d1b6352dff","name":"<10 ?","property":"payload","propertyType":"msg","rules":[{"t":"lt","v":"10","vt":"num"},{"t":"else"}],"checkall":"true","repair":false,"outputs":2,"x":642,"y":96,"wires":[["7a52cd85ee1cfb8e"],["a6cd85a8efca5712"]]},{"id":"a6cd85a8efca5712","type":"debug","z":"f8b839d1b6352dff","name":"no","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":786,"y":120,"wires":[]},{"id":"4398cdd8acb0f2ed","type":"inject","z":"f8b839d1b6352dff","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"","payloadType":"date","x":156,"y":96,"wires":[["7cba216f9bea0f5d"]]},{"id":"daf8e598e8677e04","type":"debug","z":"f8b839d1b6352dff","name":"yes","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":478,"y":192,"wires":[]}]