Develop a simple script counter

Hi, I need a script on my website which reads whether a certain city in the UK has received rainfall in the last 24hrs if not the counter adds 1 day, if it has the counter resets to zero. i.e the counter records how many days since rainfall.

Potential API
http://environment.data.gov.uk/flood-monitoring/doc/rainfall#api-requests

Output should be similar to this:

http://www.rainchester.com/

My website is shopify.