Clicking on NOAA’s radar images gives you weather that ranges from 5 minutes out of date to around 70 minutes out of date. Ever wonder why such a range and why they’d give us weather images that are so old?
A little while back, I was working for a major retailer and had the opportunity to see how Content Delivery Networks (CDNs) were used in the real world, and just what sorts of problems they caused. It turns out that NOAA uses a CDN called Akamai and that they’ve mis-configured it so that static content and quickly changing content are all cached for the same time rather than allowing the dynamic content to be handled specially. To top that off, their complaint email address is uninterested in resolving the problem. In the several years since I noticed the solution, they have improved the most local radar images so that they are only caching about 3 times longer than they should and they have still not implemented an update trigger system that cause the CDN to get new content as soon as it is available.
There is good news. Due to the simplistic way NOAA is using their CDN, we can force the CDN to poll for updated content just for us by adjusting the URL slightly. The full national radar loop is normally accessed via http://radar.weather.gov/Conus/full_loop.php, but by changing that to http://radar.weather.gov/Conus/full_loop.php?x=38, where the “38” is the current minute then the image will update every 10 minutes on the 8s. The radar is still slightly out of date, but only because it takes a few minutes for NOAA to actually process the data and build the images for the Web and not because of CDN caching problems. This works because Akamai sees the ?x=38 part and considers the complete URL to be different and therefore polls NOAA for updated data. Adding ?x=38 (again 38 is just an example, use the current minute) to the end of any noaa.gov or weather.gov URL that should update but doesn’t, will resolve the problem.
If you’d like the problem fully resolved, contact your congressman and tell them that NOAA is wasting money by updating their weather images but not pushing those updates to Akamai so that you can see them.