Synchronicity of deaths

What explains the unprecedented rise in deaths in the spring of 2020?

On TTE, we've been interested in deaths and their reporting. Some of our most viewed and shared posts are on this topic (See here, here and here).

But something has been bothering us for quite some time - the unprecedented rise in deaths in the spring of 2020. 

To look at the issue, we used the ONS data on registered deaths for 2020 that report monthly by county (data available here).