Thread by @mikarantane

Summer is approaching in northern extratropics and with summer comes the heatwaves.

Although it's still April, a major summer-like heatwave will hit Spain this week. Temperatures are forecast to rise close to 40°C which would be unprecedented for April. #AprilHeatwave

The dynamic development of the heatwave is worth highlighting.

Blocking high acts like a stone in the river by causing a split of the jet stream and the occurrence of a double jet situation.

As a side note, the synoptic situation reminds me of the recent paper by @syn_efou et al. who found that the increasing trends of western European heatwaves are to linked more persistent double jet situations:

nature.com/articles/s4146…

However, the most worrying aspect of the heatwave is that it comes when a large part of Spain is already suffering from drought.

You can easily see how the terrain is much browner this year than a year ago in April.

Imagery from NASA Worldview.

So the incoming heatwave will dry the soils even more, forming a well-known positive soil moisture feedback. Thus, a larger fraction of solar radiation is consumed to warm the air which exaggerates the heatwave magnitude.

nyaspubs.onlinelibrary.wiley.com/doi/10.1111/ny…

The latest extended range forecast by ECMWF indicates that warm and dry conditions would continue in SW-Europe in the coming weeks.

This is bad news for agriculture which is already in a trouble with the drought.

charts.ecmwf.int/products/exten…

Finally, every heatwave in the current climate is of course worsened by human-induced climate change.

This does not mean that the heatwave is caused by climate change: it means that temperatures will rise higher than they would have risen without climate change.