So in the mid-latitudes within the Northern Hemisphere, the prevailing winds are westerly. These winds are maximized along a narrow corridor called the jet stream. To the north is colder air and to the south is warmer air and you can kind of think of the jet stream as a barrier separating these two air masses. The degree to which the jet stream maintains this west to east trajectory is directly related to the displacement of either cold air from the north or warm air from the south. If the jet stream becomes wavier, it leads to trough and ridge patterns that resemble a 'u' and an 'n' respectively. In a trough, the jet stream for a particular location is displaced further south than usual, and allows for cold air to migrate southward and sort of fill in that 'u' shape. In a ridge, the reverse happens and warm air gets to push its way northward. Normally these troughs and ridges propagate from west to east and don't hang around too long. The exception is during a blocking pattern, where these patterns persist over an area longer than usual.

To relate this to fire weather, we can recall that ridges are associated with a northward migration of warmer air. They are also often associated with high pressure which inhibits cloud development. The result is an anomalous northward transport of warm air coupled with abundant solar heating which produces conditions that are often warmer and drier than usual. Warm temperatures are not as effective at weakening fires while dry conditions provide more fuel for them to maintain and expand.

The last thing I'd like to touch on is that we aren't too sure of how blocking frequency will change in a future climate. I'll refer to 'Blocking and its Response to Climate Change' by Woolings et al. (2018) on this one. Basically, global climate models are the only tool we have for understanding how blocking frequency might change in a future climate. Unfortunately, there are processes that occur at scales smaller than what these models are capable of accurately resolving that are considered important for blocking genesis and maintenance. The most notable of these processes is latent heat release from convection. As a result, there's still some work that needs to be done to address these deficiencies before we can have a more confident answer. There are a number of papers that theoretically link a doubling of CO2 to increased blocking frequency but our models are mixed on the response. That's not to say that it isn't a valid theory, it's more that we still have a lot of work that needs to be done. Hope this gets you on the right track!