Halloween and Bonfire weather

A big change on the way?

Storms Austen and Boelo have brought disruption recently, and at the time of publication, an unsettled pattern persists. Atlantic disturbances continue to bring spells of rain and strong winds. However, later this week a significant shift is likely to begin as high pressure builds from the south. While it promises a period of more settled weather, several caveats and uncertainties remain:

1. How long will it remain settled?

2. Where exactly will the high pressure centre itself?

Point 1 highlights the uncertainty inherent in medium range forecasting: model skill drops beyond 5 to 7 days, and even ensemble guidance, designed to quantify risk and highlight the most probable outcome, can shift from run to run.

Point 2 is a crucial distinction. The exact positioning determines whether we end up with a "dirty high" feeding mild, cloudy Atlantic air around its flank, or a high centred  over the UK or to the north, that allows clearer skies and cold air to take hold, bringing crisp days and overnight frosts.

The most likely scenarios currently

By 31st October (Halloween), forecast models suggest high pressure cells will be centred to the northeast and southwest of the UK. Although high pressure will increasingly influence conditions, Atlantic disturbances may still push rain into parts of the country. Pinpoint precision remains impossible five days out, but generally wetter weather is more likely across the north and northwest, while a weakening frontal system sinking southeastwards could bring patchy outbreaks of rain elsewhere. 

The chart below from the ECMWF IFS model illustrates this mixed picture across the British Isles.

The headline takeaway: check the short-range forecasts if you have outdoor plans on Halloween. While a good deal of dry weather is likely, patchy rain or drizzle cannot be ruled out, which could make for a rather damp and murky evening for trick-or-treaters! 

High pressure strengthens for Bonfire Night

There is currently strong agreement among numerical models that high pressure will become the dominant feature across the UK next week, controlling the weather around Bonfire Night. The chart below shows the most probable synoptic setups on 4th November, based on ECMWF IFS ensemble clusters. Both scenarios (A and B) feature blocking high pressure firmly in charge.

What can we expect on the ground? Both scenarios heavily favour predominantly dry conditions. However, because weak remnant fronts could still push through, patchy drizzle or light rain cannot be entirely discounted. Forecast confidence also remains low regarding how widespread the frost and fog risk will be, though the strength and positioning of the anticyclone make cold, foggy nights significantly more probable than average.

Drier and more settled weather on the way

In summary, there is a strong signal for a much more settled and drier pattern to establish as high pressure builds across the UK. Key details to monitor over the coming days include:

1.  The potential for patchy rain or drizzle affecting some regions on Halloween

2. Whether the high pressure delivers crisp, clear skies with frost and fog, or locks in a mild, cloudy "anticyclonic gloom" around Bonfire Night