September has brought fluctuating temperatures across the United Kingdom, with a recent warm and humid spell pushing daytime highs to around 26 degrees Celsius in many areas. Although not reaching heatwave levels, the conditions have evoked a brief return of summer as high pressure systems draw warm air from the southwest. This pattern is expected to be short-lived in northern regions, where winds and rain are forecast to return soon. Meanwhile, parts of southern England may begin the day with autumnal mist and fog.

Warm and humid weather during this time of year can sometimes trigger thunderstorms. One of the most notable events occurred on the night of September 21, 1935, when a severe hailstorm swept across south Wales and parts of England. The storm was characterized by intense thunder and lightning, combined with torrential rain and damaging hail.

According to contemporary reports, the thunderstorm over south Wales lasted for more than two hours, illuminating the countryside with near-continuous lightning flashes. The violent winds accompanying the storm uprooted trees, while hail accumulated in deposits up to four feet deep, blocking roads and creating significant disruption.

As the storm progressed eastward into England, it intensified further, expanding to a width of approximately ten miles. Northamptonshire was particularly affected, with witnesses describing the storm clouds taking on an unusual grey-green hue punctuated by frequent lightning. Such coloration is sometimes noted in powerful thunderstorms, including those associated with tornadoes and large hail events in the United States.

In Northamptonshire, the hailstones reached extraordinary sizes, with many comparable to hens' eggs. One hailstone measured six inches (150 millimeters) in circumference and weighed about four ounces (113 grams). The force of the hail caused widespread damage, puncturing roofs and breaking windows, leading to water ingress and flooding inside homes.

What distinguishes the 1935 storm as historic is the remarkable length of its hailstorm path. The storm traveled some 208 miles, beginning near Newport in south Wales and continuing to Mundesley on the Norfolk coast in East Anglia. This track remains a record in the UK for the longest continuous hailstorm documented.

The 1935 event serves as a stark reminder of the severe weather phenomena that can develop during transitional seasons and highlights the potential for significant damage even outside of summer’s peak thunderstorm period.