Why frost can still occur in late Spring

11 May 2026 12:26 PM

With a cooler northerly flow bringing lower than average temperatures for the time of year and the risk of overnight frost for some, we explore why frost can still occur late into Spring.

As days grow longer and sunshine strengthens, frost is often the last thing people expect. Yet frosts can and do still occur well into late spring, including May.

While these events are usually short‑lived and localised, they can catch gardeners and growers by surprise and help explain why frost may still be referenced in weather forecasts at this time of year.

Understanding how frost forms, and the conditions that favour it, helps explain why cold nights can still develop even as daytime temperatures rise.

What is frost?

Frost forms when temperatures at the ground or in the air fall to or below the freezing point of water. It is possible for frost to occur even when daytime conditions feel mild, particularly under the right overnight conditions.

There are two key types of frost to consider. Air frost occurs when the air temperature falls below freezing, typically measured at around one metre above the ground. Ground frost happens when the temperature at the surface drops below 0°C, even if the air temperature slightly above remains positive.

Gardens and crops are most commonly affected by ground or grass frost, which can damage tender plants despite thermometer readings staying just above freezing.

Clear skies and rapid cooling

One of the most important ingredients for frost is a clear night sky. After sunset, the ground loses heat as it radiates energy back into the atmosphere and out to space. Cloud acts like a blanket, trapping some of this heat and slowing the cooling process.

On clear nights, heat escapes more efficiently, allowing the ground and objects close to the surface to cool quickly. Even during late spring, when days are noticeably warmer, clear skies overnight can still allow temperatures at ground level to fall below freezing.

READ MORE: May Bank Holiday weather extremes

Light winds and cold air pooling

Wind plays a key role in determining how cold it becomes overnight. Light winds allow colder, denser air to settle near the ground, forming a shallow layer of cold air where frost can develop. Stronger winds mix the air, drawing in slightly milder air from above and reducing the chance of frost forming at the surface.

This is why frost risk is often highlighted on calm nights, particularly beneath areas of high pressure, which typically bring lighter winds and clearer skies.

Ground cooling and grass frost

In May, ground frost is more common than air frost. At this stage of the year, the ground has not yet accumulated as much stored warmth as it does later in summer. This means that similar air temperatures can lead to colder ground conditions than they would in early autumn.

Different surfaces also cool at different rates. Short grass, soil and vegetation lose heat more quickly than materials such as concrete or roads, which retain warmth for longer. As a result, grass frost can occur even when nearby paved surfaces remain frost‑free.

This type of frost can develop during late spring and even early summer, particularly after a clear and calm night, and is often localised to rural areas.

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