Snow is expected to fall across high regions in Wales and Scotland on Tuesday, according to weather forecasters.
The cold temperatures and heavy rainfall mean especially wet areas may well see some snowflakes, though it is not expected to settle.
Experts are forecasting some distinctly unseasonal snow
Emma Corrigan, a forecaster at the Met Office said: "At the moment we've got quite cool air across the UK and through tomorrow as the weather system pushes northwards potentially where you get really quite heavy rain you may see summer flakes of snow.
"It's only where you get the really heavy rain so the main risk will be Wales, mainly over the hills but not just the hills depending on how heavy the rain will be and then potentially up towards the Peak District and Pennines, that sort of area."
Paul Mott, a forecaster with Meteogroup, the weather division of the Press Association, said snow would only be in higher regions.
He said: "There is a small chance of a little bit of wet snow perhaps over the Welsh hills tomorrow particularly in south Wales but it will be pretty high up. Any snow would be probably above about 400m or 500m elevation so I don't think any populated areas are likely to see any snow tomorrow."
Snowfall in May is rare but not unheard of, according to Ms Corrigan.
She said: "You wouldn't necessarily expect May to be cold and it snow, but it's happened in the past so it's not out the realms of possibility basically.
"It is fairly rare to get it in May but it's happened before. In 1979 in early May there were four consecutive days of snowfall."
Mr Mott said tomorrow would also be be a noticeably cold and wet day for much of Britain, with a high chance of flooding and temperatures below average for May.
He said: "The main thing about tomorrow is it's going to be a cold and very wet day really particularly in the south west so there's likely to be some localised flooding over the south west of England and also into the midlands, particularly tomorrow night.
"It's going to feel very cold for the time of year I think, temperatures in parts of south west England and south Wales probably not much higher than about 6C or 7C tomorrow, and the average for this time of year would be nearer 15C so temperatures well below the seasonal average."