White Christmas Forecasts: What It Takes for Snow on Christmas Day

The Naked Scientists investigate what a white Christmas really means, how forecasts are made, and whether the UK can expect snow this December. Experts explain the essential ingredients for snow, the Met Office definition of a white Christmas, and how ocean patterns and climate trends shape Christmas weather.

Introduction: What is a white Christmas?

Chris Smith introduces the topic in partnership with UK Research and Innovation, with meteorologist Aisling Creevey outlining how forecasts are produced and what low pressure means for weather fronts.

"One of my favourite weather instruments is a barometer, and the barometer tells me about pressure change." - Aisling Creevey

Snow ingredients and formation

Snowfall requires cold air and moisture, with condensation nuclei helping ice crystals form and grow into snowflakes as they descend through the atmosphere.

"It needs to be cold, obviously, and you need moisture." - Peter Gibbs

Defining a white Christmas

The Met Office uses an observational criterion: a single snowflake observed at an official station within the 24 hours of Christmas Day qualifies as a white Christmas.

"The official definition from the Met Office simply requires that a single snowflake be observed at one of the official Met Office observing stations." - Aidan McGibbon

Forecast horizons and regional variability

Forecasts are probabilistic and look for trends weeks ahead. The emergence of high-pressure patterns in computer models could make a drier, colder Christmas more likely, even if exact snow timings remain uncertain.

"There are emerging signals from the computer modelling. Higher pressure is becoming more likely for the Christmas period." - Aidan McGibbon

Ocean and climate influences

Len Shaffrey explains the Atlantic Meridional Overturning Circulation and how oceans move heat toward the north, shaping winter climate in Europe and the UK, with potential cooling if circulation slows under climate change.

"The oceans move heat from the tropics to the poles and have a huge influence on the climate we have in Europe and in the UK." - Len Shaffrey

Forecasting technologies and the future

AI-driven forecasting is transforming weather prediction by pattern recognition in large data sets, complementing traditional physics-based models for both atmosphere and oceans.

"AI has revolutionised weather forecasting, picking out patterns that the human brain cannot see." - Len Shaffrey

Closing outlook

Looking ahead to Christmas, the experts suggest a trend toward less wet and milder conditions, with the possibility of a crisper, drier, and perhaps frosty Christmas, though exact snowfall remains uncertain.

"It does look likely that it'll be less wet and less mild." - Aidan McGibbon