Extreme cold, cold snap, cold snap… These terms are very different, what they really mean

Frost, negative temperatures, very low feelings… Right now, it's cold. With falling temperaturesa large part of the territory is, for this Monday January 13 and Tuesday January 14, 2025, placed on extreme cold yellow vigilance by Météo France.

Like heat episodes, cold episodes are characterized according to their intensity, extent and duration. For example, we distinguish between a simple cold snap and a cold snap, the consequences of which are more serious.

So how do you tell the difference between all these names? A quick reminder of this glossary.

Cold snap

« The cold snap can occur over a period from October to May,” indicates La Chaîne Météo.

This phenomenon is characterized by a brief period of 1 to 3 days with temperatures 2 to 4°C below average. In these conditions, we can speak of a cold snap.

Furthermore, it may only concern one region or extend to a larger part of the country.

Cold snap

« Cold waves can occur over the period from November to March, with a greater probability of occurrence during the months of January and February,” explains La Chaîne Météo.

It is a phenomenon characterized by “its persistence, its intensity and its geographical extent”, according to the definition given by Météo France. It is illustrated in particular by “frequent days without thaw in the heart of winter and widespread and severe frosts in the morning”, describes La Chaîne Météo.

In short, it is a lasting and extended episode of cold lasting at least three days. To really speak of a cold spell, several criteria are needed. Namely: that the average temperature drops below -2°C at least once (according to the national thermal indicator*) and that it does not rise “sustainably (more than 2 days)” above 0.9°C.

The cold snap episode is interrupted as soon as we cross the 2.2°C mark.

The Weather Channel speaks of “very poor temperatures[…]generalized to several regions, or even to the entire country in certain situations.

But Météo France adds that the phenomenon can also be characterized “on the scale of a region when the episode lasts at least two days and the temperatures reach values ​​significantly lower than seasonal norms for the region concerned”.

Drops in temperature, episodes of cold…

If the conditions are met, we will speak of a cold snap. “Conversely, if one of them is not, we will tend to speak of a cold snap,” continues La Chaîne Météo. And for the rest?

With regard to these definitions and these precise criteria, certain drops in temperature cannot therefore be qualified as a cold snap or wavelack of intensity or duration for example.

Sometimes the temperature just isn't abnormally low. On the contrary, remarkably low temperatures can be observed, but for a short time: it may be a cold peak or a short-lived cold episode.

In summary, it can be cold without it being part of a specific meteorological phenomenon.

Vigilance in extreme cold

This is one of Météo France's vigilance measures, just like the nine others (heatwave, storms, etc.) which signal the potential dangers of a meteorological situation for one or more departments. The aim is to remind citizens of the advice established by public authorities to protect themselves.

In this case, extreme cold vigilance aims to inform the authorities and the population about cold waves likely to have a health impact, explains Météo France.

It has existed since 2004. As with other weather phenomena, there are four levels (green, yellow, orange and red) which each involve different measures corresponding to the seriousness of the event and a given situation.

To trigger this vigilance, the criteria take into account the climate of each region. They require values ​​significantly lower than seasonal norms for the region concerned.

Once characterized by Météo France, the severe cold allows the authorities to activate (at the departmental or regional level) the “very cold” plan. A provision which makes it possible to offer more accommodation to the most vulnerable and to strengthen the 115 service.

More and more rare

As for extreme heat,episodes of extreme cold can be dangerous for your healthcausing risks of aggravation of certain pathologies, hypothermia or frostbite, etc.

With global warming, these episodes will, according to Météo France, be shorter, less intense, and increasingly rare.

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