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What is a cold snap?

With its freezing temperatures and shortened days, winter is not many people’s favorite season. At the heart of this season, cold waves, which can paralyze entire populations and sectors, are feared.

Cold snap or cold wave: what’s the difference?

These two meteorological phenomena are not to be confused. The cold snap occurs in winter, generally from October to May, over a short period of 1 to 3 days with temperatures 2 or 4°C lower than the seasonal average.

In the same way as a cold snap, a cold wave is characterized by abnormally low temperatures compared to seasonal norms and a duration of several days or weeks, in the period from November to March. But a cold snap is an extreme weather phenomenon that requires different conditions:

  1. The observed temperatures must be at least 5°C lower than the average. They must drop to -2°C during the day and be characterized by days without thawing.
  2. The cold spell must last at least 3 days in a row with a national average temperature below 0.9°C.
  3. These temperatures must concern several regions or even an entire country.

The biggest cold waves date from the winters of 1956, 1963 and more recently 2010. For the latter, it is the Center region which was particularly affected with -15°C in Orléans and -13°C in Châteaudun.

This lingering cold air mass is typically associated with severe winter weather conditions. The temperatures are freezing, the winds are strong, the snowfall is heavy, the ice is omnipresent… The consequences are significant on daily life, agriculture, energy, transport and even the health of the populations concerned.

What are the different types of cold waves?

A cold snap occurs when atmospheric circulation is disrupted on a large scale. Then, several weather conditions are observed during this period as well as different sources of cold air masses. There are 4 main types of cold snap:

  1. Synoptic. A synoptic cold spell is associated with anticyclones which favor the descent of cold, dry air and therefore cause extremely low temperatures.
  2. Advice. This cold wave results from the horizontal movement of a mass of cold air from the polar or arctic regions towards more temperate zones and which stagnates over large areas.
  3. Occluded. It occurs when a cold air mass is trapped between two warmer air masses. Cold air is trapped in the center causing temperatures to drop and also causing precipitation.
  4. Overflowing. Cold air spills beyond usual boundaries and extends into lower latitudes. This phenomenon affects warmer regions that are not ordinarily subject to such conditions.

These cold waves can arrive from the north, that is to say the polar and arctic regions, but also from Siberia or Russia, which are closer. There are also oceanic cold waves which occur when masses of cold air coming from the sea move towards coastal regions. These cold spells can be accompanied by humidity and precipitation.

What are the characteristics of a cold snap?

A cold snap is characterized by abnormally low temperatures compared to the season, particularly with negative temperatures at night. Unlike a brief drop in temperature as is the case with a cold snap, a cold snap persists for an extended period of time. It is frequently accompanied by strong winds which increase the feeling of cold.

A cold snap favors heavy snowfall, the formation of frost and black ice, etc. Since atmospheric conditions are unstable, other weather phenomena may occur such as snowstorms or blizzards.

What causes cold waves?

  • The weakening of the polar vortex. The polar vortex is a phenomenon of polar wind vortices (North and South), which exists permanently, but varies in intensity depending on the seasons. It is a shield for the Earth because it absorbs these powerful winds and regulates temperatures at polar latitudes. When it weakens, it can allow cold air in lower latitudes to reach us and thus cause cold waves.
  • The ripples of the jet stream cause movements of air masses from the polar regions to lower regions. The jet stream is a fast and intense air current. It circulates in the atmosphere at high altitudes, usually between 10 and 15 kilometers above the Earth’s surface. These powerful winds move from west to east at high speeds, often exceeding 100 km per hour. The jet stream forms at the boundary between polar and tropical air masses, where there is a significant temperature difference. Although the jet stream does not directly impact the formation of cold waves, it influences their movement, intensity and duration.
  • La Nina generally participates in colder winters. This climate phenomenon is characterized by colder than normal sea surface temperatures in the equatorial Pacific Ocean.
  • The great lakes in certain regions can also contribute to the formation of cold waves. Cold air passes over warmer lake waters, absorbs heat and moisture, cools further, and causes heavy snowfall.

All of these weather patterns can create blockages in the atmosphere and therefore lead to stagnation of cold air masses. The mountains in certain places also accentuate this blocking phenomenon.

What is the impact on health and society?

A cold snap is an extreme weather situation that can have significant consequences on people’s daily lives.

Impact on population health

Since a cold spell lasts several days or weeks, prolonged exposure to freezing temperatures can lead to loss of body heat and therefore risk of hypothermia.

The extremities of the body are particularly vulnerable. Fingers, toes, noses and ears are put under strain and susceptible to developing frostbite.

Cold air irritates the respiratory tract and increases the risk of respiratory illnesses. Homeless people are particularly vulnerable during these cold waves. Emergency shelters are being set up with distribution of clothes, blankets and other essential supplies.

Impact on transport and the economy

Transport may be disrupted with delays, cancellations, accidents and driving difficulties. Accumulating snow and ice can damage power lines and infrastructure, causing power outages. As cold spells lead to increased demand for energy for heating, electricity networks can also be overloaded.

These transport, energy and snow problems impact all types of infrastructure, particularly businesses and public services. The latter may be forced to close while waiting for the cold snap to pass or to adapt working conditions (teleworking, staggered hours, etc.). Slowdown in production and financial losses are possible. Agricultural crops can also be heavily damaged by cold, frost and snow, which has consequences for livestock or harvests.

Impact on fauna and flora

Cold spells weaken plants and animals and can lead to their destruction. In cases of intense cold, watercourses freeze and cause flooding due to ice jams. The ice formed creates an obstacle and blocks the natural flow of a river. Water builds up and since it cannot circulate normally, it eventually overflows. This rising water causes flooding of the surrounding banks and possibly the homes located there.

When ice traps vegetation.  Icon Sports / Jan Woitas
When ice traps vegetation. Icon Sports / Jan Woitas PictureAlliance / Icon Sport

In order to best cope with these cold waves, the authorities monitor weather conditions to warn the population in advance. All emergency services are mobilized to manage road accidents, power outages and health problems. During a cold snap, you need to stay informed, keep in touch with your neighbors, avoid unnecessary travel and stock up on water and food. In the event of power outages, flashlights, batteries, candles and blankets will also be welcome.

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