Nature has no bad weather
Weather phenomena can be divided into two types – global and local. Global weather phenomena, such as the change of seasons, are well known and studied.
For example, we all know that the best time for a cruise in the Mediterranean starts from about mid-late April and ends around mid-October. By the end of October, the weather in the Mediterranean starts to get worse. On the contrary, in the Caribbean, the best time for a yacht trip starts in December and ends around May.
However, local weather is well known for its inconstancy. A sudden rough sea or a storm with thunderstorms can be an extremely unpleasant surprise, especially during a long passage in the open sea. In order to avoid encounters with unpleasant weather conditions, yachtsmen use meteorological sites, data from coastal weather stations, etc.
One of the most reliable ways to know if a storm is coming soon is the so-called CAPE index.
What is the CAPE index?
As you might have guessed, CAPE is an acronym. So, CAPE (Convective Available Potential Energy) or convective instability potential energy is an indicator of atmospheric instability. The index indicates the amount of energy in the atmosphere that can eventually be converted into thunderstorms or storms.
The higher the CAPE, the more unstable the atmosphere in that region is, making it more likely to cause severe weather. In more technical terms, high CAPE values indicate more intense convection within the cloud.
Increased convection rates lead to the formation of cumulus and cumulonimbus clouds. These clouds are known to cause heavy precipitation and thunderstorms.
CAPE Index Values
Like other atmospheric indices, the CAPE index has its own scale. However, this scale does not use points, but actual convection values. Here is an example of such a scale:
- <0 J/kg — steady state (cumulus and cumulonimbus clouds, heavy rainfall, thunderstorms, etc. are impossible)
- 0-1000 J/kg - slight instability (with sufficient moisture in the air, cumulus clouds, cumulonimbus clouds, light rainfalls are observed, thunderstorms are possible);
- 1000-2500 J/kg - moderate instability (cumulonimbus with showers, thunderstorms);
- 2500-3500 J/kg - strong instability (thunderstorms, strong in places, hail, squalls);
- ≥ 3500 J/kg - very strong instability (strong and very strong thunderstorms, tornadoes)
These values can be seen on the corresponding maps or tables on weather websites.
How to use the CAPE index?
We have received a general theoretical basis, but how to use the knowledge we have received? Most modern weather sites support the function of displaying or visualizing the values of the CAPE index. Let's use the Windy.com site.
To get a map with the index displayed, select the "More layers" option just below the list of main layers. In the window that opens, find the "Clouds, aviation" section, which contains the CAPE index. In the default settings, areas with a high CAPE index are marked in bright color, while areas with a low index are marked in a colder shade or without color at all. An example is shown in the screenshot below.
At the time of writing (evening of November 5, 2024), a zone of high instability has formed between Mallorca and the northern coast of Africa, with an index of over 2500 J/kg. In this zone, right now, there is a high probability of a strong storm with thunderstorms and squalls.
The direct use of the index in travel planning is the same as in weather preloading. Places and areas where the index value is high should be avoided and the route should be planned with an eye on the CAPE value. If the values are high for the entire region where the cruise is planned, it may be better to postpone the event for a few days or weeks until the weather stabilizes.
Why should you use the CAPE index?
Unlike many other available parameters, the CAPE index is relatively stable. It almost never tends to change values quickly (from zero to a hundred in an hour), so it can be checked several times a week. Due to this, you can rely on the index indicator for longer-term planning.
What to do if the CAPE index is high?
The actions are generally the same as when preparing for a normal storm. The best option is to change the route and try to find shelter in a safe marina or port. Anchoring should be done carefully and be vigilant, because the weather may deteriorate in the near future.
Of course, the CAPE index should not be your only reference. Use all available means when planning a cruise or long-distance passage to obtain the most reliable weather forecast.
New video on the Interparus channel🎥
Yachting innovations are always cool. In a new video on the Interparus channel, Sasha Goron will talk about the yachting innovations that Le Grand Pavois 2024 brought to us. Enjoy watching❤️
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07.11.2024
