Gusty winds
Wind is the natural movement of atmospheric air flowing generally parallel to the ground. The cause of wind is the horizontal difference in atmospheric pressure. The greater the pressure difference between two given points, the greater the intensity of the wind.
Wind direction is the direction from which the wind blows and wind intensity is the measure of wind speed. Wind intensity can be measured using various observational (empirical) and numerical scales. A widely used empirical scale is the Beaufort scale, while numerical scales are m/s, km/h and knots. The following table shows the correspondence between the Beaufort scale and m/s, km/h and knots.
Strong winds are generated in areas where a low barometric pressure system and a high barometric pressure system are combined. Typical examples in the Greek area are the combination of low pressures during the passage of a depression with relatively high pressures in the surrounding areas, or the occurrence of annuals (melemias), which are created by the combination of low pressures in the Eastern Mediterranean with high pressures in the Balkan region. Locally strong winds (bourines) are generated in areas affected by storms due to the strong pressure gradient generated.
Tornado
The tornado, or waterspout, is the most violent and destructive atmospheric phenomenon. A tornado is a powerful swirling column of air, usually projected from a storm cloud. The swirling of the air in the tornado column has low pressure at the center and rotates counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. Siphons are divided into land and sea siphons.
Dry land siphons are large-scale air vortices that extend from the base of a storm cloud to the ground surface, and their formation is due to high atmospheric instability. This instability is caused when cold, dry air in motion is over an area of warm air. Dry siphons can be accompanied by thunderstorms, rain and hail.
Waterspouts are smaller than land tornadoes, form below the storm cloud, and can reach the sea surface. However, there are also siphons that form above the sea surface without the presence of a storm cloud. Sea squalls occur more frequently in the tropics than in the temperate zones. The conditions for their formation are the same as for land siphons, with a diameter of up to 150 m and a lifetime of 10′-30′ minutes.
The horizontal extent of the tornado reaches up to 250m, and its speed of movement is relatively low (8-20m/s). The speed of the swirling column of air in the central area can reach 100 m/s, and in extreme cases, it can exceed 200 m/s. At the same time, the vertical movements of the air are also strong. The pressure from the periphery to the centre of the tornado shows a large drop and can reach 25hPa. The result of this decrease is the severity of the rotational movement of the wind in the siphon. The trajectory that a siphon travels is relatively short, 10Km, not missing the cases when the trajectory reaches 200Km and the period of its life is 4-5 hours. The passage of a tornado causes great destruction due to gusty winds and a large drop in atmospheric pressure.
According to researcher Dr. Michalis Sioutas (ELGA – Centre for Meteorological Applications, Thessaloniki), tornadoes can occur in any region of Greece. Based on his research, in recent years the majority of tornadoes have occurred in western and southern Greece, mainly in coastal areas. An average of 8 tornadoes (land tornadoes), ranging from moderate to major damage, and 10 sea tornadoes occurred annually. Tornadoes in Greece occur most frequently in July, September, November and December.
The following map shows the areas where tornadoes (land and sea tornadoes) and sea tornadoes occurred in Greece during the period 2000-2002. Their intensity is also given, as calculated in the study of Dr. M. Siouta based on the international TORRO scale (T0 to T10). WS indicates the occurrence of water siphons (Waterspouts).
Prepare for the Tornado
Before and during gusty winds
- Secure objects that may cause damage or injury if blown by the wind
- Fix any billboards you may have posted.
- Secure the doors and windows of your home or workplace.
- Avoid activities in marine and coastal areas.
- Avoid crossing under large trees, under posted signs and generally from areas where light objects (e.g. pots, broken glass, etc.) can become detached and fall to the ground (e.g. under balconies).
Storms
Thunderstorms are among the most violent atmospheric phenomena and are accompanied by heavy rain, strong winds with variable intensity and direction, which can reach 50 to 80km/h or even 100km/h, strong electrical discharges, i.e. lightning and often hail.
The duration of a storm is a maximum of two hours. The heavy rains of thunderstorms are capable of causing flooding.
A storm develops when the atmosphere is highly unstable (i.e., the upward movement of gas masses is favoured) and there is a large amount of water vapour in the lower parts of the atmosphere. Under these conditions, warm and moist air near the ground surface rises rapidly and cools down. The moisture present in the atmospheric mass condenses into ice crystals and hydrocarbons, resulting in the formation of massive clouds.
The development of cumulonimbus clouds (Cb) is the main feature of a storm. These clouds have a very large volume and a high vertical growth. Their peak can exceed 12 km. Their upper part almost always spreads out in the form of a limb, while their base is horizontal at a low height from the ground. Ice crystals are observed in their upper part.
Thunderstorms fall into three categories, depending on how they form, and these are air mass storms (local or thermal), orographic storms and frontal storms.
- Air mass storms (local or thermal)
These storms are the result of a) intense heating of the ground surface, resulting in strong upward movements and convergence on the ground surface of gas masses or b) the movement of cold gas masses over warm surfaces resulting in instability. In Greece these storms are mainly generated during the summer months over the continental areas. - Orographic storms
In this case, thunderstorms are created when a moist and unstable air mass is forced to rise over a mountain range, leading to cooling and the formation of storm clouds. In Greece, these thunderstorms are mainly formed over the western foothills of the mainland. - Frontal storms
Frontal storms form along warm and cold fronts. Their formation is dynamic, as warm air is forced to rise when cold air pushes beneath it. Cold front storms are more intense than warm front storms as the upward movement of warm air along the frontal surface is much more intense. Storms of this type are mainly generated in November-May and are associated with the arrival of precipitation from the Greek area.
How to estimate the distance to a storm?
- Measure the time between lightning and thunder in seconds. Divide the measured time by 3 to calculate the distance of the thunderstorm in kilometres.
- Take the necessary measures quickly before the storm approaches you. The distance is indicative as the storm can appear very quickly over the area you are in.
- Ασφαλίστε αντικείμενα, που μπορεί να παρασυρθούν από τον άνεμο ή τη ραγδαία βροχόπτωση και ενδέχεται να προκαλέσουν καταστροφές ή τραυματισμούς.
- Ελέγξτε τον τρόπο στερέωσης διαφημιστικών πινακίδων που τυχόν έχετε αναρτήσει.
- Ασφαλίστε τις πόρτες και τα παράθυρα.
- Μην κρατάτε ηλεκτρικές συσκευές ή το τηλέφωνο διότι ο κεραυνός μπορεί να περάσει μέσα από τα καλώδια. Αποσυνδέστε τις συσκευές τηλεόρασης από την κεραία και την παροχή του ηλεκτρικού ρεύματος.
- Αποφύγετε να αγγίξετε τις σωληνώσεις των υδραυλικών (κουζίνα, μπάνιο) καθώς συνιστούν καλούς αγωγούς του ηλεκτρισμού.
- Ακινητοποιείστε το στην άκρη του δρόμου και μακριά από δέντρα που ενδέχεται να πέσουν πάνω του.
- Μείνετε μέσα και ανάψτε τα προειδοποιητικά φώτα στάσης (φώτα έκτακτης ανάγκης) μέχρι να κοπάσει η καταιγίδα.
- Κλείστε τα τζάμια και μην ακουμπάτε σε μεταλλικά αντικείμενα.
- Αποφύγετε τους πλημμυρισμένους δρόμους.
- Καταφύγετε σε κτίριο ή σε αυτοκίνητο διαφορετικά καθίστε αμέσως στο έδαφος χωρίς να ξαπλώσετε.
- Προστατευτείτε κάτω από συμπαγή κλαδιά χαμηλών δέντρων στην περίπτωση που είστε μέσα σε δάσος.
- Μην καταφύγετε ποτέ κάτω από ένα ψηλό δέντρο σε ανοιχτό χώρο.
- Αποφύγετε τα χαμηλά εδάφη για τον κίνδυνο πλημμύρας.
- Μην στέκεστε πλάι σε πυλώνες, γραμμές μεταφοράς ηλεκτρικού ρεύματος, τηλεφωνικές γραμμές και φράκτες.
- Μην πλησιάζετε μεταλλικά αντικείμενα (π.χ. αυτοκίνητα, ποδήλατα, σύνεργα κατασκήνωσης κλπ.).
- Απομακρυνθείτε από ποτάμια, λίμνες ή άλλες μάζες νερού.
- Αν είστε μέσα στη θάλασσα βγείτε αμέσως έξω.
- Αν βρίσκεστε απομονωμένοι σε μια επίπεδη έκταση και νιώσετε να σηκώνονται τα μαλλιά σας (γεγονός που δηλώνει ότι σύντομα θα εκδηλωθεί κεραυνός), κάντε βαθύ κάθισμα με το κεφάλι ανάμεσα στα πόδια (ώστε να ελαχιστοποιήσετε την επιφάνεια του σώματός σας και την επαφή σας με το έδαφος) πετώντας τα μεταλλικά αντικείμενα που έχετε επάνω σας.
During a hailstorm
Take immediate precautions. Do not leave the safe area until you are certain the storm has passed. Hail can also be very dangerous for animals.
Snowfall / Severe cold
During the winter, snowfalls last from a few hours to a few days and are often accompanied by low temperatures and strong winds.
Snowfall may be local or affect a large part of the country. Usually, the heaviest snowfall occurs in the northern and mountainous regions of the country, where snow remains for most of the winter season.
A blizzard is considered a heavy snowfall accompanied by very strong winds, which drift the snow resulting in very low visibility.
Snow forms when ice crystals in clouds, where temperatures are below 0°C, begin to fall to the ground. If the air temperature is not far below zero, the outer surface of the ice crystals remains moist and so when they collide, irregularly shaped snowflakes, sometimes several centimetres long, are formed and fall slowly.
At much lower temperatures (e.g. in polar regions, at high altitudes, etc.), the crystals do not form flakes, but reach the ground in the form of small ice grains. Instead, higher temperatures will cause the flakes to melt, reaching the ground as rain or sleet.
Snowfall and low temperatures can severely disrupt daily life and cause serious problems in transport, agriculture and livestock farming as well as problems in electricity, water supply and telecommunications, especially in remote areas. Snowfall is often dangerous for both driving and walking. Most accidents during a snowfall involve transport accidents and pedestrian falls due to slipperiness.
Exercise stress and heart attacks due to excessive exercise are also two possible causes of deaths associated with heavy snowfall and low temperatures. The elderly, who live alone and often in poor living conditions, are also reported to have the highest rate of deaths from hypothermia or asphyxiation due to the use of inappropriate heaters, which emit carbon monoxide when burning. It is not uncommon for fires to occur in homes due to the use of alternative heating sources (lighting a fire without proper precautions, removing ashes without extinguishing them, operating heaters in inappropriate places in the home, etc.). Extinguishing a fire during such severe weather is very difficult, as water may be frozen in the pipes or it may be impossible for firefighters to reach the scene.
If you live in a mountainous or rugged area that has problems with snowfall
- Stock up on heating material and food for several days.
- Provide snow-clearing equipment (e.g. shovels).
- Διατηρείστε το ζεστό και παραμείνετε σε αυτό όσο μπορείτε.
- Μην αφήνετε τα παιδιά να βγουν έξω ασυνόδευτα.
- Φορέστε κατάλληλα ρούχα και παπούτσια.
- Ελέγξτε το δίκτυο ύδρευσης, τους σωλήνες και τον υαλοπίνακα του ηλιακού θερμοσίφωνα.
- Αποφύγετε την οδήγηση σε δύσβατες ορεινές περιοχές.
- Αλλάξτε πορεία αν είστε σε δύσβατο δρόμο και υπάρχει έντονη χιονόπτωση.
- Τηρείτε τις αποστάσεις ασφαλείας από τα προπορευόμενα οχήματα.
- Παραμείνετε στο αυτοκίνητο αν ακινητοποιηθεί. Τοποθετείστε στην κεραία του ραδιοφώνου ή σε άλλο εμφανές σημείο ένα ύφασμα με έντονο χρώμα ώστε να σας εντοπίσουν οι ομάδες διάσωσης. Ανάβετε τη μηχανή για 10 λεπτά ανά ώρα και διατηρείστε την εξάτμιση καθαρή από το χιόνι.
- Πηγαίνετε σε ασφαλές μέρος χωρίς να εκτεθείτε στη χιονοθύελλα.
- Ντυθείτε με πολλά στρώματα από ελαφριά και ζεστά ρούχα αντί για ένα βαρύ ρούχο και φορέστε ζεστές αδιάβροχες μπότες. Προτιμήστε ένα αδιάβροχο εξωτερικό ρούχο.
- Προσέξτε τις μετακινήσεις σας σε περιοχές όπου προβλέπονται χιονοπτώσεις.
- Χρησιμοποιήστε αντιολισθητικές αλυσίδες αν είναι απολύτως απαραίτητο να μετακινηθείτε με αυτοκίνητο. Είναι προτιμότερο να ταξιδέψετε κατά τη διάρκεια της ημέρας χρησιμοποιώντας κεντρικούς δρόμους. Ενημερώστε τους οικείους σας για τη διαδρομή που θα ακολουθήσετε.
- Προτιμήστε τα μέσα μαζικής μεταφοράς για μετακινήσεις στην πόλη.
Frost
Prepare for the Frost
- In areas where frost has formed, caution is required when driving. Be aware of the road conditions and have anti-skid chains.
- If you are moving on foot, wear suitable shoes to avoid injuries due to slipperiness.
In the water supply networks of residential buildings
- Find out where your home’s water meter (clock) is located and where the main and peripheral water supply switches are located.
- Check and make sure that the water main switches open and operate smoothly.
- Make sure that external pipes (e.g. solar water heater, balcony taps) are insulated, otherwise make sure they are insulated as soon as possible.
- Isolate or better yet, evacuate the solar water heater grid if you are going to be away for a long period of time during the winter. Set the home heating system to run automatically at low temperatures.
- Turn off the water supply to the solar water heater and drain the water from the system if you are at home during freezing temperatures, especially in the evening.
- Don’t waste water unnecessarily to remove snow and ice.
- Limit activities that require increased water consumption (washing machines, etc.).
- Find out if antifreeze has been installed in the solar water heater by the manufacturer or the installation specialist, in case of a closed circuit. Otherwise, obtain the appropriate antifreeze and ensure that it is installed.
- Check for leaks in the taps or flushes.
- Make sure that gutters on balconies and terraces are clear of leaves and debris and run smoothly.
When Frost Prevails
If the water mains freeze
- Immediately turn off the main water supply switch of the house and check the water meter. If it still works (“writes”) then there is a leak in the mains. Turn off the main supply switch and call a plumber.
- If you decide to defrost the tubes, start from the part of the tube near the switch so that the temperature change is gradual. If you do not get results contact a plumber.
- Check if electrical installations are wet or dangerous so that you can isolate them.
The above guidelines are general. For further instructions you can contact the local water supply authorities (DEYA, EYDAP, EYATH).
Hot weather
High temperature days are days when temperatures rise to high levels in the midday and early afternoon, but during the night temperatures drop considerably, so that the human body can take over and cope with the stress of high temperatures.
A heatwave, under the climatic conditions of Greece, is a period of at least 3 days during which temperatures in lowland areas exceed 37°C, and the average daily temperature is at least 31°C, i.e. the temperature does not decrease enough during the night hours (it does not fall below 25-26°C).
The effects on the population from high temperatures can range from simple discomfort, heat exhaustion to heat stroke which requires immediate medical attention. Most vulnerable are the sensitive groups of the population (children, elderly, chronic disease sufferers) and people working outdoors.
Episodes of high temperatures or heatwave are observed in Greece during the summer season, when warm invasion conditions are created. In these cases, warm air masses are transported from North Africa to our country raising the temperature to high levels. The areas which are usually most affected by high temperatures are Western Greece and the continental areas of central and southern Greece.
During days with high temperatures, the impact on the population may be worse if other aggravating factors, such as:
- The relative humidity of the air remains at high levels, reducing the ability to remove heat from the human body through the mechanism of perspiration.
- The wind intensity is low, making it difficult to dissipate heat from the surface of the skin (about 90% of the total heat transfer to the environment takes place through the skin).
- Air pollution combined with high temperatures is particularly harmful to vulnerable groups of the population. Usually the atmospheric conditions that create the high temperatures also favour the accumulation of air pollutants in the atmosphere.
- In large urban centres, high temperatures can create more difficult situations than in the countryside. Buildings and road surfaces accumulate large amounts of heat during the day and release it into the atmosphere at night, so that in the centre of large cities, even at night, the temperature remains high, exacerbating the feeling of high temperatures for residents.
- Avoid sun exposure and stay in shaded, cool areas away from crowded places.
- Avoid heavy physical work especially in areas with high temperature, lack of air and high humidity.
- Avoid walking for too long or running in the sun.
- Prefer light, comfortable and light-coloured clothes made of natural materials to facilitate ventilation of the body and evaporation of sweat. Choose a hat that ensures good ventilation of the head. Wear black or dark-coloured glasses with a special coating that protects against the sun’s reflection.
- Make sure your diet consists of light and small meals, with an emphasis on fruits and vegetables. Limit fats.
- Drink plenty of fluids (water and fruit juices). If you sweat a lot, add salt to your food. Avoid alcoholic drinks.
- Take lukewarm showers during the day and if necessary, place wet covers on your head and neck.
- Take care of your family members suffering from chronic illnesses (respiratory, cardiovascular, etc.). Consult their doctor for special instructions and for those taking medication.
- Avoid long journeys by public transport when the heat is at very high levels.
- Ντύστε τα όσο γίνεται πιο ελαφρά. Φροντίστε ώστε τα χέρια και τα πόδια τους να είναι ελεύθερα και να μην τυλίγονται σε πάνες.
- Φροντίστε να μην μένουν στον ήλιο μετά το μπάνιο στη θάλασσα και να φορούν πάντα καπέλο.
- Εκτός από γάλα συνιστάται η χορήγηση και άλλων υγρών. Συμβουλευτείτε τον παιδίατρο.
- Για τα μεγαλύτερα παιδιά, φροντίστε να πίνουν πολλά υγρά (νερό και χυμούς φρούτων) και να τρώνε περισσότερα λαχανικά και φρούτα και λιγότερα λίπη.
- Μετακινείστε τους σε δροσερότερους χώρους ή περιοχές (παραθαλάσσια ή σε βουνό), διότι το πολύ ζεστό και υγρό περιβάλλον αποβαίνει επικίνδυνο. Εναλλακτικά φροντίστε να παραμένουν στα κατώτερα διαμερίσματα πολυώροφων σπιτιών.
- Ανοίξτε το σπίτι τη νύχτα για να δροσίζει και κρατάτε το ερμητικά κλειστό τις ζεστές ώρες της ημέρας.
- Μην εγκαταλείπετε τα ηλικιωμένα μέλη της οικογένειας μόνα τους σε περιπτώσεις θερινών διακοπών ή πολυήμερης απουσίας σας από το σπίτι. Διαφορετικά εξασφαλίστε ένα άτομο για την καθημερινή τους φροντίδα.
General Instructions for Severe Weather Events
- Make sure you keep up to date with weather developments on radio and TV. The official sources of information are the National Meteorological Service (NMS) and the General Secretariat for Civil Protection.
- In case of emergency call alternatively: Police 100, Fire Brigade 199, Emergency Medical Services 166, European Emergency Number 112.
- Place the above emergency phone numbers in a prominent place in the house if your children are able to use them and make sure they know it.
- Help your children to memorise family details such as their surname, address and home phone number.
- Explain to all family members how and when to turn off the electricity, gas and water, how to use the fire extinguisher and how to call for help.
- Get essentials such as a first aid kit, fire extinguisher, torch and batteries, portable radio, etc.
- Take special care of children and the elderly.
As soon as the bad weather passes
- You are constantly monitoring official warnings or advice on radio and TV.
- Check your home and other assets to record any damage.
If you are moving
- Find out about the weather and the state of the road network.
- Depending on your destination, consider the type of weather phenomena you may encounter (snow, frost, hail, rainfall, etc.).
- Change your travel schedule to avoid the peak weather.
- Travel during the day, preferring the main arteries rather than the inaccessible and deserted roads.
- Inform your family and friends about the route you will take.
- Do not ignore the instructions of the General Secretariat for Civil Protection, the weather reports of the National Weather Service and the instructions of local authorities, such as the Traffic Police, the Coast Guard, the Fire Brigade, etc.
- Check the condition of your car before every move.
- Equip the car with the necessary means of coping with severe weather phenomena (anti-slip chains, antifreeze, umbrellas, raincoats, galoshes, torch, first aid kit, etc.).
- Wear suitable clothing if you are going to move on foot.
- Take care when walking to avoid injuries due to slippery pavement and sidewalks or due to falling objects caused by excessive wind or hail.
- Prefer public transport for your commute.
- Stay calm and patient. Panic aggravates the situation.
- Facilitate the work of the authorities.
