Introduction: Local winds in any area are caused by a combination of factors. The predominant factor will normally relate to current meteorological conditions as measured on the synoptic scale, i.e. nationally or continentally. However others are localised factors which can generate micro-climatic conditions in sometimes very restricted locations. In general terms synoptic conditions provide the background meteorological scenario for a wind’s generation, and local situations produce more detailed and various micro-wind effects which can be short-lived or long-lasting, and can affect areas ranging from part of a small valley to an extensive plain.
In order to understand local winds in detail it is important to have some background knowledge of the factors which can combine to affect them. These are considered first on a global and general scale, and later with reference to specific localities and winds.
Global Factors
Horizontal and Vertical air movement.
Movements of air occur both horizontally and vertically on a global and local scale. Both types of movement are inter-relational to an extent, and occur because of a combination of factors.
1. Horizontal movement is caused by a combination of pressure gradient force, Coriolis (earth’s rotational deflective) force, centripetal acceleration and frictional forces.
Pressure Gradient Force:
This is the motivating force1 which generates a movement of air away from an area of high atmospheric pressure to one of relatively low pressure - exactly as when a balloon or tyre bursts. Lines of equal pressure on a weather map (synoptic chart) are known as isobars, and although it might be expected that air will move straight from a high pressure area to a low, there are other forces which prevent air moving directly in this way, perpendicular to the isobars, the main one being the Coriolis force (see below).
As in the case of contour lines on a relief map, on a synoptic chart a steeper pressure gradient will be shown by closer isobars, and this will lead to faster air movement - wind.
The continuing changes of pressure which cause this air movement have the main contributing effects on sea level weather conditions on a synoptic scale. They only occur in the lower levels of the earth’s atmosphere - the troposphere. Above the troposphere, air movement tends to be much more free and less variable.
Coriolis Force:
This is the deflective force which is caused by the rotation of the earth. There is an apparent deflection of all moving objects, including air, to the right in the northern hemisphere, and to the left in the southern hemisphere. Thus all air which is moving from high to low pressure will tend to be deflected to the right or left, depending on the latitude of the place concerned. The amount of deflection is greater at the poles, and zero at the equator.
Centripetal Acceleration:
The effect of the Coriolis Force on air movement from high to low causes winds to have a curving path. For any body to follow a curved path there must be an inward acceleration towards the centre of rotation.1 This is often referred to as a centrifugal force which operates outwards.
For example, in a northern hemisphere low pressure system (depression), air will tend to move in towards the point of lowest pressure, deflected to the right by the Coriolis force, therefore rotating anti-clockwise (the gradient wind). The difference between the Coriolis force and the pressure force gives the level of centripetal acceleration inwards.
Similarly, in a northern hemisphere high pressure system (anticyclone), air will tend to move outwards from the point of highest pressure, in a clockwise direction, balanced between the same two forces.
Frictional forces:
Below about 500 metres above sea level, on flat terrain, friction begins to decrease the velocity of the wind. Thus wind speeds tend to be more constant and liable to acceleration over sea areas, and levels of friction tend to increase over land, and particularly over areas of high relief.
2. Vertical movement of air is caused by the main heat source (the sun). Air which is heated at sea level expands and rises through the lower atmosphere. As it rises it cools and begins to diverge, i.e. spread out. Eventually the air will become cool and heavy enough to sink, and again when it reaches sea level it will diverge. Thus vertical circulation cells are produced, generating wind at sea or ground level.
Global Scale:
In the above way, around the world there is a continuous vertical movement of air, with ascent over areas of higher temperature and a convergence of air at sea level to replace the rising air. Converging air at higher altitudes descends and eventually diverges again at sea level, becoming part of the movement which replaces the rising air - thus completing the circulation cell.
This vertical movement occurs on a global scale causing a general ascent of air over the equator and descent at approximately 30 degrees of latitude. The general tendency therefore over France, is for a movement of air from the south, as part of the divergence at 30oN, which is deflected to the right by the Coriolis Force, forming a prevailing south-westerly wind. This is the most common wind direction in SW France, a result, therefore of the above factors rather than local effects.
Local Scale:
On a more local scale, vertical movement can occur on a clear day near to a coast, generated by the fact that the land surface will tend to be warmer than the sea by day, and cooler by night. Thus air movement will tend to be onshore at sea level during the day, rising over the land - diverging - and sinking over the sea; and offshore at night, with a reversed vertical circulation. These local wind patterns are known as Land and Sea Breezes, and they do not affect areas far inland.
Local Winds - Causes.
The basic causes of wind patterns on the global scale form the basis for all air movements around the world. However, on the more local scale, these global factors have local conditions superimposed upon them, sometimes causing patterns of air movement which only affect a relatively limited area. As these patterns produce essentially local conditions, sometimes even on a micro scale, they are often given local names.
All winds will be affected by diurnal temperature changes - as in the case of Land and Sea Breezes (above). Generally, and in normal conditions, wind speed will be at its least at about dawn, at which time there will be little or no vertical movement of air, and the free moving upper air will have no bearing on surface conditions, except perhaps in the appearance of any clouds it may be carrying. With little or no vertical movement of air, there is little other than general global and synoptic conditions to generate surface winds.
Hence when there is a gentle or no global pressure gradient, air conditions will tend to be still in morning and evening.
Conversely, local wind speeds will be greatest between about 1300 and 1400 hours, the time of greatest incoming solar radiation, and therefore also the time of greatest vertical air movement. This vertical movement will draw in converging air horizontally, causing the greater surface air movement, and this can affect a local area even if there is no global wind generation.
Relief features have a distinct effect on surface air movement, both in their ability to divert airflow and in the local mountain and valley winds which they are able to generate.
Mountain and valley winds:
During warm afternoons, expanding air which is constricted within a valley will tend to move up the line of the valley. This movement produces valley winds which are generally very light, but can in some cases work in conjunction with anabatic winds which move upslope in situations where valley slopes are being heated at a greater rate than the valley floor. Air which rises to the upper valley sides in this way will flow along the upper valley side and eventually return to the valley floor to complete the circulation cell.
The speeds of winds such as this will reach a maximum at about 1400 (the time of greatest solar heating).
At night there is a reverse process by which colder, denser air will sink down the valley sides into the valley floor and along down the valley. This air movement is known as a katabatic wind. If the lower valley eventually opens out onto a plain, this cool air can spread out to lower the surface temperature across the plain. It can also be the cause of frost hollows in hill and mountain areas, as well as on lowlands. This effect is most marked just before sunrise, and can lead to dramatic visual features, particularly in autumn and spring.
An example of this is when cold air collects in a field where it is contained behind and below the hedge line. If the temperature of this trapped air cools below the dew point (the temperature at which condensation of water vapour occurs) a mist will be created within the field up to the level of the hedge line.
Mountain Barrier winds:
Many of the subtleties of Mountain Barrier winds do not affect the local wind regimes of SW France, but one affect is relevant and that is the so called föhn effect, which causes the föhn winds of the northern Alps and Caucasus Mountains of Eurasia, and the Chinook of the western plains of N. America. This effect could occur to a limited extent when winds descend from the Montagne Noir to the Aude valley and the Plain of Languedoc, and also as air moves down from the higher parts of the Corbières to its valleys and the coast.
When air rises it cools through expansion at a rate known as the adiabatic lapse rate. The environmental lapse rate is, on average, about 0.6oC per 100 metres, and it continues to the top of the troposphere. Above the troposphere temperatures remain generally constant.
Saturated air cools at a different rate from dry air. The dry adiabatic lapse rate (d.a.l.r.) is 1oC per 100 metres, a physical constant, and the saturated a.l.r. varies between 0.4oC and 0.9oC per 100 metres.
When moist air is forced to rise over an area of high relief, it cools. When the temperature of the cooling air falls below dew point, condensation will cause clouds to form, and rain can be expected on the windward upper slopes of the mountain. This is the cause of most relief or orographic precipitation, and explains why high relief areas tend to receive higher levels of rainfall, e.g. Scotland and N. Wales in Great Britain, and Cameroon Mountain in Equatorial Africa.
On the leeward side of the mountain the air will sink, contracting as it does so causing a rise in temperature. This rise will cause the clouds to disperse (they have lost most of their moisture in rain and snow anyway) and the area in the lee of the mountains will tend to be dry. This is called the rain shadow effect.
The rising air on the windward side of the mountain will have cooled at the s.a.l.r. (between 0.4oC and 0.9oC per 100 metres), and it will then descend and warm at the faster d.a.l.r. (1oC per 100 metres) as it is now dry air. Thus the air moving down the leeward side will be warmer than it was as it rose up the windward slope, causing a warming wind, and this warming is the föhn effect.
Föhn / Chinook winds tend to occur most often during winter and spring, and the sudden warming which they cause can trigger avalanches on upper mountain slopes. At Tashkent in central Asia, where the mean winter temperature is about freezing point, temperatures may rise to more than 21oC during the föhn.1
It is possible that the above effect may have a bearing on the generally higher temperatures of areas of SW France which lie in the lee of local winds.
Local winds in any area are, therefore, caused as part of a global pattern, with local factors adding micro-climatic effects over relatively small areas.
Local Winds - General Descriptions, with particular reference to SW France.
Introduction translated from an article by France Meteo:
It is possible to define a ‘local wind’ as a regional wind which has an influence on a sufficiently restrictive geographical area for its details to be clearly made out and its effects shown on a large scale map. Some wind regimes, provided with a specific name, relate clearly to a regional climate and can be individualised to the spatial dimensions of the synoptic (wider than local, perhaps even national) scale. However a local wind is a wind regime, provided in some cases with a specific name, which is tied to a local climate not covering or affecting such large spatial dimensions.
It often happens that the particularities of a local wind coincide with those of a synoptic or regional wind in that region, in terms of certain of its characteristics, e.g. the strength, the gusts, the temperature, the local economic influence etc. For example the Bise is a common local name of a cold and quite dry wind, which blows from N to NE, especially on the hill slopes in the centre of eastern France and in Switzerland. In other winds the Bise is a regional wind affecting a relatively wide geographical area, although it is thought of as a local wind in the areas which it affects.
Other local winds, in contrast, present peculiarities in speed and direction which strongly distinguish them from the synoptic or regional wind. They reveal the existence of an interference on a local scale with the meteorological situation at the synoptic scale. This interference will be caused by certain factors, mostly hydrological and topographical. The best known local winds of metropolitan France - Mistral, Autun, Tramontane - fit this category.
As well as these, a number of other regional winds could be counted, and the following are examples:
The Galerne is a cold and most NE wind which blows in gusts in the centre west and SW of France.
The Traverse is the name given to a W - NW wind in a number of areas of the Jura and Lyonnais, the Alps and the Massif Central (where, in the south, it is called the High Traverse, as opposed to the Low Traverse from the SW). This moderate wind is quite strong and often blows in gusts. It is mild and moist in the warm season when it can bring storms, whereas in the cold season it is the carrier of cold air, sudden downpours and sometimes snow.
The Matinière (sometimes also called Matinal) is an E - NE wind which blows in an area of the NE Massif Central to the northern Alps, crossing the Rhône and Saône valleys. This wind, cold and dry in winter, is generally accompanied by good weather.
The Cers is a violent and turbulent wind blowing from the W or SW in lower Languedoc (or over a wider area according to some sources); cold in winter, warm in summer, it is always dry and brings the good weather required by the vineyards.
The Grec is a NE wind blowing on the Mediterranean coast where it has various names. Cold and dry in Corsica and on the major part of the continent, it becomes moist on the Côte d’Azur and particularly in the Aude and Roussillon.
The Levant is an E wind blowing on the southern Alps and the Mediterranean littoral as far as Corsica. This moderate to strong wind raises a sea swell. Most often gentle and moist, it brings cloud and rain, except in the case of the Levant Blanc, which is dry.
Specific examples, relating to SW France, in more detail:
This information has been collected from a variety of sources, some of which do not agree.
The Cers
The Cers wind blows at times from any direction between SW and N and often heralds sunny, warm weather. Its similarity with the Tramontane, in direction, frequency and strength, make it difficult to distinguish between them in many cases. (see below) It is generally cold in winter, sometimes bringing rain, and in summer it is generally hot and dry. Its gusts frequently reach wind speeds up to 10 Beaufort and can be quite violent.
(Around Narbonne it is also known as the Narbonnais).
It is essentially a katabatic wind, draining off the lower slopes of the Pyrenees and Montagne Noire. The Cers is very common across the Aude region in SW France, blowing at sustained wind speeds greater than 20 knots for a total of about 200 days per year.2
Originating from moist Atlantic air-masses, it flows across the Toulouse area and can become intensified through the Lauragais gap, before being violently felt in the Narbonne area. Exceptionally red sunsets and lenticularis clouds usually herald the onset of the Cers. In winter it might persist for more than a week.
The Marin
The coastal counterpart of the Cers is the Marin, a warm, humid SE wind from the Mediterranean Sea which blows most frequently between early autumn and spring. It is associated with low pressure across the Iberian Peninsula, tracking eastward, and frequently winds can reach gale-force during the passage of a warm front.
It brings close, humid, cloudy and misty weather along the coasts and over the Corbières, and is often associated with thunder. Sea mist can be dense on the coastal plain.
In winter the wind causes heavy rain in coastal areas, whereas in summer the clouds tend to dissipate, but can stay for days, causing the air to smell rather salty. The Marin can be strong, even violent, sometimes bringing heavy rain well inland and frequently triggering particularly heavy storms and violent flooding across the Cevennes and adjacent mountain regions.
In this latter case the mild, unstable and extremely wet Mediterranean air blows against the already relative cool uplands and slopes of the Cevennes, causing strong convection and intense orographic rainfall, eventually leading to the formation of one or more thunderstorm supercells. As a result intensifying local low pressure starts to suck in more and more humid and mild air from the Mediterranean in order to fuel itself and the Marin might eventually reach strong gale force, blowing at 9 to 10 Beaufort.
While rainfall rarely exceeds 10 or 20 mm along the coasts, official readings from mountain rain gauges frequently record several hundreds of litres of rainfall within 24 hours during such events. This phenomenon is locally known as the 'cevenol'. The devastating flash floods of autumn 1999 and late summer 2002 are good examples for this.
If rain does not fall, the wind is referred to as a Marin blanc (A white Marin).
When the Marin blows through the Lauragais Gap it becomes the Autun (Antane noir) of Aquitaine. (see below)
According to some sources the name Marin, although appearing to point to its marine origin, is, in fact, simply the local word for 'Autun', which is said to derive from the Latin altanus = from off shore. This is curious as the Marin is an onshore wind.
In addition Autun is an old french word meaning 'the East', which is equally curious as it tends to occur inland from the east coast, although deriving from the easterly Marin.
The Autun
The Autun is described by one source as a SW, föhn-type wind deriving from the Mediterranean and blowing across the Languedoc into the Tarn and Garonne valleys, affecting the Lauragais and the Toulouse area. This is curious as a wind with a Mediterranean source must originate in the east. The Autun can affect an area between Perpignan in the S, Auch to the W, and Cahors to the N. This does not fit the description Autun of Aquitaine (see above). To the west of Carcassonne, on the hills of the Lauragais and Razès it can be particularly strong, whipping up to a fury around hilltop houses in the area.
It begins as the warm Marin from the Mediterranean and often heralds heavy rainfall and it has a more southerly component in the Cantal region.
Some days before it blows, a calmness descends, characterised by crystal clear air. During this period the Pyrenees may be seen from 150 kilometres away. As farmers say when this happens - "the Autun wants to blow".
The Autun occurs as the Autun blanc and Autun noir. The Autun blanc is a wind of good weather, as with the Marin blanc - fresh in winter, warm in summer. It is created by ascending air rotating around a zone of high pressure (typically, an anticyclone centred over Eastern Europe), balancing a depression over Iceland. This causes currents of air to turn clockwise, starting on the coast of the Gulf of Lions and moving to the region of Cahors. (definitely not a SW wind, as described above)
The Autun noir is also warm, but brings heavy showers. It is much less frequent than the Autun blanc but seems to be getting more common.
When a depression is centred on Spain, balancing an anticyclone over the Azores, it creates an air flow moving anticlockwise around the lowest pressure. This flow progresses along the coast of Spain picking up humidity from the sea. It generally hits the Languedoc between Perpignan and Béziers, tracking towards Carcassonne, Toulouse and Agen where it dissipates. (again, not a SW wind)
This wind is called the "Autun noir" or "Black Sailor" in the Lauragais, and is characterised by heavy black clouds from the Mediterranean Sea. Sometimes rain falls over the Corbières protecting areas further west, but if not the rain is carried further inland before falling.
The Autun has distinct föhn characteristics when descending in the west and may easily reach gale force. Its gustiness is enhanced along the steep and narrow valleys of the River Aude and Thauré, north of the Pyrenees and the Montagne Noir. Gusts can exceed twice mean speed, possibly enhanced by lee-wave activity. The effects on humans is similar to the föhn: a warm and close wind, sweltering and oppressive, causing headaches and general indisposition.
The noise of this hot, dry wind can cause insomnia. It is sometimes known as the Vent des Fous (the wind of the mad) as it can blow for up to nine days on end, allegedly driving people as mad as the Mistral, and is also known, rather dramatically, as the devil's wind and the wind of death.
The Autun clears the sky, dries the ground, and heralds good weather. Gusts regularly reach 80 to 100 km/h.
Confusion as to the direction of the Autun could relate to different points of measurement. In lower Languedoc, coming off the sea, the wind will have an easterly component, but as it swings to the right over the land, it will tend to become more south-westerly.
The Tramontane
The Tramontane is a violent, cold wind, characteristically and markedly turbulent, which blows from between W and NW, descending the foothills of the Pyrenees (into Spain) and the hills of the southern Massif Central and travelling through the Gateway of Naurouze (Lauragais) between the Côte de la Malepere and Razès and the Montagne Noir, before sweeping the coastal plains of lower Languedoc and Roussillon. [readers will note the similarity with the description of the Cers]
This regional/local wind presents a number of analogies with the cold Mistral:
1. it blows in all seasons, but with more vigour in winter and spring
2. it blows in gusts
3. it is often very strong and agricultural activities, homes and routeways need protection from it.
4. it accelerates as it passes through narrow, deep corridors of land
In contrast with the Mistral however, it is oriented at right angles to the Rhône valley.
Most often it is a dry wind, accompanied by a clear, bright sky, although there can be cloudy periods with brief showers on some occasions.
The meteorological situation which leads to the Tramontane is comparable to that which gives rise to the Mistral. An anticyclone approaching Spain and SW France leads a north-west or northerly airflow towards the Mediterranean (often in the form of a cold front) which carries cold air between the anticyclone to the west and a depression in the Gulf of Genoa or the Tyrrhenian Sea in the east.
The duration of the Tramontane is then correlated, as with the Mistral, to the duration of the filling of the depression in the Gulf of Genoa, and the two types of wind can maintain themselves more or less simultaneously; for example the force of the Tramontane, as with the Mistral, tends to diminish each night.
The appearance of the Tramontane can also be linked with the displacement towards the east of a depression circulating in the western Mediterranean. In this type of circulation the regions of the Balearic Islands in the Gulf of Lions find themselves covered either by a fast moving depression coming out of the Iberian peninsula (this is more often the case in autumn and in spring), or by depressions which follow a flow from NW to SE around the Azores anticyclone (more often the case in winter). In all cases NW winds blow in these regions which maintain the low temperatures during a period of about four days.
When such situations establish themselves the Tramontane is of a different origin and becomes a moist wind, accompanied by cloud and rain.3
In Italy, the tramontana (Italian tramontano = from the mountains) is a cold wind from the N or NE tinged with frigid air from the Alps and northern Apennines, particularly to the west coast of Italy and Northern Corsica. It is associated with the advance of an anticyclone from the west following a depression over the Mediterranean known as the 'Genoa Low'. The Gulf of Genoa is among the most active regions of cyclogenesis, especially during autumn and winter. Thus the tramontana blows most frequently in the winter, but may occur from mid-September through April.
The tramontana is also known locally as garigliano. It may reach force 8 Beaufort (35 to 40 knots) or even stronger during night to mid-morning, when it is enhanced by a land-sea breeze. Hence it reaches its maximum just before sunrise and usually decreases to force 5 Beaufort(17 to 21 knots) during afternoon. During winter, the tramontana poses a quite significant wind chill hazard to exposed persons, e.g. ships’ crews.
The Scirocco
As a depression moves into the central Mediterranean a strong southerly wind can develop ahead of it near North Africa, which can be very hot and dry and carry dust. If the conditions are right these winds move across the Mediterranean Sea picking up moisture from the sea and by the time they reach Europe they bring warm, humid air and low cloud. This is the Scirocco.
The Scirocco is therefore a S wind. The hot, dry air it brings from Africa can be uncomfortable in a particularly hot summer.
The wind blows only rarely, and then generally only for a few hours, but may last for between half a day or many days.
The Scirocco causes dusty, dry conditions along the northern coast of Africa and also causes storms in the Mediterranean Sea, and many people attribute health problems to it. The dust carried by the wind can damage mechanical devices and invade buildings. Rain bearing its dust can cause a fine layer of sand to be deposited on cars and buildings across southern Europe.
Winds can blow with speeds of almost 100 kilometres per hour (55 knots, hurricane-force) and these are most common during the autumn and the spring. They reach peaks in March and in November.
Scirocco and Sirocco are Italian names. Jugo is the name used in Croatia and ghibli in Libya.
Comparisons between the Tramontane and the Cers
*
Tramontane is a word which essentially means across mountains, and it is used to describe winds in Italy (see above), Spain and France. It could be inferred therefore that it is a general term for a wind which crosses areas of highland, and this is made more likely from the suggestion that its direction and characteristics can vary widely.
Conditions which cause the French Tramontane involve areas of high and low pressure on the synoptic scale, bringing air from the W and NW across SW France. The Cers, although similar in direction, seasonality and effect, is caused by more local conditions.
The Cers will only occur within the same general synoptic conditions as the Tramontane, i.e. a westerly to northerly airflow. This suggests that the Tramontane is a general name for winds of its type, and that the Cers is a more local wind which forms a component of it.
Comparisons between the Marin and the Autun
*
It is interesting that both the Marin and the Autun have blanc and noir varieties, bringing dry and wet conditions respectively. The Autun is said to develop from the Marin, but it is generally more strong and gusty. However there are times when the Autun brings dry, hot and oppressive weather, which is very similar to the Marin, but more extreme.
Descriptions of the origins of the two names are contradictory, suggesting perhaps that in some areas Marin and Autun are interchangeable names for the same wind. However, the general differences in weather brought about by each, and the regions which are affected by them, tend to make them quite distinct from each other. The similarities which exist may be down to coincidence or a confusion in some areas as to which is which.
General conclusion
It is a well known fact that the SW corner of France is the windiest part of the country. However it would be wrong to assume that every windy day is being affected by one or other of the locally named winds. As France lies in the global belt of SW winds, this wind direction remains the most common, and winds blowing from this direction cannot necessarily be labelled as Tramontane or Cers, merely winds blowing from the SW as part of a global pattern.
Despite the detailed descriptions which are offered of the Tramontane, it is likely that this is the generic name used locally for westerly winds, especially those which cross highlands. A more detailed consideration suggests, however, that the most common westerly wind in some areas, notably the lower slopes of the Pyrenees and Montagne Noir, (when it is mainly caused by local factors and not as part of a global pattern) is not the Tramontane, but the Cers.
Winds of both the above types tend to blow strongest during the warmest part of the day, due to convection, and within a prolonged period of quite intense westerly winds mornings and evenings can be relatively calm. However these winds will blow more consistently when there is a steeper pressure gradient, and this will generally be caused by an intense low pressure area in the Mediterranean which is pulling air in from an anticyclone to the west of France.
Easterly winds are generally known in Languedoc Roussillon as the Marin, and these tend to be less strong than the westerlies and bring cloudy conditions with occasional light rain. However, occasionally, strong easterly winds can bring heavy rain, and it is not clear whether these conditions can still be contributed to the Marin, or whether this is the Autun. Some authorities are clear that the Autun occurs only further inland.
The most distinct wind in its effect, although the least common, is the Scirocco, and its sand bearing rains bear evidence to its origin.
Notes
A list of world wide local winds can be found at http://perso.orange.fr/boreal/noms_de_vents.htm
A list of French local winds can be found at www.outilssolaires.com/Glossaire/pop-vents.htm
Beaufort Wind Scale
No. Speed (knots) Designation Likely Effect
0 0 calm smoke rises vertically
1 1 - 3 light air wind direction shown by smoke drift, but not vane
2 4 - 7 light breeze wind felt on face; leaves rustle; vane moves
3 8 - 12 gentle breeze leaves and small twigs in motion; a flag is extended
4 13 - 18 moderate breeze raises dust; small branches move
5 19 -24 fresh breeze small trees sway; small crests on waves on lakes
6 25 - 31 strong breeze large branches in motion; wind whistles in telephone wires
7 32 - 38 moderate gale whole trees in motion
8 39 - 46 fresh gale breaks twigs off trees
9 47 - 54 strong gale slight structural damage to houses
10 55 - 63 whole gale trees uprooted; considerable structural damage
11 64 - 75 storm widespread damage
12 above 75 hurricane devastation
