Sea breeze, land breeze and slope winds
The simplest local winds come from one surface heating or cooling faster than its neighbour. The pressure difference that follows drives the wind, and Coriolis force, terrain and the background gradient wind then modify it.
A sea breeze sets in during the day. Land warms faster than the sea, pressure over the land falls, and cooler air flows in from the water, often with a sea breeze front, a wind shift, convergence and a line of Cu or even thunderstorms a little inland. With the onset of the sea breeze the surface temperature falls and the relative humidity rises. It builds through the day and dies away at night. A land breeze is the weaker night time reverse: the land cools faster, and a shallow flow drains offshore. The sea breeze is the stronger of the two because daytime heating is more vigorous than night time cooling.
Slope winds follow the same heating idea on a hillside. By day an anabatic wind flows up a sunlit slope as the air against it warms and rises; it occurs during the day and is generally weaker than its night time counterpart. By night a katabatic wind drains cold dense air down the slope as the ground cools by radiation. In an enclosed valley this cold air can pool at the bottom, trapping fog, frost and smoke, and a strong katabatic flow off a large cold plateau or ice sheet can reach gale force.
For flight, these winds matter most on the approach and in the circuit. Expect a crosswind that changes direction and strength as a sea breeze front passes, wind shear along that front, and light or drainage winds in a valley at dawn that do not match the aerodrome forecast.
Föhn winds and the mountain wave setting
A Föhn is a warm, dry, often gusty wind on the lee side of a mountain range. It is not just a named wind, it is the result of air being forced across terrain and losing moisture on the windward side.
As air rises on the windward slope it cools. If it reaches saturation, cloud and precipitation remove moisture, and the descending lee side air then warms by compression and arrives markedly warmer and drier. Föhn originally refers to the Alps but is used generically for this lee side effect. The operational trap is that clear, warm lee side conditions can sit right alongside dangerous mountain wave turbulence aloft.
Joshi gives the conditions that make a strong wave pattern likely: flow generally within about 30 degrees of perpendicular to the ridge; at least about 7 m/s across a smaller range and 15 m/s across a larger one; a deep, steady flow that strengthens with height; a stable layer below the ridge with a less stable layer above. These conditions set up alternating ascent and descent on the lee side, which is why a single wind report on its own cannot show the full mountain hazard.
Chinook, cloud clues and vertical currents
The Chinook is the North American Föhn. It descends the eastern side of the Rocky Mountains, mostly in winter, and can bring a very rapid temperature rise and melting snow.
Oxford notes that the Chinook can persist for days across a large region east of the Rockies, and that a rise of about 20 degrees in 15 minutes is not unusual. The useful lesson is not the record figure, it is the speed of the change. Expect strong gusts, turbulence, wind shear and a completely different weather picture on the two sides of the range.
Mountain waves have alternating lift and sink. The first significant lee side sink is just downwind of the ridge, and over large mountains the vertical currents can be intense. Flying along a long ridge while caught in a downdraught can cause a continuing loss of height, so terrain clearance must be protected before entering the lee area. In humid air, cap cloud, lenticular cloud, rotor or roll cloud and layers of St, Sc, As or Ci form on the windward side and dissolve to leeward, so they appear stationary. Lenticular cloud marks the wave crests, and a rotor below the first crest is the most serious visible warning. A Föhn wall can look like cloud spilling down the lee slope.
Valley winds: the Mistral and the Bora
Valleys and mountain gaps funnel air. A pressure difference that would give a moderate wind over open ground can become a severe, gusty crosswind or downslope flow where the terrain narrows.
The Mistral blows down the Rhône Valley between the Massif Central and the Alps toward the French Mediterranean. It is mainly a winter wind, favoured by high pressure over central France and lower pressure near the Gulf of Genoa. It is cold, strong, about 40 to 75 kt in Oxford's description, and turbulent.
The Bora blows down the northern Adriatic. It is both valley channelled and katabatic: cold dense air descends from the Balkan side toward lower pressure over the Adriatic. It is strongest and most frequent in winter, commonly near 70 kt and capable of gusts above 100 kt. Treat it as a katabatic wind for exam purposes.
Joshi's mountain wave cautions apply to either terrain setting: turbulence can change abruptly from smooth to severe, ragged wave cloud edges warn of turbulence, and rotor, cap cloud and a Föhn wall can all contain severe turbulence and strong gusts. Rapid height changes can also drive altimeter hysteresis, and a non standard temperature adds terrain clearance error.
Mediterranean desert winds and timing
The Sirocco, Ghibli and Khamsin share a synoptic setting: they blow ahead of depressions tracking along the North African Mediterranean coast. The source region gives them their heat and dust, and the track can add moisture.
The Sirocco is a hot, dusty southerly over Algeria, usually in spring and often lasting a day or so. Dust can cut visibility below 1000 m. If it reaches the French coast after a sea track it can pick up moisture and produce low stratus, drizzle and fog. The Ghibli is the comparable Libyan wind. The Khamsin affects Egypt ahead of similar depressions, and the name is also used for south or southwest gales in the Red Sea.
The decision sequence is source, then path, then hazard. A desert source means heat, dust and poor visibility; a long sea path means adding low cloud, drizzle or fog. Do not rely on the wind's name alone. Check the depression track, the pressure gradient, the visibility trend, the cloud base and the runway crosswind component.
Joshi's seasonal point completes the terrain picture: small and medium mountain evening waves can form after sunset, when radiative cooling stabilises the low levels, then weaken after sunrise. Large mountain waves are especially common in winter because the flow is steadier and strengthens with height. Waves can extend 100 to 200 km downwind and vertically well into the stratosphere, with wavelengths of about 10 km or more.
Squalls: the Pampero and Sumatras
A squall is a sudden, strong increase in wind tied to a fast moving weather process. The main danger is the rate of change: wind, temperature, visibility and turbulence can all deteriorate within minutes.
The Pampero is a severe cold, dusty south to southwest wind around the River Plate in Uruguay and Argentina. It occurs behind a cold frontal depression, is most common in spring and summer, and brings stormy gusts and a sharp temperature fall. The squall itself is short lived, although a strong steady wind can persist for hours.
Sumatras occur in the Malacca Straits, usually from April to November during the southwest monsoon. Daytime thunderstorms build over the high ground of Sumatra with sea breeze help. At night, decaying Cb drift east under a land breeze, are renewed over the warm sea, and can form violent late night or early morning storms. Their Cb anvils make a pronounced arched line, and a temperature drop comes with the passage.
The correct action is avoidance and early planning, not trying to outrun a squall line. Expect severe turbulence, strong gusts and wind shear near the Cb and its outflow.
The Harmattan and a usable local wind briefing
A named local wind is a shorthand for a predictable combination of source, route, season, terrain and aviation hazard. Turn the name into those five questions before you make a flight decision.
The Harmattan is a cool, dusty northeasterly, effectively the northeast trade wind, blowing from the North African desert high pressure toward the ITCZ. It is mainly a winter wind, roughly November to April. Around desert border stations such as Kano in Nigeria it can reduce visibility below 1000 m, the dust layer can reach roughly 7000 to 10,000 ft or more, and visibility improves nearer the coast.
Use a compact briefing. First, what drives it: terrain, desert outflow, frontal passage or a land and sea circulation? Second, when is it most likely? Third, does the air cross land, sea or a ridge? Fourth, which phase of flight is exposed to gusts, low visibility, turbulence, icing or wind shear? Fifth, what is the alternate or escape plan? That turns the Chinook, Mistral, Bora, Sirocco, Pampero, Sumatras and Harmattan from labels into operational weather.