Meteorology

The PPL lesson covered the basics: the ISA, pressure and wind, clouds, fronts, METARs and TAFs. Commercial flying goes higher and further, so this lesson adds the upper atmosphere, jet streams and clear-air turbulence, the charts used for flight planning, and the hazards that matter most to IFR flights.

1. The upper atmosphere

• The tropopause separates the troposphere (where almost all weather happens) from the stratosphere. It is higher over the tropics (around FL500–550) and lower over the poles (around FL250–300); in the Middle East it is typically near FL400–FL500 in summer.
• Above it the temperature stops falling. Breaks in the tropopause are where jet streams form.

2. Upper-air charts

Planners use charts drawn for standard pressure levels:

Pressure level	Approximate flight level
850 hPa	FL050
700 hPa	FL100
500 hPa	FL180
300 hPa	FL300
250 hPa	FL340
200 hPa	FL390

Wind and temperature charts show the wind as arrows with barbs (a short barb is 5 kt, a long barb 10 kt, a flag 50 kt) and the temperature in °C (usually negative without the minus sign at high levels). Use them to choose the best cruise level and to calculate the average wind component for the route.

3. Jet streams

• Narrow bands of very strong wind – at least 60 kt, often 100–200 kt – usually near the tropopause, around FL300–FL400, thousands of kilometres long, a few hundred wide and a few thousand feet deep.
• The polar front jet follows the boundary between polar and tropical air; the subtropical jet lies around 25°–35° latitude and often sits over the Middle East and North Africa in winter.
• In the northern hemisphere, with your back to the jet stream wind, the cold air is on your left.
• Eastbound flights ride the jet for a big time saving; westbound flights avoid it.

4. Clear-air turbulence

CAT occurs in clear air where the wind changes sharply with height or distance (wind shear), especially:

• on the cold (polar) side of the jet core, just below it,
• near troughs and ridges where the jet curves sharply,
• where jet streams merge or split.

A vertical wind shear of more than about 5 kt per 1,000 ft or a horizontal shear of more than 30 kt per 100 NM is a warning. If you meet CAT, a level change of a few thousand feet usually gets you out of it; slow to the turbulence penetration speed and keep seat belts fastened.

5. Mountain waves

Strong wind blowing at right angles across a mountain range in stable air can set up standing waves downwind, sometimes up to the stratosphere. Signs: lenticular (lens-shaped) clouds, rotor clouds below them, and strong up- and downdraughts – downdraughts can exceed the aircraft's climb performance. The ranges of Turkey, Lebanon and Iran produce mountain waves in winter westerlies.

6. Thunderstorms in detail

• Air-mass storms: from daytime heating, isolated, late afternoon.
• Frontal and line storms: along cold fronts or squall lines ahead of them – long lines that are hard to go around.
• Embedded CBs hide inside layers of cloud – use weather radar.

Hazards include severe turbulence up to 20 NM away, hail (also below the anvil, and in clear air beside it), lightning, icing, microbursts and gust fronts. Weather radar shows precipitation: green light, yellow moderate, red heavy, magenta extreme. Avoid red and magenta returns by at least 20 NM at high level, and never fly between two storms less than 40 NM apart.

7. Icing

Type	Conditions	Features
Clear (glaze) ice	Large supercooled drops, 0 to −10 °C, cumuliform cloud, freezing rain	Heavy, transparent, spreads back over the wing – the most dangerous
Rime ice	Small drops, −10 to −20 °C, stratiform cloud	White, rough, builds forward on the leading edge
Mixed ice	Mixture of drop sizes	Both kinds
Hoar frost	Clear air, a cold aircraft descending into warm moist air	Thin white crystals, light but can block windscreens

Freezing rain (rain falling from warm air above into sub-zero air below) is extremely dangerous: climb into the warmer layer or leave the area.

8. Weather in the region

• Shamal: a strong north-westerly wind over Iraq and the Gulf, mostly in summer, raising dust and sand and cutting visibility for days.
• Khamsin / sharav: hot, dry southerly winds from the desert in spring, with dust storms over Egypt, Jordan and the Levant.
• Winter Mediterranean lows: rain, low cloud, snow on high ground (Amman, Damascus and the Lebanese mountains) and embedded thunderstorms.
• Summer heat: very high density altitudes and turbulence in the afternoon at low level.

9. Information for IFR flights

• SIGMET: severe hazards for all aircraft – severe turbulence, severe icing, thunderstorms (embedded or lines), mountain waves, volcanic ash, sandstorms, tropical cyclones.
• AIRMET: lesser hazards for low-level flights.
• Significant weather charts (SWC) for high and medium levels: jet streams, CAT areas, CB areas, tropopause heights, fronts.
• Volcanic ash: never fly into it – it can stop jet engines. Volcanic Ash Advisory Centres issue forecasts.

Flying it at Levant

SimBrief's OFP includes the winds for every waypoint and the SIGMETs on the route. Before departure, read the significant weather chart for jet streams and CB areas, look at the wind at your planned level and the levels above and below, and on the radar avoid red cells by a wide margin – most simulators model turbulence near storms realistically.

Check yourself

1. Which pressure level is about FL180? 500 hPa.
2. What is the minimum wind speed of a jet stream? 60 kt.
3. Where is CAT most likely around a jet stream? On the cold (polar) side, just below the core.
4. Which icing is the most dangerous and where does it form? Clear ice, from large supercooled drops near 0 to −10 °C.
5. What is the shamal? A strong north-westerly wind over Iraq and the Gulf, bringing dust and sand.

Simulation training material based on standard commercial meteorology. Always use current official forecasts.