Meteorology (CMET)

Cold Front Passage

Wind, cloud, temperature and pressure sequence as a Southern Hemisphere cold front crosses an aerodrome.

• CASR Part 61 MOS Schedule 3 (MT) 2.6.1 (p.505) — Typical flying weather associated with frontsVerified“Describe typical ‘flying weather’ associated with the following using the factors described in subclause 2.6.2: (a) cold fronts; (b) warm fronts; (c) wave depressions; (d) occluded fronts; (e) tropical cyclones; (f) the equatorial trough.”
• CASR Part 61 MOS Schedule 3 (MT) 2.6.2 (p.505) — Fronts — temperature, wind, stability, cloud and precipitation changesVerified“For subclause 2.6.1, ‘flying weather’ embraces the following: (a) temperature (warmer/colder); (b) wind changes (back/veer, stronger/weaker); (c) stability and turbulence; (d) cloud type and approximate amount, precipitation.”
• BOM Aviation Weather Services — MSLP chart frontal symbologyNeeds review

• Triangles on a cold front point in the direction the front is moving.
• Pressure falls to the frontal trough then rises sharply behind it.
• A trough of low pressure brings unsettled convective weather with no formal front.

Try the interactive animation for this topic in the app →

Mountain Wave, Rotor & Lenticular Cloud

Standing lee waves, ACSL formation and the rotor zone downwind of a ridge in stable air.

• CASR Part 61 MOS Schedule 3 (MT) 2.8.1 (p.507) — Meteorological phenomena — favourable conditions, recognition and effect on the aircraftVerified“With respect to the phenomena listed below in subclause 2.8.2, do the following: (a) state the conditions that are favourable to the development of the phenomenon and, where applicable, its dispersal; (b) recognise signs which may indicate the presence of each phenomenon; (c) describe the effect of the phenomenon on flight characteristics; (d) where applicable, state the pilot actions required.”
• CASR Part 61 MOS Schedule 3 (MT) 2.8.2 (p.507) — Phenomena list including mountain waves and föhn windsVerified“The following is a list of meteorological phenomena that is for the purposes of subclause 2.8.1: (i) thermals, turbulence; (iii) wind gradient, wind shear and low-level jetstreams; (v) mountain waves and fohn winds; (ix) downdrafts associated with terrain/cloud.”

• Lenticular cloud is stationary while the air rushes through it.
• The most severe turbulence is in the rotor beneath the crests, not in the smooth cloud.
• Lee-side downdraughts can exceed a light aircraft’s maximum rate of climb.

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Sea Breeze & Land Breeze — the Diurnal Cycle

The 24-hour coastal wind cycle: a cool onshore sea breeze that builds through the day behind an advancing sea-breeze front, and the weaker, shallower offshore land breeze that replaces it overnight.

• CASR Part 61 MOS Schedule 3 (MT) 2.7.1 (p.505) — Meteorological phenomena — conditions, recognition, effect on flight and pilot action, including land and sea breezesVerified“With respect to the phenomena listed below (i) – (vi): (a) state the conditions favourable to their development and, where applicable, their dispersal; (b) recognise signs which may indicate their presence; (c) describe their effect on flight characteristics where applicable, state the pilot actions required to minimise their effect on an aircraft in flight: (i) turbulence; (ii) windshear; (iii) mountain waves; (iv) land and sea breezes; (v) thunderstorms; (vi) downdrafts associated with terrain and cloud.”
• CASR Part 61 MOS Schedule 3 (MT) 2.2.3 (p.506) — Factors in the diurnal variation of surface air temperature and the land–sea temperature gradientVerified“List factors that influence the diurnal variation of surface air temperature and explain the temperature gradient between land and sea surfaces.”
• CASR Part 61 MOS Schedule 3 (MT) 2.5.4 (p.505) — Factors in the diurnal variation of wind and typical surface wind variation over 24 hoursVerified“List the ‘factors’ that effect the diurnal variation of wind and describe typical ‘variations’ in surface wind strength during a 24-hour period.”

• A sea breeze is named for where it comes FROM — it blows onshore, off the sea and onto the warmer land. A land breeze blows offshore.
• The sea breeze arrives as a front: an abrupt wind shift (often 90° or more), a temperature drop, a rising dewpoint, gusts and low-level shear — a runway change on an otherwise fine day.
• The circulation is a closed loop — the surface flow is only half of it; the return flow aloft runs the opposite way.
• The cycle is asymmetric: the daytime sea breeze is stronger, deeper and reaches further inland than the night land breeze, because the land–sea temperature contrast is larger by day.
• A strong opposing gradient wind can hold the sea breeze offshore all day; the weak night land breeze is swamped more easily still, and it will not clear fog or smoke — only carry it out to sea.

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Thunderstorm Life Cycle & the Gust Front

The three-stage life of a cumulonimbus cell — cumulus, mature and dissipating — and the gust front the mature-stage downdraft drives out ahead of the storm.

• CASR Part 61 MOS Schedule 3 (MT) 2.7.1 (p.500) — Meteorological phenomena — conditions, recognition, effect on flight and pilot action, including thunderstormsVerified“With respect to the phenomena listed below (i) – (vi): (a) state the conditions favourable to their development and, where applicable, their dispersal; (b) recognise signs which may indicate their presence; (c) describe their effect on flight characteristics where applicable, state the pilot actions required to minimise their effect on an aircraft in flight: (i) turbulence; (ii) windshear; (iii) mountain waves; (iv) land and sea breezes; (v) thunderstorms; (vi) downdrafts associated with terrain and cloud.”

• Mature stage is officially defined by precipitation reaching the ground, not by cloud height or anvil size.
• The gust front outruns the storm itself — a sharp wind shift and temperature drop can arrive well ahead of any rain.
• Coexisting updrafts and downdrafts side-by-side within the same cell are what make the mature stage the most hazardous.
• Never fly under the glaciated anvil overhang: large hail and severe downdrafts fall from it well clear of the visible core.

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Microburst Encounter & Low-Level Windshear on Approach

A concentrated downdraft below convective clouds that spreads radially on impact: initial performance-increasing headwind, followed by severe downdraft and rapid performance-decreasing tailwind shear.

• CASR Part 61 MOS Schedule 3 (MT) 2.7.1 (p.500) — Meteorological phenomena — conditions, recognition, effect on flight and pilot action, including windshearVerified“With respect to the phenomena listed below (i) – (vi): (a) state the conditions favourable to their development and, where applicable, their dispersal; (b) recognise signs which may indicate their presence; (c) describe their effect on flight characteristics where applicable, state the pilot actions required to minimise their effect on an aircraft in flight: (i) turbulence; (ii) windshear; (iii) mountain waves; (iv) land and sea breezes; (v) thunderstorms; (vi) downdrafts associated with terrain and cloud.”

• Initial performance-increasing headwind causes IAS and altitude to rise, tempting the pilot to reduce power — setting up the crash when the shear flips.
• Downdraft speeds in a microburst can exceed 6,000 ft/min — far beyond the max climb rate of any general aviation aircraft.
• The transition from headwind to tailwind causes a rapid loss of airspeed and lift near the ground.
• At the first indication of windshear, apply MAX go-around power and rotate to escape pitch attitude immediately — do not alter gear/flaps until clear.

Try the interactive animation for this topic in the app →

International Standard Atmosphere (ISA) & Density Altitude

MSL standard temperature (15°C) and pressure (1013.25 hPa), 2°C/1,000 ft lapse rate, pressure altitude conversion, and hot-day aircraft performance degradation.

• CASR Part 61 MOS Schedule 3 (MT) 1.2.1 — ISA standard atmosphere, pressure altitude and density altitudeVerified“State the MSL pressure and temperature in the standard atmosphere and calculate pressure height and density height.”

• High temperature, high elevation, and high humidity REDUCE air density (raise density altitude), degrading climb rate and extending takeoff ground roll.
• Pressure altitude uses 1013.2 hPa datum; density altitude is pressure altitude corrected for non-standard temperature.

Altimeter Subscale Traps & Convective Cloud Base Calculations

Flying from high to low pressure ("High to low, look out below"), QNH vs QFE vs 1013 Standard Pressure, and the spread formula for convective cloud base (Spread / 4 * 1,000 ft).

• CASR Part 61 MOS Schedule 3 (MT) 1.4.1 — Altimeter subscale settings and pressure errorsVerified“Explain the effect of flying from high to low pressure without adjusting altimeter subscale and calculate cloud base from surface temperature and dewpoint.”

• Flying from High to Low pressure without resetting subscale causes altimeter to OVER-READ (aircraft is lower than indicated).
• Convective cloud base (ft AGL) = (Temp - Dewpoint) / 2.5 * 1,000 ft in °C (or / 4.4 in °F).