CAA NZ PPL Meteorology cheat sheet

ISA: sea-level temperature 15 °C, pressure 1013.25 hPa, lapse rate 1.98 °C per 1000 ft; tropopause at 36,090 ft where temperature is −56.5 °C.

Pressure altitude = indicated altitude corrected for subscale setting; density altitude = pressure altitude corrected for non-standard temperature; high density altitude lengthens takeoff roll and reduces climb rate.

QNH set on the subscale gives elevation above mean sea level on the ground; QFE gives height above the aerodrome reference point; QNE (1013.25 hPa) gives flight levels above the transition altitude.

Standard atmosphere pressure lapse near the surface is about 1 hPa per 30 ft; the 1-in-60 rule applies to altimeter error: 1 hPa ≈ 30 ft, so a 4 hPa error is roughly 120 ft.

Coriolis force deflects air to the left in the Southern Hemisphere; combined with the pressure gradient force it produces geostrophic wind aloft and surface friction causing cross-isobar flow toward low pressure.

In the Southern Hemisphere air circulates clockwise around a low and anticlockwise around a high; Buys Ballot's law: stand with back to wind, low pressure is on your right.

Relative humidity rises toward dewpoint; when temperature falls to the dewpoint (spread zero) cloud base or fog forms, with convective cloud base approximated by 400 ft per 1 °C of surface temperature-dewpoint spread.

Stability: a rising parcel cools at the dry adiabatic lapse rate (about 3 °C per 1000 ft) until saturation, then at the saturated rate (about 1.5 °C per 1000 ft); if the environmental lapse rate exceeds the dry rate the air is absolutely unstable.

Fronts: cold front moves fast with narrow band of heavy showers and squall lines, warm front has a wide gentle slope giving prolonged stratiform rain, occluded front combines both; the frontal surface slope is about 1:50 for warm and 1:100 for cold fronts.

Fog types: radiation fog forms on clear calm nights with high relative humidity after surface cooling; advection fog forms when warm moist air moves over a colder surface; upslope and steaming fog require specific terrain or water temperature contrasts.

Icing: airframe icing occurs between 0 °C and about −20 °C in visible moisture; clear ice from large supercooled droplets, rime ice from small droplets; carburettor icing can occur at outside air temperatures up to about 20 °C with high humidity.

Wind shear and turbulence: mechanical turbulence from surface friction and obstructions, thermal turbulence from convection, and low-level wind shear near fronts, inversions and thunderstorm outflow; report significant shear to ATC.

METAR: routine aerodrome report issued typically every 30 or 60 minutes; elements in order are wind, visibility, present weather, cloud, temperature/dewpoint, QNH, and trend; CAVOK replaces visibility, weather and cloud when visibility ≥10 km, no cloud below 5000 ft and no significant weather.

TAF: aerodrome forecast valid typically 24-30 hours with change groups FM (from), TEMPO (temporary fluctuations), BECMG (becoming, gradual change) and PROB (probability); AMD denotes amendment, COR correction, NIL unavailable.

Cloud amounts in eighths: FEW 1-2, SCT 3-4, BKN 5-7, OVC 8; heights are given in feet above aerodrome level; CB and TCU denote cumulonimbus and towering cumulus.

SPECI is a special report issued when conditions change significantly, for example visibility crossing 1500 m or 5000 m thresholds, cloud base crossing 500/1000/1500 ft, or onset of thunderstorms or severe weather.

Wind in reports is in degrees true at aerodromes and degrees magnetic in ATIS and tower communications; gusts are shown as G after the mean, e.g. 27015G30KT, and VRB indicates variable direction.

SIGMET: information on significant en-route weather such as severe turbulence, severe icing, volcanic ash, tropical cyclones, severe squall lines and widespread sandstorms; AIRMET covers less severe phenomena affecting low-level flights.

GAFOR and area forecasts give expected conditions over a region; interpret trend forecasts (BECMG, TEMPO) with the validity period and be aware that TEMPO changes are expected to last less than an hour at a time and less than half the period overall.

Upper wind and temperature charts: winds are given in degrees true and knots, temperatures in degrees Celsius, heights in feet; the 500 hPa chart approximates 18,000 ft and the 200 hPa chart about 39,000 ft.

Interpretation decision rule: cross-check METAR, TAF, trend and area forecast; a forecast is not a guarantee, so plan alternates when TEMPO or PROB30 groups involve conditions below your minima.

Thunderstorm recognition: cumulonimbus with anvil, lightning, hail, gust fronts and microburst risk; avoid by at least 20 nm from severe cells, do not fly beneath an anvil, and expect wind shear on the gust front.

New Zealand synoptic patterns: prevailing westerlies in the latitudes of New Zealand, with travelling anticyclones and frontal systems; the Southern Alps create a strong föhn-like nor'wester and lee turbulence east of the divide.

Sea breeze: daytime onshore flow caused by land heating; land breeze: night-time offshore flow; sea breeze fronts can produce a wind shift and shear line along the coast in the afternoon.

Mountain wave: stable air crossing a ridge with wind speed increasing with height can produce standing waves, lenticular cloud, rotor turbulence and strong downslope winds on the lee side.

Föhn effect: air descending the lee side of a range warms at the dry adiabatic rate after losing moisture on the windward side, giving warmer drier conditions and often clear skies downwind.

Katabatic and anabatic winds: cold dense air drains down valleys at night (katabatic), warm air rises up slopes by day (anabatic); both affect low-level wind and turbulence near hilly terrain.

Tropical cyclone structure: warm core low with eye, eyewall of strongest winds and spiral rainbands; in the Southern Hemisphere circulation is clockwise and the system tracks generally westward then poleward; gale and hurricane force wind radii are given in warnings.

Volcanic ash: ash is hazardous to turbine and piston engines and abrasive to windscreens; SIGMET and NOTAM are the primary warnings; avoid ash cloud entirely and report any encounter.

Icing forecast interpretation: use temperature, freezing level and visible moisture; freezing level is the height of the 0 °C isotherm; in NZ a frontal system often brings the freezing level down, raising icing risk at lower levels.

Wind and altimeter interpretation: crosswind component = wind speed × sine of the angle between wind and runway; headwind component = wind speed × cosine of the angle; use these to decide runway and personal limits.

Density altitude calculation: pressure altitude plus 120 ft for each 1 °C above ISA temperature at that level; use it for takeoff, climb and landing performance planning on hot or high-elevation days.

Visibility reporting: prevailing visibility is the greatest visibility achieved over at least half the horizon; RVR is runway visual range measured by transmissometers, reported when visibility is low or in fog.

Hail and icing risk in cumulonimbus: strong updraughts support large hail; do not penetrate a cell, and expect severe turbulence, icing and lightning in and near the cloud.

Lightning and static: thunderstorms produce lightning strikes and static interference to radios; stay clear of cells and avoid holding near them.

Cloud classification: low cloud (stratus, stratocumulus, cumulus), middle cloud (altostratus, altocumulus), high cloud (cirrus, cirrostratus, cirrocumulus); vertical development cloud (cumulonimbus, towering cumulus) indicates instability.

Pressure systems: anticyclone gives subsidence, light winds and often clear skies but can trap haze or fog under an inversion; depression gives ascending air, cloud and precipitation; a trough is an elongated area of low pressure with associated cloud and showers.

Wind reporting and ATIS: ATIS gives current aerodrome weather including wind direction and speed, visibility, cloud, temperature, dewpoint and QNH; update ATIS is important for landing and takeoff data.

Weather decision rule for VFR: maintain cloud clearance and visibility minima for the airspace class; if the forecast or actual conditions trend below minima, divert or hold rather than continue into deteriorating weather.

Mountain and terrain weather: orographic cloud forms when moist air is forced upslope; cloud base lowers on the windward side and clears on the lee side; expect turbulence and downdraughts near ridges.

Tropical and local weather: sea surface temperature above about 26.5 °C supports tropical cyclone development; in NZ ex-tropical cyclones bring heavy rain and gales even after losing tropical characteristics.

Weather radar and satellite interpretation: radar reflectivity indicates precipitation intensity and can show hail and heavy showers; satellite imagery shows cloud tops, fronts and cyclone structure; use both to cross-check forecasts.