Transport Canada Flight Dispatcher Meteorology Exam cheat sheet

Composition by volume of dry air: nitrogen about 78%, oxygen about 21%, argon about 0.93%, carbon dioxide about 0.04%; water vapour varies from near zero to about 4%.

Standard sea-level pressure is 1013.25 hPa (29.92 inHg); standard sea-level temperature is 15 °C (59 °F); standard sea-level density is 1.225 kg/m³.

Standard lapse rates: 1.98 °C per 1000 ft in the troposphere (6.5 °C per km); the tropopause is where the lapse rate falls below 2 °C per km.

Troposphere contains about 80% of atmospheric mass and nearly all water vapour and weather; its depth averages about 36,000 ft, higher at the equator than at the poles.

Stratosphere temperature rises with height because ozone absorbs ultraviolet radiation; the tropopause marks the boundary where temperature stops decreasing.

Pressure halves roughly every 18,000 ft in the lower atmosphere; at 18,000 ft it is about 500 hPa, at 34,000 ft about 250 hPa.

ISA temperature at a pressure level: T = 15 − 1.98 × (altitude in thousands of ft); ISA pressure altitude deviation is measured against 1013.25 hPa.

Above 11 km (36,089 ft) ISA temperature is constant at −56.5 °C; the standard atmosphere is used to calibrate altimeters and aircraft performance.

Altimeter set to QNH reads elevation above mean sea level at the aerodrome; QFE reads height above the aerodrome reference point; 1013.25 hPa gives pressure altitude.

High-to-low or hot-to-cold flight path: true altitude is lower than indicated; low-to-high or cold-to-hot, true altitude is higher than indicated.

Rule of thumb: about 1 hPa pressure change equals 30 ft near sea level; a 1 °C temperature error affects true altitude by roughly 0.4% per 1000 ft.

Density altitude rises with high temperature, high humidity, low pressure, and high elevation; it governs takeoff and climb performance.

Pressure decreases with altitude and with warm air columns (warm air is less dense, so pressure falls more slowly with height in warm columns).

QNE transition: above the transition altitude all aircraft set 1013.25 hPa, so the transition layer separates altitude from flight level.

Altimeter errors: mountain-wave and cold-air effects cause the altimeter to over-read; strong surface pressure gradients cause rapid changes requiring frequent updates.

Density ρ = P / (R × T) with R = 287 J/(kg·K) and T in kelvin; a 10 °C rise at constant pressure lowers density about 3.5%.

Relative humidity = (actual vapour pressure ÷ saturation vapour pressure) × 100; saturation vapour pressure rises with temperature.

Dew point is the temperature to which air must cool at constant pressure and moisture to reach saturation; spread = temperature − dew point.

Condensation occurs when air cools to its dew point or when moisture is added; condensation nuclei are required for cloud droplets.

Lifting condensation level (LCL) ≈ 400 ft per 1 °C of surface temperature–dew point spread (about 125 m per °C).

Environmental lapse rate categories: absolutely unstable above 3 °C per 1000 ft, conditionally unstable between 3 and 2 °C per 1000 ft, absolutely stable below 2 °C per 1000 ft.

Dry adiabatic lapse rate is 3 °C per 1000 ft; saturated adiabatic lapse rate is about 1.5 °C per 1000 ft, smaller in warm air.

Stable air resists vertical motion, giving smooth stratus cloud and steady precipitation; unstable air gives convective cloud, showers, and turbulence.

Temperature inversions trap moisture and pollutants below them and produce wind shear at the inversion top; they form by radiation, subsidence, advection, or frontal processes.

Cloud genera: cirrus, cirrostratus, cirrocumulus (high, above 20,000 ft); altostratus, altocumulus (middle, 6,500–20,000 ft); stratus, stratocumulus, nimbostratus (low); cumulus and cumulonimbus (vertical).

Stable lifting produces layered stratus, altostratus, and nimbostratus; convective lifting produces cumulus and cumulonimbus.

Continuous steady precipitation indicates nimbostratus; showery precipitation indicates cumuliform cloud; drizzle indicates stratus; hail indicates cumulonimbus.

Cumulonimbus hazards: icing, hail, turbulence, lightning, microbursts, and tornadoes; avoid by at least 20 nautical miles.

Freezing rain occurs when snow falls through a warm layer aloft and then a subfreezing layer near the surface; it signals severe airframe icing risk.

Ice pellets indicate a refreezing layer aloft; snow flurries indicate shallow moisture; virga indicates precipitation evaporating before reaching the ground.

Fog forms when temperature reaches the dew point; radiation fog needs clear skies, light wind, and high humidity; advection fog needs warm moist air over a cold surface.

Obscurations: mist reduces visibility to 1–5 km, fog below 1 km, haze is dry particulate, blowing snow and sand reduce visibility in strong wind.

Air mass classification: cA, cP, mP, cT, mT; source regions are polar, tropical, continental, and maritime; mT is warm and moist, cP is cold and dry.

Cold front: steep slope (about 1:50), narrow band of heavy showers, squalls, and thunderstorms, rapid clearing behind, sharp wind veer and pressure rise.

Warm front: shallow slope (about 1:150), broad band of layered cloud and steady precipitation, gradual clearing, wind veer, and slow pressure fall.

Occluded front: cold front overtakes warm front; weather resembles warm front followed by cold front; wrapped occlusion in mature cyclones.

Stationary front: little movement, prolonged cloud and precipitation, often parallel to upper flow; may regenerate into a wave cyclone.

Frontal slope: a 1:150 slope reaches 20,000 ft about 570 nm ahead of the surface front; cirrus appears first, then altostratus, then nimbostratus.

Dry line: boundary between moist and dry air, common in the southern plains; a focus for severe thunderstorm development.

Post-frontal weather: cold advection, unstable showers, good visibility, gusty northwest winds, and building high pressure.

Mid-latitude cyclone life cycle: wave development on a front, open wave, mature (occluded) stage, and decay; typical duration 3–7 days.

Cyclogenesis is favoured by upper-level divergence, strong temperature gradients, and a short-wave trough; surface pressure falls ahead of the trough.

Norwegian cyclone model: warm sector between cold and warm fronts, apex at the low centre where the occlusion begins.

Upper-air analysis: 500 hPa troughs and ridges steer surface systems; vorticity maxima and jet streaks enhance lift and cyclogenesis.

Blocking patterns (omega block, Rex block) stall surface systems and cause prolonged weather; they are common over the North Atlantic and Pacific.

Anticyclones: subsidence, clear skies, light winds, radiation fog and inversions; they steer cyclones along their periphery.

Tropical cyclones require sea-surface temperature above 26.5 °C, low shear, and Coriolis effect beyond 5° latitude; they weaken over land or cold water.

Polar lows and lee lows form in cold air and can deepen rapidly; they are small and hard to forecast, producing severe icing and turbulence.

Thunderstorm stages: cumulus (updraft), mature (updraft and downdraft, lightning, rain, hail), dissipating (downdraft only); mature stage is most hazardous.

Ingredients for thunderstorms: conditional instability, a lifting mechanism, and sufficient moisture; severe storms need strong vertical wind shear.

Microburst: downdraft less than 2.5 nm across, lasting 5–15 minutes; headwind then tailwind shear can exceed 45 kt, causing performance loss.

Icing types: clear (rime mixed) ice from large supercooled drops in stratiform cloud, rime ice from small drops in cumuliform cloud; most severe in the 0 to −20 °C band.

Icing intensity increases with liquid water content, droplet size, and airspeed; freezing rain is severe icing; ice accumulates on leading edges and increases stall speed.

Turbulence: mechanical from surface friction and terrain, thermal from convection, frontal shear, and clear-air turbulence near jet streams.

Clear-air turbulence is most likely near jet-stream cores, in strong wind shear, and near mountain waves; it is invisible to radar.

Lightning, hail, and wind shear are thunderstorm hazards; hail size above 2 cm is severe; avoid all thunderstorms by at least 20 nm.

Foehn or chinook: air descends the lee slope, warming at the dry adiabatic rate; lee slopes are warm, dry, and often clear.

Orographic lift on windward slopes produces cloud, precipitation, and turbulence; the lee side experiences subsidence, clear skies, and possible rotors.

Mountain wave conditions: wind within 30° of perpendicular to the ridge, speed above 25–30 kt at ridge top, and a stable layer near the ridge.

Sea breeze: daytime heating causes onshore flow; land breeze: night cooling causes offshore flow; sea-breeze fronts can trigger thunderstorms.

Valley and slope winds: anabatic upslope winds by day, katabatic downslope winds at night; cold-air drainage creates frost pockets in valleys.

Santa Ana, mistral, and bora are strong downslope or gap winds that cause severe low-level turbulence and crosswind problems.

Lake-effect snow forms when cold air crosses a warm lake, with low-level instability and fetch along the wind; heavy snow bands downwind.

Coastal fog: warm moist air over cold upwelling water; advection fog forms and can persist for days, reducing visibility below minima.

METAR sequence: type, station, time (UTC), wind, visibility, runway visual range, present weather, sky cover, temperature/dew point, altimeter, remarks.

Wind group: direction in tens of degrees true, speed in knots, gusts as G; VRB for variable direction; 00000KT for calm; 18010KT for 180° at 10 kt.

Visibility in statute miles in Canada and the US; prevailing visibility is the greatest visibility equal to or exceeded in at least half the horizon circle.

Sky cover: FEW (1–2 oktas), SCT (3–4), BKN (5–7), OVC (8); BKN or OVC is a ceiling; VV indicates vertical visibility into obscuration.

Weather codes: RA rain, SN snow, SH showers, TS thunderstorm, DZ drizzle, FG fog, BR mist, HZ haze, FZ freezing prefix, + heavy and − light.

SPECI is issued for significant changes: ceiling or visibility crossing criteria, thunderstorm onset, wind shift, or aircraft mishap.

PIREP: UA routine, UUA urgent; reports time, location, altitude, type, and phenomena such as turbulence, icing, or wind shear.

Upper-air data: radiosondes report pressure, temperature, dew point, and wind at mandatory and significant levels; tephigrams and Skew-T plots show stability and shear.

TAF: type, station, issue time, validity period, wind, visibility, weather, sky cover; change groups BECMG, TEMPO, FM, and probability groups PROB30 and PROB40.

TAF validity in Canada is typically 24 or 30 hours; TAFs are issued four times daily at 00, 06, 12, and 18 UTC; amended TAFs correct errors.

GFA (Graphical Forecast Areas) provides cloud, weather, visibility, wind, and icing/turbulence graphics in time steps; it replaces the former FA.

SIGMET: significant meteorological information for severe turbulence, severe icing, volcanic ash, tropical cyclones, and severe squall lines; valid up to 4 hours (6 for hurricanes).

AIRMET: moderate icing, moderate turbulence, and extensive mountain obscuration or low ceilings; issued for hazards below SIGMET thresholds.

Airmet/Sigmet in Canada: AIRMET for moderate icing and turbulence, low-level wind shear, and extensive obscuration; SIGMET for severe conditions.

Wind shear and microburst alerts, LLWS alerts, and aerodrome warnings supplement TAFs; convective SIGMETs cover thunderstorms with hail above 2 cm or wind above 50 kt.

Volcanic ash advisories and tropical cyclone advisories are issued by VAACs and RSMCs; they supplement SIGMETs for ash or hurricane hazards.

Surface analysis charts show isobars at 4 hPa intervals, fronts, pressure centres, and station models; they are issued every 3 or 6 hours.

Upper-air charts: 850, 700, 500, 300, and 250 hPa; they show heights, temperature, wind, and troughs and ridges used for forecasting.

Significant weather (SIGWX) charts depict fronts, jet streams, turbulence, icing, and cumulonimbus areas for flight planning.

Icing and turbulence charts show forecast areas by intensity and altitude band; they are used for route and altitude selection.

GFA and upper-air charts are available through NAV CANADA and Environment Canada aviation weather services; METARs, TAFs, and SIGMETs are available online.

Wind and temperature aloft forecasts (FD) give winds and temperatures at 3,000-ft intervals up to 53,000 ft for flight planning.

Satellite imagery: visible, infrared, and water-vapour channels; infrared shows cloud-top temperature and convective intensity; water vapour shows upper moisture and dry slots.

Weather radar shows precipitation intensity and movement; it does not detect turbulence, icing, or clear-air hazards.