EASA PPL Meteorology (P30) — Study Guide

Meteorology shares the 60-minute paper format with Navigation and Flight Performance & Planning for good reason: shallow weather knowledge is dangerous in ways shallow Air Law rarely is. The P30 exam is 20 questions in 60 minutes; at 75% you need 15 correct. It spans the atmosphere, pressure and wind, clouds and precipitation, fog, fronts, icing, thunderstorms, and decoding METARs, TAFs, and charts you will use for your entire flying career.

Candidates who memorise disconnected facts struggle. Candidates who picture how the atmosphere moves retain detail because it follows from physics. Start from principles, then anchor the numbers (ISA, lapse rates, formations) to those principles.

The atmosphere

Structure

Almost all weather lives in the troposphere. It reaches roughly 36,000 ft at mid-latitudes (tropopause height varies with latitude and season). Temperature falls with height throughout the troposphere — the foundation for stability and cloud formation.

The tropopause separates troposphere from stratosphere; above it, temperature trends change and vertical mixing across the boundary is weak — which is why significant weather generally stays below.

International Standard Atmosphere (ISA)

ISA is the reference model for performance work. Know it tightly for the exam:

• Sea-level temperature: 15 °C
• Sea-level pressure: 1013.25 hPa
• Temperature lapse rate: 1.98 °C per 1,000 ft (often rounded to 2 °C operationally)

Real atmospheres diverge; ISA deviation feeds performance. For P30, precise ISA constants matter more than deriving corrections.

Pressure and density

Density drops with altitude. At equal pressure, warm air is less dense than cold air; moist air is slightly less dense than dry air. Those facts tie aircraft performance to temperature and humidity and underpin the stability chapter.

Pressure and wind

How pressure drives wind

Horizontal pressure differences create pressure gradients; air accelerates from high toward low pressure. Earth rotation introduces Coriolis: deflection to the right in the northern hemisphere (left in the southern). Wind therefore crosses isobars at an angle near the surface and runs roughly parallel aloft as gradient wind.

Buys Ballot's law

Northern hemisphere rule of thumb: stand with your back to the wind; low pressure lies on your left, high pressure on your right. It lets you orient roughly to synoptic systems from surface wind alone.

Surface wind vs upper wind

Surface friction slows wind and causes backing relative to the gradient wind aloft. The friction layer reaches roughly 2,000 ft over land (less over water). Descending into friction changes wind direction and speed versus free-air forecasts — expect MET surface winds to differ from upper-level winds used for nav.

Isobars and wind speed

Tight isobar spacing ⇒ steep gradient ⇒ strong wind; widely spaced isobars ⇒ light winds. Be ready to interpret charts qualitatively under exam time.

Thermal processes and stability

Adiabatic processes

Rising parcels expand and cool without external heat exchange; sinking parcels compress and warm — adiabatic temperature changes.

• Unsaturated (dry) ascent: DALR ≈ 3 °C per 1,000 ft.
• Saturated ascent releases latent heat; cooling slows — SALR averages ~1.5 °C per 1,000 ft but varies with temperature and moisture.

Atmospheric stability

Compare the environmental lapse rate (ELR) — actual temperature profile — with DALR and SALR:

• Absolutely stable: ELR < SALR. Displaced parcels sink back; layer clouds, stratus, drizzle, poor visibility dominate.
• Conditionally unstable: SALR < ELR < DALR. Dry parcels resist lift; saturated parcels may become buoyant and keep rising — typical mid-latitude summer pattern.
• Absolutely unstable: ELR > DALR. Vigorous convection, towering cumulus, thunderstorms possible.

Examiners love numeric stability drills — rehearse the decision tree until it is automatic.

Clouds — ten genera

Classification blends height band and form. Know weather significance, not just names.

High (≈ above 20,000 ft mid-latitudes)

• Ci — wispy ice crystals; warm-front harbinger, not heavy precip.
• Cs — veil halos; thickening signals worsening skies ahead.
• Cc — rippled tufts; usually benign.

Medium (≈ 6,500–20,000 ft)

• As — grey sheet; frontal rain/snow possible.
• Ac — patch/wave layers; Ac castellanus warns of instability aloft and potential storms later.

Low (surface–6,500 ft)

• St — dull layer; drizzle and poor VFR.
• Sc — patchy rolls; usually light precip at most.
• Ns — thick continuous rain/snow; multi-layer depth.

Vertical development

• Cu — thermals; benign small Cu vs towering congestus signalling energy.
• Cb — full-stack hazards: turbulence, icing, hail, lightning, windshear, microbursts. Maintain generous lateral clearance from active cells.

Fog

Fog is cloud on the surface — a serious VFR trap.

Radiation fog

Surface radiational cooling on clear, calm(ish), humid nights. Pools in valleys; peaks after midnight; often lifts/burns off after sunrise but can linger — schedule accordingly.

Advection fog

Warm moist air advects over a colder surface until saturated — needs neither clear skies nor calm wind. Irish coastal/sea fog exemplifies persistence independent of diurnal cycle; don't assume morning clearance.

Hill fog

Cloud base intersecting terrain — operationally identical to IMC on ridges though technically embedded stratus. Sharp terrain plus low bases equals frequent VFR traps.

Steam fog

Very cold air over warmer water; shallow steam-like wisps — usually thin but illustrates moisture flux concepts.

Frontal systems

Mid-latitude depression lifecycle

Classic sequence approaching from the west: high cirrus thickening and lowering through Cs → As → Ns with gradual lowering bases and deteriorating visibility; continuous precip hours ahead of the warm front; bases may fall below 500 ft.

Warm-front passage: rain eases, bases lift somewhat, temperature rises, pressure trend shifts, wind backs then steadies — you enter the warm sector.

Warm sector: murky stratus, drizzle, marginal VFR common.

Cold front: narrower, sharper band — heavy showers, gusts, wind shift, embedded convection possible.

Behind cold front: rapid improvement, showery Cu between clearer spells — classic post-frontal sparkle when showers miss you.

Occlusion

Faster cold front overtakes warm front, lifting warm-sector air; weather becomes messy — often sustained poor conditions until system clears.

Icing

• Clear ice: large supercooled droplets freeze slowly — dense, hard, aerodynamically nasty — typical of vigorous Cu/Cb.
• Rime ice: tiny droplets flash-freeze — opaque, rough, common in stratiform layers well below freezing.
• Mixed: hybrid textures across droplet spectrum.

Carburettor ice: venturi cooling can drop intake air far below OAT — risk persists even when outside air feels warm if humidity is high; unexplained RPM decay ⇒ carb heat on immediately per POH habit.

Thunderstorms

• Cumulus stage: dominated by updrafts; precip not yet at surface.
• Mature stage: updrafts and downdrafts coexist — lightning, hail, severe turbulence, windshear; anvil tops flatten at tropopause.
• Dissipating stage: downdrafts cut inflow; precip wanes while anvil remnants drift downwind.

Hazards tested repeatedly: turbulence (in and below cells), windshear on approach/departure, severe icing in updrafts, lightning and hail (hail can fall miles downwind), microbursts. Conservative avoidance beats threading cells — plan ≥10 NM from active Cb under VFR when practical, more if bumpiness demands.

Weather reports and forecasts

METAR essentials

Example skeleton:

EIDW 011250Z 25015KT 9999 FEW018 SCT025 11/06 Q1013 NOSIG

• Wind is degrees true, speed in knots — unlike typical ATC/ATIS magnetic references.
• Cloud amounts use oktas: FEW (1–2), SCT (3–4), BKN (5–7), OVC (8).
• Ceiling = lowest BKN or OVC; FEW/SCT alone mean no formal ceiling even if bases are low for VFR judgement.

TAF essentials

• BECMG — gradual change reaching stated conditions inside window.
• TEMPO — short-lived fluctuations (<1 h episodes, < half the window total).
• PROB30 / PROB40 — probabilistic hazards still deserve conservative planning (especially TS).

Where students lose marks

• Stability maths: misordering ELR vs SALR/DALR — drill numbered scenarios.
• Radiation vs advection fog: diurnal clearing vs persistent maritime stream — scenario cues beat rote labels.
• METAR wind reference: true vs magnetic awareness even when variation is small — the exam checks the concept.
• Ceiling selection: lowest BKN/OVC only — ignore FEW/SCT for ceiling definition.

How to prepare

Meteorology rewards causal reasoning: why SALR differs from DALR (latent heat release), why valleys collect radiation fog (cold-air pooling), why coastal advection ignores sunrise fixes. Pair that narrative with hard facts — ISA, lapse rates, frontal sequences, METAR tokens.

With three minutes per question on average, slow down on decoding questions: parse METAR/TAF groups methodically instead of skimming. Pilots who already brief real METARs usually absorb the products section faster — start reading them before the exam sitting if you can.