Chapter 3: Cloud Types, Storm Structure, Light Scattering

Created by Sarah Choi (prompt writer using ChatGPT)

Cloud Types, Storm Structure, Light Scattering — Sky Language for Environment Concept Artists

Why sky language matters

Skies set mood, time, scale, and weather logic in a single glance. When your clouds, storms, and color obey the physics of moisture and light, scenes feel inevitable. This article turns atmospheric science into visual cues you can sketch fast and implement in production—so your cloudscapes read at thumbnail distance and hold up in close shots.

The four dials behind every sky

  1. Moisture (humidity and where it condenses), 2) Stability (does rising air keep rising?), 3) Lift (fronts, terrain, convergence, surface heating), 4) Wind shear (variation with height). Set these, and the cloud family, storm type, and lighting almost choose themselves.

Cloud families and what they want to do

Cloud names combine form (cumulus = heap, stratus = layer, cirrus = hair‑like, nimbus = rain) and height.

High clouds (6–13 km / 20–43k ft)

  • Cirrus (Ci): Wispy filaments aligned with upper winds; often splayed by jet‑stream shear. Portend changing weather 12–24 hours ahead. Cues: ice‑crystal streaks, hooked “mares’ tails,” subtle parallax.
  • Cirrostratus (Cs): Thin, milky veils that create 22° halos and sundogs; sun/moon still visible. Cues: uniform glare plate with halo optics.
  • Cirrocumulus (Cc): Tiny ripples or “mackerel sky.” Short‑lived, signal upper‑level instability. Cues: fine cellular texture, strong perspective foreshortening.

Mid clouds (2–6 km / 6.5–20k ft)

  • Altostratus (As): Gray sheets, sun a bright disc; steady large‑scale lift ahead of warm fronts. Cues: featureless slab with gentle tonal gradient.
  • Altocumulus (Ac): Mid‑level patches/streets, often with cast shadows on lower layers; can form lenticular stacks near mountains. Cues: larger cells than Cc, shading indicates depth.

Low clouds (surface–2 km / 0–6.5k ft)

  • Stratus (St): Ground‑hugging sheet; drizzle/fog. Cues: very low ceiling, soft horizon disappearance.
  • Stratocumulus (Sc): Lumpy layer with breaks; widespread in marine layers. Cues: honeycomb or streets with sunlight “pooling” in gaps.
  • Cumulus humilis (Cu): Fair‑weather puffs with flat, dark bases at lifting condensation level (LCL). Cues: cauliflower tops, consistent base height.

Vertical development

  • Towering cumulus (TCu): Deepening convection; sharp edges, vertical turrets; can evolve into storms. Cues: bright crisp sunward edges, dark bases with rain curtains forming.
  • Cumulonimbus (Cb): Thunderstorm clouds with anvil tops. Anatomy: updraft tower, overshooting top, anvil (downwind), rain/hail core, flanking line of towers, gust front/shelf cloud. Cues: crisp illuminated updraft face, diffuse anvil ice, virga curtains, lightning.

Special morphologies

  • Lenticular (mountain waves): Smooth lens stacks fixed over ridges, aligned perpendicular to wind; fast changing internal texture.
  • Mammatus: Pouchlike under‑anvil sacs—ice/sinking air—post‑storm drama.
  • Asperitas: Agitated, wavy underbellies—turbulent stratocumulus.
  • Roll cloud (arcus): Detached horizontal tube at gust front; leads squall lines.
  • Wall cloud: Localized lowering under the rain‑free base, in supercells; may spin.
  • Virga: Precipitation evaporating before ground—streaks beneath cloud base.
  • Fog: Cloud at the ground (radiation, advection, upslope). Cues: layered visibility slices, halos around lights.

Storm structure for believable drama

Air‑mass thunderstorms

Single cell; 30–60 minutes; afternoon heating + weak shear. Look: isolated towers; rain core collapses, gust front spreads, cloud dissolves.

Multicell clusters/lines

Series of short‑lived cells; new towers form on upwind flank. Squall lines feature a shelf cloud at the gust front and a trailing stratiform region. Look: sawtooth leading edge, curtains of rain, frequent lightning along the line.

Supercells (rotating monsters)

Strong instability + strong vertical shear yields a persistent mesocyclone. Anatomy: rotating updraft (rain‑free base) with wall cloud, rear‑flank downdraft (RFD) clearing slot, forward‑flank rain/hail core, tilted, vented anvil, overshooting top. Look cues: barber‑pole striations around the updraft, inflow tail, sculpted “stacked plates.” Tornadoes form beneath the wall cloud in rare cases.

Frontal systems and large‑scale setups

  • Warm front: Wide swath of layered clouds: Ci → Cs (halo) → As → Ns; light steady rain. Look: stacked veils thickening toward the front.
  • Cold front: Narrow line of Cb with squalls, then clearing Sc. Look: sharp shelf cloud leading edge, blue‑sky behind.
  • Dryline: Boundary between moist and dry air; explosive late‑day towers. Look: crisp cu field transitions into towers along a line.

Design translation: Put your most detailed, high‑contrast geometry on the inflow/updraft side; smear/soften on the anvil side. Place dust and low scud under gust fronts; rain curtains obscure mid‑ground to stage reveals.

Light scattering: why the sky is blue and sunsets are on fire

Scattering modes

  • Rayleigh (molecules): Strongly wavelength‑dependent (~1/λ⁴). Gives blue daytime sky, red sunsets (blue removed along long paths at low sun).
  • Mie (aerosols): Weakly wavelength‑dependent; forward‑scattering highlights near the sun; hazy, milky skies; bright aureole around sun.
  • Tyndall (in colloids/cloud edges): Visible when particles are near light wavelength; gives iridescent edges.

Skylight color logic

  • High sun, dry air: Deep cobalt zenith transitioning to lighter horizon; hard shadows.
  • Humid/hazy: Pale blue/whitish dome; reduced contrast; strong sun aureole.
  • Golden hour: Long path removes blue/green; direct light warms (amber/orange) while shadows go cool cyan/blue. Clouds lit from below take fiery lower edges and cooler tops.
  • Afterglow/alpenglow: Even after sunset, high clouds still lit—peach/magenta anvil undersides; mountains glow from scattered skylight.

Optical phenomena (quick placement guide)

  • 22° halo, sundogs (parhelia), circumzenithal arc: Ice‑crystal optics in Cs/Ci; require sun ~22° below the arc center; sundogs sit horizontally from the sun at 22°.
  • Coronas & iridescence: Small‑droplet diffraction around the sun/moon; seen in thin Ac/Cu edges. Place near the sun with subtle pastel rings.
  • Glory & Brocken spectre: Opposition effect on cloud/fog beneath viewer with sun at your back—your shadow surrounded by colored rings.
  • Rainbows: Observer between sun and rain; primary at ~42° radius with red outer; secondary dimmer and reversed at ~51°; supernumerary fringes inside primary in fine drops.

Design translation: Use angle‑correct placement: halos at 22°, rainbows opposite the sun. Don’t sprinkle optics randomly—tie to the right cloud types and geometry.

Reading and staging scale

  • Parallax ladders: Stack three height regimes—low Sc streets, mid Ac patches, high Ci streamers—moving at different speeds/directions.
  • Edge sharpness vs. humidity: Crisp turret edges in dry upper air; soft, smeared anvils in humid sheared environments.
  • Base height consistency: Fair‑weather Cu share one flat base; vary only tops to imply shared LCL and give scale reliability.

Production translation (volumetrics & shading)

  • Volume representation: Use large 3D noise fields (erosion‑warped Perlin/Worley) for macro mass; add billow/ridge noise for cauliflower edges; apply height‑dependent density falloff to keep flat bases and fibrous anvils.
  • Phase function: Start with Henyey–Greenstein (g≈0.6–0.85 forward) for cloud droplets (Mie‑like), add a weaker backscatter lobe for silver linings at grazing angles. Ice anvils can be more forward‑scattering.
  • Lighting: One or two directional lights (sun/moon) plus ambient skylight from an analytic sky model. Enable multi‑scattering approximation to avoid under‑lit cloud cores.
  • Shadowing: Deep self‑shadow along sunward turrets; soft penumbra across anvils. Bake/temporal‑accumulate cloud shadows for stable ground movement.
  • Wind layers & shear: Drive low, mid, high decks with distinct vectors and speeds; let anvils advect faster with upper winds than bases.
  • Weather presets: Fair‑weather Cu, Marine Sc deck, Dryline towers, Squall line, Classic supercell, Post‑frontal Sc breakup, Warm‑front veil. Each preset swaps density fields, wind vectors, base height, and light coloration.
  • Performance: Distant skybox billboards or sky domes for high Ci/Cs; real volumetrics only for mid/low decks and storm towers near camera. Use temporal reprojection and low‑frequency noise for stability.

Troubleshooting quick fixes

  • Puffy spheres: Add flat bases, anvil outflow, and turret asymmetry; sharpen sunward edges, soften leeward.
  • Clouds moving as one slab: Split into decks with distinct parallax and speeds; rotate high Ci with jet‑stream.
  • Sunset too orange everywhere: Warm direct light but keep skylight cool; preserve complementary shadow hue.
  • Random lightning: Concentrate strikes in precipitation cores and along gust fronts; occasionally in anvil stratiform region.
  • Featureless overcast: Introduce subtle mammatus/asperitas patches, embedded brighter “windows,” and rain shafts; add directional gradients from the sun’s azimuth.

Field studies for concept practice

  • Paint a dryline evening: shallow Cu field, sharpening into a line of towering Cu with anvils sheared downwind; add a golden‑hour warm rim on towers and cool shadowed flanks.
  • Design a coastal marine layer morning: Sc sheet with open‑cell “honeycomb,” sun shafts through gaps, coastal hills poking into the deck; transition to broken Cu by noon.
  • Stage a classic supercell: stacked‑plate updraft with barber‑pole striations, rain‑free base with wall cloud, forward‑flank hail shaft, rear‑flank clear slot, and a laminar anvil with mammatus at dusk.

Final checklist

  • Do cloud forms match lift/stability and share consistent base heights where appropriate?
  • Are storm features placed on the correct flank (inflow/updraft vs. anvil/downwind)?
  • Do light colors split correctly between warm direct light and cool skylight, with angle‑true optics?
  • Is multi‑deck parallax present to sell depth and scale?
  • Do wind vectors and shear organize cloud motion and texture orientation?

When cloud physics, storm anatomy, and light scattering all agree, your skies won’t just decorate the scene—they’ll drive story, time, and emotion from horizon to horizon.