Cloud PointField Guide

The library

Fifty-two entries — genera, species, supplementary features and the optical phenomena that ride along with them. Photographed plates, in order of altitude.

High — above 6,000 m10

22° Halo — The bright ring around sun or moon22° HaloIIIOften an early sign of an approaching warm front - rain possible within 12-24 hoursNoctilucent — Earth's highest, glowing-at-night cloudsNoctilucentIVNone - forms far above the weather, in the mesosphereCirrus — Delicate ice-crystal brushstrokesCirrusVIFair weather currently, but may signal approaching warm frontNacreous — 'Mother-of-pearl' clouds glowing in winter twilightNacreousXIIINone - forms in the polar winter stratosphere, far above the weatherSun dogs — Twin 'false suns' flanking the real oneSun dogsXVIIHigh cirrus moving in; can precede a warm front and rain within a day or twoCirrocumulus — Tiny rippled grains — rarest of the high cloudsCirrocumulusXXIGenerally fair weather, but may indicate approaching front within 24-48 hoursSun Pillar — A shaft of light standing above a low sunSun PillarXXVIIIIce crystals or diamond dust in the air; often bitterly coldCircumzenithal Arc — The 'upside-down rainbow' overheadCircumzenithal ArcXLIIHigh ice cloud with a low sun; can precede a warm frontHomomutatus — Aircraft contrails spread into man-made cirrusHomomutatusXLVIHumid air aloft preserving contrails; can precede a warm frontCirrostratus — The thin ice veil that haloes the sunCirrostratusXLVIIIRain or snow likely within 12-24 hours; often precedes warm fronts

Middle — 2,000 to 6,000 m18

Corona — Coloured rings hugging the sun or moonCoronaVIIThin cloud crossing the sun or moon; little weather significance on its ownAsperitas — The newest, most ominous wavy undersideAsperitasXUnsettled, turbulent air, but usually disperses without a stormAltostratus — The featureless grey veil that dims the sunAltostratusXVIRain or snow likely within 12-24 hoursBanner cloud — The flag streaming off a sharp peakBanner cloudXVIIIStrong wind streaming over a sharp peak, otherwise clearKelvin-Helmholtz — Breaking ocean waves, frozen in the skyKelvin-HelmholtzXIXStrong wind shear aloft; little direct weather significanceGlory — Rainbow rings around your own shadowGloryXXThin cloud or fog below you with the sun behind; no weather significanceVirga — Rain that falls but never landsVirgaXXIIDry air below the cloud - rain is evaporating before it can landLenticular — The 'flying saucer' of the skyLenticularXXVStrong, moist winds crossing high ground; turbulence likely aloftHorseshoe Vortex — A horseshoe that vanishes in minutesHorseshoe VortexXXIXDaytime thermals with wind shear; fair but breezyFallstreak Hole — The hole-punch cloud that sparks UFO reportsFallstreak HoleXXXThin supercooled cloud, often near flight paths; no significant weatherCloud Iridescence — Pastel rainbow colours in thin cloudCloud IridescenceXXXIIIThin cloud near the sun; no weather significanceCastellanus — Turrets that warn of afternoon thunderstormsCastellanusXXXVMid-level instability; afternoon thunderstorms may followAltocumulus — Mid-level cloudlets in patches and wavesAltocumulusXXXVIGenerally fair; morning altocumulus on humid days may signal afternoon thunderstormsNimbostratus — The thick, sunless rain- and snow-makerNimbostratusXLIProlonged precipitation, overcast conditions for extended periodsUndulatus — Ripples revealing waves in the air itselfUndulatusXLIIIWind shear between air layers; little direct weather significancePileus — The fleeting 'halo cap' on a rising towerPileusXLVIIVigorous rising convection; a thunderstorm may be developingVelum — The thin veil draped through a storm towerVelumLMoist, stable air pierced by storm towers; convection buildingLacunosus — A honeycomb of cloud holesLacunosusLIPockets of sinking air in thin cloud; no weather significance

Low — below 2,000 m17

Cumulus — The classic fair-weather puffballCumulusIFair weather when small; if growing tall, possible showers laterMorning Glory — A 1,000 km tube of cloud glider pilots surfMorning GloryVMarks a passing atmospheric wave; often a sudden wind shift as it arrivesFog — Cloud at ground levelFogIXDamp, calm conditions and poor visibility, often clearing as the day warmsStratocumulus — The world's most common cloud, in lumpy rollsStratocumulusXIGenerally settled weather; often clears by afternoonRainbow — Sunlight unravelled by falling raindropsRainbowXIIShowers nearby with sunshine - a sign of scattered, passing rainShelf cloud — The menacing wedge on a storm's leading edgeShelf cloudXIVA thunderstorm's gust front - strong straight-line winds and rain imminentDiamond dust — Glittering airborne ice that makes halos at eye levelDiamond dustXXIIIVery cold, clear, calm airFogbow — A ghostly white rainbow in fogFogbowXXIVFog or thin cloud with a low sun behind youSteam Fog — When the sea appears to smokeSteam FogXXVIICold air over much warmer water; calm and clearStratus — The grey blanket that becomes fogStratusXXXIGrey, overcast conditions; possible light precipitationWall Cloud — The lowered base where tornadoes are bornWall CloudXXXIIA severe storm's updraught - a possible tornado if it begins to rotateCloud Streets — Parallel cloud rows along the windCloud StreetsXXXVIIICold air streaming over a warmer surface; brisk, fair but coolCataractagenitusXXXIXLocalised to large waterfalls; no broader weather significanceFractus / Scud — Ragged shreds racing beneath a stormFractus / ScudXLIVRain falling nearby; gusty, showery conditionsMoonbow — A rainbow made by moonlightMoonbowXLVRain or spray opposite a bright moon at nightLight Pillars — Vertical beams above ground lights on frozen nightsLight PillarsXLIXVery cold, calm night with ice crystals suspended in the airGreen Flash — The split-second green at the horizon at sunsetGreen FlashLIIClean air over a low, distant horizon at sunset or sunrise

Multi-level — spanning several layers7

Mammatus — The sky's hanging pouchesMammatusIISevere weather in the vicinity; often seen during or after thunderstormsPyrocumulus — The cloud a wildfire builds above itselfPyrocumulusVIIIMarks intense surface heat (wildfire or volcano); can build into stormsCrepuscular rays — Sunbeams fanning through gaps in cloudCrepuscular raysXVBroken cloud with a low sun; little weather significanceCumulonimbus — The towering storm factoryCumulonimbusXXVISevere weather imminent - thunderstorms, heavy precipitation, possible tornadoesPyrocumulonimbus — When a fire grows its own thunderstormPyrocumulonimbusXXXIVAn extreme fire-driven storm - lightning, fierce gusts, even fire tornadoesAnticrepuscular Rays — Sunbeams converging opposite the sunAnticrepuscular RaysXXXVIIBroken cloud with a low sun; little weather significanceFunnel Cloud & Tornado — The spinning column reaching for the groundFunnel Cloud & TornadoXLA severe rotating storm - destructive winds if it reaches the ground