Cloud Identification Guide — All Cloud Types Plus Storm-Spotter Clouds

Cloud Identification Guide — All Cloud Types Plus Storm-Spotter CloudsA field guide to cloud types: the WMO's 10 genera (cirrus, cumulus, stratus, cumulonimbus, etc.) plus the storm-spotter taxonomy (wall cloud, shelf cloud, mammatus, beaver tail). How to distinguish wall from shelf.Clouds get sorted by altitude first — high, middle, low, vertical — and then by shape (heap, layer, wisp, anvil). The WMO has 10 main genera. The ones a storm spotter actually cares about — wall clouds, shelf clouds, mammatus — sit in their own taxonomy below the main 10.High clouds (above 20,000 ft)

Cirrus (Ci): Thin wispy streaks ("mare's tails"). Ice crystals. Often the first sign a warm front is approaching ~24-48 hours out.

Cirrocumulus (Cc): Small white tufts in patterns ("mackerel sky"). Rare, short-lived; signals upper-level instability.

Cirrostratus (Cs): Thin transparent veil. Causes a halo around the sun or moon (ice-crystal refraction). Often precedes precipitation 12-24 hours.

Middle clouds (6,500–20,000 ft)

Altocumulus (Ac): Patches of "puffy" elements, gray or white. Morning Ac in summer often means thunderstorms by afternoon.

Altostratus (As): Gray uniform sheet. Sun looks "watered down" through it. Often precedes steady precipitation.

Nimbostratus (Ns): Thick dark gray layer actively producing precipitation. The classic "rainy day overcast."

Low clouds (below 6,500 ft)

Stratus (St): Featureless gray sheet, like elevated fog. Produces drizzle, mist, or light snow.

Stratocumulus (Sc): Gray patches/rolls/lumps. Most common cloud worldwide. Light drizzle at most.

Cumulus (Cu): Detached puffy "fair weather" clouds. Often grow vertically through the day.

Vertical / convective

Cumulus congestus / TCu: "Towering cumulus" — vertical heap clouds with cauliflower tops. Transition between fair-weather Cu and Cb.

Cumulonimbus (Cb): The thunderstorm cloud. Tower extends from low altitudes up to the tropopause. Anvil top spreads horizontally. Produces lightning, hail, heavy rain, microbursts, and rotation.

Storm-spotter clouds

Wall cloud: Localized lowering attached to the rain-free base of a thunderstorm, usually under the updraft. Can rotate. Tornadoes most often form from rotating wall clouds.

Funnel cloud: Visible rotating column descending from a wall cloud, NOT touching the ground. Becomes a tornado on contact OR if dust is being kicked up directly below it.

Shelf cloud (arcus): Wedge-shaped cloud along the leading edge of a gust front (cold outflow). Looks dramatic but is NOT tornadic — it's straight-line wind.

Roll cloud: Horizontal tube-shaped cloud detached from the parent storm. Forms in stable air ahead of an outflow boundary. Rare and photogenic.

Mammatus: Pouch-like protrusions hanging UNDER a storm anvil. Sign of very turbulent air. NOT directly tornadic but indicates intensity.

Tail cloud: Horizontal cloud band extending from a wall cloud toward the precipitation core. Indicates inflow.

Beaver tail: Flat smooth horizontal inflow band on the right-rear flank of a supercell. Long tongue-shaped — looks like its namesake. Indicates a strong organized supercell.

Wall vs shelf cloud — the most-confused pair

Wall cloud: Localized, under the rain-free base, may rotate, ahead of where rain is falling. Forms in INFLOW air. Tornado risk.

Shelf cloud: Long horizontal wedge, at the leading edge of rain, kicked up by OUTFLOW air, doesn't rotate. Straight-line wind only.

Quick test: which way is the wind blowing under it? Inflow (toward the cloud) = wall cloud, possibly tornadic. Outflow (away from the cloud, gusting in your face from the storm) = shelf cloud, straight-line wind.Reference

NOAA JetStream Cloud Classification: noaa.gov/jetstream/clouds

NWS Spotter Field Guide: weather.gov/safety/thunderstorm-spotterguide

WMO International Cloud Atlas: cloudatlas.wmo.int

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