Storm Station 247

The Field Book/Vol. III, The Sky/Cloud classification/FB-SKY-041

Cumulonimbus architecture

A cumulonimbus is built of parts a spotter learns to name: the updraft tower and the flanking line of towers feeding it, the anvil at the tropopause and the dome above it, mamma under the anvil, the rain free base and wall cloud under the updraft, and the rain and hail ahead.

Plate FB-SKY-041Storm cloudsRevision 1, 2026-09-24Status draftAlso called supercell structure, flanking line, backsheared anvil, rain free base, inflow band, beaver tail, low precipitation supercell, high precipitation supercell, classic supercell

A painted elevation of a classic supercell over a prairie, heights to scale from the ground to 49,000 feet (15 kilometres), moving left to right: a flanking line of towering cumulus stepping up from the left to the main updraft tower; a small dome of overshooting top above the anvil near 44,000 feet (13.4 kilometres); the anvil spread along the tropopause at 39,000 feet (12 kilometres), carried downwind to the right and backsheared a short way to the left; mamma under the downwind anvil; a rain free base near 4,500 feet (1.4 kilometres) with a dark wall cloud beneath the updraft; the rain and hail core falling from the forward flank; and a low inflow band feeding the storm from the right.
Fig. A A supercell from outside. A classic supercell seen from the side, moving left to right.MaximizeThe drawing, to scale

What it is

A cumulonimbus, Cumulonimbus FB-SKY-019, is one cloud built of many parts, and a storm spotter learns to name each. Fig. A draws a classic supercell side on, moving left to right, with every visible part numbered.

The main updraft rises in a tower from a flat, rain free base to the tropopause, near 39,000 ft (12 km) in the middle latitudes in summer. There its top spreads into the anvil, carried far downwind and, in a strong storm, backsheared a short way upwind against the wind aloft. Above the updraft a dome can push through the anvil: the overshooting top, Overshooting top and above anvil plume FB-SKY-042. Under the downwind anvil hang the pouches of mamma. Behind the updraft, a flanking line of towering cumulus steps up toward it, each tower a younger updraft joining the old. Under the updraft the base lowers into a wall cloud, Wall cloud FB-SKY-040; ahead of it, rain and hail fall from the forward flank; and a band of low cloud, the inflow band, can be seen feeding moist air into the storm from ahead.

What it is not

It is not a single tower. A cumulus congestus has no anvil, no ice top and no thunder. A multicell cluster has several updrafts at different stages, none lasting; a supercell has one, lasting for hours and turning, Supercell FB-EVT-007.

Lookalikes

Cumulus congestus
A single tower with no anvil, no ice top and no thunder
Multicell cluster
Several cells at different stages, none dominant, and no one lasting updraft
Nimbostratus
A layer with steady rain and no towers

The machine

The parts are the storm's circulation made visible. The updraft condenses its moisture into the tower and, at the tropopause, spreads it as the anvil. The downdraft beneath the rain and hail spreads out as the gust front. The wind changing with height tilts the whole storm, keeps its rain from falling back into its updraft, and in a supercell sets the updraft turning.

Supercells come in three kinds, drawn in Fig. B, by how much rain falls and where. A low precipitation storm drops little rain, and its bare, striated updraft stands in plain sight. A classic storm drops rain and hail ahead of the updraft, and its wall cloud hangs behind them. A high precipitation storm wraps heavy rain around its updraft and can hide the wall cloud, and a tornado, inside it.

Three small paintings of a supercell under its anvil. Low precipitation: a bare striated updraft tower with a small wall cloud and a thin shaft of rain. Classic: a wall cloud under the updraft, and rain and hail falling ahead of it on the right. High precipitation: heavy rain wrapped around the updraft, hiding the wall cloud.
Fig. B The three kinds of supercell. The same storm with little rain, some, and a great deal.MaximizeThe drawing, to scale

The drawings

Each figure drawn as an engineering sheet, its parts numbered, to print at 11 by 17.

Elevation of a classic supercell from the ground to 49,000 feet (15 kilometres), moving left to right: a flanking line of towering cumulus stepping up from the left to the main updraft tower; an overshooting dome above the anvil near 44,000 feet (13.4 kilometres); the anvil spread along the tropopause near 39,000 feet (12 kilometres), carried downwind to the right and backsheared a short way to the left; mamma under the downwind anvil; a rain free base near 4,500 feet (1.4 kilometres) with a wall cloud beneath the updraft; the rain and hail core falling from the forward flank; and an inflow band feeding the storm from ahead.1122334455667788AABBCCDDEESTORM STATION 247THE FIELD BOOKPLATE FB-SKY-041-AA CLASSIC SUPERCELL SIDE ON, MOVING LEFT TO RIGHT, EVERY VISIBLE PART NUMBERED; HEIGHTS TYPICALFIG. A A SUPERCELL FROM OUTSIDE01020304002468101214kft(km)LOWMIDDLEHIGHTROPOPAUSEINFLOWSTORM MOTIONKEYIce crystalsWater dropletsRain and hailUpdraft123456789TITLECumulonimbus architecture, a supercell from outsideVOL. III THE SKY · STORM CLOUDSTYPEELEVATIONSCALEHEIGHT TO SCALE, WIDTH NTSREVREV 1 DRAFT SHEET 1 of 2DATE2026-09-24IDFB-SKY-041-ADRAWN AS linework on paperSOURCES WMO, Markowski, Wallace
Fig. A, the drawing A supercell from outside. A classic supercell side on, moving left to right, every visible part numbered; heights typical HEIGHT TO SCALE, WIDTH NTSMaximizeThe sheet, SVG, 11 by 17The painting
  1. The overshooting top
  2. The anvil
  3. The backsheared anvil
  4. Mamma
  5. The flanking line
  6. The main updraft tower
  7. The rain free base and wall cloud
  8. The rain and hail core
  9. The inflow band, flumen
Three small elevations of a supercell with their names and a line each: low precipitation, with a bare striated updraft tower and little rain; classic, with rain and hail ahead and the wall cloud behind them under a rain free base; and high precipitation, with heavy rain wrapping around the updraft and hiding the wall cloud.1122334455667788AABBCCDDEESTORM STATION 247THE FIELD BOOKPLATE FB-SKY-041-BLOW PRECIPITATION, CLASSIC AND HIGH PRECIPITATION, TOLD APART BY HOW MUCH RAIN FALLS AND WHEREFIG. B THE THREE KINDS OF SUPERCELL1LOW PRECIPITATIONLittle rain, often large hail; the updraft towerstands bare and striated, and the whole stormcan be seen. Common on the western High Plains.2CLASSICRain and hail ahead, the wall cloud behind themunder a rain free base. The storm drawn inFig. A, and the one spotters learn first.3HIGH PRECIPITATIONHeavy rain wraps around the updraft and canhide the wall cloud and any tornado inside it.Common in the moist air of the East and South.EACH DRAWN SMALL AND NOT TO SCALE, THE STORM MOVING LEFT TO RIGHT. MANY STORMS FALL BETWEEN THE THREE.TITLECumulonimbus architecture, the three kinds of supercellVOL. III THE SKY · STORM CLOUDSTYPECLASSIFICATIONSCALENOT TO SCALEREVREV 1 DRAFT SHEET 2 of 2DATE2026-09-24IDFB-SKY-041-BDRAWN AS linework on paperSOURCES WMO, Markowski, Wallace
Fig. B, the drawing The three kinds of supercell. Low precipitation, classic and high precipitation, told apart by how much rain falls and where NOT TO SCALEMaximizeThe sheet, SVG, 11 by 17The painting
  1. Low precipitation
  2. Classic
  3. High precipitation

Ingredients

  • A deep unstable atmosphere, so an updraft can rise to the tropopause
  • Wind that changes speed and direction with height, which tilts the storm and, in a supercell, sets its updraft turning
  • Moist air near the ground feeding the updraft from ahead of the storm

Scales

time
an hour for one cell; several hours for a supercell
horizontal
10 to 30 mi (16 to 48 km) for a supercell, with an anvil that can spread over 100 mi (160 km)
vertical
from a base near 4,500 ft (1.4 km) to above the tropopause
orlanski
meso beta

Signatures

surface
CB in the sky report; the storm's parts are seen, not measured
satellite
the anvil spreading downwind, and overshooting tops above it
radar
the rain and hail core; in a supercell, a hook of echo round the updraft and a rotation couplet in the velocity data

The numbers

QuantityValue, and the kind of number it is
AnvilSpread along the tropopause, near 39,000 ft (12 km) in the middle latitudes in summerTypical, Wallace 2006
Flanking lineA line of towering cumulus stepping up toward the main updraft, usually on the storm's rear flankTextbook, Markowski 2010
Backsheared anvilAnvil spreading upwind against the wind aloft, a sign of a strong updraftTextbook, Markowski 2010
Kinds of supercellLow precipitation, classic and high precipitation, by how much rain falls and whereTextbook, Markowski 2010
Atlas namesincus, mamma, murus, cauda, arcus, praecipitatio; the inflow band is the accessory cloud flumenStandard, International Cloud Atlas
Severe thunderstormHail of 1 inch (2.5 cm) or more, a gust of 58 mph (50 knots, 26 m/s) or more, or a tornadoStandard, Directive 10-511
Airport ceilometerCloud bases to 12,000 ft (3.7 km) overheadStandard, Automated Surface Observing System (ASOS) User's Guide

How the station sees it

A station sees the storm by what reaches it: the gust, the pressure jump, the rain and hail, and thunder. Radar sees its rain, its hook and its rotation, and satellites its anvil and overshooting tops.

How it is warned

The Weather Service warns the storm, not its parts, Thunderstorm FB-EVT-001; spotters report the parts that radar cannot see near the ground.

See also

Sources

  1. World Meteorological Organization. International Cloud Atlas.
  2. Markowski, P. and Y. Richardson. Mesoscale Meteorology in Midlatitudes (2010).
  3. Wallace, J. M. and P. V. Hobbs. Atmospheric Science, An Introductory Survey, 2nd ed. (2006).
  4. National Weather Service. Directive 10-511, WFO Severe Weather Products Specification.
  5. National Weather Service. Automated Surface Observing System (ASOS) User's Guide.

Definition after the International Cloud Atlas. Plate FB-SKY-041, revision 1, 2026-09-24. The number is permanent; cite it.