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Symbols for significant Weather (SIGWX)

Table of contents

I. Symbols for significant weather

Moderate turbulence
Severe turbulence
Drizzle
Rain
Snow
Shower
Hail
Widespread blowing snow
Moderate aircraft icing
Severe aircraft icing
Freezing precipitation
Widespread smoke
Severe sand or dust haze
Widespread sandstorm or duststorm
Widespread mist
Widespread fog
Widespread haze
Volcanic eruption
Radioactive materials in the atmosphere
Mountain waves
Mountain obscuration
Severe squall line
Tropical cyclone
Cold front at the surface
Warm front at the surface
Occluded front at the surface
Quasi-stationary front at the surface
Convergence line
Intertropical convergence zone
Tropopause low
Tropopause high
Tropopause level
Freezing level
State of the sea
Sea-surface temperature
Position, speed and level of maximum wind
Widespread strong surface wind
Height of the jet axis changes by /–3000 ft or the speed changes by /–20 kt

Wind arrows indicate the maximum wind in jet and the flight level at which it occurs. If the maximum wind speed is 120 kt or more, the flight levels between which winds are greater than 80 kt is placed below the maximum wind level. In the example, winds are greater than 80 kt between FL220 and FL400. The heavy line delineating the jet axis begins/ends at the points where a wind speed of 80 kt is forecast.

Wind arrows indicate the maximum wind in jet and the flight level at which it occurs. If the maximum wind speed is 120 kt or more, the flight levels between which winds are greater than 80 kt is placed below the maximum wind level. In the example, winds are greater than 80 kt between FL220 and FL400. The heavy line delineating the jet axis begins/ends at the points where a wind speed of 80 kt is forecast.

II. SWL Charts (low level)

X
Position of pressure centres given in hectopascals
L
Centre of low pressure
H
Centre of high pressure
Scalloped lines
Demarcation of area of significant weather

III. Clouds

III.1 Type

ST
Stratus
CU
Cumulus
CB
Cumulonimbus
SC
Stratocumulus
NS
Nimbostratus
AS
Altostratus
AC
Altocumulus
CI
Cirrus
CS
Cirrostratus
CC
Cirrocumulus

III.2 Amount (except CB)

FEW
Few (1 to 2 oktas)
SCT
Scattered (3 to 4 oktas)
BKN
Broken (5 to 7 oktas)
OVC
Overcast (8 oktas)

III.3 Amount (CB)

ISOL
Isolated (individual CBs)
OCNL
Occasional (well-separated CBs)
FRQ
Frequent (CBs with little or no separation)
EMBD
Embedded (CBs embedded in layers of other clouds or concealed by haze)

III.4 Heights

  • Heights are indicated on SWH and SWM charts in FL, top over base,
  • In SWL charts heights are indicated as altitudes AMSL,
When XXX is used, tops or bases are outside the layer of the atmosphere to which the chart applies

IV. References

MET.TR.215 (Commission Implementing Regulation (EU) 2017/373)