Meteorological Charts

Wing Commander Rajagopal

Meteorological Charts

WAFS Significant Weather Charts

  • WAFS Significant Weather (SIGWX) Charts are issued by the World Area Forecast Centres (WAFC) in London and Washington.
  • Chart documentation provided for international flights includes:
    • Significant Weather (SIGWX) Charts
    • Wind Forecast Charts
    • Temperature Forecast Charts
  • SIGWX charts are generated from WAFC forecasts for flight levels between FL250 and FL630.
  • Wind and temperature forecast charts are prepared for the 250 hPa pressure level.
  • Chart documentation for national flights includes:
    • National Significant Weather Charts
    • WAFC Upper Wind and Temperature Charts for:
      • 600 m (2,000 ft)
      • 1,500 m (5,000 ft)
      • 3,000 m (10,000 ft)

WAFC Chart Validity and Coverage

  • High-Level WAFC charts are issued every 6 hours for flight levels FL250–FL630.
  • Medium-Level WAFC charts are issued every 6 hours for flight levels FL100–FL450.
  • WAFC charts cover the entire globe and are identified using ICAO area codes.

WAFC Significant Weather Information

WAFC Significant Weather (SIGWX) charts include the following information:

  • Thunderstorms
  • Embedded Cumulonimbus (CB) and significant clouding
  • Tropical Cyclones
  • Moderate and Severe Turbulence
  • Clear Air Turbulence (CAT)
  • Moderate and Severe Icing
  • Widespread Sand and Dust Storms
  • Frontal Zones and Inter Tropical Convergence Zone (ITCZ)
  • Significant Tropopause Flight Levels
  • Jet Streams
  • Volcanic Ash

Thunderstorms

  • Embedded CB clouds and thunderstorms are shown using curved lines.

Significant Clouds

  • Medium and high clouds are depicted along with associated aviation hazards.

Tropical Cyclones

  • Tropical cyclones are shown on the chart along with their names.

Severe Turbulence

  • Areas and flight levels affected by severe turbulence are marked.

Clear Air Turbulence (CAT)

  • CAT areas and flight levels are indicated along with wind speeds in knots.

Aircraft Icing

  • Moderate and severe icing areas are identified using standard chart symbols.

Convergence Zones

  • Convergence zones such as the Inter Tropical Convergence Zone (ITCZ) are marked.
  • Cloud development is generally expected within convergence zones.

Tropopause Heights

  • Tropopause heights are shown on the charts.
  • Jet streams are generally expected near the tropopause.

Jet Streams

  • The presence and location of jet streams are indicated.

Volcanic Ash

  • Areas affected by active volcanic ash from erupting volcanoes are shown.

National Significant Weather Charts

  • National Significant Weather (SIGWX) Charts are prepared four times daily at:
    • 0000 UTC
    • 0600 UTC
    • 1200 UTC
    • 1800 UTC
  • Prepared by Meteorological Watch Offices (MWO) for their respective Flight Information Regions (FIR).
  • Compiled and distributed by MWO Chennai.
  • SIGWX charts may be valid for 9 hours or 24 hours from the time of issue.
  • Medium-Level Charts cover FL100–FL250.
  • High-Level Charts cover FL250–FL630.

Contents of National SIGWX Charts

  • Tropical Cyclones with wind speeds greater than 34 knots.
  • CB clouds associated with:
    • Thunderstorms (TS)
    • Tropical Cyclones (TC)
    • Line Squalls
    • Hail
    • Moderate or Severe Icing
    • Turbulence
    • Clear Air Turbulence (CAT)
    • Marked Mountain Waves
    • Widespread Sand or Dust Storms
  • Freezing Level and Tropopause Height.
  • Location of volcanic eruptions or radioactive material release.
  • Jet Streams.

Local Forecast Chart

  • Forecast zones are identified using alphabetic labels.
  • Weather within each zone is described in plain language.
  • Frontal boundaries, direction (using arrows), and movement speed (knots) are indicated.
  • Weather phenomena are represented using meteorological symbols.

Local Forecast – Weather Information

  • Weather information includes:
    • Surface Wind
    • Visibility
    • Clouds
    • 0°C Isotherm
  • Information is presented in abbreviated meteorological format.

Weather Codes

Weather codes used are similar to those used in METAR reports.

Example – Surface Winds and Weather

Zone A:

  • Generally no significant weather.
  • Visibility generally 30 km.
  • Occasionally reduced to 7 km in rain showers.
  • Isolated areas with visibility of 4,000 m.
  • Thunderstorms and hail expected in the western part of the zone from 2100 UTC.
  • Locally 800 m visibility in moderate snow showers over mountainous areas.
  • Moderate turbulence with widespread severe turbulence to the north.
  • Isolated hill fog reducing visibility below 200 m.

Example – Clouds and Outlook

  • Generally scattered (SCT) or broken (BKN) Cumulus (CU) and Stratocumulus (SC).
  • Moderate icing and turbulence expected.
  • Cloud bases between 1,500 and 3,000 ft.
  • Cloud tops from 7,000 ft to above 10,000 ft.
  • Isolated CB clouds with bases from 1,500 ft and tops above 10,000 ft after 2100 UTC.
  • 0°C Isotherm between 4,000 and 5,000 ft (expressed in hundreds of feet).
  • Outlook until 11th – 0600 UTC: Showers spreading from the southeast to all areas.

Prognosis Chart

  • Prognosis charts become effective for 6 hours after the validity period of the main chart.
  • They show the expected future position of the weather systems depicted on the main chart.

Spot Wind Chart

  • Spot Wind Charts are issued four times daily.
  • Each chart is valid for 6 hours.
  • Charts provide:
    • Altitude
    • True Wind Direction
    • Wind Speed (knots)
    • Temperature (°C)
  • Used for route wind calculations during flight planning.