National - Change to Rainfall Intensity Thresholds used in Bureau of Meteorology Surface Observations (METAR, SPECI and AWIS)

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    Open advisory
    74 days remaining
    Start 14/11/2022
    AEDT 11:00
    End 31/01/2023
    AEDT 11:00

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    Cathy  Kingston
    Bureau of Meteorology

    The Bureau of Meteorology (Bureau) will adopt the Rainfall Intensity Thresholds (RIT), recommended by the International Civil Aviation Organization (ICAO), to report the intensity of showers, rain and thunderstorms.

    Purpose

    This notice provides information regarding a change in the Rainfall Intensity Thresholds (RIT) used for reporting present weather intensity for showers, rain and thunderstorms in surface observations, including METAR, SPECI and the Automatic Weather Information Service (AWIS).

    The Bureau will adopt the RIT recommended by ICAO to report the intensity of showers, rain and thunderstorms.

    The change will align the Bureau’s observation reporting with approved international standards and will standardise the reporting of precipitation intensity across all Bureau surface observation products.

     The new RIT will be reported as follows:

    • Light (-) intensity is less than 2.5mm/hour
    • Moderate (no prefix) intensity is between 2.5 and 10 mm/hour
    • Heavy (+) intensity is greater than 10 mm/hour No change will be made in intensity reporting for frozen precipitation or drizzle.

    The RIT change will be implemented at all Bureau owned and operated AWS and manual observation sites starting 14 November 2022, with CAT A aerodromes scheduled to be completed by 31 January 2023. Updates for remaining CAT B, C and D aerodromes are scheduled for completion by 30 November 2023. Further advice may be obtained by contacting Aviation Meteorological Services via email: webav@bom.gov.au. Refer also to Aeronautical Information Circular (AIC) H27/22.

    Submitted by

    Cathy  Kingston
    Bureau of Meteorology
    cathy.kingston@bom.gov.au