PRINCIPLES OF AERODROME WEATHER OBSERVATIONS Course Notes BUREAU OF METEOROLOGY TRAINING CENTRE 08AUG2018 Contents Cloud Observations ................................................................................................................ 1 Definition of a cloud ........................................................................................................................1 Common terms used when making cloud observations .................................................................2 Cloud Classification ........................................................................................................................3 Table of Classification of Clouds ....................................................................................................4 The 11 basic cloud types ................................................................................................................5 Observing conditions to which the cloud descriptions apply ..........................................................6 Cirrus: Ci ........................................................................................................................................7 Cirrocumulus: Cc ...........................................................................................................................8 Cirrostratus: Cs ..............................................................................................................................9 Altocumulus: Ac .......................................................................................................................... 10 Altostratus: As ............................................................................................................................. 11 Nimbostratus: Ns ........................................................................................................................ 12 Stratocumulus: Sc ....................................................................................................................... 13 Stratus: St ................................................................................................................................... 14 Cumulus: Cu ............................................................................................................................... 15 Towering Cumulus: TCu ............................................................................................................. 16 Cumulonimbus: Cb ..................................................................................................................... 17 Performing a cloud observation ................................................................................................... 18 Identifying the types of cloud present .......................................................................................... 18 Cloud levels – the height range of clouds .................................................................................... 19 Cloud composition ....................................................................................................................... 21 Optical phenomena associated with clouds ................................................................................ 22 Clouds and precipitation .............................................................................................................. 22 Factors affecting the appearance of clouds ................................................................................. 23 Determining cloud types at night ................................................................................................. 24 Estimation of cloud amount ......................................................................................................... 25 Estimation of the height of the cloud base ................................................................................... 26 Laser Ceilometer – Cloud Height and Amount ............................................................................ 32 Cloud observations - Further considerations ............................................................................... 34 Further reading ............................................................................................................................ 34 Visibility Observations .......................................................................................................... 35 Definition ...................................................................................................................................... 35 Factors affecting visibility ............................................................................................................. 35 Weather phenomena and visibility ............................................................................................... 36 Selection of visibility markers ....................................................................................................... 36 Procedure for making visibility observations ............................................................................... 38 Visibility terminology .................................................................................................................... 39 Visibility Meter .............................................................................................................................. 40 Weather Observations .......................................................................................................... 42 Definitions .................................................................................................................................... 42 Precipitation phenomena ............................................................................................................. 43 Precipitation Intensity - TBRG ..................................................................................................... 44 Drizzle DZ .................................................................................................................................. 44 Rain RA..................................................................................................................................... 46 Freezing Rain FZRA and Freezing Drizzle FZDZ............................................................... 46 Snow SN ................................................................................................................................... 47 Hail GR ..................................................................................................................................... 47 Small Hail/Snow Pellets GS...................................................................................................... 48 Snow Grains SG ....................................................................................................................... 48 Ice Pellets PL ............................................................................................................................ 48 Weather watch radar and precipitation identification ................................................................... 49 Approximate rainfall rates ............................................................................................................ 49 Rain bands from Altostratus and Nimbostratus ........................................................................... 49 Showers from cumuliform clouds ................................................................................................ 50 i Heavy precipitation from thunderstorms ...................................................................................... 50 Obscuration phenomena ............................................................................................................. 51 Fog FG ...................................................................................................................................... 51 Fog Patches BCFG ................................................................................................................... 51 Partial Fog (Fog Bank) PRFG .................................................................................................. 51 Shallow Fog MIFG .................................................................................................................... 51 Freezing Fog FZFG .................................................................................................................. 52 Mist BR ..................................................................................................................................... 52 Smoke FU ................................................................................................................................. 52 Haze HZ .................................................................................................................................... 52 Dust DU .................................................................................................................................... 52 Drifting Dust DRDU ................................................................................................................... 52 Drifting Sand DRSA .................................................................................................................. 53 Blowing Dust BLDU .................................................................................................................. 53 Blowing Sand BLSA .................................................................................................................