Ruby Class/script to decode METAR Reports

metar.rb

#!/usr/bin/ruby
unless ARGV.any?
  puts 'Usage: metar.rb <paste your METAR report here>'
  exit
end

# Example METAR report:
# METAR KITH 162256Z 15006KT 10SM BKN080 19/08 A2997 RMK AO2 SLP149 T01940078

class Metar

  require 'time'

  # General storage fields
  attr_accessor :original, :metar
  # METAR specific fields
  attr_accessor :airport_code, :time, :wind, :visibility,
                :weather, :clouds, :temp_dew, :altimeter, :remarks

  def initialize(metar)
    raise ArgumentError, 'Expected METAR to be a String' unless metar.instance_of? String
    self.original = metar.upcase
    self.metar = metar.upcase.split
    remove_report_type
    # raise ArgumentError, 'Incomplete METAR report' if report_incomplete?
  end

  def print_report
    puts "#{report_type} Weather report for #{airport_code}"
    puts "Observed at #{report_time}"
    puts "Wind #{combined_wind_speed} #{wind_direction_cardinal} (#{wind_direction} deg.)"
    puts "Visibility #{visibility_distance} #{visibility_units}"
    puts "Clouds: #{clouds}"
    puts "Temperature: #{temperature}C - Dew Point #{dew_point}C"
    puts "Altimeter: #{pressure}Hg"
  end

  def report_type
    if %w[SPECI METAR].include? original.split.first
      original.split.first
    else
      'UNKNOWN'
    end
  end

  def report_type_unknown?
    report_type == 'UNKNOWN'
  end

  def report_incomplete?
    metar.count < 11
  end

  def airport_code
    # KITH
    @airport_code || metar.first
  end

  def report_time
    # 162256Z
    Time.strptime(metar[1].sub('Z', '+0000'), '%d%H%M%z')
  end

  def wind
    # 15006KT
    metar[2]
  end

  def combined_wind_speed
    if wind_gusting?
      "#{wind_speed} #{wind_units} with gusts up to #{wind_gust_speed} #{wind_units}"
    else
      wind_speed
    end
  end

  def wind_speed
    wind[3, 2].to_i
  end

  def wind_units
    speed_to_english wind[-2, 2]
  end

  def wind_gusting?
    !wind_gust.nil?
  end

  def wind_gust
    metar[2].match(/(G\d+)/).to_s
  end

  def wind_gust_speed
    wind_gust.match(/(\d+)/).to_s
  end

  def wind_direction
    wind[0, 3].to_i
  end

  def wind_direction_cardinal
    if wind_direction > 315 || wind_direction < 45
      'N'
    elsif wind_direction == 45
      'NE'
    elsif wind_direction > 45 && wind_direction < 135
      'E'
    elsif wind_direction == 135
      'SE'
    elsif wind_direction > 135 && wind_direction < 225
      'S'
    elsif wind_direction == 225
      'NE'
    elsif wind_direction > 225 && wind_direction < 315
      'W'
    elsif wind_direction == 315
      'NE'
    else 'U'
    end
  end

  def visibility
    # 10SM
    metar[3]
  end

  def visibility_distance
    visibility[0...-2]
  end

  def visibility_units
    speed_to_english visibility[-2, 2]
  end

  def clouds
    metar[4]
  end

  def temperature
    temperature_dew_point.match(/^\d+/).to_s
  end

  def dew_point
    temperature_dew_point.match(/\d+$/).to_s
  end

  def altimeter
    metar[6]
  end

  def pressure
    altimeter.match(/\d+$/).to_s.to_f / 100
  end

  private

  def temperature_dew_point
    metar[5]
  end

  def speed_to_english(acronym)
    case acronym
    when 'KT' then 'Knots'
    when 'SM' then 'Miles'
    else ''
    end
  end

  def precipitation_to_english(acronym)
    case acronym
    when 'DZ' then 'drizzle'
    when 'RA' then 'rain'
    when 'SN' then 'snow'
    when 'SG' then 'snow grains'
    when 'IC' then 'ice crystals'
    when 'PE' then 'ice pellets'
    when 'GR' then 'hail'
    when 'GS' then 'small hail/snow pellets'
    when 'UP' then 'unknown'
    else 'unknown'
    end
  end

  def remove_report_type
    unless report_type_unknown?
      self.metar = original.split
      self.metar.shift
    end
  end

end

Metar.new(ARGV.join(' ')).print_report