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yr_weather

This gem converts yr.no forecasts into application friendly structures. It summarises and aggregates the data to make it easy to deliver weather forecasts, for any place on earth, using the awesome yr.no forecasts.

Specifically, the Gem repackages yr's data to make it easy to:

  1. Present it
  2. Draw graphs
  3. Make decisions
  4. Script forecasts into databases or other systems

The Gem deals with caching (either using the file system, or in Redis), and constructs the API request to YR in a manner that complies with their requirements.

Takes the heavy lifting out of creating a forecast like this:

alt text

Code is below.

Terms of Service

YR are pretty permissive. There is a request for attribution, and a twenty requests per second rate limit. Before you get to far, please review this.

Installation

Either add it to your Gemfile: gem 'yr_weather'

And then bundle install.

Or: bundle install yr_weather

Configuration

While YR don't require any registration or API keys, they do as that you provide a site name and email address. Specifically:

the name of your website and some contact info (e.g. a GitHub URL, a non-personal email address, a working website or a mobile app store appname)

To this end, the gem will require at least an @ symbol in the site name.

/config/initializers/weather.rb

YrWeather.config do |c|
  c.sitename   = '<the_name_of_your_website>;<an_email_address>'
  c.utc_offset = '+02:00'
  c.redis      = Redis.new(:host => 'localhost', :port => 6379)
end

utc_offset is optional, and is used to calculate the day start time.

If redis is configured, it will be used to cache the forecasts. If it is nil or omitted, the gem will cache data in the file system.

Usage

parser = YrWeather.new(latitude: -33.953109, longitude: 18.480635)
pp parser.metadata
pp parser.current
pp parser.next_12_hours
pp parser.daily
pp parser.six_hourly
pp parser.tomorrow
pp parser.three_days
pp parser.week
pp parser.arrays
Method Description
metadata Returns a hash describing the forecast. It includes units, expiry times, and geographic detail.
current Current meteorological conditions: temperature, wind speed, etc.
next_12_hours Conditions over the next twelve hours.
daily For the next week, per day, minima and maxima, maximum windspeeds, rainfall, etc.
six_hourly Six hourly forecast detail.
tomorrow Tomorrow's maximum and minimum temperature, maximum windspeed, as well as cumulative forecast precipitation.
three_days Maximum and minimum temperature over the next three days, maximum windspeed, as well as cumulative forecast precipitation for those three days.
week Maximum and minimum temperature over the next week, maximum windspeed, as well as cumulative forecast precipitation for the week.
arrays A hash of six, equally sized, arrays: at, temperature, wind_speed, wind_speed_knots, precipitation, and hours. Use this data for graphing.

Returned Values

You will generally get back hashes, with some or all of the following:

Parameter Description
temperature_maximum Maximum temperature
temperature_minimum Minimum temperature
wind_speed_max Wind speed (meters per second)
wind_speed_max_knots Wind speed (knots)
wind_description A Beaufort scale descriptor: Breezy or hurricane force. Human friendly.
wind_direction N, S, SE etc. Will be the predominant wind direction for the period.
precipitation How much it's going to rain in that period.
from, to, at The range or time that this forecast, or forecast period, relates to.
symbol_code Maps to an icon.

Icons

YR provide a set of icons here.

Caching

YR only run their model periodically. As such, there's no point in beating up their API's endlessly. The gem will cache results based on the "expires" guidance provided by their API servers.

The gem will either need to be able to write to Redis, or to the Linux temporary directory (internally, we call Dir.tmpdir).

Dependencies

Requires a reasonably recent version of ruby. There are no other dependencies.

Sample Code

To render the forecast as illustrated above:

<%
  @weather = YrWeather.new(latitude: @latitude, longitude: @longitude)
  current  = @weather.current
%>

  <div class="d-flex mb-4 ml-1">
    
    <div class="card h-120 mr-4">
      <div class="card-body">
        <h4 class="card-title">Current Conditions</h5>
        <div class="d-flex">
          <div><img src="/img/weather_icons/<%=current[:symbol_code]%>.svg" width="128" height="128" /></div>
          <div class="h2">
            <%=current[:air_temperature].round%><small class="text-muted">&deg;C</small><br/>
            <small class="text-muted"><%=current[:wind_direction]%></small> <%=current[:wind_speed].round%> <small class="text-muted">ms<sup>-1</sup> (<%=current[:wind_description]%>)</small><br/>
            <%=current[:precipitation_amount]%> <small class="text-muted">mm rain</small><br/>
          </div>
        </div>
      </div>
    </div>
    
    <div class="card h-120 mr-4">
      <div class="card-body">
        <h4 class="card-title">Three Day View</h5>
        <div class="d-flex">
          <div class="h2">
            High: <%=@weather.three_days[:temperature_maximum].round%><small class="text-muted">&deg;C</small><br/>
            Low: <%=@weather.three_days[:temperature_minimum].round%><small class="text-muted">&deg;C</small><br/>
            Max: <%=@weather.three_days[:wind_speed_max].round%> <small class="text-muted">ms<sup>-1</sup> mostly <%=@weather.three_days[:wind_direction]%></small><br/>
            Cumm: <%=@weather.three_days[:precipitation].round%> <small class="text-muted">mm rain</small><br/>
          </div>
        </div>
      </div>
    </div>
    
    <div class="card h-120">
      <div class="card-body">
        <h4 class="card-title">Week View</h5>
        <div class="d-flex">
          <div class="h2">
            High: <%=@weather.week[:temperature_maximum].round%><small class="text-muted">&deg;C</small><br/>
            Low: <%=@weather.week[:temperature_minimum].round%><small class="text-muted">&deg;C</small><br/>
            Max: <%=@weather.week[:wind_speed_max].round%> <small class="text-muted">ms<sup>-1</sup> mostly <%=@weather.week[:wind_direction]%></small><br/>
            Cumm: <%=@weather.week[:precipitation].round%> <small class="text-muted">mm rain</small><br/>
          </div>
        </div>
      </div>
    </div>

  </div>

  <div class="d-flex flex-wrap" >
    <% @weather.six_hourly.each do |forecast| %>
      <div class="mb-2 mr-2" style="width: 220px;">
        <div class="card h-100">
          <div class="card-body">
            <h5 class="card-title"><span data-format="ddd, HH:mm" class="time"><%=forecast[:from]%></span> to <span data-format="HH:mm" class="time"><%=forecast[:to]%></span></h5>
            <div class="d-flex">
              <div class="mr-2"><img src="/img/weather_icons/<%=forecast[:symbol_code]%>.svg" width="64" height="64" /></div>
              <p class="card-text">
                Max: <%=forecast[:temperature_maximum].round%><small class="text-muted">&deg;C</small><br/>
                <small class="text-muted"><%=forecast[:wind_direction]%></small> <%=forecast[:wind_speed_max]%> <small class="text-muted">ms<sup>-1</sup></small><br/>
                <%=forecast[:precipitation]%> <small class="text-muted">mm rain</small><br/>
              </p>
            </div>
          </div>
        </div>
      </div>
    <% end %>
  </div>

This code has dependencies on Bootstrap, as well as some JavaScript magic we use for formatting dates and times. But, hopefully you get a sense of what's involved in using the gem.

Contributing

Please do! There's plenty that can be improved here!

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Downloads and parses YR.no weather forecasts

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