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Forecaster is a gem wrapping wgrib2 to
fetch and read weather data directly from the Global Forecast System.
It comes with a library and a CLI allowing you to type commands like forecast for this afternoon in paris in your terminal to get the latest weather
forecast.
gem install forecaster
Alternatively you can build the gem from its repository:
git clone git://github.com/vinc/forecaster.git
cd forecaster
gem build forecaster.gemspec
gem install forecaster-1.0.0.gemIn both cases you need to make sure that you have wgrib2 present in your
system.
To install the wgrib2 from source:
wget https://ftp.cpc.ncep.noaa.gov/wd51we/wgrib2/wgrib2.tgz tar -xzvf wgrib2.tgz cd grib2 export CC=gcc export FC=gfortran make sudo cp wgrib2/wgrib2 /usr/local/bin/
require "forecaster"
To configure the gem:
Forecaster.configure do |config| config.wgrib2_path = "/usr/local/bin/wgrib2" config.cache_dir = "/tmp/forecaster" config.records = { temperature: ":TMP:2 m above ground:", humidity: ":RH:2 m above ground:", pressure: ":PRES:surface:" } end
Forecaster saves large files containing the data of GFS runs from the NOAA servers in the cache directory, but only the parts of the files containing the records defined in the configuration will be downloaded.
You can find the list of available records online or by reading any
.idx files distributed along with the GFS files.
A record is identified by a variable and a layer separated by colon
characters. In the case of the temperature for example, those attributes
are TMP and 2 m above ground. See the documentation of wgrib2 for
more information.
To fetch a forecast:
t = Time.now.utc # All the dates should be expressed in UTC y = t.year # year of GFS run m = t.month # month of GFS run d = t.day # day of GFS run c = 0 # hour of GFS run (must be a multiple of 6) h = 12 # hour of forecast (must be a multiple of 3) forecast = Forecaster.fetch(y, m, d, c, h) # Forecaster::Forecast
To read the record of a forecast:
res = forecast.read(:temperature, longitude: 48.1147, latitude: -1.6794) # String in Kelvin val = res.to_f - 273.15 # Float in degree Celsius
Forecaster has a command line tool that try to be smart:
$ forecast for tomorrow afternoon in auckland
GFS Weather Forecast
Date: 2016年05月13日
Time: 12:00:00
Zone: +1200
Latitude: -36.8 °
Longitude: 174.8 °
Pressure: 1013.8 hPa
Temperature: 21.7 °C
Nebulosity: 0.0 %
Humidity: 65.1 %
Precipitation: 0.0 mm
Wind: 8.0 m/s (NE)
But you can use it in a more verbose way:
$ TZ=America/Los_Angeles forecast --time "2016-05-12 09:00:00" \
--latitude "37.7749295" \
--longitude "-122.4194155" \
--debug
Requested time: 2016年05月12日 09:00:00 -0700
GFS Run time: 2016年05月11日 23:00:00 -0700
Forecast time: 2016年05月12日 08:00:00 -0700
Downloading: 'http://www.ftp.ncep.noaa.gov/data/nccf/com/gfs/prod/gfs.20160
51200/gfs.t00z.pgrb2.0p25.f015'
Reading index file...
Length: 4992281 (4.76M)
100% [===========================================>] 696 KB/s Time: 00:00:07
GFS Weather Forecast
Date: 2016年05月12日
Time: 08:00:00
Zone: -0700
Latitude: 37.8 °
Longitude: -122.4 °
Pressure: 1013.5 hPa
Temperature: 13.4 °C
Nebulosity: 0.0 %
Humidity: 89.7 %
Precipitation: 0.0 mm
Wind: 1.0 m/s (NE)
To use automatically the timezone of a location you will need to create a free GeoNames account and export your username in an environment variable:
export GEONAMES_USERNAME=<username>
And while you're doing that, you can also export your favorite location to avoid typing it every time:
export FORECAST_LATITUDE=<latitude>
export FORECAST_LONGITUDE=<longitude>
Copyright (c) 2015-2018 Vincent Ollivier. Released under MIT.