4caster.net

This post is all about Metcheck, a website based in the UK that not only provides both free and chargeable weather forecasting, but also has interesting challenges for its community. At the time of writing the challenge is to try to predict the weather for London 5 days into the future! OK so the prize is only getting to the top of the leaderboard, but if you want to test any of your weather prediction software/algorithms out it’s worth a go!

More traditionally, Metcheck has a variety of forecasting options around the world (even oddly for up to 300 days into the future – something that sounds more fantasy than fact!). Not surprises here… Metcheck get their data from the site that we’ve covered a few times before – the NOAA National Weather Service! But their selling point is that they have experience of corporate clients and do take pride in not just providing weather forecast data, but linking it to key subjects that people are interested in weather conditions for – such as farmers and Formula 1 !

Metcheck Premium is their chargeable service, as of November 2008 this was £3.95 a month, approximately $6. For this sum you get access to more comprehensive forecast data, archive data for the UK, live data and more.

Really situated as a weather data service provider rather than focusing on raw data, Metcheck is a well established business with many topics of interest.

If you’ve done any Googling about weather data then it should be clear that the National Weather Service provides one of the largest and most comprehensive sources of weather data.

This posting is to discuss the Current Conditions page on the NWS website and in particular the XML formatted data that is available. As I’m sure you know, one of the advantages of XML is that is strongly structures data so that there is no doubt what each element specifically is. To process XML in any language it’s always best to use inbuilt code or existing library extensions that will parse the XML data allowing you to extract just the information you require. For this example we’ll use PHP (specifically version 5) as it’s a very popular language….

So, we’ll start with working out which site we require weather data for. On the NWS page there is a link to a large zip file that covers all known weather data sites… it’s worth downloading that now.

Unfortunately you’ll just end up with approx 2800 files with obscure four character names! These are known as ICAO codes (International Civil Aviation Organization) and you’ll need to check around on the internet for a site that allows you to match a code to a particular site. For example, the Airline Industry Update site has a handy facility (as of November 2008) that allows you to match a code with a location.

So, now you should have worked out which locations you’re interested in current observations for. Let’s choose KJFK – Kennedy International Airport in New York.

Next we can see from the website that the correct xml address for each of the weather data sites looks like…

http://www.weather.gov/xml/current_obs/XXXX.xml

Of course, where XXXX is the 4 letter ICAO code! So to retrieve the current observations for JFK we’d use the following address…

http://www.weather.gov/xml/current_obs/KJFK.xml

Now if you load that into a browser you get a wealth of weather data… but not in an easily readable format. Next we need to create an XML object in our PHP application like this…

$webAddress = 'http://www.nws.noaa.gov/data/current_obs/KJFK.xml';
$xmlResults = simplexml_load_file($webAddress);

If this works, you’ll end up with a new variable called $xmlResults that you can now extract key pieces of information for. Let’s look at a couple of examples…

echo $xmlResults->weather, ' : Current Weather Summary';
echo '<br>';
echo $xmlResults->temperature_string, ' : Current Temperature Information';
echo '<br>';
echo $xmlResults->wind_string, ' : Wind Information';
echo '<br>';

Pretty great!

Another small module of code now, this time for the Perl programming language. Geo::METAR is a Perl module written by Jeremy Zawodny that is easy to incorporate into an existing Perl application. It allows you to query the METAR aviation weather reports at the National Weather Service. One of the big plus points for METAR data is that it is updated approximately once per hour.

METAR stands for METeorological Aviation Report and is typically used by pilots and meteorologists, it’s not typically used by lay-people as the reports are difficult to read! This Perl module will allow you to access a METAR report for a given location and then parse the results into more useful components such as wind direction, visibility, temperature etc.

Once you’ve installed the module, you’d first capture the METAR data directly from the NWS website via LWP. The url you would use in LWP to capture the METAR data for ‘KFDY’ for example is…

http://weather.noaa.gov/cgi-bin/mgetmetar.pl?cccc=KFDY

Then pass the results of this to the METAR module for parsing into invidual variables…

$m->metar("KFDY 251450Z 21012G21KT 8SM OVC065 04/M01 A3010 RMK 57014");

You will then have access to a wealth of weather data variables. For more information about the variables and METAR in general, visit the Wikipedia site.

To find a list of sites you can retrive METAR data for, use the ICAO site code. A list is made available here.

Now, it’s true to say that Geo::Metar is pretty static… the initial version seems to have been created around 2000 and wasn’t updated until 2008… but it does still work well and like other code modules is a good starting point for your own applications and learning. You can access the module here.

Note. It is possible to access METAR data via other means. For example the National Weather Service page on METAR tells you how to use ftp to retrive METAR data or by simply entering the 4 digit ICAO location.

I’m just not sure what to make of Weather2U at the moment. One of the articles on their homepage is just made up of random characters (I guess this is because people can submit articles in their own language, but I’m not sure about the point of a multilingual site?) and once every 5 minutes for the past week or so the entire site has just given a “Service Unavailable” error. One of the key criteria for a weather data provider is trust that they’ll be consistent with their provision of data and I’m just not getting that vibe!

Next, they aim to update the weather up to 4 times a day, but on the f.a.q. they say this might only happen once a day. Also, they say they “number crunch” and “decode” the data that comes from the National Weather Service, well, I guess you’d need to find out what that means as the source data is just the source data, right? And why wouldn’t you go straight to the source?

The look of the Weather2U website when it works however is excellent. If you just want to view weather forecast information online then it has well presented data (check this link out for London) and an easy to navigate interface. I’m not sure what the 300 day forecast is all about though, seems a bit ambitious!

If you want to use the Weather2U data for your own application or website… then be prepared to pay… As of October 2008 the following charges were levied for the data (available for up to 180 hours in the future)

0-1000 Requests per month – £9.95
1000-100000 Requests per month – £29.95
100000+ Requests per month – £79.95

You need to spend some time with a calculator and work out how many locations you’re interested in weather data for… as if you get 4 data inputs a day for just 50 locations then you’d be spending ~£359 a year… for this cost you’d need to look hard at the value add that Weather2U are adding to the original National Weather Service data.

Overall Weather2U provides exactly what you’d want for a weather data provider, long term forecast data, lots of locations, well formatted data…. but this is tempered by the unreliability of the site, long term costs and an outstanding question about the value add of their data over and above the National Weather Service. We’ll have to keep a close eye on the site!

The BBC is one of the largest news sites on the internet and it’s weather forecasts are used by millions of people… but getting to the data itself isn’t easy!

The data source for BBC Weather is the UK Government Met Office (which will be covered in a future post). It is possible to access an RSS feed of the data. But according to the terms of use this is for personal use only and any use of BBC data content must include a link back to the BBC.

So in conclusion, the BBC site is useful as a full website or if you’d like an RSS feed of the data (which of course could be imbedded in your website, but accessing raw data itself is not possible at the moment.

pxWeather isn’t a full blown (there is no pun here, promise) weather data site, but just a small amount of PHP code that is easy to integrate into an existing website or application to retrieve weather data.

It’s open source and simple to integrate into an application as this snippet shows…

<?php
require_once("pxweather.class.php");
$w = new Weather($city = "Miami");
$w->load();
echo $w->getCurrent("temp.string");
? >
The downside about pxWeather is that it doesn’t seem to have been updated since 2005 so you might want to take a cached copy of the website and any documentation. However it does still work and is a good starting point if you plan on writing your own application code.

Well the title sounds promising!  rssweather.com unsurprisingly provides a feed of data to your RSS client from a large number of cities around the world. It’s got an extremely clean and simple to use interface helping you get to the country and city you’re interested in very quickly.

Unfortunately there is no raw data access directly from the rssweather site and extracting the data you require from the rss feed would not be allowed I’m sure! However what is most interesting about the site is that it is powered by HamWeather – a site that we’ll be covering in some detail in the future!

Overall, rssweather is an excellent source of well presented weather data…. but for your RSS client only.

The World Weather Information Service is provided by an group called the World Meteorological Organization. It aims to be a centralized source of official weather forecasting information by having over 150 official members providing data from around the world. In the UK for example, the official provider is the UK Met Office – but oddly there only seems to be data from 16 UK locations (as of July 2008).

The website is run by the Hong Kong Observatory and is available in different languages, but unfortunately as promising as this all sounds so far there does not appear to be direct access to any of the data, or even any indication of how often the data is updated. So, great in principal and useful to find out who the official weather data organization is around the world… but we’ll have to check back in the future to see if any useful data becomes available.