The NWX Weather Web Service
Description
The NWX Weather Service is a web service providing atmospheric weather information from a variety of sources through a common XML-based interface. It has the ability to instantly provide current weather forecast information on demand for almost anywhere in the world. This works by downloading elements from a current realisation of the Global Forecast System numeric weather model and storing them in the server in a manner that allows quick and efficient access to individual values.
The service is also capable of producing derived information in a number of ways, notably in the form of charts and vertical profiles, and complements the weather data with other useful items such as a terrain elevation model and geomagnetic data.
Its primary use is as an easy to access source of weather data for third party software, with a focus on aviation applications.
Target Audience
The NWX Weather Service is not aimed at end users, but rather to application developers who add in their software the capability to communicate with the NWX Service and use the results in further processing, or present them to the user through their own interface.
Although with an emphasis on flight planning, the service also has applications in other fields, such as land transportation, agriculture, or general weather forecasting.
As with any web service, NWX can be used both for internet-based and traditional applications, as long as internet access is available.
Main Features
- Winds aloft: NWX provides forecast winds aloft information up to four days in advance anywhere in the world, from the surface up to flight level 300, which is used by flight planning software to give a better estimate of flight time and fuel consumption en route, and to optimise both, e.g., by choosing the most rapid or economical route and flight level according to the forecast winds.
- Temperature: It provides forecast temperature information in the atmosphere as well as on the ground, which assists flight planning, e.g., by estimating the risk of icing.
- Terrain and Geopotential Altitude: This service can estimate how high you are actually flying over the ground by correcting the barometric altitude by pressure and density and thus assist in determining terrain clearance, gliding range, driftdowns, etc. It also incorporates a high resolution terrain database which gives the highest (not mean) recorded terrain elevation in each data point.
- Charts and Cross-sections: You can create on-the-fly charts showing atmospheric phenomena, such as forecast precipitation, cloud, winds, temperature, pressure, etc., and even obtain cross-sections of the atmosphere (e.g., along a flight route) with much the same information.
- METAR and TAF Reports: In addition to the forecast data, the system also provides a feed of observed weather in the form of worldwide METAR data access, as well as TAF reports. Both are archived and the historical reports are accessible via the web service interface.
- Ancillary Data: Other useful information, mainly for flight planning but also relevant to other activities is provided, including calculating the magnetic declination (variation) on any point of the Earth, sunrise/sunset times, etc.
Origin Of The Data
All the numeric forecast data is obtained from the GFS model, a copy of the relevant elements of which is downloaded four times a day at six hour intervals from NOAA servers. The model run effective at any given time is between six and twelve hours old, and epochs T+06 to T+96 are used.
The source for all METAR and TAF data is the U.S. NOAA. METAR and TAF information is refreshed at 10 minute intervals, and an archive is kept for an indeterminate period of time, dependent on demand and server resources.
The terrain model in use is version 2 of the SRTM3 data, downsampled to 1 arc-minute using a max() function (so as to keep the highest value of the sample). Coverage is, as in the original data, between 56°S and 60°N.
Geomagnetic models are obtained from NOAA's National Geophysical Data Center. The models are sampled on a 0.5°×0.5° grid, with declination and secular variation values stored in a database.
How To Access
Using the service is as simple as sending an
appropriately formatted HTTP POST request to the address http://navlost.eu/nwxs.
The body of the request should be an XML document containing a valid
NWX request, as described in the technical manual.
Examples
For illustrative purposes, the following is an example of a simple interaction with the service using the curl command-line tool.
Obtain today's sunrise and sunset times in Paris:
curl -H "Content-Type: application/xml" --data-binary '<nwx version="0.3.3"><Request><srss p="48.8,2.3"/></Request></nwx>' "http://navlost.eu/nwxs/"
Possible response (indented for clarity):
<?xml version="1.0" encoding="UTF-8"?>
<nwx version="0.3.3">
<Response>
<srss p="48.8000,2.3000" e="2010-02-08 20:25:28">
<sr>2010-02-08 07:10</sr>
<ss>2010-02-08 17:00</ss>
<bct>2010-02-08 06:37</bct>
<ect>2010-02-08 17:33</ect>
<bnt>2010-02-08 05:59</bnt>
<ent>2010-02-08 18:11</ent>
<bat>2010-02-08 05:23</bat>
<eat>2010-02-08 18:47</eat>
<st>2010-02-08 12:05</st>
</srss>
</Response>
</nwx>
Another example, this time using wget to retrieve winds aloft data overhead the Açores archipelago at FL250. When trying this example, you should replace "2010-02-11 13:21:50" by a time within the next four days:
wget -qO - --post-data '<nwx version="0.3.3"><Request><Wind p="38.43,-27.13" e="2010-02-11 13:21:50" z="250" u="F"/></Request></nwx>' "http://navlost.eu/nwxs/"
Possible response:
<?xml version="1.0" encoding="UTF-8"?>
<nwx version="0.3.3">
<Response expires="2010-02-09 00:20:00">
<Wind p="38.43,-27.13" e="2010-02-11 13:21:50" z="250" u="F">
<dir>274</dir> <!-- Wind direction in degrees true -->
<speed>49</speed> <!-- Wind speed in knots -->
</Wind>
</Response>
</nwx>
Registration And Costs
The service can be used to make a low number of requests without the need for authentication of any kind. This gives prospective users ample opportunity and convenience to evaluate the service before committing to its use.
Once you have decided that your product or service could benefit from the NWX data feed, then you should contact me to request a login, which eliminates the service cap and allows me to offer better support.
Access fees for the service range from free for open source and non-commercial applications (freeware, non-for-profit websites, etc.), to not much (non-free mobile apps for iPhone, Android, etc.), to quite a bit for users requiring SLAs, bespoke solutions, or unusually large data transfers. I'm always happy to discuss your particular case and try to come up with a cost-effective arrangement.
Further Details
For more information, and a full description of the NWX protocol, please see the Reference Manual, and stay up to date on the latest developments by subscribing to the news feed, or read the news archive. And if your question is not answered by any of those resources, you can always contact me to get a response via email.