VAAC London Quantitative Volcanic Ash v 1.0

The Service was load tested without any loss of performance against 400 unique users, 4 simultaneous volcanic events, and over a 10-minute window.

The VAAC London Manager reports periodically to the UK Civil Aviation Authority (CAA) and International Civil Aviation Organization (ICAO), who oversee the provision of the Quantitative Volcanic Ash service.

VAAC performance is monitored and reported to the ICAO Met Panel International Airways Volcano Watch operations group (METP-WG-MOG-IAVW).

Forecast data itself is verified by the Met Office regularly.

The Service has been developed with high availability in mind and is monitored via synthetic canaries. The REST API collection endpoints are monitored against provisioning response payloads advertised as ready for collection.

During a significant volcanic event, qualified end users (duly authorised and authenticated via APIM) must be able to make EDR API requests >99% of the time: 

• and the relevant API will provision a response payload; 
• and obtain a HTTP 302 signed redirect URL within 30 seconds or less of their API request; 
• and download matching payloads for datasets and volcanoes that are advertised as ‘ready for collection’.

Thereafter, and until the VAAC London forecasters decide that volcanic ash no longer represents a hazard to air traffic, the volcanic ash forecasts are updated at 6 hourly intervals and usually aligned to the main synoptic hours of 00UTC, 06UTC, 12UTC and 18UTC.

Technical support is available 24/7, although on a 'best efforts only' basis outside normal working hours (09:00-17:00 GMT Monday to Friday, except Bank Holidays).

In the event of operational issues, the equivalent VAAC Toulouse Quantitative Volcanic Ash API service is available for backup purposes (from December 2025).

The Service adheres to SWIM Yellow Profile, WS Light - Infrastructure Capabilities Binding requirements.

The system does not store or manage any personal data. Threat analysis confirmed that loss of confidentiality is deemed Low Risk.

The Met Office has robust Cyber Security protocols in place. In the unlikely event of a security breach impacting the integrity of the data, the Service will be suspended, and VAAC London would notify users to fail over to VAAC Toulouse equivalent Quantitative Volcanic Ash service until security has been fully restored. 

Application Programming Interface.

API Management - the API management platform used for Authentication and Authorisation that is integrated with the QVA Service. APIM acts as the 'front door' of the QVA APIs for our users.

A set of forecast data for one or more related meteorological parameters.

A set of forecast data nested under a 'collection'.

The 'qva_deterministic' forecasts the expected ash concentration as a deterministic gridded forecast for a specific timestep. It includes one dataset. You cannot filter payloads to receive only one threshold.

Datasets are provided for twelve vertical slices of the atmosphere between the ground and 60,000ft (Flight level 600), each 5000ft thick.

Payloads are in netCDF format.

Means the OGC Environmental Data Retrieval standard. To learn more, please visit: https://ogcapi.ogc.org/edr/

Flight Level.

Gridded data refers to climate data that has been spatially interpolated onto a regular grid, creating a consistent and complete spatial representation of weather or climate variables across a specific region. 

VAAC London QVA Gridded Data API's gridded data covers the entirety of an ash plume resulting from a volcanic eruption in Iceland, however wide the plume extends across the globe.

The International Civil Aviation Organisation - It is a specialized agency of the United Nations that coordinates the principles and techniques of international air navigation. ICAO develops standards and recommended practices for international aviation to ensure safe, efficient, and orderly global air transport. 

ICAO Meteorological Information Exchange Model (IWXXM) is a standardized format for exchanging meteorological information used in aviation. It's an XML-based model designed to represent aviation weather information, including reports like METAR/SPECI, TAF, SIGMET, and features/objects like ash concentration forecasts in the forms of polygons. IWXXM is part of the broader SWIM (System Wide Information Management) initiative within ICAO, alongside FIXM and AIXM.

The 'qvaci_iwxxm' collection consists of sets of polygons that show the expected ash areas for where ash exceeding the four concentration thresholds (0.2mg/m3, 2mg/m3, 5mg/m3 and 10mg/m3) is expected to occur. It includes one dataset, which provides only the vertical levels where the ash plume is present in the atmospheric layer between FL000 and FL600. 

The IWXXM objects/polygons represent a subset of the gridded data with each spanning the minimum to maximum height for a given threshold. All the data sets are provided covering the period from T+0 hour to T+24 hours at 3-hourly intervals from the time they are issued. In the case of a significant volcanic eruption in Iceland, the IWXXM data will be updated every 6 hours while a significant ash cloud remains.

Payloads are in XML format, as per the IWXXM schema https://schemas.wmo.int/iwxxm/2025-2RC1/WAFSSigWxFC.xsd.  Please note this is currently a release candidate, so it may be subject to further adjustment before it comes into effect in November 2025.

Please note that you cannot filter the IWXXM payloads to receive polygons for only one concentration threshold. The API response will return all the data for a particular forecast timestep.

A model run is the date and time associated to when an instance of the NAME model is started. London VAAC volcanic ash forecasts are generated by our team of forecasters using an atmospheric transport and dispersion model called NAME. The model represents the expected behaviour of the volcanic ash cloud, the direction and speed of travel as well as processes which act to remove ash from the atmosphere: through precipitation, sedimentation (falling out through gravity) and interaction with the Earth’s surface.

After the initial model run is used to produce the very first volcanic ash forecasts following a significant volcanic event, our forecasting team will update the forecasts every 6 hours, up until the time ash is no longer discernible. 

Open Geospatial Consortium. OGC is a consortium of experts committed to improving access to geospatial, or location information.

The 'qva_probabilistic' collection forecasts the likelihood of ash concentration exceeding four set thresholds in mg/m3: ≥0.2, ≥2.0, ≥5.0 and ≥10.0. It includes four separate datasets (one per threshold).

Datasets are provided for twelve vertical slices of the atmosphere between the ground and 60,000ft (Flight level 600), each 5000ft thick.

Payloads are in netCDF format.

Quantitative Volcanic Ash. QVA forecasts provide higher resolution information on the location of ash in the atmosphere than the traditional volcanic ash advisory (VAA) products and unlike the VAA, also include ash concentration information. QVA also offers operators the opportunity to move away from the traditional ‘discernible ash’- based criteria for avoiding ash and instead use certified engine susceptibility volcanic ash exposure thresholds for flight route planning and inflight replanning. Operators with approval and procedures/practices will be able to use QVA information to fly more efficient routes while maintaining safety in accordance with their safety management program.

Means “forecast period”. A period of time for which forecast data is given, usually expressed as the number of hours after the model run time, e.g. T+6 means 6 hours after the model run time.

Volcanic Ash Advisory Centre. 

VAAC London is an ICAO designated centre, responsible for issuing advisories for volcanic eruptions originating in Iceland and the north-eastern corner of the North Atlantic. It is operated by the Met Office.

VAAC London is one of 9 Volcanic Ash Advisory Centres worldwide, and has specialist forecasters who produce volcanic ash advisories and guidance products using a combination of volcano data; satellite-based, ground-based and aircraft observations; weather forecast models and dispersion models. The volcanic ash forecasts are provided to the standards and tolerances set by the regulator and ICAO.

The forecasts produced by a VAAC are provided to support the aviation industry.

We provide a reciprocal back-up facility with Toulouse VAAC, operated by Météo-France.

The World Meteorological Organization is a specialised agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology and geophysics. The WMO is responsible for the IWXXM schematron used for the provision of the volcanic ash polygon data sets.