May 2

Anticipate Threats with Weather Alerts

Previously in our severe weather series, we’ve discussed severe weather outlooks and storm cells. This article will continue the series by concentrating on the weather alerts datasets available with the AerisWeather API and the AerisWeather Mapping Platform.  This information is perfect for integration into mobile and notification platforms, allowing you to notify users quickly when severe weather events may be nearing.

These advisories datasets provides access to all currently active US advisories as issued by the National Weather Service (NWS). The NWS issues a variety of severe weather warnings, watches, advisories and statements that may be issued for individual or multiple forecast zones or counties, helping to inform and save lives. So far this year alone, there have been more than 1300 tornado warnings and over 7000 severe storm warnings issued across the United States.

Alert Map Layers

The AerisWeather Mapping Platform (AMP) offers an alerts  layer with a variety of options to display the NWS watches, warnings, and advisories that can be used as a standalone map or as map tiles within a mapping library. By default, the standard alerts  layer includes all of the NWS currently active weather related watches, warnings, and advisories. Below is an example alerts map from April 30, 2017:

Zooming into an area of severe weather, you can see how the boundaries for individual alerts cover entire counties or just specific regions within or across counties:

Weather Alerts Closeup via AMP

The above examples used a time offset of current  to display the weather alerts currently active. The alerts layer is updated every couple minutes, and offsets can be used to display alerts for periods in the past. For example, you would use an offset of   to obtain the alerts from 3 hours ago:

Categorized alert groupings are also available. For instance, alerts related to severe storms can be returned by using alerts-severe the layer name:

Here’s the complete list of alert categories:

AMP LayerDescription
alerts-severeTornado, Severe storm watches and warnings
alerts-fireFire related alerts
alerts-floodFlood and Flash flood related alerts
alerts-frost-freezeFrost and freeze related alerts
alerts-heatHeat related alerts, such as extreme heat index
alerts-windWind related alerts, including high winds and windchills watches and warnings
alerts-winterWinter related alerts, such as winter storm watches and warnings

You can further filter the weather alerts that are displayed by appending either the  -watches or -warnings modifier to the end of the layer name to return just watches or warnings respectively, as in the following warnings-only example:

By default, the map will fill the alert polygons with their respective colors. But if you prefer outlines instead, append the  -outlines moodier to the layer name:

The above modifiers can be combined to provide unique visuals, especially when integrated with other layers. For example, you may want to display the severe alert warnings as outlines on top of the radar layer:

Alert Data

The AerisWeather API provides access to the raw alert data via the advisories endpoint. Unlike the AMP alerts layer which updates every couple of minutes, the alert data within the API is available in near real-time as soon as they are issued by the local NWS offices. This means you have access to weather alerts quickly in situations where short-fuse severe weather events are occurring, as with tornado and severe thunderstorm warnings.

The advisories endpoint includes information such as the advisory type, location, text, issued/expire times, and locations included in the alert. Review the full list of properties for more information.

To obtain the currently active advisories for a specific location, just provide the place name:

You can use any location format as listed in our supported places, including latitude and longitude. Note that the advisories endpoint only includes data for the United States.

Requests Using /:id vs /closest

A common misuse of the advisories endpoint is using the closest action to obtain the active weather alerts for a location. This is not a valid request and usually provides unwanted results since the request will include alerts near the location even if the location is not included in the alert area.

Make sure you always request advisories for a specific location using the :id  action, where :id  is the exact location you are requesting data for:

Using a closest  request such as below will also return alerts for nearby counties if they are within the search radius even if the specific location does not fall under any of those alerts:

The benefit of using the /advisories/closest  is that you can monitor weather events at and around a particular area, such as an office or facility. However, don’t rely on it for querying the active alerts for an exact location.

Filtering advisories

The advisories endpoint also provides a variety of filters to allow you to return weather alerts for a specific category or grouping. For instance, use filter=severe to obtain the severe related advisories:

For severe or flood alerts, use filter=severe;flood:

Notice that a semicolon was used to join severe  and flood  as it acts as a logical OR conditional expression since we want severe or flood-related alerts.

Another method for filtering is to query the specific alert type using the VTEC code that corresponds to the type of advisory you need. Review the complete list of sorted advisory types and their respective codes that can be used for this type of query. For instance, to search for all tornado warnings across the US:

Alerts Coverage Area – The Small Polygon

Weather alerts are normally issued by the NWS for entire weather zones or counties. However, some advisories will also include a small polygon, especially short-fuse advisories such as tornado, severe thunderstorm and flood warnings. The polygon will highlight the more precise area within the county or counties that are affected by the event. The small polygon is useful as it scales down the coverage of an advisory to just the region affected by it rather than entire counties where some locales won’t be affected at all. When querying advisories for a specific location and a small polygon is available, the API will verify the requested location is within the polygon’s coverage area.

A great use for the small polygon attribute is for rendering them as vector polygons on interactive maps to highlight areas of severe or hazardous weather. As on our threats map, the small polygons will display when active for short-fuse warnings, such as tornado, severe thunderstorm and flood.

Example of Alert Small Polygons

The following query is used to obtain this information before rendering to the map:

Start Integrating Severe Weather Alerts

We’ve reviewed the many capabilities of the alerts datasets — from map layers to querying the data directly. Throughout the year and especially during severe weather season, weather alerts keep people informed of rapidly changing weather and hazards. Start with our free developer account to experiment with making your applications and notifications smarter by integrating weather alerts today!


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