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AlertWatch World

NWS, ECCC and WMO/SWIC: How the Warning Sources Fit Together

By AlertWatch World · Reviewed

Why AlertWatch uses direct U.S. and Canadian sources alongside an international WMO feed

AlertWatch World does not obtain all of its weather alerts from one source.

Its Worldwide dataset currently combines several warning pipelines:

United States → National Weather Service

Canada land → Environment and Climate Change Canada

Canada marine → Environment and Climate Change Canada / Meteorological Service of Canada

Other international coverage → WMO Severe Weather Information Centre

At first that can seem unnecessarily complicated.

If WMO provides international warnings, why not use WMO for everything?

The answer is that direct national sources and international aggregation serve different purposes.

Using both allows AlertWatch to obtain more source-specific information for the United States and Canada while using WMO/SWIC to extend coverage to many other parts of the world.

In this guide

NWS: the direct U.S. warning source

The National Weather Service is the U.S. weather-warning source used directly by AlertWatch for United States records.

NWS publishes watches, warnings, advisories and related products through its Alerts Web Service.

The service makes active alert data available through an API and supports CAP-format messages for redistribution and decision-support applications.

AlertWatch can therefore retrieve structured U.S. alert information directly from the national source.

Why direct NWS data is useful

Direct access provides AlertWatch with source-specific information such as:

It also means AlertWatch can apply NWS-specific processing rules rather than trying to infer them from a generic international representation.

For example, the NWS service provides an explicit endpoint for currently active alerts.

ECCC: the direct Canadian land source

For Canadian land weather alerts, AlertWatch uses information from Environment and Climate Change Canada.

ECCC describes its meteorologists as Canada's authoritative source for weather information and currently issues Warnings, Advisories and Watches, with a yellow/orange/red risk colour system for land alerts.

Direct Canadian information allows AlertWatch to preserve Canadian-specific characteristics rather than forcing the records through a generic international interpretation.

Canada's warning system has changed over time

The Canadian warning system is a good example of why source-specific handling matters.

Canada now combines formal land alert types with yellow, orange and red risk colours, informed by impact and forecast confidence.

In 2026 ECCC also introduced targeted polygon warnings for certain severe thunderstorms and tornadoes while retaining predetermined zones for Watches and many other alert situations.

A direct pipeline can accommodate those source changes explicitly.

Why Canadian Marine is treated separately

Marine warnings are not simply ordinary land warnings located over water.

They have different:

AlertWatch therefore processes selected Canadian Marine warning information through its own dedicated logic.

Ordinary marine forecasts are not automatically treated as warnings.

And when a specific warned marine subdivision cannot be mapped reliably, AlertWatch can withhold it rather than assign misleading geography.

Why Canadian Marine severity is currently Unknown

The marine warning information available to AlertWatch does not provide a severity field that can be mapped confidently onto the common AlertWatch severity scale in the same way as some other sources.

AlertWatch therefore does not invent one.

Canadian Marine warnings are currently displayed as:

Unknown severity

when a defensible equivalent is unavailable.

Unknown does not mean harmless or low risk.

That is a data-comparability decision—not a statement that the marine conditions are unimportant.

WMO/SWIC: the international bridge

For wider international coverage, AlertWatch uses information available through the World Meteorological Organization's Severe Weather Information Centre.

SWIC provides centralized access to official warnings issued by participating National Meteorological and Hydrological Services, as well as information from specialized tropical-cyclone centres.

This allows AlertWatch to expand beyond countries for which it has built dedicated direct-source pipelines.

WMO usually is not the original warning issuer

This point is important.

Suppose SWIC displays a warning for Country X.

That does not normally mean:

“WMO issued a weather warning for Country X.”

Rather, SWIC is making an official warning from the relevant national or specialized meteorological authority available through an international platform.

WMO states that SWIC information is based on official warnings and advisories issued by NMHSs, Regional Specialized Meteorological Centres and Tropical Cyclone Warning Centres.

The source authority should therefore remain identifiable.

Why not just use WMO for U.S. warnings too?

If both NWS and WMO/SWIC can expose U.S. warning information, ingesting both could produce overlapping representations of the same underlying official warnings.

AlertWatch already has a dedicated direct NWS pipeline.

Using the direct source provides richer source-specific handling and reduces the need to depend on an intermediary representation for U.S. records.

So AlertWatch's international merge excludes WMO records assigned to the United States where the direct NWS pipeline is intended to provide that coverage.

The same logic applies to Canada

Canada likewise has dedicated AlertWatch pipelines for:

Allowing Canadian records from WMO/SWIC to enter as a second parallel source could introduce duplicate or inconsistent representations.

AlertWatch therefore excludes the corresponding Canadian WMO member records when building the Worldwide dataset.

The result is conceptually:

Worldwide = Direct United States + Direct Canada + WMO/SWIC international records excluding overlapping U.S./Canada coverage

This is a source architecture decision, not a claim that WMO coverage for those countries is invalid.

Why direct sources are not automatically better for every country

If direct national feeds are useful, why not build one for every country?

Because each direct integration has a cost.

A dedicated national pipeline may require understanding:

There are roughly two hundred national jurisdictions and many specialized meteorological services.

WMO/SWIC provides an extremely valuable bridge by exposing standardized authoritative warnings from many participants through a common international system. At SWIC 3.0's March 2024 launch, more than 130 NMHSs had CAP warnings represented.

Source-specific processing preserves meaning

AlertWatch does not apply every transformation identically to every source.

For example:

NWS can supply its own structured severity information.

ECCC land requires Canadian-specific mapping into the AlertWatch common display.

Canadian Marine currently remains Unknown severity rather than receiving an invented equivalent.

WMO/SWIC provides standardized CAP severity categories that can be mapped into the common AlertWatch display.

A common dashboard sits on top of several different source realities.

The same applies to geometry

Geographic processing also varies.

NWS records may provide direct or resolvable U.S. warning geometry.

Canadian land alerts use Canadian source geography, including newer targeted polygons where available.

Canadian Marine requires its own zone and subdivision handling.

International WMO geometry must be interpreted according to what is available through the SWIC/CAP records.

The goal is not to make every source technically identical.

The goal is to create a consistent public view without inventing information that is absent upstream.

What if WMO/SWIC temporarily fails?

A global pipeline needs to account for source failures.

AlertWatch's publication architecture is designed so a WMO-side problem does not necessarily require healthy direct U.S. and Canadian information to disappear.

The international portion can retain the most recent successfully published data under defined failure conditions, while publication freshness indicates that the publication is aging.

That makes failure visible rather than silently pretending that the international data is current.

What if an NWS or ECCC update fails?

Direct pipelines likewise undergo validation before publication.

The general principle is:

do not knowingly replace a healthier publication with obviously failed output simply to claim that an update occurred.

Failures can therefore affect publication freshness without automatically destroying the last usable dataset.

That is why AlertWatch distinguishes publication status and freshness from the individual warnings themselves.

Why AlertWatch labels sources

A global alert without source identity loses important context.

The source tells you:

A visitor should therefore be able to distinguish a direct NWS record from a Canadian record or a warning delivered through WMO/SWIC.

An international aggregator is not another warning authority

AlertWatch's job is to:

It does not become the issuing authority merely because it displays the information.

That distinction applies to all four pipelines.

For safety-critical decisions:

NWS remains the relevant authority for its U.S. warning.

ECCC remains the relevant authority for its Canadian warning.

The national or specialized issuing authority remains authoritative for warnings distributed through WMO/SWIC.

Key takeaway

AlertWatch uses a hybrid source strategy:

Direct NWS → United States

Direct ECCC → Canadian land

Direct Canadian Marine processing → selected marine warnings

WMO/SWIC → broader international warning coverage

U.S. and Canadian WMO records are excluded from the Worldwide merge where AlertWatch's direct pipelines provide the intended coverage, helping avoid parallel representations of the same warning systems.

This approach combines:

source-specific detail where direct integrations exist

with

broad international reach through WMO/SWIC.

Learn more about AlertWatch

See Sources for attribution and provider information.

See Methodology for the detailed processing rules.

Official references