Ashfall Advisory or Warning: how volcano alerts, forecasts, and actions differ

Two agencies, different questions

A USGS Volcano Warning is not the same product as an NWS Ashfall Warning

USGS volcano observatories monitor the volcano and describe its activity. The National Weather Service uses eruption information and atmospheric forecasts to communicate where ash may affect the public. The words advisory, watch, and warning can appear in both systems, so always read the agency, hazard, affected area, and instructions—not only the severity word.

USGS Volcano Alert Level

Describes conditions and hazards primarily for people and infrastructure on the ground near a U.S. volcano. The levels are NORMAL, ADVISORY, WATCH, and WARNING. They describe the volcano's status; they do not by themselves predict ash at your address.

NWS Ashfall Advisory

Used when a minor eruption or resuspended ash is expected to affect the public with a limited hazard extent, such as less than one-quarter inch of accumulation. Even a limited amount can make travel, breathing, machinery, and cleanup difficult.

NWS Ashfall Warning

Used when a major eruption is expected to affect the public significantly, such as at least one-quarter inch of ashfall or associated significant debris, lava, or lahar hazards. Follow the complete warning and local emergency instructions now.

From background risk to immediate action

Outlooks, forecasts, watches, and warnings are not interchangeable

There is no general national volcanic-ash outlook that works like an SPC thunderstorm outlook. Long-term USGS hazard assessments and maps show where volcano hazards are possible; they are not a prediction that an eruption will occur on a particular day.

Long-term outlook or hazard assessment

Shows background hazard potential and supports community planning. It does not say that ashfall is imminent or provide an arrival time.

Forecast

Uses current eruption and weather information to estimate where an ash plume or ashfall may travel, when it may arrive, and how conditions may change. Wind can carry ash far from the volcano.

USGS WATCH

A Volcano Alert Level indicating heightened or escalating unrest with increased potential of eruption, or an eruption with limited hazards. It is a volcano-status level, not an NWS Ashfall Watch for your community.

USGS WARNING

A highly hazardous eruption is underway, imminent, or suspected. The NWS may separately issue local ashfall products based on expected public impacts.

NWS advisory or warning

A place-specific public hazard product. Read the affected area, timing, accumulation, wind, visibility, and protective actions in the newest message.

Prepare before ash arrives

Reduce exposure and keep ash out of essential systems

Preparation is most effective before the air becomes dusty and roads lose visibility or traction. Ready.gov and USGS recommend planning for respiratory and eye protection, sheltering, limited travel, and keeping ash away from equipment and water systems.

Add official notification paths before unrest escalates. The free USGS Volcano Notification Service can send notices for selected U.S. volcanoes, while local NWS alerts and emergency messages address community impacts.

During ashfall

Shelter from ash, avoid unnecessary travel, and protect your lungs

The safest general approach is to stay indoors when instructed, keep ash outside, and avoid stirring it back into the air. Falling ash can make daylight dim, hide road markings, reduce traction, and enter engines and ventilation systems.

1. Follow evacuation or shelter instructions from local authorities. Do not drive toward an eruption or through a closed area to observe it.
2. Stay indoors when practical. Close doors and windows, limit outside-air intake, and keep pets inside.
3. If you must go outside, limit exertion, protect your eyes, and use the recommended respiratory protection correctly.
4. Avoid contact lenses in ashy conditions when official guidance advises against them; ash can irritate and scratch eyes.
5. Avoid nonessential driving. If travel is unavoidable and permitted, slow down, leave extra distance, and expect poor visibility and slippery surfaces.
6. Keep listening for updates. Ash already on the ground can be lifted again by wind after the eruption or initial fall has ended.

Know what ordinary tools miss

Weather radar and the AQI do not replace an ashfall product

Radar can help show precipitation and some atmospheric features, but it is not a household ashfall detector and may not show the full plume or ground impact. Likewise, an air-quality reading answers a different question from an NWS Ashfall Advisory or Warning. Use official volcano notices, plume or ashfall forecasts, and local alerts together.

• USGS notice: explains what the volcano is doing and why its status changed.
• Ash or plume forecast: estimates transport and timing using eruption and atmospheric information.
• NWS public product: states expected impacts and actions for a defined area.
• Air-quality information: helps interpret measured or forecast pollution exposure but does not replace ashfall instructions.
• Local emergency direction: controls evacuation, road closures, sheltering, and access to affected areas.

After ash stops falling

Wait for instructions, then clean without creating a new exposure

Ash on roofs and the ground may remain hazardous, become heavier when wet, or be blown back into the air. Community cleanup plans may set priorities for roads, roofs, water, wastewater, and waste collection. Coordinate with those instructions instead of moving ash into drains or traffic areas.

1. Confirm that authorities say it is safe to go outside and begin cleanup.
2. Wear suitable eye and respiratory protection and minimize dry sweeping that puts fine ash back into the air.
3. Keep children, older adults, pets, and people with respiratory or cardiovascular conditions away from dusty cleanup.
4. Use extreme caution around roofs. Ash load can damage structures, and roof work adds fall and electrical hazards.
5. Follow local instructions for collecting and disposing of ash. Do not wash large amounts into storm drains or wastewater systems.
6. Inspect filters, engines, electronics, water systems, and ventilation equipment according to official and manufacturer guidance before normal use.