Highest reading
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You're offline — showing the last readings this device loaded. Reconnect for the latest.
Current
Current reading
Search for a location to see its reading.
Location
Readings
Readings
Select a measurement, time, or location. The map, list, table, and charts update together.
Controls
Time range
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Shows published readings only. Missing times are left blank.
| Air quality | Status |
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Nearby places group at the overview. Choose a numbered group or zoom in to inspect every reading. Drag or use arrow keys to move. The List and Table always show every place.
History
History
Line: reading. Band: range. Pattern: not final.
Use Left and Right Arrow to change the selected observation. Home and End jump to the edges of the evidence window. You can also click or tap anywhere in the plot to choose the nearest observation.
The band shows the published range around each reading. It is not a confidence interval.
Locations
Highest readings
Highest confirmed network readings at the selected observation
Select a bar to select that location. Checked readings are shown first; provisional readings are labeled. Clear the search to show all locations.
Cooling centers
Public places to cool down — libraries, community and senior centers, and cooled public buildings. The list below is the accessible equivalent of the map overlay; everything shown on the map is here in text.
Network
Network
Sensor coverage, status, and alerts.
Your alerts
Alerts evaluate only the newest published observation and update only while this page is open — there is no background push or account. Device notifications are suppressed when that observation is stale.
Across the network
Which sensors need attention
Neighborhood alerts
Published areas where heat or air quality crossed a public-health danger threshold. Every result names its observation time. Aggregate environmental data — no account, no tracking.
Subscribe by adding the alert feed to any RSS/Atom reader, or point an automation at it. The feed is public and carries no personal data; thresholds follow US-EPA and US-NWS bands.
Subscribe to the Spanish feed — Headlines and feed text are machine-translated, not reviewed by a person.
About
Data, method, and limits
Each reading shows its source, status, range, location privacy, and reuse terms.
About these readings
- Source
- Geography
- Calibration status
- Reuse terms
Air-quality categories (PM2.5)
What is AQI?
The Air Quality Index (AQI) turns a pollution concentration into a 0–500 scale and a named category. Higher is worse: 0–50 is Good, 100+ starts to affect sensitive people.
- Good — AQI 0 to 50
- Moderate — AQI 51 to 100
- Unhealthy for sensitive groups — AQI 101 to 150
- Unhealthy — AQI 151 to 200
- Very unhealthy — AQI 201 to 300
- Hazardous — AQI 301+
The AQI shown is computed from each location's hourly mean, not a 24-hour average.
- Coolest — below about 24 °C (75 °F)
- Cool — about 24 to 28 °C (75 to 82 °F)
- Warm — about 28 to 32 °C (82 to 90 °F)
- Hot — about 32 to 36 °C (90 to 97 °F)
- Hottest — about 36 °C (97 °F) and up
The shading is a coolest-to-hottest cue only — the number on each marker is the exact reading, in your chosen units.
- Minimal — little added heat or air stress
- Low — mild conditions
- Elevated — take some care outdoors
- High — limit time and exertion outdoors
- Extreme — avoid being outdoors
Heat + air exposure combines the heat index and the PM2.5 AQI into one level (Minimal to Extreme), taking the higher of the two and flagging when heat and air are both elevated. It is decision-support, not a validated health index, and never a claim that conditions are safe.
This measurement is shown by its value on each marker, not by a severity category. Higher numbers mean more of the pollutant; see the List or Table view for every location.
This is an estimated wet-bulb globe temperature, from air temperature and humidity only — there is no black-globe sensor and no solar-radiation term, so it reads cooler than a true outdoor WBGT in direct sun. Shown by its value on each marker, with "estimated" always alongside the number; see the List or Table view for every location.
Provisional locations have only early, uncalibrated readings — still being double-checked, and never shown as a confirmed category. Status is conveyed by text and pattern, not color alone.
Flagged locations are provisional too, but for a different reason. Automatic quality checks marked the reading as odd — a sudden jump or a stuck, flat value. It is shown, not dropped, so a real event is never hidden, and it is never shown as confirmed. Text and pattern show this, not color alone.
How to read this — and what it does not say
Confirmed readings are calibrated against a reference monitor and carry a ± uncertainty. Provisional readings are early and uncalibrated. This page reports what the air and heat readings are; it does not tell anyone they are safe. Use it alongside how you feel and official advisories.
How the numbers are made
- Confirmed means calibrated against a reference monitor; a sensor with no fit stays raw and is shown provisional.
- Every confirmed reading carries a ± 1-sigma uncertainty, published alongside it.
- Each source sets how exact its map points are.
- The AQI shown comes from each location's hourly mean, not the official 24-hour average.
- Heat + air exposure takes the higher of the heat and air levels — it never blends them into one number.
- Reuse terms and attribution depend on the active source and are shown above. Readings are downloadable without an account or key.