How long did the Thorn Fire last?

It burned between 15 July 2026 and 15 July 2026: 1 day, according to the start date recorded by United States agencies (MTBS / NIFC) and the heat detections seen by satellite.

How much area did it burn?

The official perimeter published by United States agencies (MTBS / NIFC) is 496 hectares (5.0 km²). Other tallies, such as daily incident reports, may give slightly different figures.

Which counties burned?

The fire only entered San Diego (498 ha, 0.0 %).

What was the weather like?

During the fire the temperature reached 37.0 °C, humidity dropped to 16 % and gusts hit 35 km/h. The fire danger index (FWI) reached 47, class Very high.

Where does this data come from?

From the official burnt perimeter of United States agencies (MTBS / NIFC, public domain), NASA FIRMS VIIRS hotspots and the administrative boundaries of United States. It is not an official report.

US · United States · 2026-07-15 → 2026-07-15

Thorn Fire, July 2026 San Diego

Out · last measured on 15 Jul 2026

The fire started on 15 July 2026 in San Diego, United States, and satellites saw it burning for 1 day. United States agencies (MTBS / NIFC) mapped an official burnt perimeter of 496 hectares, spread across a single county.

It is the 401th largest in California since 2016 (of 442 with a page). Number 374 in United States in 2026, of 423.

Compare with…

Suggestions: Border 3 · 2016 Tecate · 2024 Southern · 2021 Valley · 2020

We have the official perimeter (MTBS / NIFC) for this fire, but not yet its hotspots: NASA publishes the yearly hotspot archive only once the year closes. The page picks them up automatically when they are available.

Burnt area: 496ha; official perimeter (MTBS / NIFC)
Duration: 1day; 15 Jul 2026 – 15 Jul 2026
Counties hit: 1; counties
Started on: 15 Jul; 2026
Danger at start: 47; Very high · FWI index

The weather it burned in

37°high

35km/h · peak gust

16%lowest humidity

It had gone more than two months without rain (1 mm or more) when it started. Rain came after the fire: 3.2 mm on 16 Jul.

This area had burned before

No earlier perimeters overlap this fire since 2016, when the satellite record begins.

What happened to each county

San Diego where it started

498 ha

0.0 %

Burnt area inside each county, from crossing the official perimeter with administrative boundaries. The distance runs from the point marking the centre of each area to the nearest fire: staying a kilometre away does not mean it reached the houses.

People and buildings inside the perimeter

GHSL 2025

Built-up area0.27 ha

Residents< 20

Inside the perimeter there were about 0.27 hectares of built-up land and almost nobody lived there (GHSL 2025, satellite-based estimate).

This is an estimate on 100 m cells, made from satellite imagery and census data: it does not mean that homes burned or that anyone was harmed. The perimeter also contains land that never burned. The GHSL 2025 epoch is a projection made from 2020 and earlier data.

Source: Global Human Settlement Layer (GHS-BUILT-S and GHS-POP R2023A), European Commission Joint Research Centre (JRC), © European Union, CC BY 4.0. Sum inside the perimeter computed by WorldFires. human-settlement.emergency.copernicus.eu

The weather day by day

ECMWF ERA5 reanalysis at the fire location, the standard reference for past weather, and the Canadian Fire Weather Index (the same system Copernicus uses), computed by WorldFires from that data. Days after the fire run until the first rain.

Open-Meteo.com (CC BY 4.0) · Copernicus Climate Change Service (ERA5)

Day	High	Min. humidity	Peak gust	Rain	Danger (FWI)
15 Jul	37.0 °C	16 %	35 km/h	0.0 mm	Very high 47
16 Jul after	34.7 °C	29 %	37 km/h	3.2 mm	Moderate 18

Before and after, from space

Drag the line to compare the same ground before the fire and after it.

↔

Before · 8 Jul 2026

After · 22 Jul 2026

Before After

If the day is cloudy, change the date: each satellite passes once a day. In false colour the burnt ground looks brown or red.

The smoke

CAMS · Copernicus

On 15 July 2026 the air beside the fire reached 18 µg/m³ of PM2.5, but no daily average passed the WHO guideline (15).

PM2.5 peak18 µg/m³

Days over the guideline0 days

PM1026 µg/m³

Optical depth0.24

WHO 15

131415161718

Good Fair Moderate Poor Very poor Extremely poor

Particles from the Copernicus CAMS model at the centre of the perimeter; these are not measurements in each town. The pale bar is the worst hour, the solid one the daily average.

Open-Meteo.com (CC BY 4.0) · Copernicus Atmosphere Monitoring Service (CAMS)

Other fires nearby

All fires in United States ›

Frequently asked questions

How long did the Thorn Fire last?: It burned between 15 July 2026 and 15 July 2026: 1 day, according to the start date recorded by United States agencies (MTBS / NIFC) and the heat detections seen by satellite.
How much area did it burn?: The official perimeter published by United States agencies (MTBS / NIFC) is 496 hectares (5.0 km²). Other tallies, such as daily incident reports, may give slightly different figures.
Which counties burned?: The fire only entered San Diego (498 ha, 0.0 %).
What was the weather like?: During the fire the temperature reached 37.0 °C, humidity dropped to 16 % and gusts hit 35 km/h. The fire danger index (FWI) reached 47, class Very high.
Where does this data come from?: From the official burnt perimeter of United States agencies (MTBS / NIFC, public domain), NASA FIRMS VIIRS hotspots and the administrative boundaries of United States. It is not an official report.

Where to verify it

A satellite detection is not an official report. Final figures and the fire’s status are published by each country’s emergency service.

Emergency number: 911 · Emergency number and official warnings ›

Satellite cross-check

NASA FIRMS ↗
NIFC · Fire maps ↗

History of this page Changes in area, dates, name, official record or merged pages, compared every night since 24 October 2026.

No changes since 24 October 2026.

RSS Changes to this page

Does something look wrong on this page?

This page is built from satellite data and official records, and it sometimes gets things wrong: the wrong dates, the wrong town, two fires merged into one, or something that was not a wildfire at all. If you know this fire first-hand (you live nearby, saw it, fought it or reported on it), tell us what really happened and we will check it.

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What do you think is wrong?

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What really happened?

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We will only use your email to reply about this report. Privacy. This is not an emergency service: if there is a fire now, call 911.

How we know this

Perimeter: NIFC WFIGS (United States), official.
Dates from the perimeter: the VIIRS detections inside it did not change them. No Suomi-NPP VIIRS detections on those dates.
We have not matched this page with any official record.
Weather: Copernicus ERA5 reanalysis at the fire location, in cells of about 25 km.
Built-up area and population come from the JRC Global Human Settlement Layer (epoch 2025, 100 m cells), summed inside the perimeter: an estimate of what was there, not a damage count.

How we build fire pages: methodology ›

Where this data comes from

The perimeter is official and in the public domain. For past years it comes from MTBS (Monitoring Trends in Burn Severity), run by the U.S. Geological Survey and the USDA Forest Service, which map it on Landsat and Sentinel-2 imagery. For the current and last year it comes from WFIGS at the National Interagency Fire Center (NIFC): incident perimeters mapped by fire crews, aircraft and imagery. Heat detections come from the VIIRS sensors aboard Suomi-NPP and NOAA-20, distributed by NASA FIRMS at 375 m resolution. County boundaries come from geoBoundaries ADM2 (Public Domain). The area per county is computed by WorldFires by crossing the perimeter with those boundaries, so it may differ slightly from official figures.

Where it burned