How long did the Big Grass Fire last?

The official perimeter only gives the start date (23 July 2026). The end comes from the heat detections inside the perimeter: it burned until 1 August 2026 (10 days from 23 July 2026), the last day with detections before more than 10 days in a row without any, so it is approximate.

How much area did it burn?

The official perimeter published by United States agencies (MTBS / NIFC) is 234,319 hectares (2,343.2 km²). Other tallies, such as daily incident reports, may give slightly different figures.

Which counties burned?

The fire entered 2 counties: Owyhee (311,128 ha, 16 %); Malheur (267,640 ha, 10 %).

What was the weather like?

During the fire the temperature reached 37.3 °C, humidity dropped to 4 % and gusts hit 48 km/h. The fire danger index (FWI) reached 74, class Very extreme.

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 · 2026-07-23 → 2026-08-01

Big Grass Fire, July 2026 Owyhee, Malheur

Out · last detection 1 Aug 2026, 21:10 UTC

The fire started on 23 July 2026 in Owyhee, United States, and satellites saw it burning for 10 days. United States agencies (MTBS / NIFC) mapped an official burnt perimeter of 234,319 hectares, spread across 2 counties.

We are reviewing this page: some of its data look inconsistent (the place, the dates or the area), so treat them with caution.

Compare with…

Suggestions: Box · 2025 Garat · 2018 Juni · 2017 Jordan · 2020

Burnt area: 234,319ha; official perimeter (MTBS / NIFC)
Duration: ≈ 10days; 23 Jul 2026 – 1 Aug 2026
Counties hit: 2; counties
Started on: 23 Jul; 2026
Heat detections: 3,436; in a single hotspot: 378 MW
Danger at start: 49; Very high · FWI index
Average daily power: 6.7GW; detected power per day, on average

HOTSPOTS BY DAY 23 Jul1 Aug

Play back 1 Aug 2026

How it evolved, day by day

23 Jul 25 Jul 26 Jul 27 Jul 29 Jul 31 Jul

Fire radiative power detected each day, in megawatts, and number of hotspots. The magenta bar marks the peak day.

The weather it burned in

37°high

48km/h · peak gust

4%lowest humidity

It had gone 8 days without rain (1 mm or more) when it started.

This area had burned before

3% of the perimeter overlaps earlier fires recorded since 2016: 3,135 ha in 2017, 1,669 ha in 2018, 226 ha in 2020, 39 ha in 2024, 1,749 ha in 2025. Part of it burned more than once, so the yearly figures add up to more than the 6,015 ha that had burned before.

How big is it?

It burned the equivalent of 1.5 times the area of London (2,343 km² against 1,583 km²).

London boundary: geoBoundaries · Office for National Statistics (Open Government Licence v3.0).

This compares size, not location: both shapes are at the same scale, north up, centred on each other.

What happened to each county

Owyhee where it started

311,128 ha reached on 24 Jul

16 %
Malheur

267,640 ha reached on 23 Jul

10 %

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 area25 ha

Residents≈ 40

Inside the perimeter there were about 25 hectares of built-up land and about 40 residents (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	Danger (FWI)
23 Jul	34.4 °C	18 %	33 km/h	Very high 49
24 Jul	36.8 °C	4 %	37 km/h	Extreme 67
25 Jul	35.1 °C	4 %	48 km/h	Very extreme 74
26 Jul	33.8 °C	6 %	34 km/h	Extreme 63
27 Jul	32.7 °C	8 %	32 km/h	Extreme 54
28 Jul	34.4 °C	9 %	30 km/h	Extreme 61
29 Jul	33.2 °C	12 %	28 km/h	Extreme 52
30 Jul	34.5 °C	11 %	36 km/h	Extreme 62
31 Jul	37.3 °C	5 %	40 km/h	Extreme 69
1 Aug	36.9 °C	5 %	42 km/h	Very extreme 72
2 Aug after	29.6 °C	12 %	41 km/h	Extreme 60
3 Aug after	26.8 °C	9 %	34 km/h	Extreme 60
4 Aug after	30.6 °C	7 %	30 km/h	Extreme 52
5 Aug after	34.6 °C	4 %	29 km/h	Extreme 56
6 Aug after	36.0 °C	4 %	35 km/h	Extreme 65
7 Aug after	36.3 °C	7 %	38 km/h	Extreme 64
8 Aug after	35.6 °C	10 %	38 km/h	Very extreme 71
9 Aug after	34.8 °C	8 %	35 km/h	Extreme 63
10 Aug after	33.5 °C	8 %	34 km/h	Extreme 63
11 Aug after	33.5 °C	10 %	41 km/h	Extreme 68

Before and after, from space

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

↔

Before · 16 Jul 2026

After · 8 Aug 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 28 July 2026 the air beside the fire reached 249 µg/m³ of PM2.5. That day averaged 144: 9.6 times the WHO daily guideline (15).

PM2.5 peak249 µg/m³

Days over the guideline12 days

PM10255 µg/m³

Optical depth1.88

WHO 15

21222324252627282930311234

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)

Detections table · 3,436Every satellite heat detection, one by one, with time, satellite, power and coordinates.

⬇ Download CSV Times in UTC. Each detection is a 375 m pixel: a large fire yields hundreds per pass.

Date and time	Satellite	FRP (MW)	Lat	Lon

Other fires nearby

All fires in United States ›

Frequently asked questions

How long did the Big Grass Fire last?: The official perimeter only gives the start date (23 July 2026). The end comes from the heat detections inside the perimeter: it burned until 1 August 2026 (10 days from 23 July 2026), the last day with detections before more than 10 days in a row without any, so it is approximate.
How much area did it burn?: The official perimeter published by United States agencies (MTBS / NIFC) is 234,319 hectares (2,343.2 km²). Other tallies, such as daily incident reports, may give slightly different figures.
Which counties burned?: The fire entered 2 counties: Owyhee (311,128 ha, 16 %); Malheur (267,640 ha, 10 %).
What was the weather like?: During the fire the temperature reached 37.3 °C, humidity dropped to 4 % and gusts hit 48 km/h. The fire danger index (FWI) reached 74, class Very extreme.
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 really happened?

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How we know this

Perimeter: NIFC WFIGS (United States), official; 3 polygons grouped in this page.
The official perimeter has no end date: the end is the last day with VIIRS detections inside the perimeter before a gap of more than 10 days (150 days at most), so it is approximate. 3,436 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