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American Fork Fire, July 2021 Park, Sweet Grass, Meagher

Out · last detection 17 Aug 2021, 10:12 UTC

The fire started on 17 July 2021 in Park, United States, and satellites saw it burning for 32 days. United States agencies (MTBS / NIFC) mapped an official burnt perimeter of 8,384 hectares, spread across 3 counties.

It is the 35th largest in Montana since 2016 (of 302 with a page). Number 66 in United States in 2021, of 385.

Compare with…

Suggestions: Blacktail · 2017

Burnt area
8,384ha
official perimeter (MTBS / NIFC)
Duration
≈ 32days
17 Jul 2021 – 17 Aug 2021
Counties hit
3
counties
Started on
17 Jul
2021
Heat detections
1,047
in a single hotspot: 501 MW
Danger at start
27
High · FWI index
Average daily power
1.2GW
detected power per day, on average

Where it burned

HOTSPOTS BY DAY 17 Jul17 Aug
17 Aug 2021

How it evolved, day by day

17 Jul 2021 · 4,341 MW · 51 18 Jul 2021 · 265 MW · 26 19 Jul 2021 · 7,460 MW · 191 20 Jul 2021 · 260 MW · 12 23 Jul 2021 · 48 MW · 5 24 Jul 2021 · 86 MW · 8 25 Jul 2021 · 1,209 MW · 33 26 Jul 2021 · 1,773 MW · 161 27 Jul 2021 · 569 MW · 100 28 Jul 2021 · 4,494 MW · 61 29 Jul 2021 · 14 MW · 5 30 Jul 2021 · 139 MW · 13 31 Jul 2021 · 712 MW · 41 1 Aug 2021 · 560 MW · 161 2 Aug 2021 · 126 MW · 30 5 Aug 2021 · 7 MW · 1 8 Aug 2021 · 949 MW · 50 13 Aug 2021 · 61 MW · 7 14 Aug 2021 · 1,844 MW · 42 15 Aug 2021 · 976 MW · 30 16 Aug 2021 · 370 MW · 14 17 Aug 2021 · 4 MW · 5
17 Jul 19 Jul 23 Jul 27 Jul 31 Jul 8 Aug 16 Aug

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

The weather it burned in

30°high
70km/h · peak gust
11%lowest humidity

It had gone 0 days without rain (1 mm or more) when it started. Rain came after the fire: 23.2 mm on 18 Aug.

This area had burned before

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

How big is it?

10 km
It burned the equivalent of 5.3% of the area of London (84 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

  1. Park where it started
    4,100 ha reached on 17 Jul
    0.6 %
  2. Sweet Grass
    2,783 ha reached on 17 Jul
    0.6 %
  3. Meagher
    1,569 ha reached on 19 Jul
    0.2 %

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 2020
Built-up area< 0.1 ha
Residents< 20

Inside the perimeter there was no noticeable built-up land and almost nobody lived there (GHSL 2020, 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.

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)
17 Jul 26.7 °C 15 % 39 km/h 0.5 mm High 27
18 Jul 29.5 °C 14 % 25 km/h 0.0 mm High 30
19 Jul 26.9 °C 19 % 28 km/h 0.2 mm High 30
20 Jul 25.4 °C 35 % 39 km/h 8.6 mm Very low 3
21 Jul 23.8 °C 45 % 24 km/h 1.7 mm Very low 4
22 Jul 26.0 °C 25 % 46 km/h 1.9 mm Low 9
23 Jul 24.3 °C 17 % 52 km/h 0.2 mm High 25
24 Jul 26.2 °C 13 % 20 km/h 0.0 mm High 24
25 Jul 28.2 °C 13 % 41 km/h 0.0 mm High 30
26 Jul 29.0 °C 11 % 32 km/h 0.0 mm High 31
27 Jul 29.2 °C 15 % 29 km/h 0.0 mm High 32
28 Jul 23.2 °C 32 % 50 km/h 0.0 mm High 31
29 Jul 25.6 °C 33 % 25 km/h 1.8 mm Low 9
30 Jul 25.9 °C 23 % 38 km/h 0.1 mm High 25
31 Jul 26.2 °C 23 % 53 km/h 0.0 mm High 31
1 Aug 25.8 °C 20 % 44 km/h 0.0 mm High 32
2 Aug 24.4 °C 36 % 30 km/h 18.7 mm Very low 2
3 Aug 20.8 °C 42 % 46 km/h 2.3 mm Very low 3
4 Aug 24.4 °C 20 % 40 km/h 0.0 mm Moderate 14
5 Aug 24.6 °C 20 % 21 km/h 0.0 mm Moderate 19
6 Aug 20.3 °C 39 % 42 km/h 2.7 mm Very low 4
7 Aug 22.7 °C 31 % 57 km/h 0.0 mm Moderate 15
8 Aug 23.9 °C 25 % 67 km/h 10.5 mm Very low 4
9 Aug 15.4 °C 31 % 69 km/h 4.6 mm Very low 3
10 Aug 21.1 °C 28 % 70 km/h 0.0 mm Low 11
11 Aug 24.9 °C 28 % 60 km/h 0.0 mm Moderate 17
12 Aug 21.0 °C 37 % 30 km/h 0.0 mm Moderate 13
13 Aug 23.4 °C 27 % 24 km/h 0.0 mm Moderate 14
14 Aug 26.9 °C 15 % 35 km/h 0.0 mm High 22
15 Aug 25.9 °C 17 % 43 km/h 0.0 mm High 24
16 Aug 28.1 °C 18 % 63 km/h 0.2 mm High 32
17 Aug 23.9 °C 25 % 38 km/h 1.6 mm Moderate 12
18 Aug after 9.8 °C 80 % 39 km/h 23.2 mm Very low 0

Before and after, from space

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

Before · 10 Jul 2021
After · 24 Aug 2021

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

Detections table · 1,047Every 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 timeSatelliteFRP (MW)LatLon

Other fires nearby

All fires in United States ›

Frequently asked questions

How long did the American Fork Fire last?
The official perimeter only gives the start date (17 July 2021). The end comes from the heat detections inside the perimeter: it burned until 17 August 2021 (32 days from 17 July 2021), 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 8,384 hectares (83.8 km²). Other tallies, such as daily incident reports, may give slightly different figures.
Which counties burned?
The fire entered 3 counties: Park (4,100 ha, 0.6 %); Sweet Grass (2,783 ha, 0.6 %); Meagher (1,569 ha, 0.2 %).
What was the weather like?
During the fire the temperature reached 29.5 °C, humidity dropped to 11 % and gusts hit 70 km/h. The fire danger index (FWI) reached 32, class 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

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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How we know this
  • Perimeter: MTBS (US Geological Survey and US Forest Service), official.
  • 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. 1,047 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 2020, 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.