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Boundary Fire, August 2021 Custer, Valley

Out · last detection 22 Oct 2021, 09:36 UTC

The fire started on 7 August 2021 in Custer, United States, and satellites saw it burning for 77 days. United States agencies (MTBS / NIFC) mapped an official burnt perimeter of 39,649 hectares, spread across 2 counties.

It is the 9th largest in Idaho since 2016 (of 379 with a page). Number 15 in United States in 2021, of 385.

Compare with…

Suggestions: Prospect · 2018Honeymoon · 2017Shady · 2019Kiwah · 2018

Burnt area
39,649ha
official perimeter (MTBS / NIFC)
Duration
77days
7 Aug 2021 – 22 Oct 2021
Municipalities hit
2
counties
Started on
7 Aug
2021
Heat detections
7,942
in a single hotspot: 517 MW
Danger at start
2
Very low · FWI index
Average daily power
2.9GW
detected power per day, on average

Where it burned

HOTSPOTS BY DAY 7 Aug22 Oct
22 Oct 2021

How it evolved, day by day

7 Aug 2021 · 6 MW · 1 8 Aug 2021 · 9 MW · 2 9 Aug 2021 · 107 MW · 14 10 Aug 2021 · 5 MW · 3 11 Aug 2021 · 40 MW · 14 12 Aug 2021 · 50 MW · 5 13 Aug 2021 · 54 MW · 8 14 Aug 2021 · 155 MW · 15 15 Aug 2021 · 89 MW · 22 16 Aug 2021 · 108 MW · 19 17 Aug 2021 · 43 MW · 12 18 Aug 2021 · 52 MW · 15 19 Aug 2021 · 11 MW · 1 20 Aug 2021 · 22 MW · 6 22 Aug 2021 · 11 MW · 3 23 Aug 2021 · 547 MW · 9 24 Aug 2021 · 139 MW · 12 26 Aug 2021 · 22 MW · 2 27 Aug 2021 · 74 MW · 7 28 Aug 2021 · 492 MW · 27 29 Aug 2021 · 3,798 MW · 57 30 Aug 2021 · 3,956 MW · 165 31 Aug 2021 · 3,544 MW · 167 1 Sept 2021 · 7,085 MW · 365 2 Sept 2021 · 7,004 MW · 345 3 Sept 2021 · 10,777 MW · 380 4 Sept 2021 · 8,768 MW · 323 5 Sept 2021 · 7,349 MW · 395 6 Sept 2021 · 11,077 MW · 517 7 Sept 2021 · 4,194 MW · 407 8 Sept 2021 · 32,036 MW · 604 9 Sept 2021 · 12,314 MW · 646 10 Sept 2021 · 1,512 MW · 221 11 Sept 2021 · 521 MW · 67 12 Sept 2021 · 575 MW · 36 13 Sept 2021 · 2,340 MW · 119 14 Sept 2021 · 2,599 MW · 193 15 Sept 2021 · 7,632 MW · 323 16 Sept 2021 · 2,087 MW · 216 17 Sept 2021 · 9,842 MW · 446 18 Sept 2021 · 13,613 MW · 726 21 Sept 2021 · 8 MW · 2 23 Sept 2021 · 91 MW · 10 24 Sept 2021 · 407 MW · 36 25 Sept 2021 · 1,407 MW · 90 26 Sept 2021 · 2,298 MW · 115 27 Sept 2021 · 6,302 MW · 195 28 Sept 2021 · 656 MW · 131 30 Sept 2021 · 82 MW · 9 1 Oct 2021 · 37 MW · 8 2 Oct 2021 · 308 MW · 35 3 Oct 2021 · 462 MW · 58 4 Oct 2021 · 4,806 MW · 141 5 Oct 2021 · 681 MW · 103 6 Oct 2021 · 742 MW · 83 16 Oct 2021 · 3 MW · 1 19 Oct 2021 · 2 MW · 2 21 Oct 2021 · 33 MW · 7 22 Oct 2021 · 2 MW · 1
7 Aug 16 Aug 27 Aug 5 Sept 8 Sept 14 Sept 26 Sept 6 Oct

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

The weather it burned in

28°high
82km/h · peak gust
14%lowest humidity

It had gone 0 days without rain (1 mm or more) when it started. Rain came after the fire: 2.5 mm on 23 Oct.

This area had burned before

1% of the perimeter overlaps earlier fires recorded since 2016: 75 ha in 2017, 172 ha in 2018.

How big is it?

10 km
It burned the equivalent of 25% of the area of London (396 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 town

  1. Custer where it started
    29,265 ha reached on 7 Aug
    2.3 %
  2. Valley
    10,518 ha reached on 11 Aug
    1.1 %

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

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)
7 Aug 23.1 °C 34 % 48 km/h 0.0 mm Very low 2
8 Aug 17.1 °C 41 % 76 km/h 1.3 mm Very low 4
9 Aug 20.9 °C 27 % 31 km/h 0.0 mm Low 7
10 Aug 23.8 °C 22 % 41 km/h 0.0 mm Moderate 14
11 Aug 27.0 °C 28 % 34 km/h 0.0 mm Moderate 14
12 Aug 28.0 °C 22 % 30 km/h 0.0 mm Moderate 18
13 Aug 27.7 °C 20 % 33 km/h 0.0 mm Moderate 20
14 Aug 26.4 °C 21 % 45 km/h 0.0 mm High 22
15 Aug 27.2 °C 22 % 35 km/h 0.0 mm Moderate 21
16 Aug 26.0 °C 22 % 58 km/h 0.0 mm High 26
17 Aug 17.4 °C 35 % 67 km/h 1.5 mm Low 11
18 Aug 13.0 °C 49 % 35 km/h 6.8 mm Very low 0
19 Aug 16.6 °C 36 % 41 km/h 0.0 mm Very low 3
20 Aug 17.9 °C 32 % 35 km/h 0.4 mm Low 8
21 Aug 12.5 °C 62 % 49 km/h 11.4 mm Very low 0
22 Aug 17.4 °C 33 % 49 km/h 0.0 mm Very low 2
23 Aug 17.9 °C 17 % 60 km/h 0.0 mm Low 10
24 Aug 19.5 °C 22 % 43 km/h 0.0 mm Moderate 13
25 Aug 19.1 °C 20 % 60 km/h 0.0 mm Moderate 18
26 Aug 17.4 °C 31 % 58 km/h 0.5 mm Moderate 17
27 Aug 17.1 °C 30 % 45 km/h 0.0 mm Moderate 16
28 Aug 21.1 °C 21 % 26 km/h 0.0 mm Moderate 15
29 Aug 23.1 °C 16 % 37 km/h 0.0 mm Moderate 21
30 Aug 21.4 °C 19 % 56 km/h 0.0 mm High 26
31 Aug 17.8 °C 18 % 55 km/h 0.0 mm High 25
1 Sept 18.4 °C 15 % 38 km/h 0.0 mm High 23
2 Sept 17.6 °C 18 % 51 km/h 0.0 mm High 26
3 Sept 19.2 °C 15 % 38 km/h 0.0 mm High 24
4 Sept 21.5 °C 14 % 41 km/h 0.0 mm High 26
5 Sept 23.8 °C 14 % 49 km/h 0.0 mm High 30
6 Sept 23.9 °C 18 % 52 km/h 0.0 mm High 31
7 Sept 25.0 °C 17 % 32 km/h 0.0 mm High 27
8 Sept 24.6 °C 20 % 52 km/h 0.0 mm High 33
9 Sept 23.4 °C 22 % 59 km/h 0.3 mm High 33
10 Sept 19.1 °C 38 % 60 km/h 4.8 mm Very low 4
11 Sept 17.6 °C 31 % 42 km/h 0.0 mm Low 8
12 Sept 19.2 °C 25 % 43 km/h 0.0 mm Moderate 16
13 Sept 19.0 °C 21 % 40 km/h 0.0 mm Moderate 21
14 Sept 19.5 °C 20 % 39 km/h 0.0 mm High 22
15 Sept 19.5 °C 23 % 59 km/h 0.0 mm High 27
16 Sept 15.3 °C 15 % 31 km/h 0.0 mm High 22
17 Sept 18.6 °C 17 % 58 km/h 0.0 mm High 29
18 Sept 18.2 °C 16 % 82 km/h 1.9 mm Moderate 19
19 Sept 4.9 °C 87 % 43 km/h 8.0 mm Very low 0
20 Sept 10.6 °C 31 % 37 km/h 0.0 mm Very low 1
21 Sept 18.3 °C 23 % 28 km/h 0.0 mm Very low 4
22 Sept 17.1 °C 29 % 51 km/h 0.1 mm Moderate 12
23 Sept 17.6 °C 27 % 27 km/h 0.0 mm Moderate 13
24 Sept 21.2 °C 23 % 26 km/h 0.0 mm Moderate 16
25 Sept 21.5 °C 23 % 42 km/h 0.0 mm Moderate 20
26 Sept 19.8 °C 23 % 48 km/h 0.0 mm High 22
27 Sept 17.7 °C 19 % 55 km/h 0.0 mm High 24
28 Sept 7.8 °C 39 % 46 km/h 5.6 mm Very low 1
29 Sept 9.9 °C 27 % 28 km/h 0.0 mm Very low 2
30 Sept 15.1 °C 23 % 26 km/h 0.0 mm Low 7
1 Oct 14.9 °C 24 % 25 km/h 0.5 mm Low 11
2 Oct 16.2 °C 23 % 32 km/h 0.0 mm Moderate 15
3 Oct 17.9 °C 24 % 36 km/h 0.0 mm Moderate 17
4 Oct 17.8 °C 19 % 46 km/h 0.0 mm Moderate 21
5 Oct 17.9 °C 20 % 49 km/h 0.0 mm Moderate 21
6 Oct 12.5 °C 35 % 50 km/h 0.0 mm Moderate 19
7 Oct 8.1 °C 65 % 52 km/h 1.1 mm Very low 5
8 Oct 4.2 °C 81 % 23 km/h 9.7 mm Very low 0
9 Oct 8.2 °C 39 % 32 km/h 2.2 mm Very low 0
10 Oct 7.2 °C 55 % 47 km/h 1.1 mm Very low 1
11 Oct 0.0 °C 64 % 54 km/h 4.6 mm Very low 0
12 Oct 0.6 °C 48 % 54 km/h 0.0 mm Very low 0
13 Oct 0.1 °C 57 % 36 km/h 0.0 mm Very low 1
14 Oct 1.4 °C 51 % 45 km/h 0.2 mm Very low 1
15 Oct 7.0 °C 44 % 40 km/h 0.0 mm Very low 2
16 Oct 13.8 °C 29 % 35 km/h 0.0 mm Low 5
17 Oct 13.7 °C 25 % 42 km/h 0.0 mm Low 9
18 Oct 10.8 °C 41 % 39 km/h 0.8 mm Very low 5
19 Oct 10.6 °C 40 % 29 km/h 0.0 mm Low 6
20 Oct 6.9 °C 55 % 67 km/h 1.0 mm Very low 4
21 Oct 11.8 °C 44 % 53 km/h 0.0 mm Low 6
22 Oct 12.0 °C 42 % 58 km/h 7.9 mm Very low 0
23 Oct after 4.3 °C 60 % 43 km/h 2.5 mm Very low 0

Before and after, from space

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

Before · 31 Jul 2021
After · 29 Oct 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 · 7,942Every 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 Boundary fire last?
According to the heat detections seen by satellite inside the perimeter, it burned from 7 August 2021 to 22 October 2021 (77 days). The perimeter dates it from 10 August 2021 to 10 August 2021.
How much area did it burn?
The official perimeter published by United States agencies (MTBS / NIFC) is 39,649 hectares (396.5 km²). Other tallies, such as daily incident reports, may give slightly different figures.
Which counties burned?
The fire entered 2 counties: Custer (29,265 ha, 2.3 %); Valley (10,518 ha, 1.1 %).
What was the weather like?
During the fire the temperature reached 28.0 °C, humidity dropped to 14 % and gusts hit 82 km/h. The fire danger index (FWI) reached 33, 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

Satellite cross-check

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.

Report an error
What do you think is wrong?

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: MTBS (US Geological Survey and US Forest Service), official.
  • Dates adjusted with the VIIRS detections inside the perimeter, which said 10 August 2021 to 10 August 2021. 7,942 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.

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.