How long did the Porphyry Fire last?

The official perimeter only gives the start date (26 August 2020). The end comes from the heat detections inside the perimeter: it burned until 24 September 2020 (30 days from 26 August 2020), 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 5,570 hectares (55.7 km²). Other tallies, such as daily incident reports, may give slightly different figures.

Which counties burned?

The fire only entered Idaho (5,497 ha, 0.2 %).

What was the weather like?

During the fire the temperature reached 28.6 °C, humidity dropped to 12 % and gusts hit 67 km/h. The fire danger index (FWI) reached 35, 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.

US · United States · 2020-08-26 → 2020-09-24

Porphyry Fire, August 2020 Idaho

Out · last detection 24 Sept 2020, 09:03 UTC

The fire started on 26 August 2020 in Idaho, United States, and satellites saw it burning for 30 days. United States agencies (MTBS / NIFC) mapped an official burnt perimeter of 5,570 hectares, spread across a single county.

It is the 65th largest in Idaho since 2016 (of 379 with a page). Number 101 in United States in 2020, of 441.

Compare with…

Suggestions: Highline · 2017 Logan · 2024 Dixie · 2021 Elkhorn · 2023

Burnt area: 5,570ha; official perimeter (MTBS / NIFC)
Duration: ≈ 30days; 26 Aug 2020 – 24 Sept 2020
Counties hit: 1; counties
Started on: 26 Aug; 2020
Heat detections: 1,330; in a single hotspot: 228 MW
Danger at start: 5; Low · FWI index
Average daily power: 658MW; detected power per day, on average

HOTSPOTS BY DAY 26 Aug24 Sept

Play back 24 Sept 2020

How it evolved, day by day

28 Aug 3 Sept 6 Sept 9 Sept 12 Sept 15 Sept 18 Sept

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

The weather it burned in

29°high

67km/h · peak gust

12%lowest humidity

It had gone 0 days without rain (1 mm or more) when it started. Rain came after the fire: 6.5 mm on 25 Sept.

This area had burned before

1% of the perimeter overlaps earlier fires recorded since 2016: 32 ha in 2017.

32 ha Highline fire, July 2017 37,911 ha in total; the hectares shown are those it shares with this fire

How big is it?

It burned the equivalent of 3.5% of the area of London (56 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

Idaho where it started

5,497 ha reached on 28 Aug

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 area0.10 ha

Residents< 20

Inside the perimeter there were about 0.10 hectares of 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)
26 Aug	22.1 °C	32 %	34 km/h	1.2 mm	Low 5
27 Aug	20.9 °C	23 %	36 km/h	0.0 mm	Moderate 15
28 Aug	23.5 °C	17 %	30 km/h	0.0 mm	High 24
29 Aug	23.0 °C	17 %	53 km/h	0.0 mm	High 30
30 Aug	14.8 °C	22 %	41 km/h	0.0 mm	High 27
31 Aug	7.0 °C	38 %	35 km/h	5.6 mm	Very low 1
1 Sept	20.4 °C	33 %	46 km/h	0.0 mm	Low 6
2 Sept	22.8 °C	21 %	52 km/h	0.0 mm	Moderate 18
3 Sept	24.6 °C	19 %	37 km/h	0.0 mm	High 23
4 Sept	28.6 °C	12 %	29 km/h	0.0 mm	High 29
5 Sept	27.9 °C	13 %	55 km/h	0.0 mm	High 35
6 Sept	24.7 °C	16 %	38 km/h	0.0 mm	High 32
7 Sept	16.6 °C	34 %	67 km/h	2.1 mm	Low 8
8 Sept	11.9 °C	20 %	48 km/h	0.0 mm	Moderate 13
9 Sept	19.0 °C	18 %	24 km/h	0.0 mm	Moderate 19
10 Sept	22.2 °C	16 %	29 km/h	0.0 mm	High 24
11 Sept	21.5 °C	16 %	35 km/h	0.0 mm	High 26
12 Sept	21.5 °C	14 %	33 km/h	0.0 mm	High 27
13 Sept	20.7 °C	20 %	39 km/h	0.0 mm	High 29
14 Sept	19.7 °C	19 %	43 km/h	0.0 mm	High 31
15 Sept	20.8 °C	16 %	40 km/h	0.0 mm	High 30
16 Sept	20.1 °C	17 %	26 km/h	0.0 mm	High 28
17 Sept	20.6 °C	17 %	29 km/h	0.0 mm	High 28
18 Sept	17.7 °C	20 %	49 km/h	1.7 mm	Moderate 13
19 Sept	9.6 °C	67 %	45 km/h	10.0 mm	Very low 0
20 Sept	14.9 °C	29 %	39 km/h	0.0 mm	Very low 3
21 Sept	20.1 °C	20 %	36 km/h	0.0 mm	Low 10
22 Sept	16.3 °C	30 %	50 km/h	0.0 mm	Moderate 16
23 Sept	17.6 °C	26 %	48 km/h	0.0 mm	Moderate 18
24 Sept	8.7 °C	49 %	44 km/h	3.5 mm	Very low 1
25 Sept after	8.5 °C	48 %	72 km/h	6.5 mm	Very low 0

Before and after, from space

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

↔

Before · 19 Aug 2020

After · 1 Oct 2020

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.

Detections table · 1,330Every 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 Porphyry Fire last?: The official perimeter only gives the start date (26 August 2020). The end comes from the heat detections inside the perimeter: it burned until 24 September 2020 (30 days from 26 August 2020), 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 5,570 hectares (55.7 km²). Other tallies, such as daily incident reports, may give slightly different figures.
Which counties burned?: The fire only entered Idaho (5,497 ha, 0.2 %).
What was the weather like?: During the fire the temperature reached 28.6 °C, humidity dropped to 12 % and gusts hit 67 km/h. The fire danger index (FWI) reached 35, 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

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

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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. 1,330 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.

Where it burned