How long did the Post Office Fire last?

The official perimeter only gives the start date (21 August 2022). The end comes from the heat detections inside the perimeter: it burned until 12 September 2022 (23 days from 21 August 2022), 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 939 hectares (9.4 km²). Other tallies, such as daily incident reports, may give slightly different figures.

Which counties burned?

The fire only entered Idaho (945 ha, 0.0 %).

What was the weather like?

During the fire the temperature reached 31.3 °C, humidity dropped to 11 % and gusts hit 65 km/h. The fire danger index (FWI) reached 48, 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 · 2022-08-21 → 2022-09-12

Post Office Fire, August 2022 Idaho

Out · last detection 12 Sept 2022, 21:07 UTC

The fire started on 21 August 2022 in Idaho, United States, and satellites saw it burning for 23 days. United States agencies (MTBS / NIFC) mapped an official burnt perimeter of 939 hectares, spread across a single county.

It is the 237th largest in Idaho since 2016 (of 379 with a page). Number 325 in United States in 2022, of 493.

Compare with…

Suggestions: Warm Springs · 2022 Bm Hill · 2021 Cedar · 2016 Storm Creek · 2021

Burnt area: 939ha; official perimeter (MTBS / NIFC)
Duration: ≈ 23days; 21 Aug 2022 – 12 Sept 2022
Counties hit: 1; counties
Started on: 21 Aug; 2022
Heat detections: 323; in a single hotspot: 84 MW
Danger at start: 24; High · FWI index
Average daily power: 133MW; detected power per day, on average

HOTSPOTS BY DAY 21 Aug12 Sept

Play back 12 Sept 2022

How it evolved, day by day

30 Aug 1 Sept 3 Sept 5 Sept 7 Sept 8 Sept 9 Sept 11 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

31°high

65km/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: 7.3 mm on 15 Sept.

This area had burned before

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

How big is it?

It burned the equivalent of 0.6% of the area of London (9.4 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

945 ha reached on 30 Aug

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 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)
21 Aug	28.3 °C	25 %	35 km/h	0.4 mm	High 24
22 Aug	25.9 °C	24 %	45 km/h	0.1 mm	High 29
23 Aug	26.3 °C	28 %	22 km/h	0.4 mm	High 26
24 Aug	23.9 °C	39 %	29 km/h	7.5 mm	Very low 3
25 Aug	24.0 °C	39 %	46 km/h	1.7 mm	Low 7
26 Aug	24.1 °C	33 %	49 km/h	0.0 mm	Moderate 18
27 Aug	18.1 °C	47 %	62 km/h	0.6 mm	Moderate 17
28 Aug	19.0 °C	32 %	40 km/h	0.0 mm	Moderate 18
29 Aug	26.6 °C	20 %	26 km/h	0.0 mm	High 24
30 Aug	29.5 °C	14 %	35 km/h	0.0 mm	High 34
31 Aug	30.9 °C	14 %	30 km/h	0.0 mm	High 33
1 Sept	27.6 °C	20 %	41 km/h	0.0 mm	High 36
2 Sept	31.3 °C	11 %	24 km/h	0.0 mm	High 35
3 Sept	29.7 °C	16 %	63 km/h	0.0 mm	Very high 48
4 Sept	27.1 °C	15 %	46 km/h	0.0 mm	Very high 42
5 Sept	24.6 °C	22 %	49 km/h	0.0 mm	Very high 38
6 Sept	31.3 °C	12 %	37 km/h	0.0 mm	Very high 40
7 Sept	27.7 °C	20 %	65 km/h	0.2 mm	Very high 43
8 Sept	17.9 °C	15 %	52 km/h	0.0 mm	Very high 40
9 Sept	17.7 °C	22 %	40 km/h	0.0 mm	High 34
10 Sept	23.4 °C	15 %	23 km/h	0.0 mm	High 31
11 Sept	24.2 °C	15 %	38 km/h	0.0 mm	High 35
12 Sept	25.6 °C	14 %	39 km/h	0.0 mm	High 36
13 Sept after	17.5 °C	40 %	20 km/h	0.4 mm	High 23
14 Sept after	19.8 °C	39 %	28 km/h	0.6 mm	Moderate 19
15 Sept after	17.2 °C	55 %	32 km/h	7.3 mm	Very low 1

Before and after, from space

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

↔

Before · 14 Aug 2022

After · 19 Sept 2022

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 20 August 2022 the air beside the fire reached 43 µg/m³ of PM2.5. That day averaged 24: 1.6 times the WHO daily guideline (15).

PM2.5 peak43 µg/m³

Days over the guideline1 day

PM1061 µg/m³

Optical depth1.05

WHO 15

192021222324

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 · 323Every 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 Post Office Fire last?: The official perimeter only gives the start date (21 August 2022). The end comes from the heat detections inside the perimeter: it burned until 12 September 2022 (23 days from 21 August 2022), 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 939 hectares (9.4 km²). Other tallies, such as daily incident reports, may give slightly different figures.
Which counties burned?: The fire only entered Idaho (945 ha, 0.0 %).
What was the weather like?: During the fire the temperature reached 31.3 °C, humidity dropped to 11 % and gusts hit 65 km/h. The fire danger index (FWI) reached 48, 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

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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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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.
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. 323 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