How long did the Bald Mountain Fire last?

The official perimeter only gives the start date (24 August 2018). The end comes from the heat detections inside the perimeter: it burned until 28 September 2018 (36 days from 24 August 2018), 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 8,501 hectares (85.0 km²). Other tallies, such as daily incident reports, may give slightly different figures.

Which counties burned?

The fire entered 2 counties: Utah (8,465 ha, 1.5 %); Juab (15 ha, 0.0 %).

What was the weather like?

During the fire the temperature reached 29.1 °C, humidity dropped to 3 % and gusts hit 66 km/h. The fire danger index (FWI) reached 62, class 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 · 2018-08-24 → 2018-09-28

Bald Mountain Fire, August 2018 Utah, Juab

Out · last detection 28 Sept 2018, 19:18 UTC

The fire started on 24 August 2018 in Utah, United States, and satellites saw it burning for 36 days. United States agencies (MTBS / NIFC) mapped an official burnt perimeter of 8,501 hectares, spread across 2 counties.

It is the 19th largest in Utah since 2016 (of 165 with a page). Number 73 in United States in 2018, of 511.

Compare with…

Suggestions: William · 2020 Pole Creek · 2018 Goose Point · 2019 Coal Hollow · 2018

Burnt area: 8,501ha; official perimeter (MTBS / NIFC)
Duration: ≈ 36days; 24 Aug 2018 – 28 Sept 2018
Counties hit: 2; counties
Started on: 24 Aug; 2018
Heat detections: 1,409; in a single hotspot: 593 MW
Danger at start: 24; High · FWI index
Average daily power: 2.6GW; detected power per day, on average

HOTSPOTS BY DAY 24 Aug28 Sept

Play back 28 Sept 2018

How it evolved, day by day

12 Sept 14 Sept 15 Sept 16 Sept 18 Sept 20 Sept 22 Sept 28 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

66km/h · peak gust

3%lowest humidity

It had gone 0 days without rain (1 mm or more) when it started. Rain came after the fire: 4.6 mm on 2 Oct.

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 5.4% of the area of London (85 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

Utah where it started

8,465 ha reached on 12 Sept

1.5 %
Juab

15 ha reached on 12 Sept

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 area0.47 ha

Residents< 20

Inside the perimeter there were about 0.47 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)
24 Aug	26.8 °C	18 %	46 km/h	0.0 mm	High 24
25 Aug	27.1 °C	13 %	38 km/h	0.0 mm	High 31
26 Aug	26.3 °C	6 %	55 km/h	0.0 mm	Very high 40
27 Aug	24.2 °C	15 %	49 km/h	0.0 mm	Very high 38
28 Aug	21.7 °C	21 %	31 km/h	0.0 mm	High 30
29 Aug	26.5 °C	9 %	34 km/h	0.0 mm	High 34
30 Aug	26.8 °C	9 %	57 km/h	0.0 mm	Very high 43
31 Aug	25.7 °C	12 %	34 km/h	0.0 mm	High 37
1 Sept	24.5 °C	12 %	35 km/h	0.0 mm	Very high 38
2 Sept	26.0 °C	9 %	34 km/h	0.0 mm	Very high 38
3 Sept	26.2 °C	8 %	29 km/h	0.0 mm	High 37
4 Sept	25.3 °C	8 %	29 km/h	0.0 mm	High 37
5 Sept	26.2 °C	13 %	27 km/h	0.0 mm	High 37
6 Sept	25.9 °C	14 %	22 km/h	0.0 mm	High 38
7 Sept	27.0 °C	13 %	26 km/h	0.0 mm	Very high 39
8 Sept	27.8 °C	9 %	49 km/h	0.0 mm	Very high 45
9 Sept	27.0 °C	7 %	32 km/h	0.0 mm	Very high 40
10 Sept	29.1 °C	6 %	41 km/h	0.0 mm	Very high 47
11 Sept	27.8 °C	7 %	47 km/h	0.0 mm	Extreme 50
12 Sept	26.5 °C	6 %	53 km/h	0.0 mm	Extreme 56
13 Sept	25.0 °C	6 %	54 km/h	0.0 mm	Extreme 54
14 Sept	27.0 °C	5 %	40 km/h	0.0 mm	Very high 49
15 Sept	28.5 °C	10 %	66 km/h	0.0 mm	Extreme 62
16 Sept	27.7 °C	12 %	61 km/h	0.0 mm	Extreme 55
17 Sept	26.7 °C	13 %	38 km/h	0.0 mm	Very high 45
18 Sept	26.4 °C	5 %	49 km/h	0.0 mm	Extreme 52
19 Sept	24.7 °C	3 %	45 km/h	0.0 mm	Extreme 52
20 Sept	19.4 °C	14 %	41 km/h	0.0 mm	Very high 44
21 Sept	23.3 °C	6 %	28 km/h	0.0 mm	Very high 40
22 Sept	24.8 °C	11 %	41 km/h	0.0 mm	Very high 46
23 Sept	23.6 °C	15 %	60 km/h	0.0 mm	Very high 50
24 Sept	20.2 °C	18 %	44 km/h	0.0 mm	Very high 41
25 Sept	18.2 °C	10 %	33 km/h	0.0 mm	High 38
26 Sept	18.7 °C	9 %	32 km/h	0.0 mm	High 37
27 Sept	22.1 °C	9 %	33 km/h	0.0 mm	Very high 39
28 Sept	24.8 °C	7 %	31 km/h	0.0 mm	Very high 41
29 Sept after	25.0 °C	13 %	51 km/h	0.0 mm	Extreme 50
30 Sept after	22.5 °C	12 %	69 km/h	0.0 mm	Extreme 56
1 Oct after	21.2 °C	27 %	42 km/h	0.0 mm	Very high 38
2 Oct after	20.9 °C	33 %	38 km/h	4.6 mm	Low 6

Before and after, from space

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

↔

Before · 17 Aug 2018

After · 5 Oct 2018

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 · 1,409Every 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

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Frequently asked questions

How long did the Bald Mountain Fire last?: The official perimeter only gives the start date (24 August 2018). The end comes from the heat detections inside the perimeter: it burned until 28 September 2018 (36 days from 24 August 2018), 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 8,501 hectares (85.0 km²). Other tallies, such as daily incident reports, may give slightly different figures.
Which counties burned?: The fire entered 2 counties: Utah (8,465 ha, 1.5 %); Juab (15 ha, 0.0 %).
What was the weather like?: During the fire the temperature reached 29.1 °C, humidity dropped to 3 % and gusts hit 66 km/h. The fire danger index (FWI) reached 62, class 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

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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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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. 1,409 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