How long did the Moldy Fire last?

The official perimeter only gives the start date (21 June 2025). The end comes from the heat detections inside the perimeter: it burned until 14 July 2025 (25 days from 20 June 2025), 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 29,225 hectares (292.2 km²). Other tallies, such as daily incident reports, may give slightly different figures.

Which counties burned?

The fire only entered Yukon-Koyukuk (29,505 ha, 0.1 %).

What was the weather like?

During the fire the temperature reached 31.6 °C, humidity dropped to 20 % and gusts hit 44 km/h. The fire danger index (FWI) reached 26, 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 · 2025-06-20 → 2025-07-14

Moldy Fire, June 2025 Yukon-Koyukuk

Out · last detection 14 Jul 2025, 00:31 UTC

The fire started on 20 June 2025 in Yukon-Koyukuk, United States, and satellites saw it burning for 25 days. United States agencies (MTBS / NIFC) mapped an official burnt perimeter of 29,225 hectares, spread across a single county.

It is the 28th largest in Alaska since 2016 (of 472 with a page). Number 11 in United States in 2025, of 327.

Compare with…

Suggestions: Nogadeneoda Lake · 2019

Burnt area: 29,225ha; official perimeter (MTBS / NIFC)
Duration: ≈ 25days; 20 Jun 2025 – 14 Jul 2025
Counties hit: 1; counties
Started on: 20 Jun; 2025
Heat detections: 1,548; in a single hotspot: 445 MW
Danger at start: 15; Moderate · FWI index
Average daily power: 2.1GW; detected power per day, on average

HOTSPOTS BY DAY 20 Jun14 Jul

Play back 14 Jul 2025

How it evolved, day by day

20 Jun 23 Jun 3 Jul 9 Jul 12 Jul 13 Jul

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

The weather it burned in

32°high

44km/h · peak gust

20%lowest humidity

It had gone 0 days without rain (1 mm or more) when it started. Rain came after the fire: 17.5 mm on 15 Jul.

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 18% of the area of London (292 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

Yukon-Koyukuk where it started

29,505 ha reached on 20 Jun

0.1 %

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 2025

Built-up area< 0.1 ha

Residents< 20

Inside the perimeter there was no noticeable built-up land and almost nobody lived there (GHSL 2025, 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. The GHSL 2025 epoch is a projection made from 2020 and earlier data.

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)
20 Jun	29.7 °C	22 %	22 km/h	0.2 mm	Moderate 15
21 Jun	22.9 °C	31 %	44 km/h	0.0 mm	Moderate 21
22 Jun	22.0 °C	41 %	29 km/h	0.0 mm	Moderate 16
23 Jun	20.5 °C	59 %	24 km/h	3.6 mm	Very low 2
24 Jun	21.8 °C	38 %	19 km/h	0.0 mm	Very low 4
25 Jun	24.2 °C	32 %	26 km/h	0.2 mm	Moderate 11
26 Jun	21.4 °C	52 %	27 km/h	11.1 mm	Very low 0
27 Jun	20.8 °C	67 %	31 km/h	1.5 mm	Very low 1
28 Jun	20.9 °C	54 %	28 km/h	0.6 mm	Very low 3
29 Jun	19.3 °C	42 %	35 km/h	0.0 mm	Low 7
30 Jun	18.7 °C	51 %	35 km/h	0.3 mm	Low 9
1 Jul	22.6 °C	45 %	32 km/h	1.4 mm	Low 6
2 Jul	30.2 °C	29 %	31 km/h	0.1 mm	Moderate 16
3 Jul	29.3 °C	26 %	34 km/h	0.0 mm	Moderate 20
4 Jul	29.2 °C	32 %	22 km/h	0.0 mm	Moderate 20
5 Jul	31.1 °C	24 %	32 km/h	0.0 mm	High 23
6 Jul	31.6 °C	20 %	31 km/h	0.0 mm	High 26
7 Jul	26.6 °C	37 %	36 km/h	0.6 mm	High 22
8 Jul	20.9 °C	34 %	36 km/h	0.1 mm	High 22
9 Jul	16.1 °C	31 %	34 km/h	0.0 mm	High 21
10 Jul	19.2 °C	25 %	24 km/h	0.0 mm	High 22
11 Jul	23.7 °C	25 %	21 km/h	0.0 mm	High 23
12 Jul	24.2 °C	25 %	29 km/h	0.0 mm	High 23
13 Jul	25.8 °C	28 %	25 km/h	0.0 mm	High 25
14 Jul	19.3 °C	55 %	42 km/h	6.2 mm	Very low 2
15 Jul after	15.3 °C	70 %	42 km/h	17.5 mm	Very low 0

Before and after, from space

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

↔

Before · 13 Jun 2025

After · 21 Jul 2025

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 23 June 2025 the air beside the fire reached 77 µg/m³ of PM2.5. That day averaged 39: 2.6 times the WHO daily guideline (15).

PM2.5 peak77 µg/m³

Days over the guideline5 days

PM1078 µg/m³

Optical depth1.18

WHO 15

18192021222324

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 · 1,548Every 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

1,217 haNogadeneoda Lake Yukon-KoyukukJuly 2019 · 16 days · 40 km away

All fires in United States ›

Frequently asked questions

How long did the Moldy Fire last?: The official perimeter only gives the start date (21 June 2025). The end comes from the heat detections inside the perimeter: it burned until 14 July 2025 (25 days from 20 June 2025), 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 29,225 hectares (292.2 km²). Other tallies, such as daily incident reports, may give slightly different figures.
Which counties burned?: The fire only entered Yukon-Koyukuk (29,505 ha, 0.1 %).
What was the weather like?: During the fire the temperature reached 31.6 °C, humidity dropped to 20 % and gusts hit 44 km/h. The fire danger index (FWI) reached 26, 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

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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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: NIFC WFIGS (United States), 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. 1,548 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 2025, 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