Marshall Fire, December 2021 Boulder
The fire started on 30 December 2021 in Boulder, United States, and satellites saw it burning for 2 days. United States agencies (MTBS / NIFC) mapped an official burnt perimeter of 2,550 hectares, spread across a single county.
It is the 50th largest in Colorado since 2016 (of 167 with a page). Number 142 in United States in 2021, of 385.
Compare with…
Suggestions: Calwood · 2020
- Burnt area
- 2,550ha
- official perimeter (MTBS / NIFC)
- Duration
- ≈ 2days
- 30 Dec 2021 – 31 Dec 2021
- Counties hit
- 1
- counties
- Started on
- 30 Dec
- 2021
- Heat detections
- 108
- in a single hotspot: 251 MW
- Danger at start
- 6
- Low · FWI index
- Average daily power
- 2.5GW
- detected power per day, on average
Where it burned
How it evolved, day by day
Fire radiative power detected each day, in megawatts, and number of hotspots. The magenta bar marks the peak day.
The weather it burned in
It had gone 2 days without rain (1 mm or more) when it started. Rain came after the fire: 3.3 mm on 1 Jan.
This area had burned before
No earlier perimeters overlap this fire since 2016, when the satellite record begins.
How big is it?
London boundary: geoBoundaries · Office for National Statistics (Open Government Licence v3.0).
Paris boundary: geoBoundaries · Institut national de l'information géographique et forestière (IGN-F) (Etalab Open License 2.0).
Madrid boundary: geoBoundaries · Open Data ESRI, IGN Central Registry of Cartography Area (CC BY 4.0).
Berlin boundary: geoBoundaries · Federal Agency for Cartography and Geodesy (dl-de/by-2-0).
This compares size, not location: both shapes are at the same scale, north up, centred on each other.
What happened to each county
-
Boulder where it started2,545 ha reached on 30 Dec1.3 %
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 2020Inside the perimeter there were about 89 hectares of built-up land and about 5,200 residents (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) |
|---|---|---|---|---|---|
| 30 Dec | 6.3 °C | 32 % | 77 km/h | 0.0 mm | Low 6 |
| 31 Dec | 1.1 °C | 54 % | 36 km/h | 11.0 mm | Very low 0 |
| 1 Jan after | -9.2 °C | 70 % | 38 km/h | 3.3 mm | Very low 0 |
Before and after, from space
Drag the line to compare the same ground before the fire and after it.
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 · 108Every satellite heat detection, one by one, with time, satellite, power and coordinates.
| Date and time | Satellite | FRP (MW) | Lat | Lon |
|---|
Other fires nearby
Frequently asked questions
- How long did the Marshall Fire last?
- The official perimeter only gives the start date (30 December 2021). The end comes from the heat detections inside the perimeter: it burned until 31 December 2021 (2 days from 30 December 2021), 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 2,550 hectares (25.5 km²). Other tallies, such as daily incident reports, may give slightly different figures.
- Which counties burned?
- The fire only entered Boulder (2,545 ha, 1.3 %).
- What was the weather like?
- During the fire the temperature reached 6.3 °C, humidity dropped to 32 % and gusts hit 77 km/h. The fire danger index (FWI) reached 6, class Low.
- 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 ›
- NIFC · National Interagency Fire Center ↗
- InciWeb · Incident Information System ↗
- MTBS · Monitoring Trends in Burn Severity ↗
Satellite cross-check
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.
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
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. 108 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.
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.