Caldor Fire – 8/20/2021 Afternoon Update

Good evening. Here is the afternoon update on conditions through early afternoon on the Caldor Fire. These maps are produced by The Lookout. This information is intended to supplement, not replace information from official fire information websites like InciWeb.

We make our maps from publicly available heat scan data (we call them “IR, or infrared flights”). This information is not always captured at the same time every day, but it is almost always captured overnight. We do midday or realtime updates if fire conditions are dynamic and we have good intel. Otherwise, our morning updates will be the most reliable, usually posted by 9am. Follow @wildland_zko on Twitter for notifications on our updates. Check out my bio page here if you want to see who I am and why I am doing this work. This website is supported by your donations, so if you find the information helpful, please consider making a donation to this new website project.

It’s important to note wildfires are often most active in the late afternoon, so any midday update is usually outdated by the time we receive the data. Even so, the midday information can be useful in seeing where areas have been cooling down or are most active. We publish this data “as-is” meaning that I am working in a small office a hundred miles away from the fire and cannot tell if there are errors or omissions in the data.

Weather Concerns: From Inciweb.

A Red Flag Warning is in effect from 11am through 8pm Saturday for strong winds and low humidity.

Observed: Smoke and inversion conditions prevailed again. High ranges from 69-79° F and relative humidity remained in the 30-35% range. Winds were generally south to southwest 6-9 mph with gusts to 15 mph.

Forecast for tonight: Mostly clear with areas of smoke. Lows 58-63° lower elevations and 55-60° at 5000′. Humidity recovery 50-55%. Winds downslope (easterly) 2-6 mph through 4am, then southerly.

Forecast for Saturday: Becoming locally windy with south to southwest winds 10-15 mph with gusts to 25 mph or higher over ridges. Some local areas may have gusts to over 30 mph as a weather disturbance moves through the region. Humidity will also fall into the 17-22 percent range and this combined with the extremely dry fuels and gusty winds will create conditions for rapid fire spread and growth.

Skip to Weather and Fire Behavior Forecasts…

Between 8pm of 8/19/2021 and 2:45pm on 8/20/2021, the Caldor Fire spread in all directions except south.

Most spread on the west and northwest sides of the fire was less than 1/4 of a mile. On the east edge of the fire, east of Morrison, the fire ran a little over a mile. White lines show 18 hours of fire growth. Images are time-stamped on upper-left corner.

The fire crossed the Middle Fork Consumnes River and became established on the south side of the River north of the Eagle Mine.


Today’s 2:45pm mapping didn’t show much heat to the west of Grizzly Flats.



Defensive firing operations are occurring along the Mormon Emigrant Trail east of Sly Park Reservoir. This is visible as a strip of red along the road in map below.


Closeup of firing operations.


There are scattered hot areas on the north side of Iron Mountain, where the fire is backing down toward Plum Creek and the South Fork American River Canyon.



Between Morrison and Darlington, the fire has crossed Mill Creek and Mill Creek Ridge.



The fire has crossed Alder Ridge, and is dropping into Guard Creek.



The fire is well-established on the south side of Middle Fork Consumnes River between Omo Ranch and Croft. There is not a lot of heat showing on the heat mapping on the south flank of the fire.