Red Flag Warnings in effect across five states as critical fire-weather conditions develop
The National Weather Service (NWS) has Red Flag Warnings in effect across parts of Montana, Wyoming, North Dakota, Idaho and South Dakota on September 10, 2026, as very low relative humidity, dry vegetation and gusty winds produce critical fire-weather conditions across the northern Rockies and northern Plains. Minimum relative humidity may fall as low as 5% in southeastern Wyoming, while wind gusts may reach approximately 65 km/h (40 mph) in parts of Wyoming and Montana.
Red Flag Warnings in effect across parts of the northern Rockies and northern Plains on September 10, 2026. Credit: NWS
The warnings form a broad corridor of critical fire-weather conditions extending from southeastern Idaho and western Wyoming through much of Montana into western North Dakota and northwestern South Dakota. Across the region, dry fuels are combining with very low afternoon humidity and strengthening westerly winds, while parts of the northern Plains are experiencing the conditions ahead of an approaching cold front.
Warnings were issued by seven NWS forecast offices: Billings, Bismarck, Riverton, Glasgow, Cheyenne, Pocatello and Missoula.
Most of the warnings cover the afternoon and evening of September 10 and expire between 20:00 and 21:00 MDT, or at 21:00 CDT (02:00–03:00 UTC on September 11).
A Red Flag Warning indicates that critical fire-weather conditions are occurring or expected shortly. It does not mean that a wildfire is necessarily burning, but the combination of strong winds, low relative humidity, and warm temperatures could contribute to extreme fire behavior.
Montana and northwestern South Dakota
The NWS Billings office issued a warning for Montana fire-weather zones 123, 124 and 127 from 12:00 to 20:00 MDT on September 10 (18:00 UTC to 02:00 UTC on September 11).
The warned area includes parts of Golden Valley, Musselshell, Wheatland, Park, Sweet Grass, and Gallatin counties. Westerly winds of approximately 25–40 km/h (15–25 mph), gusting to 65 km/h (40 mph), are forecast to coincide with minimum relative humidity near 10%.
NWS said the most severe conditions are expected across lower elevations that received little precipitation during the preceding week.
A separate warning covers fire-weather zone 133, including Carter and Fallon counties in Montana and Harding County in South Dakota, during the same period. Westerly winds are forecast at approximately 15–30 km/h (10–20 mph), with gusts reaching 55 km/h (35 mph) and minimum relative humidity near 12%.
Farther north, the NWS Glasgow office issued a warning for Montana fire-weather zones 122 and 137 from 12:00 to 20:00 MDT.
The warning covers Dawson, McCone, Prairie, Richland and Wibaux counties, as well as southern Petroleum and southern Garfield counties. Westerly winds of approximately 15–30 km/h (10–20 mph), gusting to 50 km/h (30 mph), are expected as relative humidity falls to approximately 11%.
The NWS Missoula office placed East Beaverhead County, represented by Montana fire-weather zone 111, under a warning from 12:00 to 21:00 MDT on September 10 (18:00 UTC to 03:00 UTC on September 11).
Southwesterly winds of approximately 15–30 km/h (10–20 mph), with gusts to 55 km/h (35 mph), are forecast to combine with minimum relative humidity of 10–15%.
Western and south-central North Dakota
The NWS Bismarck office issued a Red Flag Warning for 14 counties across western and south-central North Dakota.
The warning covers Adams, Billings, Bowman, Dunn, Golden Valley, Grant, Hettinger, McKenzie, Mercer, Morton, Oliver, Sioux, Slope, and Stark counties.
It remains in effect from 12:00 to 20:00 MDT across western areas and from 13:00 to 21:00 CDT farther east. Both periods correspond to 18:00 UTC on September 10 through 02:00 UTC on September 11.
Westerly winds of approximately 25–40 km/h (15–25 mph), with gusts reaching 55 km/h (35 mph), are forecast as relative humidity falls to 10–20%. NWS said abundant dry vegetation would contribute to critical fire-weather conditions, with any fires that develop capable of spreading rapidly.
Central, southern and western Wyoming
The NWS Riverton office issued Red Flag Warnings for several fire-weather zones across central, southern and western Wyoming.
Zones 280, 289 and 300 remain under warning until 21:00 MDT on September 10. Relative humidity may fall to approximately 7%, while southwesterly winds reach 15–30 km/h (10–20 mph), with gusts to 50 km/h (30 mph).
Zones 277, 278 and 279 are also under warning until 21:00 MDT. Westerly winds of 15–30 km/h (10–20 mph), gusting to approximately 40 km/h (25 mph), are forecast as relative humidity falls to around 8%.
Warnings for zones 286, 287 and 288 run from 12:00 to 21:00 MDT. Westerly winds are forecast at 15–30 km/h (10–20 mph), with gusts reaching 55 km/h (35 mph). Relative humidity may fall to 12–15%, particularly below approximately 3 050 m (10 000 feet).
The Riverton warnings include parts of Fremont, Hot Springs, Lincoln, Natrona, Park, Sublette, Sweetwater and Uinta counties.
Southeastern Wyoming
The NWS Cheyenne office expanded its Red Flag Warning early on September 10 to include fire-weather zones 423, 424, 426, 428, 429 and 432. Existing warnings for zones 419, 420, 421, 422, 425 and 427 remained in effect.
All the Cheyenne warnings continue until 20:00 MDT on September 10 (02:00 UTC on September 11).
Westerly winds of approximately 25–50 km/h (15–30 mph), with gusts reaching 65 km/h (40 mph), are forecast across the warned area. Minimum relative humidity may fall to 5–13% in the newly added zones and 5–10% across areas covered by the earlier warning.
The newly added areas include southwestern Carbon County, the Sierra Madre and Snowy ranges, the southern Laramie Valley, the southern Laramie Range and the Bordeaux, Chugwater and Wheatland area.
NWS said fires that develop under these conditions would likely spread rapidly and advised against outdoor burning.
Southeastern Idaho
The NWS Pocatello office issued a Red Flag Warning for fire-weather zone 410, covering the Upper Snake River Valley and Idaho Falls Bureau of Land Management area, from 12:00 to 20:00 MDT on September 10.
Southwesterly winds of approximately 25–40 km/h (15–25 mph), with gusts reaching 55 km/h (35 mph), are expected. Minimum relative humidity may fall to approximately 11%.
NWS warned that existing or newly ignited fires could grow rapidly because of the combination of low humidity and gusty winds.
People in the warned areas should follow local fire restrictions, avoid outdoor burning, and limit activities that could produce sparks. Warning boundaries and expiration times may change as local NWS offices assess updated weather and fuel conditions.
References:
1 Red Flag Warning – NWS – September 10, 2026
I am an Assistant Editor and Severe Weather & Science Journalist at The Watchers, specializing in real-time severe weather coverage, geophysical event reporting, and research-driven scientific analysis. You can reach me at rishav(at)watchers(.)news.
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