County annual report · FIPS 30111
2021 Yellowstone County, MT Power Outage Report
In 2021, customers in Yellowstone County, MT went without power for an average of 1.6 hours, a total of 127K customer-hours (Montana average 5.0 hours). That ranks 38th worst of 51 Montana counties and 2393rd of 2,974 nationally.
Compared with MT, the US and 2020
Coverage line is EAGLE-I's share of Montana customers tracked each year.
Biggest outages in Yellowstone County, 2021
The 10 outage episodes with the most customers out at once. Times are UTC.
| # | Started (UTC) | Ended (UTC) | Duration | Peak out | Customer-hours |
|---|---|---|---|---|---|
| 1 | May 29, 2021 15:45 | May 29, 2021 20:45 | 5h | 2,153 | 6,623 |
| 2 | October 12, 2021 06:15 | October 13, 2021 05:30 | 23h 15m | 2,145 | 7,789 |
| 3 | September 5, 2021 13:45 | September 5, 2021 16:00 | 2h 15m | 1,907 | 4,289 |
| 4 | July 31, 2021 20:30 | August 1, 2021 02:30 | 6h | 1,429 | 3,940 |
| 5 | December 27, 2021 01:45 | December 27, 2021 09:45 | 8h | 1,413 | 4,310 |
| 6 | June 9, 2021 16:30 | June 9, 2021 19:45 | 3h 15m | 1,382 | 2,403 |
| 7 | September 1, 2021 18:45 | September 1, 2021 21:00 | 2h 15m | 1,308 | 699 |
| 8 | December 16, 2021 06:00 | December 16, 2021 10:00 | 4h | 1,304 | 1,975 |
| 9 | August 3, 2021 14:15 | August 4, 2021 02:15 | 12h | 1,288 | 3,960 |
| 10 | March 6, 2021 23:30 | March 7, 2021 00:45 | 1h 15m | 1,263 | 333 |
Outage episodes by size in 2021: 84 reached 100+ customers, 14 reached 1,000+ customers, 0 reached 10,000+ customers.
Utility reliability filed with the EIA
SAIDI (average outage time per customer) and SAIFI (average interruptions per customer) that utilities serving Yellowstone County reported on EIA Form 861 for 2021, or their most recent earlier filing. Utility-wide figures, not county-specific.
| Utility | EIA year | SAIDI | SAIFI | SAIDI excl. major events | SAIFI excl. major events |
|---|---|---|---|---|---|
| NorthWestern Energy LLC - (MT) | 2021 | 2.5 hrs | 1.37 | 2.1 hrs | 1.18 |
| Mid-Yellowstone Elec Coop, Inc | 2018 | 4.5 hrs | 3.82 | 4.5 hrs | 3.82 |
| WAPA-- Western Area Power Administration | - | - | - | - | - |
| NorthWestern Energy | - | - | - | - | - |
| Fergus Electric Coop, Inc | - | - | - | - | - |
| Yellowstone Valley Elec Co-op | - | - | - | - | - |
About this data
- Outage figures come from DOE/ORNL EAGLE-I, which records customers out by county every 15 minutes. EAGLE-I tracked about 76% of Montana's customers in 2021; utilities it does not see are not counted.
- Hours per customer = outage customer-minutes ÷ 77,606 customers (ORNL modeled county customer count), including major storm days. It is comparable across counties but is not the SAIDI a utility files.
- An outage event is a continuous stretch with customers out; counts at 100, 1,000 and 10,000+ use its peak.
- Years loaded: 2015–2025. Yellowstone County has data for 2019–2025.
Cite this report
MassOutage (massoutage.com), Yellowstone County, MT annual power outage report, 2021, data as of Oct 3, 2026 02:41 UTC, sources: DOE EAGLE-I (https://eagle-i.doe.gov/); EAGLE-I modeled customer counts (MCC) (https://figshare.com/); EIA Form 861 (utility reliability) (https://www.eia.gov/electricity/data/eia861/). https://massoutage.com/reports/2021/montana/yellowstone-county