Grid reliability · 2024 · 6 reporting utilities
Power outages in Montana
The utilities that reported here serve 501,041 customers between them, not the whole state. Weighted by customer count, they averaged 2.5 hr without power in an ordinary year and 5.7 hr once major events are counted. Each figure comes only from the filers that published it, and the counts are below.
What it means
Why there are two numbers
Across the utilities that filed both figures, major events account for 55% of the outage time Montana recorded once they are counted: 5.7 hr against 2.5 hr without them, a factor of 2.2×. Solar panels alone do not help during an outage, because a grid-tied array shuts down when the grid does, so riding through one is a battery question. This figure will not answer it: it is an annual average across a utility’s customers, not the length or the load of any single outage. What it does say is how much of the outage time here arrives with major events rather than on ordinary days.
The comparison is drawn from the 6 utilities that filed both figures, which is all of them, so both sides of the ratio describe the same set of customers. The two headline figures above are averaged over everyone who filed each one, so dividing them would not give this number.
The utilities behind the average
Each of Montana’s figures is a customer-weighted average of the filings that carried that metric, not of the table as a whole: the ordinary-year average is built from 6 filings and the storm-inclusive average from 6 filings, out of 6 filings that published an outage figure at all. Those are the same utilities on both sides. A utility that filed without publishing a metric, or whose two major-event variants contradicted each other, is absent from that metric rather than counted as zero.
| Utility | Customers | Ordinary year | With major events | Interruptions |
|---|---|---|---|---|
| NorthWestern Energy LLC - (MT) | 376,392 | 118 min | 3.9 hr | 1.0× |
| Flathead Electric Coop Inc | 78,834 | 3.9 hr | 9.8 hr | 1.9× |
| Montana-Dakota Utilities Co | 26,559 | 3.0 hr | 6.0 hr | 1.4× |
| Missoula Electric Coop, Inc | 17,133 | 8.4 hr | 27 hr | 2.2× |
| Fall River Rural Elec Coop Inc | 2,080 | 8 min | 17 min | 0.1× |
| Black Hills Power, Inc. | 43 | 59 min | 59 min | 1.2× |
What this page is not
It is a state average of utility filings, not a measurement at any address. Each filing is itself an average over a whole service territory, so a rural feeder and a downtown network arrive here as one number, and nothing in this dataset says how far an individual address sits from it. Nothing here predicts a future year either, and a single severe storm can move a utility’s figure by an order of magnitude.
The methodology page states the sources, the definitions, and the limits. Back to the Grid Reliability Index
Source: U.S. Energy Information Administration, Form EIA-861 reliability file, data year 2024, covering 2024-01-01 through 2024-12-31. The snapshot covers no later period.