USGS Streamgage 12381400
South Fork Jocko River near Arlee, MT
South Fork Jocko River near Arlee, MT is USGS streamgage 12381400 in Montana, monitoring river discharge in hydrologic subbasin 17010212. It drains a watershed of about 58 square miles. Discharge records at this site go back to 1982. Typical flow runs near 77.9 cfs in July and 52.1 cfs in April, with the higher of the two arriving in July. Rivermatics issues a daily machine-learned flow outlook for this gauge, reaching 14 days ahead.
View live conditions & forecast →
Gauge details
- State
- Montana
- Drainage area
- 58 sq mi
- Gauge elevation
- 3,970 ft
- Subbasin (HUC-8)
- 17010212
- Coordinates
- 47.19555, -113.85074
- USGS site number
- 12381400
- Records begin
- 1982-09-28 (44 years)
- Rivermatics forecast
- 14-day flow outlook
14-day flow forecast
Based on observations through for South Fork Jocko River near Arlee, MT. Each day carries a median estimate and the band the model expects the flow to fall within — not a single number to plan against. Forecasts are re-issued daily; see the live screen for the current outlook.
| Date | Low p10 | Expected p50 | High p90 | Range |
|---|---|---|---|---|
| 27.2 | 28.8 | 31.2 | ||
| 26 | 28.1 | 30.5 | ||
| 25.2 | 27.3 | 29.8 | ||
| 24.8 | 27 | 29.6 | ||
| 24.1 | 26.2 | 28.4 | ||
| 24.6 | 27.5 | 32.2 | ||
| 24.3 | 27.1 | 31.3 | ||
| 23.5 | 25.9 | 29.1 | ||
| 22.8 | 25.1 | 27.8 | ||
| 22.2 | 24.4 | 26.8 | ||
| 21.6 | 23.8 | 26.1 | ||
| 21.1 | 23.3 | 25.5 | ||
| 20.8 | 22.9 | 25.1 | ||
| 20.5 | 22.7 | 24.7 |
All values in cubic feet per second (cfs). Estimates only — do not use them for navigation or for any safety, rescue, or emergency decision.
Typical flow by month
Long-term daily discharge percentiles from the USGS record (up to 43 years of data), averaged within each month. These describe the historical normal range — they are not a forecast and not today's reading.
| Month | Low p10 | Typical p50 | High p90 | Range |
|---|---|---|---|---|
| January | 5.9 | 11.5 | 20.5 | |
| February | 6.3 | 10.9 | 19 | |
| March | 8.8 | 14.5 | 33.5 | |
| April | 20.2 | 52.1 | 116.4 | |
| May | 100.6 | 197 | 372.9 | |
| June | 97.8 | 195.8 | 348.2 | |
| July | 44.4 | 77.9 | 117.2 | |
| August | 24.6 | 38.9 | 50.5 | |
| September | 18 | 25.8 | 34.7 | |
| October | 15.1 | 20.9 | 28.5 | |
| November | 12.2 | 18.3 | 27.3 | |
| December | 7.6 | 13.6 | 23.5 |
All values in cubic feet per second (cfs).
Common questions
- When does South Fork Jocko River near Arlee, MT normally run highest?
- May, on the long-term record. The median daily flow that month is about 197 cfs, against 10.9 cfs in February, the lowest month. These are historical normals for the date, not a forecast and not today's reading.
- What is a normal flow for South Fork Jocko River near Arlee, MT?
- It depends on the month. In January, half of days historically fall near 11.5 cfs, with the middle 80% of days between 5.9 and 20.5 cfs. The month-by-month table on this page gives the full range.
- How long has South Fork Jocko River near Arlee, MT been measured?
- Discharge records at USGS site 12381400 begin in 1982, about 44 years, covering roughly 9,196 days of published daily values. The long record is what makes the monthly percentiles on this page meaningful.
- Is there a flow forecast for South Fork Jocko River near Arlee, MT?
- Yes. Rivermatics trains a machine-learned model — a temporal-fusion transformer — on this basin's observed flows, weather, and snowpack, and issues a daily flow outlook reaching 14 days ahead: a median estimate inside a confidence band, not a single number to bet on. Every forecast is scored against days the model never trained on, and that track record is published on the live gauge screen. Open live conditions to see the current outlook.
- Where is South Fork Jocko River near Arlee, MT?
- The gauge sits at 47.19555, -113.85074, in Montana, in hydrologic subbasin 17010212, at an elevation of about 3,970 feet, draining roughly 58 square miles.
- Can I use South Fork Jocko River near Arlee, MT data for flood or safety decisions?
- No. Rivermatics provides estimates, not guarantees, and the readings and forecasts here may be delayed, inaccurate, or wrong. Do not use them for navigation or for any safety, rescue, or emergency decision. Check the National Weather Service and USGS directly, and use your own judgment.