USGS Streamgage 11456000
Napa River near St Helena, CA
Napa River near St Helena, CA is USGS streamgage 11456000 in California, monitoring river discharge in hydrologic subbasin 18050002. It sits on the Napa River, alongside 1 other gauge Rivermatics tracks on the same river. It drains a watershed of about 79 square miles. Discharge records at this site go back to 1929. Typical flow runs near 1.8 cfs in July and 38.3 cfs in April, with the higher of the two arriving in April. Rivermatics issues a daily machine-learned flow outlook for this gauge, reaching 14 days ahead.
View live conditions & forecast →
Gauge details
- State
- California
- Drainage area
- 79 sq mi
- Gauge elevation
- 191 ft
- Subbasin (HUC-8)
- 18050002
- Coordinates
- 38.51126, -122.45578
- USGS site number
- 11456000
- Records begin
- 1929-10-01 (97 years)
- Rivermatics forecast
- 14-day flow outlook
14-day flow forecast
Based on observations through for Napa River near St Helena, CA. 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 |
|---|---|---|---|---|
| 0 | 0 | 0 | ||
| 0 | 0 | 0 | ||
| 0 | 0 | 0 | ||
| 0 | 0 | 0.1 | ||
| 0 | 0 | 0.1 | ||
| 0 | 0 | 0.1 | ||
| 0 | 0 | 0.1 | ||
| 0 | 0 | 0.1 | ||
| 0 | 0 | 0.1 | ||
| 0 | 0 | 0.1 | ||
| 0 | 0 | 0.1 | ||
| 0 | 0 | 0.1 | ||
| 0 | 0 | 0.1 | ||
| 0 | 0 | 0.1 |
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 97 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 | 6.2 | 68 | 819.2 | |
| February | 10.4 | 85.4 | 719.5 | |
| March | 16.5 | 81.5 | 512.9 | |
| April | 10.3 | 38.3 | 197.8 | |
| May | 5 | 14.6 | 45.8 | |
| June | 1.4 | 5.5 | 16 | |
| July | 0 | 1.8 | 5.3 | |
| August | 0 | 0.7 | 2.4 | |
| September | 0 | 0.4 | 1.7 | |
| October | 0 | 0.6 | 5.2 | |
| November | 0.1 | 2.8 | 56.7 | |
| December | 1.8 | 21.8 | 533.4 |
All values in cubic feet per second (cfs).
Common questions
- When does Napa River near St Helena, CA normally run highest?
- February, on the long-term record. The median daily flow that month is about 85.4 cfs, against 0.4 cfs in September, the lowest month. These are historical normals for the date, not a forecast and not today's reading.
- What is a normal flow for Napa River near St Helena, CA?
- It depends on the month. In January, half of days historically fall near 68 cfs, with the middle 80% of days between 6.2 and 819.2 cfs. The month-by-month table on this page gives the full range.
- How long has Napa River near St Helena, CA been measured?
- Discharge records at USGS site 11456000 begin in 1929, about 97 years, covering roughly 9,130 days of published daily values. The long record is what makes the monthly percentiles on this page meaningful.
- Is there a flow forecast for Napa River near St Helena, CA?
- 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 Napa River near St Helena, CA?
- The gauge sits at 38.51126, -122.45578, in California, in hydrologic subbasin 18050002, at an elevation of about 191 feet, draining roughly 79 square miles.
- Can I use Napa River near St Helena, CA 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.
Upstream and downstream on the Napa River
Every gauge Rivermatics tracks on this river, ordered by drainage area — upstream first. See the Napa River in full.
- Napa River near St Helena, CA this page
- Napa River near Napa, CA 218 sq mi