Methodology

Gauge readings

Flow (cfs) and gage height (ft) are the latest continuous readings from the USGS Water Data API, shown with the time they were observed in the gauge's local time. USGS gauges report about every 15 minutes, some hourly. Readings are provisional until USGS reviews them.

Percentile for the date

USGS publishes daily statistics for each calendar date from the gauge's record: the 5th, 10th, 20th, 25th, 50th, 75th, 80th, 90th and 95th percentiles of flow. We place the current flow between those published values by linear interpolation. The flow used is the trailing 24-hour mean when the last 24 hours hold at least 80% of the expected readings and span at least 20 hours, and the page says which; otherwise it is the latest reading. Values below the 5th or above the 95th percentile are shown as such. The number is our estimate, not a USGS value.

Daily means

Each daily mean averages the readings on one gauge-local date and is shown only with at least 80% of the expected readings.

Comparison with the gauge's record

Computed from the USGS daily mean flow record (method record-v1): the highest daily mean of the last 7 days, the last day before those 7 days with a daily mean that high or higher, the last day before those 7 days above the 90th percentile for its date, the days above the 75th percentile in the last 30 days, and the rank of this month's mean among the same days in other years (years with at least 80% of days).

Earlier years, annual peaks and the rating

The same 50 days in earlier years are USGS daily means shifted to the same calendar dates. Annual peaks are USGS annual peak streamflow, with the median and largest peak by decade for decades with at least five peaks. The rating curve is the USGS gage height to flow table for the gauge, thinned for display; the dot is the latest reading. The 12-month chart is USGS daily means with the 25th to 75th percentile band and median for each date.

Rate of rise and fall

The latest reading minus the reading closest to 1, 3, 6, 12 and 24 hours earlier (within 20 minutes or 60% of the reporting interval). The arrow is steady when the flow changed by 1% or less. Where flow cycles several times a day (for example tidal reaches) the change is not shown, because it would compare two phases of a cycle; the 24-hour range is shown instead.

Observed lag between gauges

For up to three upstream and three downstream gauges, hourly mean flows over the last 8 days are shifted from 1 to 72 hours; the shift with the highest correlation is shown if the correlation is at least 0.85, both series vary by at least 3%, and at least 96 hours overlap. It is empirical, not a travel time.

Flood stages, crests, impacts and outlook

Flood stages, historic crests, impact statements, the long-range flood outlook and river forecasts are National Weather Service products for the forecast point linked to the USGS gauge, shown as published. Crest dates that the NWS gives without a time are shown as that date. Dashed lines on the gage height chart are drawn only where they fall inside the chart's range.

Flood history for the county

Flood events are the county-level Flood and Flash Flood rows of the NOAA NCEI Storm Events Database for the last ten years; damage and casualties are as reported there. Federal flood disaster declarations come from FEMA's OpenFEMA Disaster Declarations Summaries for the county, where the incident type is Flood or the title contains FLOOD. These describe the county, not the river at the gauge.

Rain

Recent rain totals are NWS River Forecast Center multisensor estimates on a 4 km grid at the gauge location. The 24-hour product is hourly; the 2-day and 3-day products are daily, so each window shows its own end time. Forecast rain totals and the hourly heatmap come from the NWS gridpoint forecast.

Snow, water temperature, outlook, watershed

Snow water equivalent is from the three nearest USDA SNOTEL stations within 37 miles; a station may not drain to the gauge. Water temperature by month is the mean of all published daily mean values in each calendar month; months with fewer than 150 values are marked. The 8 to 14 day and 6 to 10 day outlooks are NOAA Climate Prediction Center products at the gauge location. Watershed characteristics and water quality assessments are U.S. EPA StreamCat and ATTAINS values for the reach and for assessment units within about 400 m of the gauge, shown as published.

Public land, maps and downloads

Public land is from the USGS Protected Areas Database (PAD-US) within about half a mile of the gauge; mapped land is not proof of legal access. Maps are U.S. Geological Survey National Map services. The CSV download is built in your browser from the USGS API for the last 7 days of flow and gage height.

Freshness limits

A gauge whose latest flow is more than 24 hours old shows a Gauge not reporting notice with the time of its last reading; after 30 days without a reading the page is no longer rebuilt. Forecasts older than 12 hours are marked and older than 72 hours are hidden. Weather observations older than 3 hours are marked and older than 12 hours hidden. Rain estimates older than 6 hours are marked and older than 24 hours hidden. Alerts older than 3 hours are marked. Snow data older than 5 days and outlooks older than 3 days are hidden.

What we do not do

We do not make forecasts, rate conditions or give advice. Every number is a source value or a calculation described on this page.

Corrections

Errors that come from a source are the source's to correct; we show the source's current value on the next refresh. Errors in our calculations are corrected as soon as they are found. Last reviewed October 17, 2026.