About the numbers.
RiverBrief compares observed discharge at selected Pennsylvania monitoring locations. It is not affiliated with USGS and is not a safety assessment, access guide, fishing recommendation, or forecast.
Source & units
Readings come from the USGS Water Data API, instantaneous discharge (parameter 00060, statistic 00011). Discharge is volume per second, shown in cubic feet per second (cfs). The time shown is the actual observation time, in Eastern time, not the retrieval time. USGS readings may be provisional and subject to revision; approval status is shown when available.
Freshness & change
Our product labels readings fresh through 2 hours old, delayed after 2 through 24 hours, and stale after 24 hours. These are RiverBrief display thresholds, not USGS quality ratings. Change compares the latest reading with the closest observation to exactly 24 elapsed hours earlier, within 45 minutes. If no match exists it is unavailable; if the baseline is zero, absolute change is shown but percentage is unavailable.
History & interruptions
The chart covers the previous 30 hours; a gap over 90 minutes breaks the line. Missing data is not interpolated. Each chart uses its own scale. Multiple distinct discharge series for one site are not silently combined.
Shared readings, not constant polling
Our server requests one snapshot for the eight supported gauges and caches validated readings for 15 minutes. Refresh checks that shared snapshot; it does not force a new USGS request for every visitor. There is no automatic background polling.
If USGS is unavailable, a previously validated snapshot retrieved within the last 24 hours may appear clearly labeled as an outage fallback. Original observation and retrieval timestamps are retained. The server cache is temporary and is lost on restart or deployment. With no valid fallback, we show unavailable. No example readings are substituted.