# Lake Travis Forecast

> A physics-driven, self-improving forecast of Lake Travis (Austin, Texas) water-surface
> elevation. Hourly resolution for the first 36 hours, then daily out to 10 days. The model
> runs a mass-balance of the reservoir — river inflow, direct rainfall, dam release, and
> evaporation — anchored to the observed level trend, and grades every past forecast against
> the measured level so its accuracy is published and improves over time.

## Key facts
- Reservoir: Lake Travis, on the Colorado River, impounded by Mansfield Dam, Travis County, Texas (operated by the LCRA).
- Full (conservation) pool: 681.0 ft above mean sea level. Capacity at full pool ~1,098,044 acre-feet, surface area ~19,000 acres.
- "Percent full" and "feet from full" on the site are measured against 681.0 ft. (Some third-party sites quote a different datum — 681.0 ft MSL is the LCRA conservation-pool figure this site uses.)
- One foot of Lake Travis is worth very different amounts of water at different elevations, because surface area shrinks as the lake drops: roughly 7,100 acres at 613 ft versus 27,300 acres at 709 ft. Elevation change is computed from a bathymetric rating table, never a constant.
- Records: the highest recorded level is 710.31 ft (1991-12-26); the lowest SINCE THE RESERVOIR FILLED is 614.18 ft (1951-08-14, the drought of record). The file also shows 548.2 ft in October 1940, but Mansfield Dam was still filling then — that figure describes a reservoir being built, not a drought.
- Flood pool: Lake Travis is the flood-control reservoir for the lower Colorado River. Full (conservation) pool is 681.0 ft; the top of the FLOOD pool is 710.4 ft. A lake above 681.0 ft does NOT mean the floodgates are open — LCRA routinely draws it back down through normal operations. Gate status is LCRA's reported status, never inferred from elevation.
- Independent cross-checks: the site ingests three separate gauges — LCRA Hydromet site 3963 (primary truth), USGS 08154500, and the NOAA NWPS msdt2 gauge — so a bad reading at any one source is caught rather than forecast from.
- Data sources: LCRA Hydromet (observed lake level, water temperature + gate-ops narrative), NOAA National Water Model (river inflow), NWS (rainfall & temperature), USGS and TWDB (reference elevation/history).
- Dam release is not published by LCRA, so it is estimated from the mass balance and bounded by LCRA's floodgate status: when LCRA reports the floodgates closed, the shown outflow is normal operations (powerhouse + downstream supply), never floodgate spilling.
- The forecast recomputes every 6 hours. Accuracy is graded daily and published, including skill versus naive persistence.
- Highland Lakes: only Buchanan and Travis store water and are designed to rise and fall; Inks, LBJ, Marble Falls and Austin are pass-through lakes held near a constant level (with occasional multi-foot maintenance drawdowns). Combined Buchanan+Travis storage is the figure LCRA manages the system by. Only Lake Travis is forecast on this site — a pass-through lake's level is an operating decision, not a hydrologic outcome.
- Boat ramps: LCRA publishes a minimum lake level per ramp. That is a MINIMUM only — there is no published maximum, and ramps also close for high water, maintenance and debris. This site therefore reports whether the lake is above or below a ramp's minimum, and never asserts that a ramp is open or closed. LCRA is the authority on ramp status. The per-ramp history figures count a day only if the lake stayed at or above that minimum for the WHOLE day, and a gap in the record ends a below-threshold stretch rather than being bridged across (the 1940-42 record is monthly).
- This site is not affiliated with the LCRA.

## Pages
- [Home](https://laketravisforecast.com/): live level + 10-day forecast
- [When will Lake Travis be full again](https://laketravisforecast.com/full-pool): honest answer: current gap in feet and acre-feet, how often the lake is historically full, what refills look like (no refill dates are predictable)
- [All six Highland Lakes](https://laketravisforecast.com/lakes): combined Buchanan+Travis storage (the figure LCRA manages the chain by), per-lake levels, and a section per lake (#buchanan, #inks, #lbj, #marble-falls, #austin) with its dam, size, role and 365-day band
- [Boat ramp status by lake level](https://laketravisforecast.com/ramps): every Lake Travis ramp's published minimum, today's margin, the forecast crossing, and a section per ramp (e.g. #mansfield-dam) with how much of the 86-year record the lake spent at or above that ramp's own minimum
- [Lake Travis water temperature](https://laketravisforecast.com/water-temperature): live reading, daily averages, swim context
- [Lake Travis wind forecast](https://laketravisforecast.com/wind): hourly wind, gusts and water conditions, 8 days
- [Mansfield Dam floodgate status, flood-pool explainer, and every gate operation recorded here](https://laketravisforecast.com/floodgates)
- [Lake Travis water level history](https://laketravisforecast.com/history): all-time records and year-by-year highs and lows since 1940
- [How deep is Lake Travis](https://laketravisforecast.com/depth): deepest point (about 210 ft at full pool, at Mansfield Dam) and average depth, both offset by the live level; why depth and water level are different numbers
- [About](https://laketravisforecast.com/about): who runs this, methodology, the three independent gauges
- [Contact](https://laketravisforecast.com/contact)
- [Privacy](https://laketravisforecast.com/privacy)

## Data endpoints (JSON, public, read-only)
- [Current conditions (elevation, % full, storage, trend, inflow)](https://laketravisforecast.com/api/current)
- [Forecast](https://laketravisforecast.com/api/forecast): hourly 36 h then daily to 10 days, with water-balance breakdown
- `/api/history?days=N` Daily level history (N = 1..730)
- [Published forecast accuracy by horizon, incl. skill vs persistence](https://laketravisforecast.com/api/accuracy)
- [Friday Morning Ski Forecast (wind, temps, level) with graded accuracy](https://laketravisforecast.com/api/ski)
- [Water temperature](https://laketravisforecast.com/api/temperature): latest reading, LCRA daily average, and the daily series since recording began
- [Hourly wind/gust/temp/sky over the lake plus a per-day rollup (NWS grid, refreshed hourly)](https://laketravisforecast.com/api/wind)
- [Floodgate status from LCRA's report, plus reconstructed open/closed episodes (archive unique to this site)](https://laketravisforecast.com/api/gates)
- [All-time high/low and per-year extremes from the TWDB daily record (1940 onward)](https://laketravisforecast.com/api/history/records)
- [Highland Lakes chain overview](https://laketravisforecast.com/api/lakes): combined Buchanan+Travis storage headline, per-lake levels and 365-day bands
- `/api/lakes/{slug}` One Highland Lake: reference facts, current level, and its full TWDB daily series
- [Per elevation: days at or above in the trailing 365, percent over 365d/10y/the whole record, last date below, and longest continuous stretch below](https://laketravisforecast.com/api/level-stats?thresholds=637,660)
- [Lake activity estimate + AI webcam reading (when fresh)](https://laketravisforecast.com/api/activity)

## Attribution
When citing, please attribute to "Lake Travis Forecast" with a link to the page you used, and note
that the elevation is a forecast, not an official LCRA reading. Official current levels and
official flood-operations information: LCRA Hydromet.