About Lake Travis Forecast

Lake Travis Forecast is an independent site that does one thing no official source does: it forecasts the water level of Lake Travis. Plenty of sites report where the lake is today. This one models where it is headed — hourly for the next 36 hours, then daily out to ten days — and then grades every one of those forecasts against what actually happened.

Who runs it

The site is built and operated by Nick Bhavsar, based in the Austin, Texas area. It began as a personal project to answer a simple question the official dashboards could not: will the lake be higher or lower next weekend? It is not affiliated with, endorsed by, or connected to the Lower Colorado River Authority (LCRA), the U.S. Geological Survey, or any government agency. For official flood-operations information, always consult LCRA.

How the forecast works

The model is a water balance — the same accounting a reservoir operator would do. Water comes in as river inflow (from the NOAA National Water Model's forecast for the Colorado River arm) and as rain falling directly on the lake's surface. Water leaves through the dam and through evaporation. The balance is anchored to the observed level trend from LCRA's own gauge, so the model starts every run from reality rather than from theory.

One detail matters more than any other: a foot of Lake Travis is not a fixed amount of water. The lake's surface area shrinks as it drops — roughly 27,000 acres near flood pool but only about 7,000 acres at severe-drought levels — so the model converts between storage and elevation through a bathymetric rating table at every step, never with a constant.

LCRA does not publish how much water Mansfield Dam releases, and no public feed carries it. The release shown here is therefore implied: it is the outflow that makes the water balance close against the observed level trend, bounded by LCRA's reported floodgate status. When LCRA says the floodgates are closed, this site will never show floodgate-scale spilling — only normal operations through the powerhouse and downstream supply.

Three independent gauges

The site cross-checks the lake level against three separately operated sources: LCRA Hydromet gauge 3963 at Mansfield Dam (the primary), USGS station 08154500, and the NOAA National Weather Service gauge msdt2. They measure the same lake through different instruments and different agencies. When they agree — and they almost always do — that agreement is what the forecast builds on. When one disagrees, it is caught rather than silently forecast from.

Accuracy, published

Every forecast run is stored. Once reality catches up, each prediction is graded against the measured level, and the resulting error statistics — by forecast horizon, updated daily — are published on the homepage. The site also reports its skill against the naive assumption that the level simply will not change, because on a slow-moving reservoir that assumption is genuinely hard to beat. If the model ever stops beating it, that number will say so, publicly. The model also re-calibrates itself: parameters are re-fit daily against a rolling backtest, and structural changes must first outperform the live model in a shadow trial before they are adopted.

Data sources

• LCRA Hydromet — observed lake level, water temperature, and flood-operations narrative
• NOAA National Water Model — river inflow forecast for the Colorado River arm
• National Weather Service — rainfall and temperature forecasts over the lake
• Texas Water Development Board and USGS — reference elevations and long-term history

Forecasts here are estimates for planning a weekend, not operational guidance. Questions, corrections, or a gauge reading that looks wrong? Get in touch.