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Cossatot River — Daily Analysis: 2026-08-24

Classification: correct Confidence: Model confidence remains stable. Correctly handled a low-signal event without false positives, validating the recent reductions in Band 2-4 sensitivity.

Event Summary

The model accurately predicted a negligible rise (1.86 ft) for a day with minimal rainfall and no gauge precipitation, closely matching the observed baseline (1.84 ft).

Prediction vs Actual

Metric Predicted Actual Error
Peak height 1.86 ft 1.84 ft +0.02 ft
Total rise 0.01 ft

Band Contributions

Band Precip Predicted Rise Intensity Moisture
4 0.36" 0.12 ft MODERATE NORMAL
5 0.33" 0.07 ft LIGHT NORMAL

Empirical Forecast

Headline: No rise indicated by recent rainfall Settled outcome: None (reached None) LLM said headline was correct: True Notes: The empirical headline 'No rise indicated by recent rainfall' was borne out by the actual gauge outcome (only 0.01 ft rise).

Analysis

The prediction magnitude was highly accurate, with a 1.1% error in peak stage (predicted 1.86 ft vs. actual 1.84 ft). This confirms that the current coefficients for Band 4 and Band 5 are appropriately calibrated for NORMAL moisture conditions, as the model correctly identified that the small amount of QPE (approx. 0.3-0.4 inches) in the headwaters would not generate significant runoff given the lack of saturation and zero gauge precipitation.

The primary discrepancy is in timing, with a ~10-hour lag between the predicted peak and the observed daily maximum. However, given the hydrograph was flat with a rise of only 0.01 ft, this timing difference is likely an artifact of the daily snapshot comparison rather than a physical model failure. The model correctly classified this as a 'quiet day' event, similar to the August 6th event which was also classified as correct despite timing differences.

No adjustments are recommended as the model successfully avoided a false positive, which was a risk given the presence of some QPE in Bands 4-5. The conservative approach of maintaining current coefficients is supported by the consistent performance on low-magnitude events.

Coefficient Adjustments

No changes made.

Notes

Model confidence remains stable. Correctly handled a low-signal event without false positives, validating the recent reductions in Band 2-4 sensitivity.

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