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CHEHALIS--NEAR GRAND MOUND
   State:  Washington    County:  THURSTON
   Latitude:  46 46' 33" North    Longitude:  123 2' 9" West
   Elevation:  124 feet
   Supporting WFO:  Seattle    
   Action Stage:  138.5'   Flood Stage:  141'   Moderate Flood Stage:  142.5'
   Major Flood Stage:  144'

Forecasts are calculated from a forecast time series that approximates flow at a 6 hour time step interval. Observed instantaneous peaks can be higher than model forecast peaks.

CHEHALIS--NEAR GRAND MOUND   (CGMW1)
Forecasts for Water Year 2026
Ensemble Date: 2026-07-10
 Forecast Period: July 10 to November 1
Exceedence
Probability 		Stage
feet 		Discharge
CFS 		Probable
Date of Peak
95 % 129.22 348 2026-07-17
90 % 129.30 381 2026-09-12
70 % 130.26 878 2026-10-18
50 % 131.81 2222 2026-10-26
30 % 133.82 4850 2026-10-30
10 % 136.45 9107 2026-11-01
05 % 137.59 11026 2026-11-01

Peakflow exceedence plot for CGMW1

 Click to download runoff traces used in forecast.  Click for comma delimited data used in plot.csv icon