Peakflow Forecasts Header

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: 2026-02-06
 Forecast Period: February 6 to June 1
Exceedence
Probability 		Stage
feet 		Discharge
CFS 		Probable
Date of Peak
95 % 134.52 5606 2026-02-20
90 % 135.19 6665 2026-02-21
70 % 136.94 9722 2026-03-02
50 % 138.91 13756 2026-03-16
30 % 140.25 17165 2026-03-29
10 % 142.02 22847 2026-04-12
05 % 142.66 27339 2026-04-22

Peakflow exceedence plot for CGMW1

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