When does Chehalis River near Grand Mound, WA normally run highest?

January, on the long-term record. The median daily flow that month is about 4,633.5 cfs, against 218.1 cfs in August, the lowest month. These are historical normals for the date, not a forecast and not today's reading.

What is a normal flow for Chehalis River near Grand Mound, WA?

It depends on the month. In January, half of days historically fall near 4,633.5 cfs, with the middle 80% of days between 1,658.7 and 14,348.4 cfs. The month-by-month table on this page gives the full range.

How long has Chehalis River near Grand Mound, WA been measured?

Discharge records at USGS site 12027500 begin in 1928, about 98 years, covering roughly 9,200 days of published daily values. The long record is what makes the monthly percentiles on this page meaningful.

Is there a flow forecast for Chehalis River near Grand Mound, WA?

Yes. Rivermatics trains a machine-learned model — a temporal-fusion transformer — on this basin's observed flows, weather, and snowpack, and issues a daily flow outlook reaching 14 days ahead: a median estimate inside a confidence band, not a single number to bet on. Every forecast is scored against days the model never trained on, and that track record is published on the live gauge screen. Open live conditions to see the current outlook.

Where is Chehalis River near Grand Mound, WA?

The gauge sits at 46.77593, -123.03569, in Washington, in hydrologic subbasin 17100103, at an elevation of about 132 feet, draining roughly 895 square miles.

Can I use Chehalis River near Grand Mound, WA data for flood or safety decisions?

No. Rivermatics provides estimates, not guarantees, and the readings and forecasts here may be delayed, inaccurate, or wrong. Do not use them for navigation or for any safety, rescue, or emergency decision. Check the National Weather Service and USGS directly, and use your own judgment.

USGS Streamgage 12027500

Chehalis River near Grand Mound, WA

Chehalis River near Grand Mound, WA is USGS streamgage 12027500 in Washington, monitoring river discharge in hydrologic subbasin 17100103. It sits on the Chehalis River, alongside 6 other gauges Rivermatics tracks on the same river. It drains a watershed of about 895 square miles. Discharge records at this site go back to 1928. Typical flow runs near 350.7 cfs in July and 2,347 cfs in April, with the higher of the two arriving in April. Rivermatics issues a daily machine-learned flow outlook for this gauge, reaching 14 days ahead.

View live conditions & forecast →

Gauge details

State: Washington
Drainage area: 895 sq mi
Gauge elevation: 132 ft
Subbasin (HUC-8): 17100103
Coordinates: 46.77593, -123.03569
USGS site number: 12027500
Records begin: 1928-10-01 (98 years)
Rivermatics forecast: 14-day flow outlook

14-day flow forecast

Based on observations through September 10 for Chehalis River near Grand Mound, WA. Each day carries a median estimate and the band the model expects the flow to fall within — not a single number to plan against. Forecasts are re-issued daily; see the live screen for the current outlook.

Forecast daily mean discharge in cubic feet per second, by date
Date	Low p10	Expected p50	High p90
September 11	233	241	247
September 12	227	238	252
September 13	235	258	313
September 14	246	291	397
September 15	242	282	368
September 16	233	267	336
September 17	224	253	307
September 18	216	242	285
September 19	211	236	274
September 20	206	230	266
September 21	202	226	259
September 22	197	221	254
September 23	193	217	248
September 24	189	214	246

All values in cubic feet per second (cfs). Estimates only — do not use them for navigation or for any safety, rescue, or emergency decision.

Typical flow by month

Long-term daily discharge percentiles from the USGS record (up to 98 years of data), averaged within each month. These describe the historical normal range — they are not a forecast and not today's reading.

Historical monthly discharge percentiles in cubic feet per second
Month	Low p10	Typical p50	High p90
January	1,658.7	4,633.5	14,348.4
February	1,642.4	3,899.3	12,247.9
March	1,544.8	3,428.4	9,288.4
April	1,193	2,347	5,769.3
May	685.2	1,151.5	2,606.5
June	390.8	665	1,442.9
July	215.1	350.7	564.5
August	141.2	218.1	353.3
September	151.6	249.8	609.7
October	216	492.3	2,136.4
November	522.7	2,451	9,424.3
December	1,348.9	4,231.9	14,193.5

All values in cubic feet per second (cfs).

Common questions

When does Chehalis River near Grand Mound, WA normally run highest?: January, on the long-term record. The median daily flow that month is about 4,633.5 cfs, against 218.1 cfs in August, the lowest month. These are historical normals for the date, not a forecast and not today's reading.
What is a normal flow for Chehalis River near Grand Mound, WA?: It depends on the month. In January, half of days historically fall near 4,633.5 cfs, with the middle 80% of days between 1,658.7 and 14,348.4 cfs. The month-by-month table on this page gives the full range.
How long has Chehalis River near Grand Mound, WA been measured?: Discharge records at USGS site 12027500 begin in 1928, about 98 years, covering roughly 9,200 days of published daily values. The long record is what makes the monthly percentiles on this page meaningful.
Is there a flow forecast for Chehalis River near Grand Mound, WA?: Yes. Rivermatics trains a machine-learned model — a temporal-fusion transformer — on this basin's observed flows, weather, and snowpack, and issues a daily flow outlook reaching 14 days ahead: a median estimate inside a confidence band, not a single number to bet on. Every forecast is scored against days the model never trained on, and that track record is published on the live gauge screen. Open live conditions to see the current outlook.
Where is Chehalis River near Grand Mound, WA?: The gauge sits at 46.77593, -123.03569, in Washington, in hydrologic subbasin 17100103, at an elevation of about 132 feet, draining roughly 895 square miles.
Can I use Chehalis River near Grand Mound, WA data for flood or safety decisions?: No. Rivermatics provides estimates, not guarantees, and the readings and forecasts here may be delayed, inaccurate, or wrong. Do not use them for navigation or for any safety, rescue, or emergency decision. Check the National Weather Service and USGS directly, and use your own judgment.

Upstream and downstream on the Chehalis River

Every gauge Rivermatics tracks on this river, ordered by drainage area — upstream first. See the Chehalis River in full.

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