Inflow forecast

modeled

NOAA’s National Water Model, short-range run issued Sep 29, 8 AM MST, for the 3 gauged tributary reaches feeding Lake Powell. The model includes rain that has already fallen plus the near-term rain forecast.

Gauged inflow now

8,870

cfs · measured

Peak next 18h

9,055

cfs · ~9 AM MST · modeled

Projected volume

12,596

acre-feet over 18h · modeled

Net lake effect

+0.02 ft

after 7,770 cfs out · inferred

Projected flow by tributary reach

Forecast inflow, next 17 hours, all gauged reaches: starts at 9,055 cfs, peaks at 9,055 cfs Tue 9 AM (modeled)
Hour	Total (cfs)	Green (cfs)	Colorado (cfs)	San Juan (cfs)
Tue 9 AM	9,055	4,230	2,576	2,250
Tue 10 AM	8,983	4,166	2,568	2,249
Tue 11 AM	8,887	4,084	2,556	2,247
Tue 12 PM	8,770	3,986	2,540	2,245
Tue 1 PM	8,644	3,881	2,520	2,243
Tue 2 PM	8,522	3,778	2,500	2,244
Tue 3 PM	8,416	3,687	2,481	2,247
Tue 4 PM	8,334	3,613	2,466	2,255
Tue 5 PM	8,279	3,556	2,455	2,268
Tue 6 PM	8,247	3,514	2,449	2,284
Tue 7 PM	8,238	3,489	2,445	2,304
Tue 8 PM	8,246	3,479	2,443	2,324
Tue 9 PM	8,265	3,482	2,440	2,343
Tue 10 PM	8,287	3,494	2,434	2,359
Tue 11 PM	8,305	3,509	2,425	2,371
Wed 12 AM	8,315	3,524	2,411	2,380
Wed 1 AM	8,314	3,536	2,393	2,385
Wed 2 AM	8,303	3,546	2,370	2,387

GreenColoradoSan JuanTotal (all gauged reaches)

Dashed lines are forecast. Values are at the gauges; water takes hours to a couple of days to get from there to the lake. National Water Model via NOAA/NWS · public domain.

The “net lake effect” is the forecast inflow volume minus the water leaving the lake now (7,770 cfs, Colorado at Lees Ferry, right now), held steady over the forecast period and spread over the lake’s estimated current surface area (before releases it would be +0.21 ft). It ignores travel time, channel losses and any change the dam operators make, so it gives a sense of scale, not a prediction. During floods, watch the main page instead.