Below Normal: February rafting flows of 1,300 cfs on Saturdays and Sundays with “fish flows” of 200 cfs.
The South Fork of the American River water year forecast as of February 8, 2019: Below Normal
The February Water Supply Forecast Report for 2019 was released Friday February 8th at 4:29 PM, with the Water-Year forecasted for Below Normal. Specifically it’s forecasting the Full Natural Flow (FNF) of the American River below Folsom at 2.245 million acre-feet (MAF), with Below Normal being considered ≥ 1.7 MAF and < 2.6 MAF.
With the vast feet of snow that have falling in the Sierra Nevada mountains over the last couple of weeks, it might sound odd that they are only forecasting Below Normal. However, we must keep in mind two important facts. 1: Until the late January storms we have been having a relatively dry winter, with the state as a whole only at 69% of average by December 31st. 2: The second of these recent storms came through the region at the start of February, just missing being included in the measurements for this report – we’ll see how that storm measures up with “normal” when the March report is released next month. But happily, as of February 7th, Central California’s snow water content is already at 87% of the April 1st average, and 126% of average for Feb 7th – so it’s a good chance we’ll see the March report bump us into Above Normal.
Since the 2017-2018 water year ended with an official designation of Below Normal, this new forecast of Below Normal will not result in any changes from what was previously being followed for February flow.
The current forecast has an 80% probability range of 1.670-2.990 MAF, which leaves a the door open for dropping to Dry (<1.7 MAF) and a decent chance for bumping up to Above Normal (≥ 2.6 MAF). Keep in mind though that our brains are terrible at truly understanding what 80% probability means. It’s better to consider that if this exact forecast played out over 10 different years, one of those years would fall below that range, and one of those years would increase to above that range.
Guaranteed Minimum Flows
The February forecast will be used to determine minimum guaranteed flows from February 11th through Mid-March [The new forecast takes effect 3 days after it is issued. Each forecast is typically issued around the 8th].
February
Saturday & Sunday: 1,300 cfs 9am-12pm
No guaranteed raftable flows Monday through Friday
Minimum Flow: 200 cfs
Early March
Monday, Tuesday, Thursday, Friday: 1,300 cfs 9am-12pm
Saturday & Sunday: 1,500 cfs 9am-12pm
No guaranteed raftable flows Wednesday
Minimum Flow: 200 cfs
Forecasted based on Current Data
If the forecast of Below Normal holds, the flows will be as follows.
April-May
Monday, Tuesday, Thursday, Friday: 1,300 cfs 9am-12pm
Saturday & Sunday: 1,500 cfs 9am-12pm
No guaranteed raftable flows Wednesday
Minimum Flow: 250 cfs
Summer Flows – Sat May 25th through Mon September 2nd
Monday, Tuesday, Thursday, Friday: 1,300 cfs 9am-12pm
Saturday & Sunday: 1,500 cfs 7am-1pm
No guaranteed raftable flows Wednesday
Minimum Flow: 250 cfs
September 3-30, 2018
Thursday and Friday: 1,300 cfs 9am-12pm
Saturday & Sunday: 1,500 cfs 9am-12pm
No guaranteed raftable flows Monday through Wednesday
Minimum Flow: 250 cfs
October
Monday and Friday: 1,300 cfs 9am-12pm
Saturday & Sunday: 1,500 cfs 9am-12pm
No guaranteed raftable flows Tuesday through Thursday
Minimum Flow: 250 cfs
November 2019 through early February 2020
Saturday & Sunday: 1,300 cfs 9am-12pm
No guaranteed raftable flows Monday through Friday
Minimum Flow: 200 cfs
The next forecast should be released around March 8th, with it taking effect 3 days after issuance.
Extra Details for Geeks
Related Links and References
Quick B120 Report – Just the numbers
Detailed DWR Bulletin 120 Report – Note: this report is typically released a week or two after the quick report comes out.
American River at Folsom – Full Natural Flow (FNF) record of what actually happened.
Most Recent Snow Water Content Data – table – Limited to American River Basin
About the Forecasts
Forecasts are issued February through May around the 2nd Tuesday or the 8th of each month. They take effect 3 days after being released.
The final forecast is issued in May, and is used to determine the flow schedule through October.
The final (actual) water year report is released in October and is used to determine flows for November until 3 days after the February forecast is released.
While some bias might slip in, as much as possible the above information is purely based on the forecasts and not based on gut, intuition, or predictions.
As new forecast are released, this page will be kept as an archive of previous forecasts. For the most current forecast, or to view previous forecasts, please view our archive of water year forecasts here.
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