Wet: Raftable flows 7 days a week through Labor Day.
The South Fork of the American River water year forecast as of March 8, 2019: Wet
The March Water Supply Forecast Report for 2019 was released Friday March 8th at 2:52 PM, with the Water-Year forecasted for Wet. Specifically it’s forecasting the Full Natural Flow (FNF) of the American River below Folsom at 3.710 million acre-feet (MAF), with Wet being considered ≥ 3.5 MAF.
This shouldn’t come as any surprise (though I am a little surprised it jumped over Above Normal all the way into Wet) with the vast amount of rain and snow that has fallen on the Sierra Nevada’s over February. This forecast represents an increase of 65% over the 2.245 MAF that had been forecasted the start of February (prior to multiple atmospheric rivers setting up residence over California).
As of March 1st, Central California’s snow water content is now at 137% of the April 1st average, and 156% of normal. And 1.126 MAF of Full Natural Flow has been recorded at Folsom Lake through February. For comparison, these numbers on February 1st had been only 63%, 100%, and 0.425 MAF respectively.
The current forecast has an 80% probability range of 2.980-4.670 MAF, which leaves a good chance of dropping to Above Normal (2.6-3.5 MAF), but fairly reasonable that it won’t drop to Below Normal. 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, and the other eight would fall within the range.
Guaranteed Minimum Flows
The March forecast will be used to determine minimum guaranteed flows from March 11th through Mid-April [The new forecast takes effect 3 days after it is issued. Each forecast is typically issued around the 8th].
March
Monday-Friday: 1,500 cfs 9am-12pm
Saturday & Sunday: 1,750 cfs 7am-1pm
Minimum Flow: 250 cfs
Forecasted based on Current Data
If the forecast of Wet holds, future guaranteed flows will be as follows. [If it drops to Above Normal, the amounts will decrease, but we won’t loose any days].
April-May
Monday-Friday: 1,500 cfs 9am-12pm
Saturday & Sunday: 1,750 cfs 7am-1pm
Minimum Flow: April: 350 cfs | May: 500 cfs
Summer Flows – Sat May 25th through Mon September 2nd
Monday-Friday: 1,500 cfs 8am-12pm
Saturday & Sunday: 1,750 cfs 7am-1pm
Minimum Flow: June: 500 cfs | July 350 cfs | Aug: 300 cfs
September 3-30
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 2019
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: 1,500 cfs 9am-12pm
No guaranteed raftable flows Monday through Friday
Minimum Flow: 250 cfs
The next forecast should be released around April 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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