Wet: Raftable flows 7 days a week through Labor Day.
The South Fork of the American River water year forecast as of April 9, 2019: Wet
The April Water Supply Forecast Report for 2019 was released Tuesday April 9th at 1:37 PM, with the Water-Year forecasted for Wet. Specifically it’s forecasting the Full Natural Flow (FNF) of the American River below Folsom at 3.950 million acre-feet (MAF), with Wet being considered ≥ 3.5 MAF.
This is in line with the March forecast. Increasing the forecast slightly by 6.5% over the March forecast of 3.710 MAF.
As of April 1st, Central California’s snow water content is now at 164% of the April 1st average, and thus 164% of normal. We’ve seen 1.881 MAF of Full Natural Flow already recorded at Folsom Lake through March.
The current forecast has an 80% probability range of 3.415-4.470 MAF, which leaves little chance of dropping to Above Normal (2.6-3.5 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, and the other eight would fall within the range.
Guaranteed Minimum Flows
The April forecast will be used to determine minimum guaranteed flows from April 12th through Mid-April [The new forecast takes effect 3 days after it is issued. Each forecast is typically issued around the 8th].
April
- Monday-Friday: 1,500 cfs 9am-12pm
- Saturday & Sunday: 1,750 cfs 7am-1pm
- Minimum Flow: April: 350 cfs | May: 500 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 lose any days].
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 May 8th, with it taking effect 3 days after issuance.
Extra Details for Geeks
Related Links and References
- SFAR River Flow Agreement
- 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.
- Short Executive Summary
- American River at Folsom – Full Natural Flow (FNF) record of what actually happened.
- Snow Water Content – graph
- Most Recent Snow Water Content Data – table – Limited to American River Basin
- NOAA Sierra Nevada snow analysis
- California Snow Water Equivalents – map
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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