Wet: Raftable flows 7 days a week through Labor Day.
The South Fork of the American River water year forecast as of May 8, 2019: Wet
The May Water Supply Forecast Report for 2019 was released Wednesday May 8th at 11:37 AM, with the final Water-Year forecast being Wet. Specifically it’s forecasting the Full Natural Flow (FNF) of the American River below Folsom at 3.910 million acre-feet (MAF), with Wet being considered ≥ 3.5 MAF.
This is in line with the April forecast. Decreasing the forecast slightly by 1% versus the April forecast of 3.950 MAF.
As of May 1st, Central California’s snow water content is now at 118% of the April 1st average, and thus 147% of normal. We’ve seen 2.647 MAF of Full Natural Flow already recorded at Folsom Lake through April.
The current forecast has an 80% probability range of 3.610-4.330 MAF, which leaves little chance of the final water year dropping to Above Normal (2.6-3.5 MAF). If it did become an Above Normal year, the minimum flows would not change until Mid-October when that final determination is made. 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 May forecast will be used to determine minimum guaranteed flows from May 11 through Mid-October.
May
Monday-Friday: 1,500 cfs 9am-12pm
Saturday & Sunday: 1,750 cfs 7am-1pm
Minimum Flow: 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
Forecasted based on Current Data
In October the actual flows will be summed up and used to determine the future minimum flow regimen
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 actual water year should be calculated around October 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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