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SFAR Water Year Forecast February 2019: Below Normal

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.

Snow water equivalents chart for Central California as of February 7, 2019

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.

campers rafting on the south fork of the american river

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

  1. Saturday & Sunday: 1,300 cfs 9am-12pm

  2. No guaranteed raftable flows Monday through Friday

  3. Minimum Flow: 200 cfs

Early March

  1. Monday, Tuesday, Thursday, Friday: 1,300 cfs 9am-12pm

  2. Saturday & Sunday: 1,500 cfs 9am-12pm

  3. No guaranteed raftable flows Wednesday

  4. Minimum Flow: 200 cfs

Forecasted based on Current Data

If the forecast of Below Normal holds, the flows will be as follows.

April-May

  1. Monday, Tuesday, Thursday, Friday: 1,300 cfs 9am-12pm

  2. Saturday & Sunday: 1,500 cfs 9am-12pm

  3. No guaranteed raftable flows Wednesday

  4. Minimum Flow: 250 cfs

Summer Flows – Sat May 25th through Mon September 2nd

  1. Monday, Tuesday, Thursday, Friday: 1,300 cfs 9am-12pm

  2. Saturday & Sunday: 1,500 cfs 7am-1pm

  3. No guaranteed raftable flows Wednesday

  4. Minimum Flow: 250 cfs

September 3-30, 2018

  1. Thursday and Friday: 1,300 cfs 9am-12pm

  2. Saturday & Sunday: 1,500 cfs 9am-12pm

  3. No guaranteed raftable flows Monday through Wednesday

  4. Minimum Flow: 250 cfs

October

  1. Monday and Friday: 1,300 cfs 9am-12pm

  2. Saturday & Sunday: 1,500 cfs 9am-12pm

  3. No guaranteed raftable flows Tuesday through Thursday

  4. Minimum Flow: 250 cfs

 November 2019 through early February 2020

  1. Saturday & Sunday: 1,300 cfs 9am-12pm

  2. No guaranteed raftable flows Monday through Friday

  3. Minimum Flow: 200 cfs

The next forecast should be released around March 8th, with it taking effect 3 days after issuance.

 
Snow water content graph for Central California as of February 7, 2019
 

Extra Details for Geeks

Related Links and References

  1. SFAR River Flow Agreement

  2. Quick B120 Report – Just the numbers

  3. Detailed DWR Bulletin 120 Report – Note: this report is typically released a week or two after the quick report comes out.

  4. Short Executive Summary

  5. American River at Folsom – Full Natural Flow (FNF) record of what actually happened.

  6. Snow Water Content – graph

  7. Most Recent Snow Water Content Data – table – Limited to American River Basin

  8. NOAA Sierra Nevada snow analysis

  9. California Snow Water Equivalents – map

About the Forecasts

  1. Forecasts are issued February through May around the 2nd Tuesday or the 8th of each month. They take effect 3 days after being released.

  2. The final forecast is issued in May, and is used to determine the flow schedule through October.

  3. 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.

  4. 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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