tl;dr: Very Very Wet. Total rainfall might exceed 1982-1983, but current snowpack is much lower at this point in time.
The April Water Report was released Monday April 10th, with the Water-Year forecast expectedly solidly in the Wet range. Specifically it’s forecasting the American River below Folsom at 7.435 million acre-feet (MAF), with 3.500 or greater being considered Wet1. In fact, we’ve already had 5.028 MAF of unimpaired runoff, so even if the heaven’s remained dry through the end of this water year, we’re already locked in on it being a Wet classification.
There has been a lot of talk in the media as of late, of different regions setting all time rainfall records. There likely will be more of those reports to come as more and more stations beat previous records with more rain likely to fall prior to the end of this water year on September 30th. While we will likely see significant spring and early summer flows, to draw comparisons to the 1982-1983 water year are, in my opinion, inflammatory and more hype than fact. I’m not saying we won’t see higher flows than we did in those years, I’m saying that to say “we will” is an oversimplification and not a certainty.
While this year will likely go down as the highest water year on record, much of that water has already moved into the ocean. Specifically, the unimpaired runoff for the American River below Folsom from Oct-March is 5.028 MAF this year versus only 3.335 MAF for the 1982-83 water year.2
This can be most clearly seen by looking at the current California snow water content:
The South Fork of the American River is part of the Central California breakdown. As you’ll notice, we currently have significantly less water on the mountains above us than we did in ’82-’83. But we do have a bit more than we did in 1997-1998.
Comparing 7 snow station readings in the April report for the American River in 1983 had 451.2 inches of water equivalent versus 2017 having 313.7 equivalent inches of water. That’s 30% less water on the mountain for April 1st than we had in ’833.
For comparison, the unimpaired runoff for the American River below Folsom in 1983 in 1,000 Acre-Feet was: 605 April, 983 May, 942 June4. Forecast for 2017 are predicting 725 April, 910 May, 560 June5. While 1998 had 582 April, 699 May, 787 June6. So if those predictions hold, we should see similar flows in May as we did in 1983, however June will likely drop to smaller flows than we saw in June of 1998.
While the April forecast is technically only valid until around May 12th, it’s a reasonable assumption that the following will not change barring an act of congress7.
It’s worth a reminder that how quickly or slowly the snowpack melts could result in significantly higher flows during the remainder of Spring.
The next water year forecast should be released around May 9th, with it taking effect 3 days after issuance.
As of April 14, 2017 – 11 AM
Note: This page is updated with current forecasts as they become available. Previous forecasts are archived for reference.