No one has mentioned the reservoir levels above Powell, they are all substantially higher then they were last year at this time. I would guess that the inflow to Powell will be higher than expected even if we only have an average snow year. Flaming Gorge 3' higher than it was last year, Blue Mesa 51' higher and Navajo 41' higher. I know this is only a drop in the bucket but all of those reservoirs where in horrible shape last year and there was enough water to bring them way up and still put 50+ into Powell.
Thats a good point about the reservoirs above Powell. That said, I'm not sure how much of a difference they will really make. The fact is that the entire capacity of those reservoirs isn't huge. The six main reservoirs--Flaming Gorge, Blue Mesa, Navajo, Morrow Point and Crystal--have a combined capacity of only about 6.5 MAF, or roughly a fourth of the total capacity of Lake Powell. It's also notable that on June 6, 2019--in the midst of the huge rise on Powell--those reservoirs were already at a collective 81% of full capacity, or 5.2 MAF. So I think the fact is there wasn't too much water that could be held back at that time.
And here's the thing: the current reservoir volume in those 6 reservoirs as of 1-7-20 is 5.3 MAF--almost identical to what they were holding in June of last year. Yes, they will likely fill even more as snowpack melts, but it's not enough to make a huge difference in Powell, if any. There's going to be some release from them even as they fill, just as there was last year. But the more important consideration is simply that USBR is going to have to release at least 8.23 MAF past Lees Ferry just as a matter of the Law of the River...last year they released 9 MAF, which was also following protocols based on relative lake levels in Mead and Powell, so the contributions of the upper reservoirs won't make a ton of difference if the release through the dam is big...
The eye-opening story is this: even with the huge runoff of spring 2019, the collective peak storage of Powell and Mead that year was only 49%, or 24.8 MAF, or only about 3% more than in 2018. And the average capacity for the year was actually less than the average of 2018--mainly because the first 3 months of 2019 were actually terrible. In 2019, the average collective capacity was at 44%, compared to 44.6% in 2018. In fact, the two reservoirs collectively have hovered in the 45-50% range pretty steadily since 2013 after the sharp drought of 2012-13. That is, it doesn't take a long drought to drop the levels, but it takes a long recovery to start bringing them back (unless you get two straight monster years like 1983-84, which has happened exactly once). In a nutshell, that's because the demand on water from the Colorado River basis, on average, far exceeds supply via precipitation. The only way out of that one is to renegotiate the shares of each of the 7 basin states, because as it is, what they are entitled to collectively is way more than what is actually there on a sustainable basis. No other way around that one...
But I'm optimistic that in the coming years there will be variability in the lake levels, up and down. Hopefully, this winter is huge, and it's promising that the snowpack is already good with some pretty full reservoirs above Powell. Let's hope for the best. In that context, you might ask why didn't we have any trouble getting the lakes to full capacity by 1980, and what has changed since then? Well, we did have trouble--it took 17 years to do that as Powell was filling, and in 1963, Mead was about 80% full already. Some big years were offset by a lot of pretty bad ones in the late 1960s and especially in the mid-1970s. But some truly giant years in there--1973 and 1979 come to mind--brought Powell to the top, and some unprecedented and never-seen-again years from 1983-86 made everyone believe that should be normal and would last forever. But those were abnormally huge runoff years, and we'll never likely see that kind of run again in our lifetimes...nor had we seen any run of years like that in the recorded data before Powell began to fill in 1963... Still, from the full pool period of 1983-87, we only dipped to a collective 75% in 1993 before slowly working back to near full in 1998-99. That's because we didn't have a truly catastrophic drought in that time. But all it took was a huge drought from 2000-04, only five years, to reduce the volume of those two reservoirs from basically full to 50%. It inched up to nearly 57% by 2012 after a few better years, but then all it took was those two bad years in 2012-13 to drop us back to closer to 45%. So you can see the trend line--short sharp drops followed by slow recoveries... that will continue... hopefully this is another year toward slow recovery...