How much do we expect the lake to rise this spring/summer

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Well, can’t readily find the deep dive discussion with the WW experts and I need to find a pillow. However, USBR most probable forecast is about a 4 foot rise, reading the graph in the latest 24 month study. That hurts to type it.
 
Powell24MS.png

That's the February 24 month study issued about three weeks ago that Trix referred to. To answer your question then, the "best guess" is that it won't go up hardly at all.

The March 24 month study will likely end up looking very similar because the most probable run off forecast it will be based on has not improved at all since the February study (in fact, it got slightly worse).

The blue line (Probable Maximum) in the above plot is fiction at this point. They don't update the Probable Maximum very frequently since that's not something they worry about at low lake levels so it isn't even based on recent forecasts.

That said, there is still a massive amount of uncertainty in forecasts even this late in the winter for the run off:

Screenshot 2026-03-05 at 6.46.24 AM.png


So the "no rise" forecast from February was based on 2400 kaf of runoff. The March forecast will be based on 2300 kaf instead (the pink "Official" bolded number above) and so a little worse. Those are the numbers that best match your "assuming we don't get a massive snowy March" condition. But it could be much worse (less than half that) or much better (nearly double that).

The other huge variable is will BoR change their operating plan to reduce outflows to protect the lake level. They've said they don't want it to drop below 3525. JFR did a nice analysis in another thread showing they could probably achieve that for this year at least if they chose to. But again, to your question, that would still be no rise at all, just preventing the currently forecast plummet.
 
THx Trix and DV. that's the info I was looking for. So, the best guess is no rise, then continued decline till 2027. If so, I assume they will continue to extend State Line Aux ramp. How far down can that be extended? I'm sure it's been mentioned in prior posts, but I must have missed it.
 
NPS indicated previously that they could chase it down to somewhere around 3490, but it may be able to go down even further. It may have just been that they defaulted to that value because of other dam operational scenarios.
 
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It is one year from now that most concerns me. I think it will require a "Hail Mary" to save this winter at this point (it's looking like the winter that never was). I think we will fall in between the red (minimum probable) and green (most probable) lines on that graph above. Both of those lines dip below minimum power pool by March of 2027. Everything rides on next winter.
They say the current La Nina condition is expected to end soon. If we get a strong El Nino next winter we might get another reprieve like we did in 2023. If not, things are looking bad.
I would expect that the BOR will engage in some kind of desperate shenanigans in order to prevent the lake from dropping below minimum power pool. The thing is that lake Mead may be even closer to reaching minimum power pool. At some point they may be forced to sacrifice one reservoir to save the other. I have a feeling, if push comes to shove, that lake Mead would win out in that battle.
But then there is the issue of passing water through GCD.
I've always said that Mother Nature is in charge here. If the drought continues, she is going to force our hand. Who knows what kind of decisions will be made in the current political climate. Things are going to get ugly if the river continues to dry up. Yeah we may get another reprieve, but I think the Ugly is not an if but a when type of thing.
 
sio2 said:
It is one year from now that most concerns me. I think it will require a "Hail Mary" to save this winter at this point (it's looking like the winter that never was). I think we will fall in between the red (minimum probable) and green (most probable) lines on that graph above. Both of those lines dip below minimum power pool by March of 2027. Everything rides on next winter.
They say the current La Nina condition is expected to end soon. If we get a strong El Nino next winter we might get another reprieve like we did in 2023. If not, things are looking bad.
I would expect that the BOR will engage in some kind of desperate shenanigans in order to prevent the lake from dropping below minimum power pool. The thing is that lake Mead may be even closer to reaching minimum power pool. At some point they may be forced to sacrifice one reservoir to save the other. I have a feeling, if push comes to shove, that lake Mead would win out in that battle.
But then there is the issue of passing water through GCD.
I've always said that Mother Nature is in charge here. If the drought continues, she is going to force our hand. Who knows what kind of decisions will be made in the current political climate. Things are going to get ugly if the river continues to dry up. Yeah we may get another reprieve, but I think the Ugly is not an if but a when type of thing.
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There is a simple (but not easy) solution to keep both reservoirs above minimum pool. Stop pretending there is 16 million acre feet of water to divide up. This fallacy is what created the crisis,
 
FIFY
That's a silly solution. Better to have more years of meetings, negotiations, and conferences while taking no actual action. AND in the meantime spending barge loads of dollars commissioning more “studies” on feasibility to keep the gaslight flame alive all while nothing is done…🤔
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Looks like winter is likely over. The past month hasn’t been disastrous, as a pattern change added a bit of snow, but that’s over now. The two week forecast is dry as a bone for the entire drainage basin, and models are forecasting a major if not record breaking high pressure system and associated heat wave for the second half of the month.
 
HMaea said:
Looks like winter is likely over. The past month hasn’t been disastrous, as a pattern change added a bit of snow, but that’s over now. The two week forecast is dry as a bone for the entire drainage basin, and models are forecasting a major if not record breaking high pressure system and associated heat wave for the second half of the month.
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Yeah, time is running out and the two week forecast now accounts for a larger and larger fraction of the remaining potential for precipitation.

The CBRFC updates its April-July runoff model daily here:


The default is to assume climatology going forward from tomorrow and at present that is for a 2302 kaf 50% exceedance. In English, if we just pretend the weather does what it did in the past from today forward - completely ignoring the weather forecasts - then half of the past years would result in more than 2302 kaf and half less. Which is to say 2302 kaf is a "best guess" (with a lot of uncertainty) of what happens if we close our eyes and ignore that actual forecast weather.

But in a pull down menu you can have it use a 5 day precipitation forecast before switching to climatology and that presently predicts 2066 kaf (select the QPF checkbox in the options menu).

Or you can extend the precipitation forecast even further using a different weather forecast (GEFS) and that's presently down to a fairly scary 1619 kaf. Of course these longer precipitation forecasts have lots of uncertainty to them and right now look particularly dire, but it does give a good idea for what a warm dry next couple of weeks could do.

For reference, last year's fairly miserable April-July runoff was 2635 kaf.

But still, so much uncertainty in these models. Even if the next two weeks are as dry as forecast, if the weather then turns quite wet we could be over 3500 kaf - which isn't good at all, but is far less grim.
 
DVexile said:
Or you can extend the precipitation forecast even further using a different weather forecast (GEFS) and that's presently down to a fairly scary 1619 kaf.
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Yikes! If we ended up with only 1619 for April to July runoff that would equate to average daily inflow of just 6,800 CFS. That's not much above where we are today, in March. Looking at currently scheduled releases the planned average daily release is currently
April: 8,300 cfs
May: 9,700 cfs
June: 13,400 cfs
July: 14,474 cfs

To answer the threads question, "How much will the lake rise?", under this scenario it won't rise at all, it will fall at an accelerating rate.

To add some additional doom, in addition to the current dry forecast, at least the next week calls for warm and wind, perfect conditions to evaporate our existing snowpack. This is scarily similar to what happened in 2002, which turned out to be the worst runoff year on record. In that year a poor but not terrible snowpack was hit by a very dry and windy March and April that led to large scale evaporation of the snowpack before it could melt and run off. On March 15 of that year the forecasted runoff was 4 million acre feet. After the dry and windy spring did its thing runoff ended up being just 1.2 million acre feet. It feels like the worst case scenario for this year keeps getting worse.
 
DVexile said:
The default is to assume climatology going forward from tomorrow and at present that is for a 2302 kaf 50% exceedance. In English, if we just pretend the weather does what it did in the past from today forward - completely ignoring the weather forecasts - then half of the past years would result in more than 2302 kaf and half less. Which is to say 2302 kaf is a "best guess" (with a lot of uncertainty) of what happens if we close our eyes and ignore that actual forecast weather.

Or you can extend the precipitation forecast even further using a different weather forecast (GEFS) and that's presently down to a fairly scary 1619 kaf. Of course these longer precipitation forecasts have lots of uncertainty to them and right now look particularly dire, but it does give a good idea for what a warm dry next couple of weeks could do.

For reference, last year's fairly miserable April-July runoff was 2635 kaf.

But still, so much uncertainty in these models. Even if the next two weeks are as dry as forecast, if the weather then turns quite wet we could be over 3500 kaf - which isn't good at all, but is far less grim.
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Just to translate these numbers into possible lake levels, here you go. Let's start with the assumption that the USBR does not alter its projected releases from Glen Canyon Dam through the summer, which I have to say are pretty modest by historic standards. We're talking about a release schedule that looks like this:

April - 490,000 af
May - 600,000 af
June - 800,000 af
July - 890,000 af

Total (Apr-Jul) - 2780 kaf

So if we've only got an inflow that might range between 1619-2302 kaf, that tells you the lake is going to drop. How much? Well here's the numbers:

If inflow is 2302 kaf, it would be 3519 on July 31...

...but if inflow is only 1619 kaf, it would be 3506 on July 31. Yikes...

And just for comparison, the USBR's March 2026 24-month study projects just under 3515 on July 31.

So the recent CBRFC forecasts are more or less consistent with the latest USBR projections.

But let's say USBR took extraordinary measures, and reduced releases through GCD each month to no more than 500 kaf. And let's say they ramped up the summer release from Flaming Gorge, which right now is projected to be a total of 292 kaf (Apr-July) to, let's say 400 kaf. That would buy an extra 900 kaf total for Lake Powell in the April-July period. And if that happened, then the range of July 31 lake levels would be 3523-3535. Basically, those moves could buy about 17 feet through the summer.

So USBR still has a few arrows left in the quiver if they choose to use them...
 
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