JFRCalifornia
Keeper of San Juan Secrets
This fall has provided a lot of encouragement for those who want to see Lake Powell rebound after several difficult years. The rains keep coming, and the lake has stabilized, even risen a bit, a rarity in October. Since bottoming out on September 15 at 3516.62, the monsoon storms have kept up, fed by subtropical flow associated with dying Pacific hurricanes, fueled by unusually warm ocean waters. And now, a month later, the lake has managed to climb nearly 4 feet, sitting just over 3520 on October 17. In that month, Lake Powell has gained about 200,000 af in volume. Not bad for the early fall, when the reservoir almost always drops.
Has this happened before? And if it did, was that a prelude to a big winter ahead?
Let’s start with the fact that big storms and runoff in October are very rare, but not unheard of. Before Lake Powell, October 1941 was one of those times. On October 15, 1941, amid a series of warm storm events, the San Juan flowed at 30,200 cfs. With the flow of the Colorado at nearly 17,000 cfs and the Green just over 5,000, the collective flow at Lees Ferry topped 50,000 cfs!
But that rare October event was short-lived, and in the next three decades never repeated itself like that. Then came October 1972. But this time, Lake Powell was there to catch the water. On October 6, the lake stood at just over 3603, with a live storage volume of 12.05 maf. In two unbelievable months of sustained precipitation, the lake rose by over 6 feet, peaking on November 27 at over 3609. In spite of sustained outflows during that time of about 12,000 cfs (the equivalent of about 8.6 maf over a year), Lake Powell increased its volume to 12.72 maf, or by about 670,000 af.
There has never been an October (or November) quite like it since that time. On October 19 and 20, 1972, inflow to Lake Powell was in the neighborhood of 50,000 cfs, and on each day, the lake rose by more than a foot! In the amazing 10-day stretch of October 15-24, the lake rose by 5 feet (!!), gaining over 500,000 af during that time. And that despite outflows of roughly 10,000 cfs. (By comparison, during the lake’s slow rise in October 2026, outflows were 20% lower—about 7-8,000 cfs on average.)
Like today, 1972 was in the midst of transitioning into a strong El Niño in 1973. So what happened over that winter? Turns out that the winter of 1972-73 was one of the stronger mountain snowfalls on record. After the November storms ended, and the lake settled back into its usual slow decline, it bottomed out in late April 1973 at about 3590. But the mountains were full of snow, and soon the melt began. Late May and all of June 1973 saw a sustained inflow in the range of 50-70,000 cfs, peaking at about 75,000 cfs in late May, and then again on June 17. Not the flashiest runoff, but a long, sustained period of big snowmelt. By the end of July, the lake stood at 3644, having risen by over 50 feet since the end of April. By the time the spring runoff was over, the lake had increased in volume by 5.5 maf!! (If a 5.5 maf increase happened in 2027, the lake would top out at about 3595.)
Does this mean the same pattern will repeat in 2027? No. But it has happened before under similar circumstances, so the possibility exists. Yes, it’s warmer in the 21st century, plus evaporation and seepage play larger roles now, and what once stayed as snow late in the season can sometimes just disappear. But the signs are at least pointing in a direction where we’ve seen what can happen. It’s worth paying close attention this winter, and hope it stays cold enough in the Rockies to hold the snow…
Has this happened before? And if it did, was that a prelude to a big winter ahead?
Let’s start with the fact that big storms and runoff in October are very rare, but not unheard of. Before Lake Powell, October 1941 was one of those times. On October 15, 1941, amid a series of warm storm events, the San Juan flowed at 30,200 cfs. With the flow of the Colorado at nearly 17,000 cfs and the Green just over 5,000, the collective flow at Lees Ferry topped 50,000 cfs!
But that rare October event was short-lived, and in the next three decades never repeated itself like that. Then came October 1972. But this time, Lake Powell was there to catch the water. On October 6, the lake stood at just over 3603, with a live storage volume of 12.05 maf. In two unbelievable months of sustained precipitation, the lake rose by over 6 feet, peaking on November 27 at over 3609. In spite of sustained outflows during that time of about 12,000 cfs (the equivalent of about 8.6 maf over a year), Lake Powell increased its volume to 12.72 maf, or by about 670,000 af.
There has never been an October (or November) quite like it since that time. On October 19 and 20, 1972, inflow to Lake Powell was in the neighborhood of 50,000 cfs, and on each day, the lake rose by more than a foot! In the amazing 10-day stretch of October 15-24, the lake rose by 5 feet (!!), gaining over 500,000 af during that time. And that despite outflows of roughly 10,000 cfs. (By comparison, during the lake’s slow rise in October 2026, outflows were 20% lower—about 7-8,000 cfs on average.)
Like today, 1972 was in the midst of transitioning into a strong El Niño in 1973. So what happened over that winter? Turns out that the winter of 1972-73 was one of the stronger mountain snowfalls on record. After the November storms ended, and the lake settled back into its usual slow decline, it bottomed out in late April 1973 at about 3590. But the mountains were full of snow, and soon the melt began. Late May and all of June 1973 saw a sustained inflow in the range of 50-70,000 cfs, peaking at about 75,000 cfs in late May, and then again on June 17. Not the flashiest runoff, but a long, sustained period of big snowmelt. By the end of July, the lake stood at 3644, having risen by over 50 feet since the end of April. By the time the spring runoff was over, the lake had increased in volume by 5.5 maf!! (If a 5.5 maf increase happened in 2027, the lake would top out at about 3595.)
Does this mean the same pattern will repeat in 2027? No. But it has happened before under similar circumstances, so the possibility exists. Yes, it’s warmer in the 21st century, plus evaporation and seepage play larger roles now, and what once stayed as snow late in the season can sometimes just disappear. But the signs are at least pointing in a direction where we’ve seen what can happen. It’s worth paying close attention this winter, and hope it stays cold enough in the Rockies to hold the snow…
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