No clear signal means water managers will be biting their nails for a few months
By Bob Berwyn
FRISCO — Without a strong El Niño or La Niña signal, Colorado weather watchers are struggling even more than usual to get a sense of how much snow to expect this coming winter, critical information for water managers who have seen reservoir storage dwindle to below 70 percent of average for this time of year.
Even if winter snowfall is close to normal, some reservoirs are unlikely to refill completely next spring, leaving utilities in the position of hoping for an above average winter.
“We’re far from through this. The story has yet to unfold,” Blue River Basin water commissioner Troy Wineland said after participating in a weekly statewide water webinar, explaining that many local streams are flowing well below seasonal averages. A few others are close to average due to upstream releases of stored water, he said.
The centerpiece of Tuesday’s webcast was a seasonal outlook from NOAA meteorologist Klaus Wolter, who offered some hope. Despite the fact that La Niña is fading, the overall combination of ocean temperatures and global circulation may bring at least normal moisture to the high country.
“What we have to play with … shows a slight preference for a little bit wetter conditions on the West Slope, but it’s not a strong signal,” said Wolter, who studies climate with the Earth Systems Research Laboratory in Boulder.
The combination of a weak El Niño, a cold phase of a large-scale Pacific oscillation known as the PDO, as well as atmospheric patterns in the Atlantic could combine push storms across the central Rockies, he said.
The El Niño Southern Oscillation is one of the best indicators for developing long-term precipitation outlooks, but it looks like the Pacific Ocean will be in a near-neutral state this winter, and perhaps slip back into a La Niña phase (cooler than average sea surface temps in the equatorial eastern Pacific) by next year.
Wolter said having a “neutral” year after a douple-dip La Niña is almost unprecedented. Almost always, after a two-year La Niña phase, the Pacific rebounds to at least a weak El Niño.
“Going back to 1905, we’ve never seen this,” Wolter said.
The last time the Pacific stayed in a La Niña to neutral phases for an extended time was in the late 1990s and early 2000s, culminating in the 2002 drought. In general, Wolter said some of Colorado’s historic long-term droughts have coincided with similar conditions.
“If you look at the big, long droughts … going back to 1910, they were all associated with conditions like we’re seeing; this is the big concern,” Wolter said, adding that he does expect at least a bit of a rebound from last winter’s epic low snowfall.
While many signs during the summer pointed to a developing El Niño, the trend tailed off in the autumn.
“Unfortunately, its demise was quicker than expected, but we won’t go back to La Niña until next year at the earliest,” Wolter said of the anticipated El Niño. “There is still the potential that it could come back, but I’m not holding my breath,” he said. “The best bet is neutral.”
“If the El Niño gets a bit stronger, it would look a lot better, with a lot more blue and green on the map, and that’s not out of the question in November and December,” he said.
But under the current set of conditions, Wolter said the forecast skill for the Upper Colorado Basin is just not very high.
“There is a huge range of possible outcomes, but in general, a negative PDO is more favorable for western Colorado … if we were to get even a smidgen of El Niño back … it would help.
For the larger Colorado River Basin, there is a chance that nothern Utah could see wet conditions, but not in the near future.
“The next seven to 10 days looks like a wet Pacific Northwest and warm and dry out east, with no big storms in sight the next two weeks,” he said.
For October through December, Wolter said signs are favorable for moisture in eastern Colorado, where winter wheat planting is under way, but added that there’s not much to go by for western Colorado.
Similarly, for the January to March period, the overall odds are for average precipitation, but without much skill in the forecast.