The latest El Niño/Southern Oscillation (ENSO) diagnostic discussion is hot off the presses from the Climate Prediction Center

Click here to read the discussion. Here’s an excerpt:

ENSO Alert System Status: El Niño Watch

Synopsis: El Niño is favored to form in the next couple of months and continue through the Northern Hemisphere winter 2018-19 (70-75% chance).

ENSO-neutral continued during September, but with increasingly more widespread regions of above-average sea surface temperatures (SSTs) across the equatorial Pacific Ocean. Over the last month, all four Niño index values increased, with the latest weekly values in each region near +0.7C. Positive subsurface temperature anomalies (averaged across 180°-100°W) also increased during the last month, due to the expansion and strengthening of above-average temperatures at depth across the equatorial Pacific. Convection was increasingly suppressed over Indonesia and around the Date Line. Low-level westerly wind anomalies were evident over the western and east-central Pacific, with some of the strongest anomalies occurring over the eastern Pacific during the past week. Upper-level wind anomalies were easterly over the east-central Pacific. Overall, the oceanic and atmospheric conditions reflected ENSO-neutral, but with recent trends indicative of a developing El Niño.

The majority of models in the IRI/CPC plume predict El Niño to form during the fall and continue through the winter. The official forecast favors the formation of a weak El Niño, consistent with the recent strengthening of westerly wind anomalies and positive temperature trends in the surface and subsurface ocean. In summary, El Niño is favored to form in the next couple of months and continue through the Northern Hemisphere winter 2018-19 (70-75% chance; click CPC/IRI consensus forecast for the chance of each outcome for each 3-month period).

Impacts of NIÑOs that form in winter on the CONUS, 1950 through 2009 via NOAA.

The latest “Intermountain West Climate Dashboard” is hot off the presses from the Western Water Assessment

West Drought Monitor October 9, 2018.

Click here to read the dashboard. Here’s an excerpt:

  • Water Year 2018 ended with a whimper, as extremely dry and very warm conditions prevailed over the region in September. Water-year precipitation and streamflows ended up at record- or near-record-low levels across most of Utah and Colorado, accompanied by record- or near-record-high average temperatures and evaporative demand. The cool and wet start to October dampened wildfire danger and raised hopes for the new water year, but deep deficits in soil moisture and water supply persist.
  • Dozens of stream gages in the Upper and Lower Green, White, Yampa, Colorado headwaters, Gunnison, Uncompahgre, Dolores, and San Juan basins saw their lowest September monthly flows on record. In late September, the Animas River ran below 100 cfs at Durango for the first time in 107 years of record. Water-year total streamflows were the lowest or 2nd-lowest on record at many gages in southwest Colorado, and at several gages in southern and eastern Utah. Unregulated water-year inflows to Lake Powell were the 3rd-lowest on record, after 1977 and 2002.
  • Statewide, Utah is at 54% of average reservoir storage for this time of year, versus 70% one year ago; Colorado is at 46% of average, versus 68% one year ago. As of October 9th, Blue Mesa Reservoir had dropped to its lowest level, 263 KAF, since 1987. Lake Powell held 11.0 MAF as of October 9th, the lowest level since 2014, and per the September 24-Month Study, the most-probable forecast for April 2019 is 9.0 MAF, which would be Powell’s lowest level since 2005.
  • September was an extremely dry month for the region, capping off a historically dry water year for most of Utah, Colorado, and southern Wyoming. Statewide, Water Year 2018 was the driest on record (since 1896) for Utah, while it was the 2nd-driest on record for Colorado, just ahead of 2002. September was much warmer than average for Utah, Colorado, and southern Wyoming, cinching a historically warm water year. For Colorado statewide, Water Year 2018 tied with 1934 and 2000 as the warmest on record, while for Utah, it was the 2nd-warmest on record, just behind 1934. Both states were 2.8 degrees F above the 1981-2010 normal.
  • Drought conditions emerged or worsened in multiple areas in Utah, Wyoming and Colorado during September. D3 and D4 conditions now cover virtually all of eastern Utah and Colorado’s Western Slope. As of October 2, 88% of Utah is in D2 or worse, and the remainder in D0 or D1; in Colorado, 64% is in D2 or worse, and 22% in D0-D1; and in Wyoming, 3% is in D2 or D3, and 37% in D0-D1. The 12-month EDDI map shows that relative to previous water years, evaporative demand over Water Year 2018 was the highest (ED4) or 2nd-highest (ED3) on record (since 1980) for much of the region.
  • The CPC seasonal precipitation outlooks for the month of October shows very strongly enhanced chances for above-normal precipitation for the region, largely reflecting the wet short-term forecasts as of October 1, i.e., precipitation that now has already fallen as of the 11th. The precipitation outlook for the October-December period shows slightly enhanced chances for above-normal precipitation for Colorado and southern Utah, consistent with the elevated odds of El Nino development by winter. Those odds are still at about 70%, per the IRI/CPC Probabilistic ENSO Forecast.
  • Water year 2018 closes as one of driest on record for upper #ColoradoRiver Basin — @AspenJournalism #COriver #aridification

    Drying in process on the Colorado River, where Lake Powell once stood, in early October 2018. Photo credit: Aspen Journalism/Brent Gardner-Smith

    From Aspen Journalism (Heather Sackett):

    Colorado water managers are saying good riddance to water year 2018. It enters the history books alongside 2002 and 1977 as one of the driest on record for the Upper Colorado River Basin.

    According to preliminary numbers from the Bureau of Reclamation, water year 2018, which ended Sept. 30, had the third-lowest unregulated inflow into Lake Powell at 4.62 million acre-feet. That’s just 43 percent of average.

    Only 1977 and 2002 saw less water flow into Lake Powell from the upper basin, at 3.53 million acre-feet and 2.64 million acre-feet, respectively.

    The average yearly inflow is 10.8 million acre-feet.

    The months of August and September 2018 were the third- and fourth-worst months for unregulated inflows into Lake Powell behind only July and August of 2002.

    The unregulated flow in August was just 2 percent of average. Lake Powell is currently 46 percent full.

    “We know if we have another drought, the risk of draining Lake Powell is real,” said Jim Pokrandt, director of community affairs for the Colorado River Water Conservation District and chairman of the Colorado Basin Roundtable. “If we have another year as bad as this one, you’re going to see lots of discussions about who’s going to take reductions. We really need three, four, several years of average or above-average snow years to get us out of this pickle.”

    Low flows in the Roaring Fork River just above Rio Grande Park, in July 2012. Water year 2018 surpassed 2012 as third driest in terms of inflow into Lake Powell from the Upper Colorado River Basin. Photo credit: Aspen Journalism/Brent Gardner-Smith

    Roaring Fork conditions

    Locally, the Roaring Fork watershed was extremely dry this water year. The region was plagued by record-low snowpack — the lowest snow-water equivalent ever recorded for some dates at the McClure Pass and Independence Pass SNOTEL sites — sparse runoff, record-low streamflows and a hot, dry summer.

    Low flows were prevalent across Colorado during the last two weeks of the water year, which runs from October through September. According to the National Oceanic and Atmospheric Administration’s drought information system, 30 percent of U.S. Geological Survey stream gauges in the intermountain West reported record-low seven-day-average stream flows for the last two weeks of September, including some in the Roaring Fork watershed.

    On Sunday, the last day of the water year, the USGS river gauge on the Roaring Fork at Stillwater Road just east of Aspen showed the river flowing at 19 cubic feet per second, beating the previous minimum flow of 21 cfs in 1977.

    Flows on the Crystal River were similarly low. Above Avalanche Creek and above a series of diversion structures, the river was running at nearly 46 cfs, lower than the previous record low of 48 cfs in 1977.

    At the river gauge near the state fish hatchery and downstream from several diversion structures just outside of Carbondale, flows dribbled down at just under 7 cfs Sunday.

    Colorado Department of Water Resources Engineer for Division 5 Alan Martellaro said the summer’s weak monsoons exacerbated conditions caused by little snowfall.

    “We had a bad snowpack,” Martellaro said. “It was not the worst, but then we have had an incredibly dry summer, a total lack of rain. I think when we start analyzing it, we are going to find the flows in late summer are unprecedented. We have done some things we have never done before.”

    Martellaro is referring to curtailment on the lower Crystal in late July. Amid rapidly dropping flows, the district 38 water commissioner turned down the headgate of the Lowline Ditch, which he determined was diverting too much water. The ditch diversion did not exceed its legally decreed amount; the problem was that it was violating new state guidelines regarding wasting water.

    According to data from the Natural Resources Conservation Service, many sites around western Colorado rank as the driest since recording began for water-year precipitation, including McClure Pass, Schofield Pass and Independence Pass.

    Statewide, the water year precipitation average at all SNOTEL sites measured just 21.4 inches, which is 64 percent of average — the second-lowest on record behind only 2002.

    “It was pretty consistently dry throughout the entire year,” said Karl Wetlaufer, a hydrologist with the NRCS Colorado Snow Survey. “February may have been the only month where we had near-normal precipitation across the state.”

    Paonia Reservoir was at 7 percent full at the end of September. Water year 2018 ranked as the third driest in the Colorado River Basin. Photo credit: Heather Sackett/Aspen Journalism

    Reservoirs low

    In some instances, reservoir releases have come to the rescue of downstream anglers, fish and ecosystems.

    Releases from Ruedi Reservoir will continue through October to bolster flows for endangered fish in what’s known as the 15-mile reach, a notoriously dry section of the Colorado River between the Palisade area and the confluence with the Gunnison River in Grand Junction.

    [Reclamation has been releasing water from] Ruedi Reservoir.

    Periodic releases from Green Mountain Reservoir near Kremmling also boosted summer flows in the Colorado River. But that water will need to be replaced this winter by snowfall, Martellaro said. Ruedi Reservoir is currently 63 percent full while Green Mountain Reservoir is nearly 46 percent full.

    “Where we have large reservoirs that can supplement the flows, yeah, we’ve gotten by,” Martellaro said. “But even that is coming to an end. We are running out. It remains to be seen what the snowpack is like to refill these large holes we’ve put in these reservoirs.”

    Water year 2018 Upper Colorado River Basin precipitation accumulation via the NRCS.