July 13, 2015

Highlights

  • June precipitation was hit-or-miss across the region; southeastern Utah and southwestern Colorado were much wetter than normal, and northern Utah was drier than normal. June temperatures were record-high in Utah, and also above-average across Colorado and Wyoming.
  • Due to the very wet May and the delayed and rapid snowmelt, peak discharges and overall runoff volumes were generally greater than one would expect given the peak SWE values.
  • Nearly all reservoirs in Colorado and Wyoming have above-average storage for the end of June; Utah's reservoirs are split between below- and above-average storage.
  • El Niño conditions have strengthened further and are expected to continue through the winter. NOAA CPC precipitation outlooks for our region show a wet tilt through the summer and early fall, partly due to El Niño’s expected influence.

 

Click on the thumbnail images in the text below to bring up the full-sized graphic
 

June Precipitation and Temperatures, and Current Drought

“Miracle May" was a hard act to follow, precipitation-wise. June reverted to a more typical pattern for our region, with distinct “haves” and “have-nots”; region-wide, precipitation was slightly above average. Due to two landfalling Pacific tropical cyclones and the timely onset of the monsoon, the “haves” were southeastern Utah and southwestern Colorado, with over 400% of average precipitation for the month in some areas.  Other areas with above-average precipitation included the rest of southern Utah, central and northeastern Colorado, and northeastern Wyoming. The northern half of Utah, northwestern and southeastern Colorado, and much of western Wyoming were drier than average.

On a statewide basis, June's precipitation was in the 78th percentile for Colorado, the 69th percentile for Utah, and the 54th percentile for Wyoming.

After a cool May, summer heat came on full-bore in June, with most areas recording 2–8°F above the monthly normal. Utah experienced its record-warmest June statewide, with Salt Lake City also setting a new record for the month, 7.8°F above normal. Wyoming was just behind, in the 98th percentile for June temperatures; Colorado was in the 89th percentile.

The latest US Drought Monitor US Drought Monitor, based on conditions as of July 7, shows several areas of improvement since early June. Portions of southeastern Utah and southwestern Colorado improved by 1 to 2 categories. Improvements of 1 category occurred in northeastern Utah and extreme southeastern Colorado. The proportion of Colorado and Wyoming in D2 or worse drought remains at zero; in Utah it decreased from 34% to 27%.

Current Streamflows

As of July 10, the maps of current streamflows for Colorado, Utah, and Wyoming show that flows are tending towards normal or above normal in Colorado and Wyoming, while in Utah the flows are more spread out among the below-normal, normal, and above-normal classes. Flows on the larger streams and rivers are heading down the declining limb of the hydrograph from peaks that occurred in mid- to late June in most basins. As of July 8, the Colorado River near the CO-UT State Line was in the 71st percentile, 202% of median flow; the Green River at Green River, WY was in the 58th percentile, 130% of median flow; and the San Juan River near Bluff, UT, was in the 58th percentile, 131% of median flow.

Snowmelt and Spring Runoff Recap

This was an unusual spring snowmelt and runoff season by any measure. After a warm and dry early spring, most basins saw well-above-average precipitation from mid-April through May, with the new accumulation keeping pace with the melt at many high-elevation sites in Colorado and Wyoming. Peak SWE and the onset of melt occurred early, in March and early April, in many basins, but then the melt season was extended over an unusually long period. And while that peak SWE was below-average in most basins, the peak daily discharges during the runoff season were typically above-average—consistent with a much larger snowpack. Likewise, the seasonal runoff volumes have generally been larger than one would expect from the peak SWE measurements, and even running ahead of the June 1 forecasts which themselves significantly higher than the May 1 forecasts. As of July 9, the observed runoff volumes had already exceeded the CBRFC's June 1 forecasts for April–July runoff at most points in the Upper Colorado River Basin. What this points out is that all SWE is not created equal; precipitation that falls on the snowpack in April, May and June—whether as snow or rain—is more likely to contribute to runoff than precipitation falling earlier in the winter.

Reservoir Storage

In Colorado and Wyoming, nearly all reservoirs were above average for end-of-June, with most reservoirs’ storage being ahead of last year at this time, and the remainder being comparable to last year. Most of Colorado’s large reservoirs (>100 KAF capacity) are full, with Blue Mesa Reservoir filling for the first time since 2011. All of Wyoming’s large reservoirs are at least 85% full.

In Utah, reservoirs in the eastern Great Basin, including the Wasatch Front, are mainly below average for the end of June, and at similar levels as last year at this time. In the Upper Colorado River Basin, reservoirs are mainly above average, and at higher levels than last year. On June 30, Lake Powell held 13.08 MAF (53% full), which is more than the 11.76 MAF (48% full) of storage on the same date in 2014, but still well below the 15.29 MAF (63% full) in 2013.

 

Seasonal Climate and Drought Forecasts, including ENSO

The monthly Climate Outlook for July released on June 30 by NOAA CPC shows a significant wet tilt for precipitation over all of Utah and Colorado, and southern Wyoming, including a very strong wet tilt for southeastern Utah and extreme southwestern Colorado. The seasonal outlooks released June 18 show similar patterns, with moderate wet tilts for the July–September and August–October periods for nearly all of the region, and stronger wet tilts over Colorado and Utah. This overall forecasted wet-tilted pattern for the region is partly due to the expected moderate to strong El Niño conditions through the summer into the fall.

The experimental PSD precipitation outlook (“SWcast”) released June 16 is not as optimistic about a wet July–September period for our region; in fact, the skill-masked map shows only a slight welt tilt for far eastern Colorado, as well as a dry tilt for northern Utah. The non-skill-masked version does show a moderate wet tilt for the Front Range.

The latest CPC Seasonal Drought Outlook released on June 18 projects that areas of drought (D1 or worse) in Utah will persist or intensify by the end of September. The small patch of D1 in western Colorado shown in the outlook as “removal likely” has already improved since June 18. No additional areas of drought development in the region are expected.

Warm sea-surface temperatures have again strengthened in the eastern tropical Pacific since early June, while dipping slightly in the central tropical Pacific. The benchmark Niño 3.4 index is at +1.4°C, just below the threshold for strong El Niño conditions. The Multivariate ENSO Index (MEI) also jumped in the May–June period to the 3rd-highest value for this time of year since 1950, clearly indicating strong El Niño conditions. Nearly all ENSO model forecasts, compiled by IRI in the mid-June ENSO Prediction Plume, project that El Niño conditions will continue through the summer, with 85% calling for persistence through the winter.

Sign up to be on our email list!

Get news and updates from Western Water Assessment.

© 2024 Western Water Assessment