July 11, 2014

Highlights

• June was much drier than average across most of the region, with southern Utah and far southwestern Colorado seeing the driest conditions.
• With the above-average spring-summer runoff in Wyoming and most of Colorado, reservoir storage there has strongly rebounded. Utah and southwestern Colorado saw below-average runoff, and reservoir storage continues to lag compared to average conditions.
• The NOAA CPC monthly and seasonal outlooks are tilted towards wetter-than-average conditions for our region for the summer and early fall. The PSD 'SWcast' is less optimistic about the monsoon season than the CPC outlooks, showing a dry tilt for most of Utah and Colorado.
• In the past month, the progression of atmospheric and oceanic conditions towards El Niño status has slowed, but an El Niño event is still expected to emerge by fall.

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June Precipitation and Temperatures, and Current Drought

June was much drier than average across most of the region. Western Colorado, south-central Wyoming, and all of Utah except for the Wasatch region received less than 50% of average precipitation, with southern Utah and far southwestern Colorado seeing virtually no precipitation. Only northern Wyoming, southwestern Wyoming, and northeastern Colorado were wetter than average for the month.

Even in the driest parts of the region, June temperatures remained close to average, with most of Utah and southern Colorado 0-2°F warmer than the monthly average, and Wyoming and northern Colorado 0-4°F to cooler than average.

The latest US Drought Monitor shows slightly more drought across the region compared to early June. Drought conditions improved further in eastern Colorado but worsened in south-central Colorado. Abnormally dry conditions emerged in southwestern Wyoming. The proportion of the region in D2 or worse drought: Utah unchanged at 22%, Colorado unchanged at 17%, and Wyoming unchanged at zero.

Spring-Summer Runoff and Current Streamflows

With the meltout of snowpacks nearly complete, streamflows across the region are quickly declining from their seasonal peaks. No further snowmelt flooding has occurred since early June. As of July 9, the maps of current streamflows for Colorado, Utah, and Wyoming show that flows are generally normal to much above normal in Colorado and Wyoming, and mainly below normal or normal in Utah. On July 9, Colorado River near Cameo, CO was in the 70th percentile, 139% of median flow; the Green River near Greendale, UT was in the 56th percentile, 105% of median flow; and the San Juan River near Bluff, UT, was only in the 25th percentile, 44% of median flow.

Reservoir Storage

With the above-average runoff in Wyoming and most of Colorado, storage has rebounded in most of the region’s reservoirs after dry years in 2012 and 2013. At the end of June, nearly all major reservoirs in Colorado tracked by NRCS had more storage than at this time last year, and a majority were above the long-term average, especially in the Upper Colorado and South Platte basins. In Wyoming, nearly all major reservoirs had both more storage than last year and more than the long-term average for end of June. In Utah, however, with a drier-than-average runoff season only about half of the major reservoirs had more storage than last year, and less than one-quarter had more than the long-term average for end of June.

As of July 9, Lake Powell held 12.70 MAF (52% full), up by more than 1 MAF from storage on the same date last year (11.60 MAF; 47% full). Powell storage now appears to be close to its annual peak for 2014.

Seasonal Climate and Drought Forecasts, including ENSO

The monthly Climate Outlook for July released on June 30 by NOAA CPC shows a wet tilt for precipitation for nearly all of Utah, Wyoming, and Colorado, with the strongest tilt in eastern Utah, western Colorado, and southern Wyoming. The seasonal outlooks released June 19 also show a wet tilt in precipitation for our entire region for the July–September and August–October periods, with the strongest tilt in eastern Utah, western Colorado, and southern Wyoming in the earlier period, and in the southern two-thirds of Utah and nearly all of Colorado for the later period. The relatively wet CPC outlooks reflect the expectation of an active monsoon season.

The latest CPC Seasonal Drought Outlook released June 19 projects that the areas of drought conditions (D1 or worse) across Colorado and Utah will improve or be removed by the end of September. No additional areas of drought development in the region are expected.

The experimental PSD precipitation forecast guidance ('SWcast'), released June 17 for the July–September period has a much drier outlook than the CPC forecasts, calling for a dry tilt over most of Utah and Colorado, with the strongest dry tilt in eastern Colorado. The difference from the CPC outlooks stems from the statistical SWcast model keying off different indicators of climate system behavior than the dynamical model that is driving the CPC outlooks.

Over the last month, the ramp-up of atmospheric and oceanic conditions towards an El Niño event has slowed somewhat, but the forecasts are still calling for an event to emerge in the next several months. The Multivariate ENSO Index (MEI) dropped slightly in the May-June time frame compared to April–May, but is still in El Niño territory. In the IRI ENSO Prediction Plume from mid-June, about 80% of the models are calling for El Niño onset by the fall period (September–November). If the El Niño develops, the forecasts indicate that it is more likely to be a weak or moderate event than a strong event.