January 13, 2015

Highlights

• December brought above-average statewide precipitation to Wyoming, Colorado, and Utah, with most mountain areas seeing wetter-than-normal conditions.
• The snowpack has generally improved in the last month, with the majority of the region's basins now reporting above-median SWE. Basins in southwestern Colorado, as well as southwestern and eastern Utah, remain near or below 75% of median SWE.
• The first spring-summer runoff forecasts for the 2015 season indicate mixed prospects for the region's basins, with mainly normal to above-normal runoff expected in Wyoming and northern and central Colorado, and below-normal to normal runoff for Utah and southern Colorado.
• The tropical Pacific continues to experience "El Limbo" conditions, though the eventual emergence of a full-blown El Niño event is still expected by most forecast models.

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December Precipitation and Temperatures, and Current Drought

In December, drier-than-average conditions in southwestern Colorado, northwestern and eastern Utah, and southern Wyoming were balanced out by areas with above-average precipitation, especially in central Wyoming and central and far eastern Colorado . For the month, Wyoming ended up in the 77th percentile for statewide precipitation, Colorado in the 73rd percentile, and Utah in the 57th percentile.

The first three weeks of December were very mild across the region, and even with cold waves intruding around the holidays, the month ended up warmer than average across nearly the entire region . Northern Utah, northwestern Colorado, and southwestern Wyoming saw temperatures 6–10°F warmer than the monthly normal. All three states were above the 80th percentile for monthly statewide average temperature.

The latest US Drought Monitor  , based on conditions as of January 6, shows virtually no changes in drought conditions compared since mid-October. The proportion of the region in D2 or worse drought remains: Utah at 13%; Colorado at 12%, and Wyoming at zero.

Current Streamflows

As of January 8, the maps of current streamflows for Colorado , Utah , and Wyoming  show that for the relatively few gages unaffected by winter icing, flows are normal to above normal in Colorado and Wyoming, and mainly normal or below normal in Utah. On January 8, the Colorado River below Glenwood Springs, CO was in the 72nd percentile, 116% of median flow; the Green River near Greendale, UT was in the 50th percentile, 101% of median flow; and the San Juan River near Bluff, UT, was in the 40th percentile, 86% of median flow.

Current Snowpack
After the relatively wet December, the Current Basin Snowpack map from NRCS  as of January 9 shows improved conditions overall, with above-median SWE in the majority of the region’s basins. The deepest snowpacks relative to normal conditions, with over 110% of median SWE, are in western and northern Wyoming and northern Utah and south-central Utah. Many other basins are near-normal, with 90-100% of median SWE. Basins in southwestern Colorado and southwestern and far eastern Utah did not improve during December and remain below 70% of median SWE.

Spring-Summer Streamflow Forecasts
The January 1 spring-summer streamflow forecasts of the season were released by NOAA CBRFC and the NRCS in early January, and show mixed prospects for the coming runoff season across the region. The NRCS Westwide Streamflow Forecast Map  shows that most forecast points in northern and central Colorado, and northern and western Wyoming are expected to have near-average (90-109%) or above-average (110-129%) spring and summer runoff. Most forecast points in central Wyoming, southern Colorado, and southern Utah are expected to have below-average (70-89%) to much-below-average (50-69%) spring and summer runoff.  In northern Utah, the forecast points are split between near-average (90-109%) and below-average (70-89%) runoff.

IMPORTANT NOTE: While NRCS and NOAA continue to collaborate on streamflow forecasts, the forecast values are no longer being strictly coordinated between NRCS and some of the RFCs, including the CBRFC. For example, the NRCS January 1 forecast for Lake Powell April–July inflows is 6400 KAF, 89% of average. The NOAA CBRFC January 1 forecast for the same point is 6500 KAF, 91% of average.

Seasonal Climate and Drought Forecasts, including ENSO

The monthly Climate Outlook for January  released on December 31 by NOAA CPC shows no tilt for precipitation. The seasonal outlooks released December 18 show a slight wet tilt in the January–March period  for much of Colorado and southern Utah. For the February–April period , the area of wet tilt covers all of Colorado and Utah, with a stronger tilt in the southern portions of those states.

The latest CPC Seasonal Drought Outlook  released December 18 projects that the areas of drought conditions (D1 or worse) in southwestern and south-central Colorado and in Utah will persist or intensify through the end of March. No additional areas of drought development in the region are expected.

As described in the previous briefing, the Experimental PSD Seasonal Precipitation Forecast Guidance ('SWcast') for the January–March period  shows a tilt towards above-average precipitation over most of Colorado and southern Utah. There is a slight dry tilt forecasted for northern Utah. (The statistical 'SWcast' model targets different indicators of climate system behavior than the dynamical model that drives the CPC outlooks.)

In the tropical Pacific region, the halting progression towards El Niño conditions continues. The Multivariate ENSO Index (MEI)  remained in weak El Niño territory for the December–January. The weekly benchmark Niño 3.4 sea-surface temperature (SST) index in late December is likewise near the threshold for El Niño conditions.

A slight majority of individual ENSO model forecasts compiled by IRI in mid-January  still favor El Niño to form and persist through spring 2015. If an El Niño does develop, it is increasingly likely to be a weak event. The forecasts indicate very little chance of a La Niña event developing before spring 2015.