January 10, 2014

Highlights

• December precipitation was highly variable over the region, with wetter-than-average conditions across most of Wyoming and northeastern Colorado, and drier-than-average across most of Utah, southwestern Wyoming, and the rest of Colorado, particularly southeastern Colorado.
• With the bitter cold wave early in the month, December saw colder-than-average temperatures throughout most of the region, with portions of northeastern Utah ending up more than 15°F below average.
• Snowpack conditions have deteriorated in most basins since early December and are generally near to above normal in Wyoming and Colorado, but generally below normal in Utah.
• The January 1 spring-summer streamflow forecasts show a mixed bag for the region, with most basins in northern and western Colorado, northern and eastern Wyoming, and southeastern Utah expected to have near-average or above-average runoff, while most basins in southeastern Colorado, southwestern Wyoming, and the remainder of Utah are expected to have below-average to much-below-average runoff. 
• The NOAA CPC climate outlooks show a slight dry tilt for southern Colorado and Utah for late winter (January–March).

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December Precipitation and Temperatures, and Current Drought

Over much of the region, most of December’s precipitation fell in the first week, associated with the strong cold wave. Storm tracks generally stayed to the north for the rest of the month. Most of Wyoming, western Utah, far northeastern Utah, and central Colorado ended the month wetter than average, while the rest of Utah, and southern and eastern Colorado were drier than average .

Temperatures in December were colder than average across nearly all of the region . Utah and western Colorado experienced the largest and most widespread cold anomalies, with most locations more than 6°F below normal and parts of northeastern Utah more than 15°F below normal. These monthly anomalies were driven by a very strong cold wave during the first week of December. Denver experienced below-zero low temperatures for six days in a row, the longest such stretch in December since 1972. Grand Junction was 13°F below normal for the month, including 10 days with below-zero temperatures, compared to the long-term average of 1 below-zero day in December. Early January conditions have been near or above average over most of the region.

The latest US Drought Monitor, representing conditions as of January 7 , shows improvement since early December in areas of central Utah (from D2 to D1) and eastern Utah (D1 to D0). Also, north-central Wyoming improved (from D0 to drought-free) due to above-average December and early fall precipitation. Drought conditions worsened in portions of east-central Colorado (D0 to D1) and southeastern Colorado (D1 to D2). The proportion of the region in D2 or worse drought saw little change, with Utah at 14% (down by 2%), Colorado at 14% (up by 2%), and Wyoming at zero (no change).

Snowpack
The Current Basin Snowpack map from NRCS  indicates that conditions have deteriorated in many basins due to below-average snowfall since early December. As of January 9, basins have near-normal or above-normal SWE (>90% of median) across nearly all of Wyoming, most of Colorado, and in south-central Utah, with the best conditions (>130% of median SWE) in north-central and northeastern Wyoming. Snowpacks are below normal to much below normal in the rest of Utah, southwestern Wyoming, and southwestern Colorado, with the driest basins at or just below 70% of median SWE. A storm coming in January 9th-12th should boost snowpacks in northwestern Wyoming, northern Utah, and northern Colorado but will not help the southern part of the region.

Current Streamflows
The maps of current streamflows for Colorado , Utah , and Wyoming show that the majority of gages are ice-affected and have no data, which is typical for this time of year. Among the gages still reporting, no clear tendencies are apparent. December unregulated inflows into Lake Powell were 81% of average.

Spring-Summer Streamflow Forecasts
The first spring-summer streamflow forecasts of the season, valid January 1, were released by NOAA CBRFC and the NRCS in early January. The NRCS Westwide Streamflow Forecast Map shows that most forecast points in northern and western Colorado, northern and eastern Wyoming, and southeastern Utah are expected to have near-average (90-109%) or above-average (110-129%) spring and summer runoff.  Most forecast points in south-central Colorado, southwestern Wyoming, and the remainder of Utah are expected to have below-average (70-89%) to much-below-average (50-69%) spring and summer 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 6500 KAF, 91% of average. The NOAA CBRFC January 1 forecast for the same point is 6810 KAF, 95% of average. Also note that the January 1 forecasts do not reflect declines in snowpack since the first of the month.

Seasonal Climate and Drought Forecasts
The latest monthly Climate Outlook released on December 31st by NOAA CPC shows a slight wet tilt for precipitation for northern Wyoming for January , and a slight dry tilt for southwestern Utah. The seasonal outlooks released December 19 show a slight tilt towards drier conditions for southern Utah and central Colorado, but no tilt elsewhere in the region, for the January–March period . For the February–April period, a slight dry tilt is shown for far southern Utah and the southwestern corner of Colorado . The latest CPC Seasonal Drought Outlook released December 19 projects that most of the areas of drought conditions (D1 or worse) in our region, mainly in Utah, will persist through at least March, with additional areas of drought developing in southeastern Utah and western Colorado.

As reported in the previous briefing, the PSD Precipitation Forecast Guidance ("SWcast") released November 13 for January–March 2014  shows a dry tilt over nearly all of Utah and Colorado, with the strongest dry tilt (-10%) over north-central Colorado. Even so, the non-ENSO indicators in the Pacific Ocean, and in the Atlantic Ocean, are not as suggestive of drought as they were last year at this time.

ENSO indicators   are yet again showing ENSO-neutral conditions, with Niño 3.4 right at the zero-anomaly line and the MEI slightly below zero. The models in IRI's mid-December ENSO Prediction Plume  once again indicate a consensus towards ENSO-neutral conditions continuing through the winter into spring, with both the dynamical and statistical models tending towards the warm side of neutral, and a handful of models calling for El Niño conditions by summer.