December 3, 2012

Highlights

  • November, like October, was drier than average for most of the region, and the 2013 water year is off to a dry start
  • Early-season snowpack is extremely low across Colorado and eastern Utah, but generally near-average for other parts of Utah, and Wyoming
  • The official NOAA CPC climate outlooks show no "tilt" for this winter's precipitation for our region; the NOAA PSD forecast guidance has a drier outlook

November Precipitation and Temperatures, and Current Drought

November was again much drier than average across most of the region. Most of eastern and central Colorado, southeast Wyoming, and eastern Utah saw less than 25% of average precipitation for the month. Conditions were wetter-than-average in north-central and southwest Wyoming and portions of northern Utah. According to the HPRCC Water Year Precipitation map, the first two months of the 2013 water year have left nearly all of the region drier than average, with most of Colorado and eastern Utah seeing less than 50% of average October–November precipitation. November was also a warm month, with temperatures 2° to 6°F above average over most of the region and up to 10°F above average in south-central Wyoming. The latest US Drought Monitor, representing conditions as of November 27, shows nearly all of the region still classified in severe (D2) or worse drought conditions. There was little change in the drought conditions across the region during November; a small pocket of D1 in north-central Colorado worsened to D2.

Current Snowpack and Streamflows

We are now far enough into the snow season (on average, 20-25% of seasonal accumulation occurs by December 1) that the percent-of-average data reported in the Current Basin Snowpack map from NRCS reliably reflect conditions on the ground. The regional snowpack map shows a pronounced difference between the generally near-average conditions in Wyoming and Utah, and the very low snowpacks in far eastern Utah and across Colorado. The Colorado statewide snowpack as of December 1 was around 40% of average, which is near the lowest level recorded since the mid-1980s. (Of the six years since 1986 with similarly low early-season snowpack across Colorado, two years (2008 and 2009) rebounded to above-average snowpacks by April 1, while one (2010) recovered to near-average conditions, and the remaining three remained well below average through the spring, including 2000 and 2002.) The December 1 basinwide snowpack for the Upper Colorado River above Lake Powell was about 60% of average.

Current streamflows in the three states reflect the gradient in recent precipitation and snowpack, with Wyoming gages generally reporting normal (green) streamflows for the date, with more gages in the below-normal (yellow) and much-below normal (brown) categories in Utah, and yet more in Colorado. The Colorado River near Cisco, UT gage, was in the 13th percentile, at 76% of the median flow for December 2.

Seasonal Climate and Drought Forecasts

As reported in the previous briefing, the latest monthly and seasonal Climate Outlooks released on November 15 by NOAA CPC are showing equal chances (EC) for above-normal or below-normal precipitation for the December through March period, with this lack of "tilt" reflecting the strong likelihood of ENSO-neutral conditions continuing through this period, as seen in the IRI's mid-November ENSO Prediction Plume. If this occurs, it will be the first ENSO-neutral winter since 2003-04. The CPC Climate Outlooks continue to show enhanced odds for above-normal temperatures for the winter season, consistent with the long-term trend towards warmer conditions. The latest CPC Seasonal Drought Outlook released November 15 projects that the drought conditions across our region will persist through at least February 2013.

The latest PSD Precipitation Forecast Guidance ("SWcast"), released November 19 for January–March 2013 conditions does find a signal in the pattern of past years with similar ocean-atmosphere conditions, apart from ENSO, and forecasts a dry tilt over that period for most of Utah and Colorado, with the strongest tilt towards dry conditions (>10%) in north-central Colorado—though the model skill is marginal in northern Colorado for this season and lead-time. A modest tilt towards wet conditions is forecasted for far northern Utah. Overall, this is a drier outlook for Utah and Colorado than the January–March forecast issued in late September, due to the now lower (almost zero) probability of El Niño while still having a warm North Atlantic Ocean and cold eastern North Pacific Ocean.

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