March 7, 2013

Highlights

  • February precipitation was mainly below-average for the region, with the driest conditions across Utah; eastern Colorado and central Wyoming saw above-average precipitation.
  • Snowpacks are now below-average in nearly every basin across the region after a dry February caused the snowpacks in Utah and western Wyoming to lose ground compared to average conditions
  • The March 1 spring-summer streamflow forecasts for the region call for well-below-average (<70%) runoff in nearly all basins, reflecting both the low snowpacks and the unusually low soil moisture last fall
  • The NOAA CPC seasonal climate outlooks show a dry "tilt" for spring and early summer precipitation for most of our region, though the one-month outlook for March has no tilt. In contrast, the “SWcast” for April–June shows a wet tilt over Colorado and eastern Utah.

February Precipitation and Temperatures, and Current Drought

February was drier-than-average across most of the region, with Utah overall the driest of the three states, especially in the far western and southern parts of the state. Mountain areas in northern Colorado and central and eastern Wyoming were generally favored by the prevailing storm tracks, and ended up with at least average precipitation, as did the plains adjacent to Colorado’s Front Range, and central Wyoming's basins. Mountain areas across Utah and in western Wyoming saw below-average precipitation. The HPRCC Water Year Precipitation map shows that almost the entire region has been drier than average since October 1. Southeastern Colorado remains the driest part of the region over that period, with less than 50% of average October–February precipitation.

February temperatures were colder than average across the region, except for parts of western and northeastern Wyoming. As in January, the largest cold anomalies, up to 15°F below average, were over Utah and were associated with persistent surface inversions. In northern Utah, a strong inversion caused another serious air pollution episode from February 2nd6th.

The latest US Drought Monitor, representing conditions as of March 5, shows some improvement in regional drought conditions since late January; an area of extreme (D3) drought in far western Colorado and eastern Utah was upgraded to D2, and a nearby area of D2 in southwestern Colorado and southeastern Utah was upgraded to D1. But the great majority of the region is still classified in severe (D2) or worse drought: Colorado, 89% (down from 100%); Wyoming, 84% (down from 86%); and Utah, 52% (down from 66%).

Current Snowpack and Streamflows

The distribution of precipitation in February tended to reduce the disparity among the region’s basin snowpacks by March 1, with the basins that had been the driest (eastern Colorado and eastern Wyoming) seeing gains and those that had been the wettest (most of Utah, and northwestern Wyoming) seeing losses compared to the average conditions. In Colorado, February brought mainly near-average accumulations, so that March 1 snowpack values, at 65–80% of average, were similar to the February 1 values, with slight declines in the southwestern basins and increases east of the Continental Divide. In Wyoming, the western portion of the state saw below-average accumulation and March 1 snowpack levels declined significantly, to 79–91% of average. Across the rest of Wyoming, March 1 snowpack values were generally improved, if slightly, compared with February 1.  In Utah, however, all basins saw below-average accumulation, leading to March 1 snowpack values that were significantly lower than February 1, at 73–96% of average. Overall, nearly all basins in the region have below-average March 1 snowpacks.

In the maps of current streamflows across the three states, many gages are still ice-affected and not reporting, especially in Wyoming. Of the gages that are reporting, the “normal” category is most frequently reported, but there are many more gages in the below-normal categories than above-normal, particularly in Colorado. The Green River near Greendale, UT gage, was in the 20th percentile, at 75% of the median flow for March 5. The Colorado River near the CO-UT State Line was in the 19th percentile, at 70% of the median flow for March 5.

Spring-Summer Streamflow Forecasts

The March 1 spring-summer streamflow forecasts of the season were just released by NOAA CBRFC and the NRCS. The NRCS Westwide Streamflow Forecast Map shows that most basins in our region are now expected to have much-below-average (50-69%) spring and summer runoff, with basins in central and southwestern Utah and northern Wyoming being in relatively better shape with forecasted below-average (70-89%) or near-average (90-109%) runoff. Several basins have slipped to the far-below-average category (25-49%) category, including overall Lake Powell inflows; the official CBRFC March 1 forecast has been reduced to 3.4 MAF, only 49% of average, compared to the February 1 forecast of 3.85 MAF. The very dry runoff outlook for the region reflects both the below-average snowpacks and the unusually dry soil moisture last fall, which is expected to significantly reduce runoff efficiency in the spring. (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.)

Seasonal Climate and Drought Forecasts

The latest monthly Climate Outlooks for March, released on February 28 by NOAA CPC, show no tilt for precipitation for our region for March, except for the extreme southwestern corner of Utah, and a tilt towards colder-than-average conditions for March over the region, especially Wyoming. The latest seasonal Climate Outlooks released on February 21 by NOAA CPC show a tilt towards drier-than-average conditions spring and early summer across most of the region, with the area of dry tilt covering more of the region than last month’s outlooks for spring. The CPC Climate Outlooks continue to show enhanced odds for above-normal temperatures for the winter and spring seasons for at least Utah and Colorado, consistent with the long-term trend towards warmer conditions. The latest CPC Seasonal Drought Outlook released February 21 projects that the drought conditions across our region will persist, through at least May 2013, and as seen in the previous outlook, some improvement is expected in far northern Wyoming.

The latest PSD Precipitation Forecast Guidance ("SWcast"), released March 5 for April–June 2013 conditions, forecasts a wet tilt for spring and early summer for all of Colorado and much of Utah, with the strongest tilt towards wet conditions (>10%) over western and south-central Colorado and far eastern Utah. A modest tilt towards dry conditions is forecasted for far northern Utah. (We will try to update soon with more explanation of the SWcast and why it might differ from the CPC forecast.)

As has been the case since fall 2012, ENSO conditions are not exerting much influence on the climate system, and thus the seasonal forecasts. ENSO indicators continue to show ENSO-neutral conditions on the cool (La Niña) side of neutral. The models in IRI's mid-February ENSO Prediction Plume indicate a consensus towards ENSO-neutral conditions continuing through next summer and fall.

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