March 11, 2015

Highlights

• February’s precipitation was very unevenly distributed across the region. Most of Colorado, especially the Front Range, saw much-wetter-than-average conditions, while Utah was overall very dry, especially in the northern part of the state.
• Since early February, the snowpack has improved relative to normal conditions in several basins, including in southwestern Colorado, while slipping in several others, particularly in northern Utah. Regionwide, the majority of basins are still reporting below-normal SWE (<90% of median).
• The March 1 spring-summer runoff forecasts came in lower than the February 1 forecasts at many locations. Most forecast points are expected to see below-average and much-below-average runoff, with an increasing number in the dreaded far-below-average (25–49%) category, especially in Utah.
• Finally: The Niño 3.4 sea-surface temperature anomaly has managed to remain above the +0.5°C threshold for the requisite period, and so NOAA last week issued an El Niño Advisory. These borderline El Niño conditions are expected to continue at least through the spring, with strengthening possible.

Click on the thumbnail images in the text below to bring up the full-sized graphic
 

February Precipitation and Temperatures, and Current Drought

After a big storm in the first week, the next ten days of February reverted to the overall dry weather of January. Then the upper-level pattern shifted again, and several more storms came through the region, but with very uneven results . Most of eastern Colorado ended up with much-above-average (>200% of normal) precipitation for the month, with record February precipitation and snowfall in several locations on the Front Range. South-central Colorado, southeastern Utah, and central Wyoming were also on the wet side. Northwestern Colorado, northern and central Utah, and western Wyoming saw below-average or well-below-average precipitation, with parts of the Wasatch Range experiencing the least snowy February on record.

For the month, Colorado was in the 75th percentile for statewide precipitation—the wettest state in the country relative to normal in an overall dry February nationwide. Wyoming was not far behind in the 61st percentile, while Utah was the driest of the three states, in the 24th percentile.

February continued what has been a very warm winter for the region, with above-average temperatures observed for the month in all but a few locations . As in December and January, the warmest areas were in northern Utah, northwestern Colorado, and southwestern Wyoming, with temperatures 9–15°F warmer than the monthly normal. As in January, the region was in or near the top decile for monthly statewide average temperature: Utah, 100th percentile (warmest February on record); Wyoming, 95th percentile; and Colorado, 89th percentile. Salt Lake City ended up with the warmest winter season (December–February) on record.

The latest US Drought Monitor , based on conditions as of March 3, shows that since early February, a large area of western Colorado and adjacent eastern and northern Utah has degraded again, from abnormally dry (D0) to moderate drought (D1). An area of severe drought (D2) in northwestern Utah has slightly expanded, and a portion of it has degraded to extreme drought (D3). The proportion of the region in D2 or worse drought is unchanged, with Utah at 13%, Colorado at 12%, and Wyoming at zero.

Current Streamflows

As of March 8, the maps of current streamflows for Colorado , Utah , and Wyoming  show that flows are generally normal to above normal in Colorado and Wyoming, and mainly below normal to normal in Utah. On March 7, the Colorado River below Glenwood Springs, CO was in the 57th percentile, 105% of median flow; the Green River near Greendale, UT was in the 68th percentile, 159% of median flow; and the San Juan River near Bluff, UT, was in the 41st percentile, 87% of median flow.

Current Snowpack

After the very uneven distribution of precipitation in February, some basins saw gains in snowpack compared to normal seasonal accumulation, while other basins regressed. The Current Basin Snowpack map from NRCS  as of March 11 shows that like one month ago, the majority of the region’s basins are below 90% of median SWE.  Northern Utah now generally has the lowest basin snowpacks, with 55–77% of median SWE. Above-median SWE is reported in several basins in northern and western Wyoming, in south-central Utah, and in eastern Colorado, but only two basins have more than 110% of median.

Spring-Summer Streamflow Forecasts

In the March 1 spring-summer streamflow forecasts, released by NOAA CBRFC and the NRCS in early March, the expected runoff has slipped at many gages across the regions compared to the February 1 forecasts. The NRCS Westwide Streamflow Forecast Map  shows that most forecast points in Utah are now expected to have much-below-average (50–69%) or far-below-average (25–49%) spring and summer runoff. Central and southern Wyoming and northwestern and southern Colorado are expected to have below-average (70–89%) or much-below-average (50–69%) runoff. Most forecast points in northern and central Colorado and northern and western Wyoming are expected to have near-average (90–109%) spring and summer runoff. The Lake Powell inflow forecast has declined slightly since February 1; see Note below.

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 March 1 forecast for Lake Powell April–July inflows is 4900 KAF, 68% of average. The NOAA CBRFC March 1 forecast for the same point is 5100 KAF, 71% of average.

Seasonal Climate and Drought Forecasts, including ENSO

The monthly Climate Outlook for March  released on February 28 by NOAA CPC shows a wet tilt for precipitation in the Four Corners, extending into western Colorado and eastern Utah. The seasonal outlooks released February 19 show a wet tilt in both the March–May  and April–June  periods for most of the region, with the strongest tilt in western Colorado and eastern Utah.

Given this wet tilt, the latest CPC Seasonal Drought Outlook  released February 19 projects that areas of drought conditions (D1 or worse) in southeastern Colorado and in far northwestern Colorado and southwestern Wyoming will improve or be removed by the end of May. Drought areas in Utah and the rest of western Colorado are expected to persist or intensify. No additional areas of drought development in the region are expected.

As reported in last month's briefing, the updated Experimental PSD Seasonal Precipitation Forecast Guidance ('SWcast') for the January–March period  issued on January 15 continues to show a tilt towards above-average precipitation over most of Colorado and southern Utah. There is again a slight dry tilt forecasted for northern Utah. (Note: "Skill-masked" means that the forecast only shows the tilts for those areas where there has been demonstrated forecast skill for this season in the past.)

As also reported in last month's briefing, the median forecast of the Experimental PSD April 1 SWE Guidance  issued on January 15 suggests that the Colorado River Headwaters will end up with above-normal SWE by April 1, with 103% of median, while the Gunnison and Rio Grande will be well below median, with 84%, with the other five basins falling in between with 90% to 96% of median.

In the tropical Pacific region, the halting shuffle towards El Niño conditions has finally met the official criteria. On March 5, NOAA CPC issued an El Niño Advisory, noting that overall, the indicators “are consistent with borderline, weak El Niño conditions.” Because of the barely-above-threshold conditions, and the unusual timing for onset (typically in summer), the climate impacts are expected to be modest. The Multivariate ENSO Index (MEI)  continued to hover in weak El Niño territory for the January–February period. A slight majority (50-60%) of the individual ENSO model forecasts compiled by IRI in the mid-February ENSO Prediction Plume  call for El Niño conditions to continue through spring 2015. The dynamical models are particularly bullish on El Niño continuing and possibly strengthening.