April 5, 2013

Highlights

• The Intermountain West is facing very low 2013 spring-summer runoff with reservoirs already depleted by dry conditions in 2012
• March precipitation was below-average over nearly all of our region
• April 1 SWE was below normal across the region, with most basins between 70-85% of normal
• April 1 spring-summer streamflow forecasts call for less than 70% of average runoff in nearly all basins, with less than 50% of average runoff in many basins
• The NOAA CPC seasonal climate outlooks show a dry "tilt" for late spring and early summer precipitation for most of our region, though the one-month outlook for April has no such tilt.

March Precipitation and Temperatures, and Current Drought

March was drier than average across the vast majority of the region, with driest conditions (>50% of average) in southern and northeastern Wyoming, southern Colorado, and northern and southeastern Utah. Only scattered areas saw above-average precipitation. The mountains across the region generally saw below-average precipitation. The HPRCC Water Year Precipitation map shows that almost the entire region has seen below-average precipitation since October 1. The largest area with <50% of average October–March precipitation is in southeastern Colorado.

March temperatures were warmer than average across most of Utah and in southwestern Colorado, and cooler than average elsewhere in the region. The largest cold anomalies, up to 6°F below average, were in northeastern Colorado and northern Wyoming.

The latest US Drought Monitor, representing conditions as of April 2, shows little change in regional drought conditions since early March. Most of the region is still classified in severe (D2) or worse drought: Colorado, 89% (unchanged since March 5); Wyoming, 84% (unchanged); and Utah, 46% (down from 52%).

Current Snowpack and Streamflows

With below-average March precipitation across nearly all mountain areas, snowpacks continued to slip with respect to normal (1981-2010 median) accumulation. April 1 SWE was well below normal across the region, with most basins between 70–85% of normal. Utah April 1 basin SWE was generally lower than on March 1, ranging from 70–90% of normal. In Colorado, April 1 basin SWE was similar to the March 1 values, at 66–82% of normal. In Wyoming, there was more variability, with the individual basin SWE ranging from 63–97% of normal. The April 1 basinwide SWE for the Upper Colorado River above Lake Powell slipped to 73% of normal, compared to 78% on March 1, and 84% on February 1.

In the maps of current streamflows across the three states, far more gages are in the below-normal categories than above-normal, particularly in Colorado. The Green River near Greendale, UT gage, was only in the 8th percentile, at 56% of the median flow for April 5. The Colorado River near the CO-UT State Line was in the 10th percentile, at 57% of the median flow for April 5.

Spring-Summer Streamflow Forecasts

The April 1 spring-summer streamflow forecasts from NOAA CBRFC and the NRCS are lower across the region than the March 1 forecasts. The NRCS Westwide Streamflow Forecast Map shows that most basins in our region are now expected to see well-below-average (50-69%) runoff or far-below-average (25-49%) runoff. Basins in northern Wyoming are in relatively better shape with forecasted below-average (70-89%) runoff. Several basins have slipped to the very lowest category (<25% of average).

For Lake Powell inflows, the official CBRFC forecast for April 1 is again lower than the previous months’, at 2.7 MAF (38% of average), compared to the March 1 forecast of 3.4 MAF. The very dry runoff outlook for the region reflects both the below-normal 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 April, released on April 1 by NOAA CPC, now show no tilt for April precipitation for our region, in contrast with a dry tilt in the previous outlook, and a tilt towards warmer temperatures for April over the region, especially Utah and Colorado.

As reported in the previous briefing: The latest seasonal (3-month) Climate Outlooks released on March 21 by NOAA CPC show a tilt towards drier-than-average conditions for late spring and early summer for western Colorado and all of Utah. The CPC Climate Outlooks continue to show enhanced odds for above-normal temperatures for the upcoming seasons, consistent with the long-term trend towards warmer conditions.

The latest CPC Seasonal Drought Outlook released April 4 projects that over most of our region drought conditions will persist, but some improvement is expected in far southeastern Wyoming and northeastern Colorado over the next three months.

ENSO indicators continue to show ENSO-neutral conditions on the cool (La Niña) side of neutral, and so we continue to see little influence of ENSO on the seasonal forecasts. The models in IRI's mid-March ENSO Prediction Plume indicate a consensus towards ENSO-neutral conditions continuing through next summer and fall.