April 9, 2014

Highlight

  • March's storm tracks and the resulting precipitation once again favored the mountains in Wyoming and northern and central Colorado. Southern Utah and southwestern and eastern Colorado ended the month drier than average.
  • As of April 8, snowpack conditions have changed little from a month ago, with near-normal to above-normal SWE over most of the region. Nearly all basins across Wyoming, and all basins in northern Colorado and far-northern Utah, are at over 120% of median SWE. Basins in southern and central Utah, and south-central and southwestern Colorado are at 90% of median SWE or less.
  • The April 1 spring-summer streamflow forecasts have likewise changed little from the March 1 forecasts, calling for most forecast points in Wyoming and northern and central Colorado to have above-average or much-above-average spring runoff. Most forecast points in south-central and southwestern Colorado, and in Utah south of the Wasatch Front, are expected to have below-average or much-below-average runoff.
  • Watersheds in the northern Front Range of Colorado that were most affected by the floods last September have well-above-normal snowpacks, and with stream channels impacted by debris and sediment, there is a high potential for snowmelt flooding.
  • In early March, NOAA CPC hoisted an El Niño Watch, indicating that “conditions are favorable for the development of El Niño conditions within the next six months.” Since then, sea-surface temperatures in the bellwether Niño 3.4 region have rapidly warmed, consistent with El Niño development.

 

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

March Precipitation and Temperatures, and Current Drought

As during much of this winter, the storm tracks and dynamics in March favored the northern portions of our region, especially the mountains. Areas with above-average to much-above-average precipitation for the month included most of Wyoming, northwestern and north-central Colorado, far northern Utah, and small areas of southern Utah and southern Colorado. The remainder of southern Utah, southwestern Colorado, and eastern Colorado were much drier than average. The first week of April saw systems that brought above-average precipitation to most of Colorado, northern and central Utah, and western Wyoming.

The pattern in temperature anomalies across the region in March reflected the continued incursions of cold air masses into the north-central and midwestern US, with northern Wyoming and central and east-central Colorado ending the month colder than average by 0–6°F. Outside of the influence of these cold waves, Utah, southern Wyoming, and the rest of Colorado were 0–6°F warmer than average.

The latest US Drought Monitor, representing conditions as of April 1, shows a net increase in drought severity in our region since early March. Improvement was seen in south-central and southeastern Wyoming (from D0 to drought-free). But drought conditions worsened in southwestern Utah (D0 to D1, and D1 to D2), southeastern Utah and adjacent southwestern Colorado (D0 to D1), and southeastern Colorado (D2 to D3). The proportion of the region in D2 or worse drought increased slightly, with Utah bumped up to 16% from 11%, Colorado nudged up to 15% from 14%, and Wyoming unchanged at zero.

Current Snowpack
The Current Basin Snowpack map from NRCS shows little change since early March, with most of the region having near- to much-above-normal SWE as of April 8. Wyoming, northern Colorado, and far northern Utah are at 120% of median SWE or greater, with over 140% of median SWE in western, north-central, and southeastern Wyoming, and northeastern Colorado. Conditions in central and south-central Utah have improved slightly since March 1, with SWE now at 70–105% of median. Southwestern and southeastern Utah basins have continued to see dry conditions, and have experienced early snowmelt, and snowpacks are well below normal at 50–55% of median. Southwestern and south-central Colorado are also lagging behind the basins to the north, at around 85% of median. Early April typically represents the peak snowpack accumulation in many basins.

According to the Colorado Dust-on-Snow Program, there were four dust-on-snow events that affected at least southwestern Colorado in February and March, and a fifth on April 1. Two of the five WY2014 events, both in late March (D3 and D4), deposited substantial amounts of dust. Both events extended to central and northern Colorado, though only D4 left a prominent dust layer in those areas. Since 2005, the number of seasonal dust-on-snow events by April 1 has ranged from one to seven, with an average of four events. The month of April has the highest occurrence of dust events, with an average of three events since 2005.

Current Streamflows

The maps of current streamflows for Colorado, Utah, and Wyoming show that the majority of gages are now free of ice and reporting. Flows are mainly near normal or above normal in Wyoming and Colorado, while they are mainly normal to below normal in Utah.

Spring-Summer Streamflow Forecasts

The Westwide Streamflow Forecast Map based on the NRCS April 1 forecasts shows little change from March 1st, with most forecast points in Wyoming and northern and central Colorado expected to have above-average (110–129%) or much-above-average (130–149%) spring and summer runoff. Most forecast points in south-central and southwestern Colorado, and most forecast points across Utah, are expected to have below-average (70–89%) to much-below-average (50-69%) spring and summer runoff, with a handful of points expected to have far-below-average (25–49%) runoff, and three southern Utah points in the under-25% category. Many points in northern Utah and west-central Colorado are expected to have near-average (90–109%) runoff.

The watersheds in the northern Front Range of Colorado (St. Vrain/Boulder, Big Thompson, upper Cache la Poudre) that were most affected by the floods last September have unusually large snowpacks for early April, at around 150% of median SWE. The NRCS April 1 forecasts for these basins call for 125–130% of average spring–summer runoff. According to NOAA NWS, there is a high potential for snowmelt flooding in these basins. Since stream channels are impacted by debris and excess sediment in many locations in these basins, the risk and severity of flooding may be greater than in previous high-runoff years. Multiple state and federal agencies are cooperating to remove debris and sediment from these channels in preparation for high 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. The NRCS April 1 forecast for Lake Powell April–July inflows is 7900 KAF, 110% of average. The NOAA CBRFC April 1 forecast for Lake Powell inflows is 7850 KAF, which is also 110% of average.

Seasonal Climate and Drought Forecasts

The latest monthly Climate Outlook released on March 31st by NOAA CPC shows a dry tilt for precipitation for far southwestern Utah for April. The seasonal outlooks released March 20 show no tilt in precipitation, and so equal chances for wet or dry conditions, for our region for the AprilJune and May–July periods. The latest CPC Seasonal Drought Outlook released March 20 projects that the areas of drought conditions (D1 or worse) in Utah and southern Colorado will persist through at least June, but no additional areas of drought development are expected.

ENSO indicators such as the Niño 3.4 anomaly that are updated daily (not shown on the Dashboard) have been rapidly shifting from cool-side-of-neutral conditions into warmer territory since mid-March. This was anticipated by the consensus of the IRI ENSO Prediction Plume  for mid-March, in which nearly all of the models called for near-term warming in the Niño 3.4 region. By the mid-summer period (June–August), over half of the models forecast El Niño onset, reaching 60% by the September–November period. Last month, NOAA CPC hoisted an El Niño Watch, indicating that “conditions are favorable for the development of El Niño conditions within the next six months.” An experimental PSD regression-based MEI forecast issued March 10 projects a still higher likelihood of El Niño development, at 64% probability for the July–September period. Based on the intensity of recent tropical wind forcing, subsurface ocean heat anomalies, and historical comparisons, the likelihood of a substantial El Niño event in 2014 has greatly increased over the last two months.

Sign up to be on our email list!

Get news and updates from Western Water Assessment.

© 2024 Western Water Assessment