February 12, 2016

Highlights

• January saw wetter-than-average conditions for most of Utah, with Colorado split between wet and dry, and Wyoming more on the dry side. February had a very wet start for most of the region.
• Snowpack conditions have improved in most basins, and are near or above normal in all of Utah and Colorado, and southern and far western Wyoming. Conditions in the rest of Wyoming are lagging well behind normal.
• The current El Niño event has peaked but remains very strong. El Niño conditions are nearly certain to continue through the spring, which is reflected in a wet tilt for Colorado and Utah in the seasonal forecasts.

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

January Precipitation and Temperatures, and Current Drought

January's precipitation was another mixed bag for the region. Wetter-than-normal conditions prevailed in most of Utah, western Colorado, and southern Wyoming. Northeastern Utah, most of eastern Colorado, and northern Wyoming were drier than normal. On a statewide basis, January's precipitation was in the 73rd percentile for Utah, the 59th percentile for Colorado, and the 36th percentile for Wyoming. So far (through the 11th), February has been very wet for most of the region, though that mainly reflects the impact of the large and intense storm from the 31st to the 3rd, with warm and dry conditions prevailing since then.

January’s temperatures were generally above normal in eastern Colorado and most of Wyoming, with cooler than normal conditions for much of Utah, and western Colorado. On a statewide basis, January's temperatures were in the 58th percentile for Utah, the 82nd percentile for Wyoming, and the 68th percentile for Colorado.

The latest US Drought Monitor, based on conditions as of February 9, shows that after above-normal precipitation in January and early February, several areas in central and western Utah improved by one or two categories in the past month. Conversely, after extended dry weather, three additional areas in northern Wyoming have degraded to D0. The proportion of Colorado and Wyoming in D2 or worse drought remains at zero; in Utah, it has declined to 13%.

Introducing EDDI

For the past month, the Drought Monitoring portion of the Dashboard has featured a new product: EDDI, the Evaporative Demand Drought Index. EDDI is based on atmospheric data--wind speed, humidity, temperature, and sunshine--and it reflects the atmosphere’s “thirst” for water from the land surface. (EDDI does not explicitly incorporate precipitation, but many of the component variables are strongly related to precipitation anomalies.)

EDDI has been shown to capture fast-emerging (“flash”) drought earlier than other drought indices, while also providing useful information at longer time scales. Like SPI, it is calculated over a specific time period in the context of normal conditions over that time period. EDDI is expressed in discrete categories based on the current conditions' percentile ranking relative to past conditions. The EDDI drought categories (ED0-ED4) have the same percentile “bins” as as the corresponding US Drought Monitor categories (D0-D4). EDDI also has wetness categories (EW0-EW4), indicating wetter-than-normal surface conditions, occupying the 70th percentile and above, mirroring the drought categories.

As of February 5, the 2-week through 12-week EDDI maps show wet or "low-thirst" conditions predominating over drought (high-thirst) conditions in our region, especially in Utah and southern and western Colorado, though there is a persistent patch of drought conditions in eastern Colorado. At longer timescales, there is more drought shown in eastern and central Colorado in the most recent 6-month EDDI map, while these are not as evident in the 12-month EDDI map.

Snowpack
The Current Basin Snowpack map from NRCS as of February 10 shows modest overall improvement in SWE conditions across the region compared to early January, though the strong southwest-northeast gradient typical of El Niño winters persists. Basins in Colorado, Utah, and in southern and western Wyoming all have near-median or above-median SWE, with the basins in southern Utah having the highest SWE (>120%) relative to median. Basins in northern and central Wyoming still have below-median SWE, with most reporting 55–85% of median SWE.

Spring-Summer Streamflow Forecasts

The February 1 spring-summer streamflow forecasts, released by NOAA CBRFC and the NRCS in early February, show only small changes in the expected runoff compared to the January 1 forecasts. The NRCS Westwide Streamflow Forecast Map shows that in Colorado, nearly all forecast points are expected to have near-average (90–109%) or above-average (110-129%) spring and summer runoff. In southern Utah, most forecast points are expected to have above-average or much-above-average (130-149%) runoff, while furthern north, the Wasatch Range-fed forecast points are expected to have near-average runoff, and the Uinta Range-fed forecast points, below-average (70–89%) runoff. In Wyoming, the picture is drier than the other two states, with near-average runoff expected at only a handful of points, with most expected to have have below-average to much-below-average (50–69%) spring and summer 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. For example, the NRCS February 1 forecast for Lake Powell April–July inflows is 7000 KAF, 98% of average. The NOAA CBRFC February 1 forecast for the same point is 6700 KAF, 94% of average. In general, the CBRFC February 1 forecasts are more pessimistic than the NRCS February 1 forecasts for most points in Utah, and for many points in western Colorado as well.

Seasonal Climate and Drought Forecasts, including ENSO

The monthly Climate Outlook for February released on January 31 by NOAA CPC shows a slight to moderate wet tilt for precipitation for all of Colorado and most of Utah, and a slight to moderate dry tilt for western and northern Wyoming. The seasonal outlook for February–April released January 21 shows the area of wet tilt expanded northwards, with most of the region seeing a wet tilt, including a strong wet tilt for southern Colorado. The outlook for March–May shows a similar pattern , with the area of wet tilt expanded further, into Wyoming. The overall forecasted pattern for the western US, including the wet and dry tilts for different parts of our region, reflects the expected strong El Niño conditions through winter into early spring.

The skill-masked experimental PSD precipitation outlook (“SWcast”) issued January 21 for the January–March period shows a moderate wet tilt (>+10%) for western and northern Utah and north-central Colorado, and a slight wet tilt for most of the rest of Utah and Colorado. The unusually extensive area of wet tilt has persisted through three iterations of the January–March SWcast, and follows on a high skill score (i.e., validation) for the October–December 2015 SWcast.

The latest CPC Seasonal Drought Outlook released on January 21 projects that areas of drought (D1 or worse) in Utah will improve or be removed by the end of March. Persistence of the drought in north-central Wyoming is expected. Again, these changes are expected mainly due to the forecasted impacts of the El Niño event.

Sea-surface temperatures in the tropical Pacific peaked in November, but have only modestly declined in the Niño 3, 4, and 3.4 regions. The latest weekly value of the benchmark Niño 3.4 index is +2.6°C, well above the threshold for strong El Niño conditions. The Multivariate ENSO Index (MEI) has held relatively steady in the past four months, recording +2.2 for the December–January period, the 3rd-highest value for this time of year since 1950.

The IRI/CPC probabilistic ENSO forecast based on the mid-January ENSO Prediction Plume calls for a ~98% chance for the El Niño to persist into spring (March–May) 2016, though weakening through the spring, with a ~50% chance of returning to neutral ENSO conditions in the summer, and a ~30% chance of rapidly transitioning to La Nina conditions in summer.