Greetings from Silverton,
Colorado is now solidly in the melt season with decreases in SWE in most parts of the state. Recent significant snowfall has slowed snowmelt driven runoff, but most CODOS sites statewide are well past peak SWE for the season, and it is likely that snowpack is increasing only at the very highest altitudes. In the Senator Beck Basin we are seeing losses in total SWE up to above 12,000 ft., even with this most recent snowfall.
In the last few days much of the state received significant snowfall as a large low-pressure system moved through the region. Here in the Senator Beck Basin we saw over a foot of snow with 1.4 inches of water, and similar values for precipitation are seen statewide.
Prior to this storm, merged dust events D1-4 were on the surface and notably lowering snow albedo. Additionally, snowpack in the Senator Beck Basin is mostly isothermal, meaning that higher elevation snowpack is beginning to contribute to runoff. For the time being, this new snow will cover the dust and raise the snow albedo again. This re-burying of the dust, along with cooler temperatures, is evident in hydrographs statewide, with discharge steadily decreasing across the region for the past few days. Currently discharge is slightly below median value for this date at nearly all locations in Colorado.
In the dust source area of the Southwestern Colorado Plateau soils are continuing to dry. Soil moisture is near median values for the date, but the change anomaly since February is well below zero. Percent change in soil moisture in our source area since March 1 are –40% to –60% at most locations. This means that soils have dried out faster than average and that those near median wetness values owe more to a very wet mid-winter in the desert southwest then to maintaining moisture. The long term outlook is characterized by sun and heat for Northern Arizona and New Mexico and Southern Utah, which suggests that accelerated drying of soil will continue. This is important because drier soils are more available for long-range transport, possibly resulting in addition dust loading in the mountains of Colorado.
The long term forecast for the rest of the month suggests mostly sunny weather with occasional slight chances of precipitation. This would mean continued melting of the new snow and eventual re-emergence of the significant dust layers D1-D4, which is currently about 1’ (30 cm) from the surface at SASP and 9.5” (24 cm) at SBSP.
Looking forward into June, longer-range outlooks are predicting above average temperatures and above average precipitation for the region. This could mean that we see some high elevation snow into June, which could work to postpone snow all gone date. The possible impact of this effect is hard to forecast, but it is unlikely that June snowfall will significantly delay the melt season.
Picture of snow profile at SASP (elevation 11,060') on May 19. D1-D4 is buried under 1' of new snow (.7" SWE).
Current snowpack status at SASP (elevation 11,060'). On May 19 SASP had 21.6" SWE. While Red Mt. SNOTEL (1 mile away) reported 20.5" SWE
Snow profile at SBSP (elevation 12,186') on May 20. D1-D4 is a diffuse layer in a 4" band located under 9.5" of new snow (1.7" SWE)
Snowpack status at SBSP (elevation 12,186'). On May 20 SBSP had 26.5" SWE.
Plot showing decreased streamflow in response to fresh snow increasing surface albedo and colder air temperatures.
More Soon,
Jeff Derry