Greetings from Silverton,
As forecasted, the last ~19 days have been sunny, unseasonably warm, and mostly dry. After a mostly warm March the snowpack statewide was 108% of normal. Now, after a mostly warm/dry first two-thirds of April, average statewide snowpack conditions are 94% of normal. When the heat was on the snowpack quickly responded. In March, enthusiastic snowmelt was seen throughout the state and for a period it appeared most basins had seen peak SWE around March 1. However a series of late March storms bumped SWE amounts creating a "double peak", with the second peak in most basins occurring around April 1. Since April 1st we have seen rather high ablation rates. Please see plots below investigating these warm conditions and increased snowmelt rates.
No new dust events have occurred since the dry dust event (D4) on April 9. Dust layers D3/D4 have been exposed at the surface of the snowpack essentially since D4 was deposited. D4 was a dry event, occurring without accompanying precipitation. Dry dust events are more subject to preferential transport, meaning dust is deposited in thicker layers on lee aspects and in depressions in the snow surface such as old wind features. A haze event was observed April 14 but did not deposit a discernible amount of dust on the already exposed D3/D4 dust layers. On April 20-21 we received a couple inches of new snow accumulation with 0.35" (9 mm) of precipitation. This minor storm event provided an albedo reset and cooler temperatures over the last few days. Now, at Red Mountain Pass D3/D4 is reemerged at the surface of the snowpack, and the patchier distribution of the dry D4 event along with the uniform distribution of D3 are both evident across the landscape. Elsewhere around the state, with somewhat similar weather across mountain areas, conditions have likely unfolded in a similar manner where dust deposition was present (please see our April Tour Update http://www.codos.org/codosupdates/apr122017).
Starting Monday, the forecast is calling for "unsettled weather" for the next ~6 days. The result will be periods of showers, isolated thunderstorms, mountain snow, and at least cloudy conditions between storm systems. Temperatures are expected to be below normal with the possibility of the snow line getting down to mountain bases. With this expected precipitation it will be interesting what kind of third bump we'll see in the snowpack, the 7-day forecast calls for 1-2" of precipitation across Colorado, with northeast Colorado looking to finally receive some much needed precipitation . It will also be interesting what sort of conditions May will bring, the last two years the month of May has been wet and cooler than normal, which was crucial not only in adding valuable SWE but also extending the snowmelt season to a near normal time-frame.
Tune into the Colorado Climate Center's, NIDIS Intermountain West, Climate, Water and Drought Assessment Webinar on Tuesday, April 25th, when NOAA's Klaus Wolter will give us his take on the long range climate forecast. Sign up here: http://ccc.atmos.colostate.edu/drought_webinar_registration.php
Water year 2017 air temperature data standardized with a mean of zero and standard deviation of one (i.e. 68% of the data falls between -1 and 1. 95% of the data falls between -2 and 2. 99% of the data falls between -3 and 3). On frequent occasions temperatures were 2 standard deviations (and greater) warmer than average. There were extended periods of warmer than average temperatures, while colder than average temperatures were short lived.
Using April 1st as the start date, rate of snowpack ablation at select SNOTEL stations. Dashed lines are average ablation rates going back to WY2006. Solid lines are ablation rates for individual SNOTEL stations so far this April. Ablation rates are 1.6" - 3" greater than average due to the recent warm/sunny conditions, and D3/D4 fully exposed on the surface of the snow exacerbating the situation.
Interestingly, compared to the long-term 1981-2010 station average, ablation is initiating much earlier than normal for most stations. This information can be ascertained by looking at regular SWE plots, but hopefully easier to digest in the above format.
Beginning April 1st, ablation rates for 2006 - 2017 at Wolf Creek Summit SNOTEL. WY2017, so far in many locations, is seeing ablation rates comparable to other years that were low snowpack conditions, dry spring conditions, and/or greater dust loading.
Beginning April 1st, ablation rates for 2006 - 2017 at Red Mountain Pass SNOTEL. It will be interesting to see events unfold with the current unsettled weather in the forecast. Updated graphs will be shown in future updates.
Warm and sunny (albedo degradation) conditions dominated the middle 2 weeks of March, warming the snowpack and melting snow at lower elevations, causing elevated streamflows. Cooler temperatures and stormy conditions returned latter March and first week of April, restoring albedo to 80%-90%. Around April 10 warm/sunny conditions returned, this time with D3/D4 located at the surface of the snow, and rapid warming and melt ensued. April 20 marked a couple days of another small storm, albedo reset, and cooler temperatures.
Looking ahead this week, cooler temperatures, snowfall bringing continued albedo resets, and a forecasted 1-2" additional precipitation. This Update will be posted to our CODOS website (http://www.codos.org/) soon.
More from Silverton Soon.