Good afternoon from Silverton on Monday, May 12.
As reported earlier today, we just logged Winter Storm #24 of the season over the Mother's Day weekend, adding another 12" to our total snow depth and 1.3" of water content. Storm #24 fell directly onto merged D3-7 dust in our locale, over most terrain except northerly aspects where Storm #23 snow was still obscuring D3-7. Storm #24 weather event blunted another statewide surge in snowmelt runoff last week.
On Sunday afternoon, after the bulk of the new snow had fallen, Storm #24 also delivered a new dust-on-snow layer on very strong S and SSW winds - event D8-WY2014. The dust deposition was followed by only an inch or so of additional low density, clean snow, thinly covering the brown band of snow near the top of the 12" Storm #24 layer, itself sitting on the very dark D3-D7 merged layers (see photo below). We have not received any D8 observations from other locales - our network of observers is shrinking as ski areas and other operations close for the season. This was a comparatively modest dust-on-snow event. A sample was collected for analysis of total mass.
The deposition of layer D8 near the end of a winter storm is somewhat unusual, in our experience. The photo below shows the collection of the 0.5 m2 sample of D8 at Swamp Angel Study Plot in progress, in three strips. A square area of snow containing the dust layer was measured out and then isolated by saw cuts, with flared end walls cut into the underlying snow to the right and left (D8 is clearly visible in the side of the left 'flare'). On the right side of the sampled square, the D8 layer has been fully removed revealing the clean snow in the underlying Storm #24 layer. In the center, the very thin layer of clean snow above D8 was removed to expose the top of the D8 layer, before collecting that strip. On the left edge of the square, the new snow still sits above D8, but notice the subtle difference in 'whiteness' between that left strip's surface and the clean snow underlying the D8 layer in the far right strip.
Because it sits so near the surface, layer D8 began absorbing solar energy as soon as the sun rose this morning, despite lingering cloud cover and light snow squalls. Besides causing "glopping" on the bottom of skis, that rapid warming and wetting of the snow containing D8 will significantly hasten the settlement and meltdown of the Storm #24 layer. D8 will then merge with the underlying merged D3-7 layer. This Storm #24 ablation process will be rapid here in our San Juan Mountain watersheds and on Grand Mesa, given the forecast for mostly sunny weather for the latter half of the week. Very warm temperatures will also aid that process. Yet another surge in runoff can be expected, perhaps containing the 'center of mass' in several San Juan Mountain watersheds.
Farther north and east, the Mother's Day storm (still in progress in some locales) has also delivered significant new snow and SWE totals . Should dust layer D8 have also reached those locales, expected partly sunny and unsettled weather will slow the ablation process until the return of mostly sunny skies next weekend. If D8 did not reach the Central, Northern, or Front Range mountains, the Mother's Day storm will ablate less quickly, further delaying the emergence of underlying dust layers until even later in May. Sustained exposure of dust in those locales in late May, as days lengthen and the sun climbs higher in the sky, will result in very high snowmelt and runoff rates.
The next CODOS field circuit is planned for later this month, as conditions enable the observation of dust at the snowpack surface at our Front Range and northern CODOS site locales.