Early Season Treat

Posted Sunday, December 2nd, 2018 by Mike Wessler

Yesterday began with a traffic-heavy trip up the canyon as droves of powder-hungry skiers and snowboards made the pilgrimage for one of the first true sunny powder days of the year. The long trip up gave us a chance to chat and reflect on how the season has been shaping up so far.

For one, we’ve got a decent early start as compared to the past two water years with just over 6” of SWE at the Brighton SNOTEL site (2017: 4”; 2018: 2.5”), and just a hair over the 1981-2010 median value (see below). Coverage is rapidly improving, and anecdotally, at the end of the day, we couldn’t seem to remember making turns this good until January last season! Waking up to valley snowfall today was the icing on the cake to tie up a wonderful weekend.

Brighton SNOTEL: 2019 (Current) Water Year
Brighton SNOTEL: 2019 (Current) Water Year
Brighton SNOTEL: 2018 Water Year
Brighton SNOTEL: 2018 Water Year
Brighton SNOTEL: 2017 Water Year
Brighton SNOTEL: 2017 Water Year

As I write this forecast, light-to-moderate snowfall continues across the valley and in the mountains, while the radar struggles to paint a clear picture of conditions in the region today.  Some areas of the valley, including the airport, have reported up to 0.3” of water since Saturday evening, while Alta Collins is reporting 0.18”. The likely shallow nature of the precipitation and weak large-scale forcing are contributing to this scenario of limited orographic enhancement, and even an ‘upside-down’ setup with a valley precipitation maximum. A weak meso-vortex is evident in the analysis of mid-level winds for northern Utah (and in the radar loop shown below), and this circulation is in part what is driving the continued lift and precipitation in the region (see a slightly more in-depth write-up on Jim Steenburgh’s blog at http://wasatchweatherweenies.blogspot.com/).

HRRR Simulated Radar Reflectivity through the next 18 hours. Note the tight cyclonic (counter-clockwise) circulation associated with the meso-vortex overhead of northern Utah.
HRRR Simulated Radar Reflectivity through the next 18 hours. Note the tight cyclonic (counter-clockwise) circulation associated with the meso-vortex overhead of northern Utah.

As the pattern progresses the upper-level trough to our east and build in a weak ridge to the southwest, we’ll see the snow become more showery in nature overnight and into Monday, with drier air throughout the column and clouds beginning to break up by Monday night. In favorable areas of high terrain throughout the Wasatch, decent accumulations are expected overnight, with a maximum of 0.2-0.4” of water (translating to 4-8” of cold, low density snow) expected in the upper cottonwoods. The HRRR does seem to taper off more quickly than the SREF and NAM, but I do think we’ll see numbers within the middle of the above range.

SREF Forecast through the near-term period highlighting a spread of 0.2-0.4" SWE likely for the upper Cottonwoods.
SREF Forecast plumes through the near-term period highlighting a spread of 0.2-0.4″ SWE likely for the upper Cottonwoods.

Monday and Tuesday should provide absolutely banner early season days on snow for the mid-week ski crowd, and excellent backcountry skiing for those with the skills, gear, and group to travel in appropriate terrain (always remember to check the Utah Avalanche Center forecast)! Cold temperatures will persist all the way to the valley floor, helping with powder preservation.

GFS Northern Hemisphere Dynamic Tropopause Pressure: 81-hour outlook highlighting a highly amplified and progressive pattern continuing for the mid-range forecast period.
GFS Northern Hemisphere Dynamic Tropopause Pressure: 81-hour outlook highlighting a highly amplified and progressive wave pattern continuing for the mid-range forecast period.

For those hungry for more, a weak upper-level trough may produce some snow showers by Wednesday – though the ensemble plumes suggest extremely limited accumulations through the period. Models suggest upper-level ridging will dominate, and thus any shortwave trough will exist under generally unfavorable conditions for appreciable snowfall. Have no fear! Though the week ahead looks relatively dry, the pattern remains progressive in the models for as far as we can reliably see.

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