Four Straight Days of Snow!

Posted Tuesday, March 5th, 2019 by usw_admin

TLDR: It is going to be a very snow rest of the work week in the mountains as an “atmospheric river” moves through into region…expect a lot of valley rain/snow as well. Two main systems will impact the region; one begins tonight through Wednesday, and the other Friday evening. From now through early Saturday morning, there could be up to 3-4 feet of snow across most Northern Utah ski locations.

ecmwf_tsnow_slc_17
ECMWF forecast snow totals from now through Saturday morning. Note this is the 10:1 ratio forecast, which means it does not account for differences in liquid water content in snow. Generally the amount of liquid water content in snow becomes less (drier) as a storm evolves through our area, meaning we could see even MORE than what is showing on this map. A “Kuchera” algorithm for total forecast snow that does take into account the evolution of liquid water content over time is shown later in this post. Courtesy: models.weatherbell.com

Today and Tonight:

First of all, a Winter Weather Advisory has been issued for the Wasatch Mountains throughout the state of Utah from 9 PM tonight through 10 Am Thursday morning for 6-18″ of snow and adverse driving conditions. Below is a clip of the advisory from the National Weather Service in Salt Lake City:

Winter driving conditions are expected,
  especially above eight thousand feet, though at times as low as
  seven thousand feet. Gusty winds may cause blowing and drifting
  snow, locally reducing visibilities to near zero.

Mostly cloudy skies and mild temperatures have been the theme of the day as moisture from a weakening low pressure system off the coast of California spills over the ridge that’s currently sitting on top of us (see water vapor imagery from weathernerds.org below).

Water vapor imagery from the GOES-17 satellite showing a lot of mid-upper level moisture moving into the West and Intermountain West. Courtesy: weathernerds.org
Water vapor imagery from the GOES-17 satellite showing a lot of mid-upper level moisture moving into the West and Intermountain West. Courtesy: weathernerds.org

That ridge will gradually weaken and move off to the east throughout the evening hours, during which precipitation should begin (already has begun in some mountain locations) as a weak short wave trough moves through. Snow levels will be high overnight (~7,000 ft) as wet bulb zero temperatures will be up near 750 hPa (~8,100 ft).

NAM forecast sounding for tonight ~11PM showing elevated freezing levels. Snow levels will be ~7,000 ft and above through the night as warm, moist air associated with the atmospheric river or "AR" event moves into our area. Courtesy: weathernerds.org
NAM12km forecast sounding for tonight ~11 PM showing elevated freezing levels. Snow levels will be ~7,000 ft and above through the night as warm, moist air associated with the atmospheric river or “AR” event moves into our area. Courtesy: weathernerds.org

From Snowbasin north, snow should taper off almost completely by 5AM Wednesday morning. In the Salt Lake Valley, expect rain overnight to last only a few hours (~11 PM – 2 AM). Through 9 AM tomorrow morning, I would expect the following snow totals:

  • Beaver/Powder/Snowbasin: 2-5″
  • Park City Area: 2-5″
  • Cottonwoods: 4-7″
  • Sundance: 1-2″

Wednesday:

The early morning hours on Wednesday should keep ski areas north of Salt Lake City pretty dry, while light/moderate snow continues in Park City area/Cottonwoods and south. During the afternoon and evening hours, though, snow will again begin falling over all Northern Utah ski locations, and snow rates will pick up somewhat over areas where it was already snowing in the morning as another short wave trough moves into our area. This short wave trough will move through during the day, and exit by late evening/early Thursday morning hours. However, snow should continue through the night into Thursday morning as low level forcing due to speed convergence and slight frontogenesis keep the action rolling (especially the Cottonwoods and north).  Although precipitation rates will not be particularly high throughout the day and evening on Wednesday, there still should be another decent accumulation of snow since temperatures should be dropping slightly through the late afternoon and evening hours, creating a “right-side-up” storm where heavier, wetter snow will create a base under somewhat more dry, powdery snow on top. Here are my current expected snow totals for 9AM Wednesday through 9AM Thursday:

  • Beaver Mountain: 6-10″
  • Powder Mountain: 13-17″
  • Snowbasin: 9-13″
  • Park City Area: 12-16″
  • Cottonwoods: 16-20″
  • Sundance: 11-15″

Thursday:

A very low amplitude short wave ridge will move into Utah Thursday morning, but since there still will be plenty of moisture in the atmosphere, expect intermittent snow showers to continue through the morning, perhaps picking up in intensity during the day with diurnal heating (especially over the Cottonwoods). Another several inches (generally in the 5-10″ range) could fall through the day and evening on Thursday across Northern Utah ski locations. As of right now, the GFS forecast for snow totals from now through Thursday night is pretty impressive, although I think we could see even more than what is forecast in that model. See the below map for details regarding snowfall totals and Northern Utah ski locations.

GFS 72 hour snowfall forecast from now through Friday morning. Courtesy: weathernerds.org
GFS 72 hour snowfall forecast from now through Friday morning. Courtesy: weathernerds.org

Extended Outlook:

Yet another system looks like it could come through during the afternoon and evening on Friday as a meridionally (north-south) elongated short wave trough moves through while pulling in colder air from a low pressure system to the north of us. The valleys could even get in on the action with moderate to heavy snowfall Friday evening! It’s unclear still how much snow we’ll get from that system, but, as of right now, it’s pretty hard to see many breaks in snowfall for most of our Northern Utah ski locations from tonight through Friday night. That’s about four straight days of snow!

 To close this out, let’s take a quick look at the ECMWF Kuchera algorithm forecast for total snowfall across the state of Utah from now through Saturday morning. The Kuchera takes into account the changes in liquid water content as a storm progresses through a given region, so in theory it should be as or more accurate than the simple 10:1 ratio snow total forecasts. In the model run below, it shows that we could get up to almost 40″ of snow for parts of the Cottonwood Canyons. With current model setups across the board, I wouldn’t be surprised if some locations get over four feet!

ECMWF total snowfall forecast through Saturday morning using the Kuchera algorithm. Courtesy: models.weatherbell.com
ECMWF total snowfall forecast through Saturday morning using the Kuchera algorithm. Up to four feet of snowCourtesy: models.weatherbell.com

Remember that a lot of the snow forecasted in this and other current model runs are from systems in which we are still unsure about their exact evolution, and thus it’s definitely not clear how much snow we’ll get. Nevertheless, it’s always fun to look ahead and hope for the best!

Enjoy this awesome week of near continuous snowfall; hopefully some of y’all are able to skip work or school to enjoy it. Be safe and check back tomorrow for more updates on the snow to come!

-Pete

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