Holiday Weekend Snow

Posted Wednesday, November 21st, 2018 by Taylor McCorkle

Happy Wednesday and day-before-Thanksgiving to all our readers!  Whether you’re having Thanksgiving dinner with family, or celebrating with friends, we are thankful you are trusting us to provide a holiday week snow forecast.

Opening date update: Snowbird announced that they will now be open for the season on November 24.

Current Conditions:
Today, the weather could not be more perfect for the pre-holiday travel frenzy.. I say this as I write this blog post from the Salt Lake City airport, which as usual, is running like a well-oiled machine.  Aside from the lingering inversion that Pete mentioned yesterday, sunny skies and high temperatures in the low 50’s are about as good as it gets for late November in the valley.

While it feels absolutely beautiful outside, a pollutant called PM 2.5 is building up in the valley, creating poor air quality conditions. PM 2.5 is a pollutant who’s diameter is 2.5 microns or smaller, and is dangerous in large quantities because its small size allows it to actually permeate the lungs. This pollutant is what is causing the valley to appear hazy, reducing visibility.  The current measurements of PM 2.5 are nearing the ambient air quality standard limit of 35 micrograms of particulate matter per cubic meter of air.  It is best to avoid exercising outdoors or spending prolonged periods outside when air quality is poor.

24-hour PM 2.5 trend at the University of Utah via mesowest.utah.edu
24-hour PM 2.5 trend at the University of Utah via mesowest.utah.edu

Timelapse from the William Browning Building looking south into the Salt Lake Valley

Short Term Forecast – Thursday through Saturday afternoon:
Ideal traveling weather today will give way to unsettled weather as the week progresses.  A series of two troughs will bring precipitation to the valleys and mountains of northern Utah through Saturday.

Trough 1: Conditions will begin to deteriorate by midday Thursday as the first upper-level trough from the Pacific moves into the Intermountain west. This trough is not associated with a particularly cold airmass, with the freezing level likely hovering around 6000′.  This means the valley floor will mainly see liquid or perhaps mixed phase precipitation depending on the strength of the cold front.  The benches and higher elevations are expected to see accumulating snow.  While not extremely cold, this trough has a sufficient amount of moisture associated with it, given its Pacific origins.  Precipitation should last into the evening hours on Thursday for low elevations, while the mountain precipitation could continue into the morning hours on Friday thanks to orographic enhancement from the WNW flow.

Trough 2: The second and stronger trough will make its way into the area on Friday.  This trough will dive into northern Utah from the northwest bringing with it colder temperatures and more available moisture than the first disturbance.  Precipitation is expected to be widespread with freezing levels crashing to the valley floor.  The timing of fronts and moisture is shown below in the time-height diagram using the 12 UTC GFS forecast. Note that time progresses from left to right. Darker greens (darker yellows) represent higher (lower) values of relative humidity

Time-Height cross section of wind and moisture produced by the GFS run initialized at 12 UTC; via weather.utah.edu
Time-Height cross section of wind and moisture produced by the GFS run initialized at 12 UTC; via weather.utah.edu

Pre-frontal precipitation will arrive Friday in the early evening, with the freezing level around ~7500′ thanks to the warm air advection at mid-levels. The second cold front will finally arrive on Saturday, in the early morning hours, dropping the freezing level to the valley floor.  Keep in mind that this timing may change over the next day or so, give or take a few hours.  After the passage of the front, northwest flow will linger for the next 12-24 hours, giving the mountains, especially the Cottonwoods, a shot at bonus-time snow.

Ok, so how much snow are we going to see?
Alas, what you all came here for.. Now we know what we are working with for the next few days, so how much of the good stuff will we get?
The models still have a relatively large spread for forecast totals through Saturday, with the GFS 13 km being more bullish and the ECMWF going conservative if you consider that they are using a 10:1 precipitation ratio.  10:1 means 10 inches of snow for each inch of liquid precipitation.

Snow totals will become more refined over the next two days, but through Saturday night, I would expect the following storm total accumulations:
– Upper Cottonwoods (Alta, Snowbird, Brighton, Solitude): 16-24″
– Ogden area (Snowbasin, Nordic Valley): 8-12″
– Sundance: 6-10″

ECMWF snow total through Saturday evening via models.weatherbell.com
ECMWF snow total through Saturday evening via models.weatherbell.com

All in all, things are shaping up for a nice base-building holiday storm.  Check back with us tomorrow for the latest!

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