Off/On Snow for the Nrn UT and a big storm for Srn UT

TLDR:  Off/On light northern UT mountain snow showers through Fri.  Expect 3-6” per day.  Another possible northern UT storm Sun-Mon.  Southern UT will get a significant storm with 18-30” for Brian Head/Eagle Point from Wed morning – Fri morning and 14-20” for the La Sal area Wed night-Fri morning.

Skiing conditions in the Wasatch are amazing right now with cold temperatures, clouds keeping the sun from impacting the recent snowfall, and a few passing mountain snow showers to give a refresh.  Any caveats?  You want to be above last Thu’s rain crust, or roughly 7.5K to 8.0K feet.  Anonymous sources confirmed the above report in the Davis County backcountry today…or did they since they also reported not seeing another soul and did not take any photos?

The aforementioned “few passing snow showers” are the result of relatively moist northwest flow amid passing short wave troughs.  Some of these appear to be enhanced by the Great Salt Lake as they pass overhead (see below image and note precipitation upstream of the lake but stronger precipitation over and downstream).  It was showers like these that dropped ~2” at Alta from 3-4pm today and ~1-2” at Snowbasin from 10-11am.  In both cases that appears to match the amount that fell during the remainder of the day.

Salt Lake City radar image valid 19 Feb 6:13pm
Salt Lake City radar image valid 19 Feb 6:13pm

Rest of the Week:  Northern Utah can expect these showers to continue and roughly 3-6” per 24-hour period to fall through Sat.  Thursday during the day should do a little better than that.  The big news for across the state is Southern Utah will get hit with a strong low-pressure system.  Precipitation will begin Wed morning for the southwest mountains and later in the day for the south-central and south-eastern mountains.  Totals for Brian Head look very impressive, with 20-28” expected by that time (maybe more if everything comes together).  Central and eastern areas should see 1-2”.

Extended Period:  Some weather prediction models have a storm skirting to our north late Sat through Mon with decent snowfall for northern UT.  However, there is a decent amount of uncertainty right now with this system so check back soon to see how strong we think it will be and if it is still on track to skirt or hit northern UT.  See below for some of the possibilities.

Image courtesy of the weather.utah.edu
Image courtesy of the weather.utah.edu

Winding down but not in a bad way

It has been a good week for the mountains for sure. There were a few smaller storms and a few bigger ones, and the holiday weekend has seen mostly fair weather with some showers adding a few inches to the total. Alta-Collins has made it up to whopping 134″ of depth. That’s 11 feet and 2 inches or 3.4 meters.

For a while now we’ve been able to see a big storm on the horizon to look forward to. Right now that isn’t the case. There are hints of something next Monday, but that’s far away and doesn’t seem all that impressive. But it’s not like we’re having an early spring. The weather pattern we’re getting into is characterized by persistent troughing. The atmosphere can be thought of as a composition of a lot of waves. Some of these waves move quickly around the Earth, others move slow as molasses, and others even go backwards. The fun weather tends to happen at the transition points between troughs and ridges of the larger waves. Have a look at how the waves will be tomorrow:

GFS 500 hPa forecast for tomorrow morning
GFS 500 hPa forecast for tomorrow morning

This is a representation of the waves in the atmosphere halfway up (and green shading for humidity). Notice that Utah is right in the middle of a large and deep trough. The winds are weak and the jet stream is well to our south. Troughs can be like ridges in that they can be a bit stagnant. However, they are significantly better than ridges for winter enthusiast for a few reasons. First is that we’re north of the jet stream and it’s cold. Second is that there’s a lot more (relative) humidity around. Third is that cold air above 40°N land in late February can be a recipe for popcorn showers.

These ingredients together mean that I think it’s going to be a good week. It’ll give the snowpack a chance to settle, and the clouds will keep that late February sun at bay (it’s as strong today as it is October 24th). Plus we’ll have weak showers that keep thing fresh all week long. Below is an ensemble forecast for the Cottonwoods, and it shows how we’ll get an inch or two several times this week just from pop-up showers and weak disturbances (the CMC members in this case is out to lunch and should be ignored). One of the troughs we’re under is one of the really slow ones, so it’ll be a while until we’re back into a super stormy pattern. But I’ll take this over a ridge any day.

Ensemble forecast via weather.utah.edu
Ensemble forecast via weather.utah.edu

Snowfall at Utah Ski Resorts is Heaviest Tonight

There’s no secret about it–western US resorts continue to be the recipients of a barrage of heavy (and just a little breezy…) snowfall events.

Tonight’s forecast is a case in point. In short, the snowfall forecast for the upcoming storm has been pretty consistent. I’d recommend you read yesterday’s discussion about some of the storm details.


Snowfall

For what it’s worth, here’s my toss in the ring for accumulations through Saturday morning, along with another list regarding the remainder of Saturday:

Snowfall forecast at major N. Utah resorts. photo courtesy alta.com
Snowfall forecast at major N. Utah resorts. photo courtesy alta.com

As you can see, the bulk of the storm’s impact will occur overnight before the blackout crowds emerge up the canyons. According to SREF (probabilistic forecast), the most substantial precipitation rates should occur between about 7 PM on Friday and 12 AM Saturday. During this time, many resorts could see an inch per hour, perhaps locally higher rates.

snowfall rate
Today’s 15Z downscaled SREF, showing 3-hour total precipitation at Alta-Collins. Box plots represent the range of possibility at each period: red ticks are the median forecast, top and bottom edges of the box are upper and lower quartiles, and lines display the complete range of values excluding outliers. Refer to this to convert from UTC to local time. Briefly, 16/06Z is equivalent to Friday the 15th at 11 PM MT. Courtesy weather.utah.edu

Wind and Temperature

Note that the difference between this storm and other storms this week is temperature; Wednesday and Thursday were warm, and temperatures tonight dip relatively cold at all elevations. For example, as I’m writing this (~3 PM Friday) temps at Alta are close to a balmy 28 degrees F.

alta temperature
Alta-Guardhouse temperature and moisture time series, ending at 3 PM MT. The red line is the temperature curve and follows the left-side axis labeled in degrees Fahrenheit. Time is in UTC. The latest temperature (22 UTC = 3 PM MT) record was 27.7 F. Courtesy mesowest.utah.edu

By comparison, the NWS forecasts at Alta project 25 degrees just before the front passes around 6 PM, followed by 14 F by midnight, 11 F by sunrise, then a Saturday high of 19 F. To no surprise, snowfall is effectively greater for every unit of snow-water equivalence when temperatures stay substantially below the freezing point. In other words, more bang (light, fluffy powder) for your buck.

Fortunately, winds are tamer during this storm compared to the early-week storm. If you’d be hanging out on some peak in the central Wasatch overnight, you might experience 25-35 mph winds. However, these die down to between 10 and 15 mph by sunrise Saturday. Naturally, wind speeds at lower elevations will be milder for Saturday skiers.


After Saturday

As Tyler alluded to yesterday, the local weather should relax by Saturday evening. However, we aren’t looking at another ridge set-up to break the pattern. Instead, we’ll be open to light snow showers beyond Saturday underneath an upper-level trough and the amplified polar jet. As a result, and over the next week, the interior west can expect relatively cold temperatures and some opportunities for quick-hitting storms.

jet stream gif
12Z GFS 1.5-5.5 day 250 mbar wind speed forecast. Wind speed shading reveals upper-level jets (purple/red shading). I’m using these jets to reveal the location of the polar jet stream. We can locate the upper-level trough where the jet follows a more-or-less “U” shape; in this case, the trough centers over the western US. Courtesy tropicaltidbits.com

At this point, forecasts deem potential mid-week storms as nothing major. Obviously, that can change as we turn the weekend corner. Stay tuned.

-marcel

More Snow and Cooler Temperatures Coming

TLDR:  More snow tonight (see totals below) with snow levels around 7500 ft but lowering. A small break on Fri with a strong cold front and mountain/valley snow Fri evening, bringing another 8-12″ by Sat morning and snow showers through Sun morning.  Read on for details.

We’ve been in warm, wet southwest flow over northern Utah today.  For some visual proof, check out the orographic (mountain induced) clouds that formed due to air rising up the southwest side of the Lone Peak area.  As an added bonus, we even got some breaking mountain waves (likely “Kelvin-Helmholtz” waves due to the presence of wind shear) over Lone Peak this morning.

Looking south Thu morning from University of Utah. Image courtesy of MesoWest cameras and Brian Blaylock at http://home.chpc.utah.edu/~u0553130/Camera_Display/wbbs.html
Looking south Thu morning from University of Utah.
Image courtesy of MesoWest cameras and Brian Blaylock at http://home.chpc.utah.edu/~u0553130/Camera_Display/wbbs.html

For Backcountry or “Sidecountry” Users (This does not apply to inbounds at ski areas or near highways)

THE FOREST SERVICE UTAH AVALANCHE CENTER IN SALT LAKE CITY HAS ISSUED A BACKCOUNTRY AVALANCHE WARNING THROUGH 6AM FRIDAY FOR THE WASATCH, BEAR RIVER, AND WESTERN UINTA RANGE. CONSULT WWW.UTAHAVALANCHECENTER.ORG FOR MORE DETAILS

Tonight/Tomorrow:  As of 4pm temperatures are pretty warm with many mountain stations above freezing (especially those below 8,000 feet).  But, snow level corresponds to wet bulb zero (level where the wetbulb ~ 32?F/0?C) and snow levels appear to be ~7,500 feet.  Luckily, the snow level will lower through this evening as cooler air comes in.  The recent snow to this point has been dense/heavy but will also get less dense  overnight tonight.  Winds have been very strong and will continue to be strong through tomorrow evening.  Expect the following amounts (above 7,500 ft) by mid-morning tomorrow:

  • Salt Lake Area 8-12″
  • Pow Mow: 10-12″
  • Snowbasin: 6-8″
  • Sundance: 7-9″
  • Beaver Mountain 4-6″

Friday Night / Weekend:  Friday will dry out a little until ~ 5pm when a cold front and associated snow (mountain/valley) will arrive.  Expect periods of heavy snow (and strong winds) Friday evening with an additional 8-12” falling across northern UT mountains from the cold front passage until resort openings on Sat.  Scattered snow showers will continue off/on Saturday with another 5-10” by mid-day Sunday.  After that we dry out with no significant chance of snow.  See below for a summary:

-Tyler

NAEFS Downscaled Ensemble Guidance for Alta, Collins. Courtesy of the University of Utah http://weather.utah.edu/index.php?runcode=2019021412&t=naefs&d=PL&r=CLN
NAEFS Downscaled Ensemble Guidance for Alta, Collins. Courtesy of the University of Utah http://weather.utah.edu/index.php?runcode=2019021412&t=naefs&d=PL&r=CLN

 

Just tons of snow!

TLDR: A series of storm systems are on the way with A LOT of snow forecasted for the mountains. A winter storm is currently impacting the state of Utah with heavy, wet mountain snow and valley rain. A cold front will barrel through Friday with heavy snowfall rates during the evening, and snow showers will linger for a few days afterward. By Sunday, the mountains should be measuring snowfall in FEET rather than inches.


 Avalanche Danger and Winter Storm Warning:

First of all there is an AVALANCHE WATCH effective now through Thursday morning, at which time it is expected to transition to an AVALANCHE WARNING. There also is a Winter Storm Warning in effect from now through Friday morning at 5Am for the northern Wasatch Mountains as 1-2+ feet of snow and dangerous driving conditions are expected. Be VERY careful in the backcountry the next couple of days.


Wednesday – Thursday:

A low pressure system off the coast of California and the “coupling” of the polar and subtropical jets have brought a lot of moisture into the West and Intermountain West (see water vapor imagery below from http://weathernerds.org. Already today, we have received a fair amount of snow in the mountains. As of 4PM, Alta has reported 6″ of snow, and Brighton has reported 3″. During the remainder of this evening through Thursday we can expect heavy, wet snow to fall in the mountains, with some of the lower mountain elevations switching to a rain/snow mix at some point during the night. Keep in mind that with some near-surface cold pools in place, some regions at lower elevations may not see a transition to rain/snow at all. Nevertheless, this wet, heavy snow (along with strong, gusty winds) is the reason why avalanche danger will be high over the next couple of days.

In the early hours Thursday morning, heavy snow should taper off a little bit. However, mountain snow is unlikely to stop altogether. During the late afternoon on Thursday, though, the remnants of the closed low currently off the California coast will move through Utah as an open wave, and heavier snow showers will resume (likely around 2-4PM). This heavier activity should last through the late evening (~midnight). Through Thursday evening, we can expect the following snow totals in the higher elevations:

  • Beaver Mountain: 15-20″
  • Snowbasin: 15-20″
  • Pow Mow: 11-16″
  • Park City Area: 10-15″
  • Cottonwoods: 18-23″
GOES 17 water vapor imagery showing a low pressure center off the coast of California, and a large stream of moisture coming in from the tropics. Courtesy: Weathernerds.org
GOES 17 water vapor imagery showing a low pressure center off the coast of California, and a large stream of moisture coming in from the tropics. Courtesy: Weathernerds.org

Friday:

During the day Friday, conditions should be cloudy but relatively calm. However, most models are showing a cold front pushing through our area Friday evening, with very heavy snow for a short period within the baroclinic zone. So, for at least an hour or two Friday evening, we might see some pretty impressive snowfall rates in the mountains (and valleys too), especially given that the airmass will be colder and allow for better snow ratios.

GFS forecast radar precipitation type and 700 mb frontogenesis. for Friday afternoon/evening. Note the dark blue shaded region (heavy snow) is associated with strong frontogenesis within the baroclinic zone as the cold front pushes through. Courtesy: weathernerds.org
GFS forecast radar precipitation type and 700 mb frontogenesis. for Friday afternoon/evening. Note the dark blue shaded region (heavy snow) is associated with strong frontogenesis within the baroclinic zone as the cold front pushes through. Courtesy: weathernerds.org

The Weekend and Beyond:

After the front passes, things will “dry out” a bit. However, we’ll still see plenty of mountain snow showers throughout the day on Saturday and Sunday as we will still be under the influence of a long wave trough that doesn’t seem like it wants to move anytime soon (we might be under the long wave trough through the end of the month). Through Sunday, snow totals should be VERY impressive. The GFS currently is forecasting over four feet, yes FOUR FEET of snow in the upper Cottonwoods from now to the end of the weekend! While that may be a little bit of an overzealous forecast and might need to be downscaled, this is for sure; there will be a TON of snow in the mountains over the next several days! Here’s a pretty cool look at what the deterministic GFS model is forecasting for snowfall totals over the next 72 hours (through Saturday afternoon):

GFS 72 hour total snowfall accumulation forecast for northern Utah. Courtesy: weathernerds.org
GFS 72 hour total snowfall accumulation forecast for northern Utah from now through Saturday afternoon. Courtesy: weathernerds.org

One other interesting note… as of now, we are well above our median accumulated snow water equivalent (SWE) for the year in the mountains according to data from https://www.nrcs.usda.gov/. The black line below represents the current (“2019”) season, and is compared to the median, minimum and maximum SWE over a 30 year timespan.

Snowbird snow water equivalent for this season/2019 (black line) compared to the median, minimum and maximum. As you can see, we are currently above the median and on a very good pace to finish the season strong with higher than normal SWE. Courtesy: https://www.nrcs.usda.gov/
Snowbird snow water equivalent for this season/2019 (black line) compared to the median (green line), minimum (red line) and maximum (purple line). As you can see, we are currently above the median and on a very good pace to finish the season strong with higher than normal SWE. Courtesy: https://www.nrcs.usda.gov/

Enjoy all the powder up there in the mountains over the next several days! More importantly, though, stay safe (especially those of you going out to the backcountry!). Check back tomorrow for more details on our upcoming storms.

-Pete

Snow for your Valentine

Yesterday’s cold front passage brought ample snowfall from the North-Central Wasatch all the way down to Southern Utah. Most resorts south of Ogden (sorry PowMow and Snowbasin) got 10+ inches of the good stuff, refreshing our ever-deepening base depths.  Here are some 24- and 72-hour storm totals courtesy of OnTheSnow

Utah resort storm totals, courtesy of onthesnow.com
Utah resort storm totals and base depths, courtesy of onthesnow.com 

 

The recent snowfall has put our snow water equivalent values well above normal for this time of year.. A welcome change from the past few seasons, especially last year which was abysmal to say the least.

Snow Water Equivalent percentage of normal for basins in Utah, plot via www.wcc.nrcs.usda.gov
Snow Water Equivalent percentage of normal for basins in Utah, plot via www.wcc.nrcs.usda.gov

Short-Term Forecast (Monday – Thursday):

The next few days look relatively calm over the state of Utah as a ridge builds in.  We should be experiencing relatively quiescent weather through Wednesday evening, which is when our next system will be moving into the area. The plot below shows the 500 mb heights and vorticity valid Thursday (Valentine’s Day!) at noon.  Note the area of red and yellow vorticity shading over Utah, indicating a strong system.

500 mb heights and vorticity valid Wednesday evening. Plot courtesy of tropicaltidbits.com
500 mb heights and vorticity valid Thursday at noon. Plot courtesy of tropicaltidbits.com

This cold system should contain ample moisture and will result in frozen precipitation at all elevations. Timing of the frontal passage currently looks poised to move through Northern Utah around 5 pm on Wednesday evening (shown as Thursday 00 UTC on plot below).  The trough is forecasted pass to our south, which will bring strong southerly winds to the area.

NAM 12 km time-height cross section via weather.utah.eduNAM 12 km time-height cross section via weather.utah.edu

According to the most recent model guidance, precipitation should continue in the mountains with intermittent showers into the weekend.  While we are getting out of our range of confident forecasting, it looks good for another fantastic holiday weekend.. Here are some too-early snow and liquid precipitation forecasts from the NAEFS ensemble

NAEFS liquid and snow accumulations at Alta Collins via weather.utah.edu
NAEFS liquid and snow accumulations at Alta Collins via weather.utah.edu

More details tomorrow!

-Taylor

Storms Lined Up

Today turned out to be a bit of a surprise powder day at the resorts. 8-12″ were reported in the Upper Cottonwoods. After a break in precipitation during the day, an intense front entered the region just a couple hours ago. It’s been absolutely dumping with strong winds at my place in SLC.

Snow should continue through the evening and begin to taper off during the overnight hours. Expect totals of 8-14″ with up to 18″ in the Upper Cottonwoods. Tomorrow will be another powder day. Expect early morning canyon closures before the resorts open.

We’ll have a brief break from tomorrow through Wednesday morning. The next system will being to impact Utah during the day Wednesday. The details aren’t iron out with this system yet, but it looks like another 1-2 ft + is a good bet.

NAEFSPL_CLN2019021012F168

There will be little rest for the weary as yet another system is looking likely for the weekend. We are in one of the better patterns in recent memory and there are no signs of it ending anytime soon. Get out and enjoy the powder and stayed tuned for details on the upcoming storms.

Snow is back already! Active period to last awhile

A weakening low pressure system currently over the Intermountain West is providing cloudy conditions over Utah’s mountains today with a bit of snowfall as well. Only up to a couple of inches of snow are forecast for today through this evening, though, as the decaying trough ejects out of our area.

View from Snowbasin Resort this afternoon. It's been mostly cloudy with snow showers for most of the day so far.
View from Snowbasin Resort this afternoon. It’s been mostly cloudy with snow showers for most of the day so far. Courtesy: snowbasin.com

In the meantime, a Winter Weather Advisory has been issued for the Wasatch Mountains from 12Pm Sunday until 4AM Monday morning. A Winter Weather advisory for snow means that periods of snow can cause difficulties traveling on roads with poor visibility. From the National Weather Service office in Salt Lake City:

WinterWxAdv_9 Feb

As a side note, there also is a Winter Weather Advisory for the valleys (and a good portion of the state of Utah).


Sunday and Monday

It should be relatively quiet Sunday morning through the early afternoon as shortwave ridging briefly moves through. There could be a few passing snow showers, but little accumulation is expected during that time. The real fun begins on Sunday afternoon/evening as a cold front associated with an upper low moves through Utah. Between 2-4PM, heavier snow showers should develop just ahead of and along the cold front as is moves into northern and central Utah. 700 mb temperatures (seen below) will be plenty cold for precipitation to be all snow, even in the valleys.

ECMWF 700 mb temperatures at 00Z 11 Feb (Sunday evening) around the time heavier snow will move into the area. Note that temperatures are at least as cold as -11 Celsius, indicating that everything that falls will be snow at all levels, including the valley floors.
ECMWF 700 mb temperatures at 00Z 11 Feb (Sunday evening) around the time heavier snow will move into the area. Note that temperatures are at least as cold as -11 Celsius, indicating that all precipitation that falls will be snow at all levels, including the valley floors. Courtesy: models.weatherbell.com

HRRR forecast analysis shows heavy snow along a convective line associated with the baroclinic zone (area in which cold/dense air is separated from warmer/less dense air) moving through Utah.

HRRR forecast snow/rain radar from 14Z 10 Feb (Sunday morning) through 06Z 11 Feb (Sunday night). Since temperatures will be cold at middle and lower levels, everything that falls should be snow, except for the far SW portion of the state.
HRRR forecast snow/rain radar from 14Z 10 Feb (Sunday morning) through 06Z 11 Feb (Sunday night). Since temperatures will be cold at middle and lower levels, everything that falls should be snow, except for the far SW portion of the state. Courtesy: weathernerds.org

Another look at the HRRR forecast radar without the rain/snow mask reveals relatively strong reflectivity values (>25 dBz) as the line of snow moves through. Contour lines of frontogenesis at 700 mb (crest level) show that these stronger reflectivities are associated with the cold front.

HRRR forecast radar reflectivity and frontogenesis at 700 mb from 14Z 10 Feb (Sunday morning) through 06Z 11 Feb (Sunday night) showing heavy precipitation moving through Utah throughout the day. Since temperatures will be cold at middle and lower levels, everything that falls should be snow, except for the far SW portion of the state. Also note that the heaviest precipitation will be along a baroclinic zone (cold front) at 700 mb noted by the purple contour lines moving along with the higher reflectivity values.
HRRR forecast radar reflectivity (shaded contours) and frontogenesis (unshaded purple contours) at 700 mb from 14Z 10 Feb (Sunday morning) through 06Z 11 Feb (Sunday night) showing heavy precipitation moving through Utah throughout the day. Since temperatures will be cold at middle and lower levels, everything that falls should be snow, except for the far SW portion of the state. Also note that the heaviest precipitation will be along a baroclinic zone (cold front) at 700 mb noted by the purple contour lines moving along with the higher reflectivity values. Courtesy: weathernerds.org

Snow showers should linger behind the low pressure system as a small warm air slowly moves through under a middle level cold pool. This instability (warm air under cold air) should allow for additional accumulations in the mountains and parts of the northern Utah valleys. So how much snow will we get? Here’s a breakdown of what we can expect as of right now through Monday evening:

  • Beaver Mountain: 15-20″
  • Powder Mountain: 20-25″
  • Snowbasin: 16-21″
  • Park City area: 10-15″
  • Cottonwoods: 17-22″
  • Sundance: 7-12″
  • Brian Head: 8-13″

Long Range

After next Monday, things look very active still. There is a lot of model agreement on another strong winter storm with a ton of moisture arriving next Wednesday into Thursday. Furthermore, the overall pattern for the second half of February looks very favorable for storms to pass through our region as models forecast us to be in a generally trough-like pattern. See the 500 mb geopotential height and anomalies animation below showing that the West and Intermountain West will generally have troughs passing through the area for the foreseeable future.

GFS forecast 500 mb geopotential height and normalized anomalies between next Tuesday and two weeks from today. This shows that as of right now the GFS is forecasting for Utah to be under generally "troughy" pattern. If this were to hold up, it could be great for winter storm activity for a long while.
GFS forecast 500 mb geopotential height and normalized anomalies between next Tuesday and two weeks from today. Blue contour shading indicates that as of right now the GFS is forecasting for Utah to be under a generally trough-like pattern. If this were to hold up, it could be great for winter storm activity for a long while. Courtesy: tropicaltidbits.com

Let’s hope we make good use of the “troughy” pattern and keep the winter storm train rolling! Check back tomorrow for an update on forecast storm totals for the storm Sunday/Monday, and we’ll keep you up to date on the potentially big storm Wednesday/Thursday.

-Pete

Snow Just Keeps Coming

Sunny skies returned to northern Utah today after a chilly start to the morning. Most valley locations met high temperatures in the 30s this afternoon, while warming at higher elevations was aided by warm air advection (but not really that warm) this afternoon as southerly winds picked up. This afternoon, Mt. Baldy warmed up to 6 F compared to a temperature of -6 F about 24 hours ago. Sustained winds up at Mt. Baldy are now around 40 mph with gusts to about 60 mph as of 3pm.

The sun will not last for much longer though as more storms are moving in over the weekend. On the GOES-17 pre-operational satellite loop below, we can see the components that will bring change to our weather this weekend, as highlighted well in Marcel’s post yesterday. There is a small circulation off the coast of California as well as what will become a much larger system working westward and southward out of British Columbia. Over the next few days the former will wrap around the latter and be ejected into the Intermountain West and approach Utah on Saturday.  The larger system will follow and bring impacts to northern Utah on Sunday afternoon.

True-color GOES-17 pre-operational satellite loop shows a circulation off of the California coast which will move into the Intermountain West on Saturday. A less distinguishable system moving out to sea off of the SW corner of British Columbia will strengthen in the coming days and impact northern Utah beginning Sunday.
True-color GOES-17 pre-operational satellite loop shows a circulation off of the California coast which will move into the Intermountain West on Saturday. A less distinguishable system moving out to sea off of the SW corner of British Columbia will strengthen in the coming days and impact northern Utah beginning Sunday. (College of Dupage – click for current view).

Clouds will filter in this evening and overnight, and snow should begin midday tomorrow at higher elevations. It will be cold enough to snow at all elevations tomorrow but the higher snowfall amounts will be confined to the mountains. The highest intensity of snowfall is expected in the late afternoon to early evening hours as moisture moves in.

Snow totals (Saturday noon through early Sunday morning):

  • Cottonwoods: 4-8″
  • Rest of Wasatch: 2-5″
  • Wasatch Front : generally less than 1″

We could see a brief lull in precipitation Sunday morning between storm segments, but snow will pick back up Sunday afternoon as a cold front moves through (looking to be close to 5pm local time on Sunday). Snow will continue overnight into Monday along with cold air similar to what we have experienced the past couple of days. Storminess looks to continue through the following week or so as we make our way into another holiday weekend.

No real end in sight for our storminess! Cool temperatures and precipitation looks to continue over the next 10-14 days.  (wetterzentrale.de)
No real end in sight for our storminess! Cool temperatures and precipitation looks to continue over the next 10-14 days based on the 18Z GEFS ensembles. (wetterzentrale.de)

Check back with us tomorrow for a more detailed look at expected snowfall totals on Sunday and into Monday. Be safe on and off the slopes this weekend with the new snow and be aware of avalanche conditions!

-Lucas

Upcoming Snowy Weekend and an Arctic Freeze

TLDR: Expect two back-to-back storms, the weaker storm hits mountains Saturday and the other dumps snow Sunday through Monday at all elevations.

We’re sitting pretty given the torrent of storms and arctic blasts to hit resorts over the past few days. To that regard, I’ve gathered some statistics about the snowfall since Sunday and the current state of the snowpack (just a handful of locations):

storm totals
Summary data at a selection of Wasatch ski resorts. Storm totals cover the period between Sunday evening February 3rd until early Thursday morning February 7th. [These use the NWS SLC’s preliminary precipitation reports, linked here. Also, for current snow depth, I used the MesoWest station data archive. For percent normal snowpack, I used the Colorado River Basin Forecast Center’s archived data. These are percentages of normal snow-water equivalent (SWE), not percentages of normal snow depth. Here, “normal” SWE means average Feb. 7 SWE]
Setup for this weekend

To summarize, an arctic vortex and a highly amplified jet stream interact to bring another strong storm to UT by Sunday.

Why are we getting this storm, and why are we in an “active pattern” for storms? These storm periods exist by nature of a weak, split, and highly-amplified jet stream.

Some people attribute this waviness of the jet stream to a few intraseasonal cycles. The Arctic Oscillation (AO), for example, results in a shift between a highly- and slightly-amplified jet stream. Perhaps the AO explains the currently frequent storms over the western US; in fact, the AO is now in its weak/highly-amplified negative phase. Just an idea.

Event Components

Given the setup, we can understand the Sunday storm’s two components. The first component is a shallow trough, traveling eastward across the North Pacific. The second part is a cold-core low whirling around a “daughter” of the arctic vortex, which is centered over northeast Canada.

vortex
12Z GFS Potential Vorticity analysis valid at 5 AM MT Thursday, February 7, 2019. Components #1 and #2 are annotated. Potential vorticity (PV) generally increases toward the northern side of the jet stream, so PV fields are useful for examining arctic air. Here, dark red colors generally represent arctic air. Courtesy tropicaltidbits.com

As the first component travels eastward, it interacts with the second, and both troughs dip southward along the west coast. Next, the second component becomes the main trough and begins to kick the first out into the western US.

vortex gif
12-18Z GFS PV valid from 5 AM MT Thursday, February 7 to 5 AM MT Saturday, February 9. Courtesy tropicaltidbits.com
Event Timing

You can expect, then a sort of one-two punch in the coming days. The first storm is delivered by the first component of this event and starts to impact Northern Utah Saturday daytime. The second component brings precipitation and an arctic blast Sunday daytime. With that, here’s a look at that timing at Alta-Collins station, just beware that precipitation totals will change before the storms hit:

QPF
12Z NAEFS QPF and Snowfall forecast for Alta-Collins station. Annotated are components #1 and #2 of the upcoming storm series. Courtesy weather.utah.edu

Lastly, you can expect the first storm to be weaker than the second. Both should impact the mountains, but only the second will impact the lowest elevations.

Tomorrow, we’ll cover storm details like temperatures, snowfall totals, and their uncertainties. Until then get hyped! More snow is on the way …

-Marcel