Bursts of Snow

Some of the coldest temperatures of the winter have nestled into the Intermountain West over the last 24 hours as our deep weekend storm exited the region. Fortunately, the cooler temps are here to stay for the next several days, and we are expected to see consecutive bursts of snow through the weekend. Finally, it’s feeling like winter!

The somewhat northerly trajectory of the storm track that we experienced last weekend – bringing fluffy snow and cold temperatures- is still persisting. The next bouts of moisture and instability will take similar tracks to our previous storms as we head into the final weekend of what is known as meteorological winter for the northern hemisphere (December 1 -February 28). We are looking at at least two quick hitting storms through Sunday. I’ll mainly focus on the first one that is looking to move into northern Utah on Thursday afternoon.

Somewhat moist south to southwesterly winds will pop up some clouds throughout the day Thursday, especially over the mountains. Light snow is possible tomorrow, but the main accumulations should start in the late afternoon/evening hours as moisture deepens through advection into the lower levels. This should increase snowfall across the mountains overnight and into Friday morning and even allow for some light snow to make it to valley floors, thanks to the cold airmass enveloping us.

A weak cold front early on Friday morning is looking to pass through, switching our wind directions to more northwesterly and bringing in slightly cooler air, which could allow for some more orographic enhancement for locations favored by NW flow (Cottonwoods). The slightly cooler air could also add to the atmospheric instability and kick up some lake effect on Friday morning. Here is a NAM-12km time height section showing some of these features:

Time height section showing 1) Crest level S/SW flow during the day Thursday, 2) Deepening moisture into the evening hours, 3) Wind shift to NW and low level moisture that may lead to additional accumulations from lake effect
Time height section showing 1) Crest level S/SW flow during the day Thursday, 2) Deepening moisture into the evening hours, 3) Wind shift to NW and low level moisture that may lead to additional accumulations from lake effect or enhancement

Through the end of the day Friday, here’s what I’m thinking for snowfall totals:

Park City Resorts: 3-6″

Northern Wasatch Resorts: 2-5″

Cottonwoods: 5-10″*

*the usual “with locally higher amounts” pertains

So, a nice refresh to the snowpack ahead of the weekend is to be expected. Additionally, you can see on the above time height section that more snow is headed our way for Saturday/Sunday. We have potential for some nice accumulations from that storm too! It’s a good time to wax those skis and boards and prepare for another fun weekend in the Wasatch!

-Lucas

 

Cold Stormy Week Ahead

TLDR: In short, the general large-scale setup through mid next week favors frequent cold frontal systems through Northern Utah. It seems that the week will end with a couple moderate orographically-enhanced (high-elevation) precipitation events. More events are likely through next Wednesday.

Hey guys! Given yesterday’s great wrap up of the cold and snowy weekend, I’ll focus mainly on the late-week forecast for this post.

First, a quick recap.


The Recap

As filling as the President’s day storm was, snow-lovers might credit the strength of the storm’s cold front for our big snow, rather than orographic (terrain-induced) effects. As rankings go, this was the 2nd largest snowfall this season at Salt Lake City Airport. In comparison, this doesn’t even make the top 5 storms at Alta-Collins this year. The minimal difference in snowfall between upper and lower elevations tells me that there was minimal orographic-enhancement in the highlands.

The storm left behind lingering lake-effect precipitation (see Taylor’s post for details) and cold temperatures. Tomorrow morning, temperatures could rival some of the coldest temperatures we’ve seen this season (14 degrees F at SLC airport occurred in late December 2017).


cold air mass
GFS 2m temperature anomaly 5PM Friday, February 23, 2018 (blues and dark purples indicate anomalously cold air near the surface). (courtesy tropicaltidbits.com)
Currently…

Furthermore, we seem to be in an isolated period of cold weather and frequent cold frontal systems. Why the sudden change after warm temperatures and few snow storms?

It does have much to do with the Pacific ridge, in two ways: First, the big guy drifted west quite a bit and is currently being held in its position. Why? I wouldn’t be able to answer that, not without wandering into mysterious theory land. Storms traveling eastward will avoid this ridge, moving up and over, then straight down to the western US. In contrast, earlier this month the ridge was further east, pushed storms past us to our northeast, and brought some love to the midwest and northeastern US. Second, the entire continent is under the influence of high amplitude waves. This means that both the ridge to our west and the trough to our east are digging deeply north and south, thus shuttling either very cold arctic air (into western US) or very warm tropical air (eastern US). See the map below for a visualization.

Cold Snowy Set-up
GFS 500 mbar heights (black solid) and relative vorticity (shaded) over North America at 11 AM Tuesday Feb 20th 2018. Note the large amplitude trough axis cutting through UT, and a large amplitude ridge axis far into the Pacific. Labeled are the center of this ridge (“H”), the current storm track (red arrows), and potential late week systems (circled in blue). (courtesy tropicaltidbits.com)

The Forecast

If we maintain this setup, and with some luck, we can anticipate seeing more cold and snowy weather over the next few days. Here’s what the forecast looks like:

I’m seeing at least three events before next Monday, all varying in strength. Furthermore, at least one could be moderately orographically-enhanced. Finally, each system would be cold enough to bring snow to the valley floor.


Wednesday night into Thursday

A weak shortwave (moderate confidence) seems to be a conditionally unstable prefrontal event, and as result should be enhanced as it pushes into the mountains. It’s a weak system, but I think we will see at least a few inches in most ski resorts.

Friday

A cold front will pass through, bringing a few inches of snow (moderate confidence). I think we will see a minimal difference in snowfall between low and high elevations with this storm. I don’t think this will outperform last weekend’s cold front.

Saturday Night into Sunday

Another weak shortwave could pass through during this timeframe (low confidence).


In combination, between Wednesday and Friday, ski resorts might see another 5 to 10 inches of snow (moderate confidence), with locally lower or higher amounts. In short, it’s one of a select few times this year we could expect frequent bursts of pow in the mountains. Enjoy!

Also stay tuned this week as we narrow down the details for each storm. In particular, check Wednesday night-Thursday snowfall forecasts in tomorrow’s post.

Happy skiing,

-marcel

Bonus Time

I think it’s safe to say this storm has not disappointed in terms of producing copious snowfall across the Wasatch Front.
Storm Totals (so far):
Alta: 19″
Snowbird: 20″
PCMR: 14″
Solitude: 15″
PowMow: 12″
Brighton: 16″
While the main trough has moved off to the west and on to Colorado, we’re still in a position to get a few more inches, courtesy of that cranking northwest flow and our friend the Great Salt Lake.

Despite the KMTX radar taking a holiday right along with everyone in the state of Utah, the HRRR is still producing a nice lake band this evening. As the flow backs to westerly, the enhancement from the lake will move north.

HRRR simulated reflectivity. models.weatherbell.com
HRRR simulated reflectivity. models.weatherbell.com

For those of you who are unfamiliar with lake effect storms, many atmospheric ingredients must be just right for snowfall to be enhanced by a large body of water (GSL in our case). Here are a few things to consider:
1. Instability – The temperature difference (lapse rate) between the lake surface and 700 mb must be large enough to ensure that the boundary layer is unstable.
2. Moisture: Boundary layer must still have sufficient moisture in order to produce precipitation
3. Wind Direction: When the wind direction is oriented parallel to the lakes longest axis, the enhancement of precipitation will be greatest.

For lake enhancement in the Salt Lake Valley and Cottonwoods, we want that northwesterly wind to do its thing.  Northern valleys will fare better from lake effect when the wind shifts back to westerly.
So hows it looking for us?
Since this system was very cold, 700 mb temperatures are forecasted to be anywhere between -18 to -22 degrees C this evening into tomorrow morning.  This will create a ~25 degree C temperature difference between the lake surface and 700 mb. This means lapse rates will be around 7C/km, creating an unstable environment (warm surface air will rise and cool).
We also will be saturated through the depth of the boundary layer (air temperature ~= dew point temperature).
Finally, the flow will be out of the northwest with speeds of around 16-18 kt, persisting until around midnight when the flow will begin to turn to a more westerly component. This will mean that the Northern Wasatch will have their turn at some lake enhancement as well.

18 UTC NAM Forecast Sounding valid 10p - weather.utah.edu
18 UTC NAM Forecast Sounding valid 10p – weather.utah.edu

For the timing of the lake effect processes, we are looking at late evening into the overnight hours for NW flow and enhancement in the SL Valley/Cottonwoods. Early morning looks best for Ogden and the Northern Wasatch.  If all goes according to plan, I wouldn’t be surprised if the Cottonwoods got an extra 2-5″ and maybe a dusting in the valley.
Given the fickle nature of this atmospheric process, the stakes are higher and the possibility for a let down is definitely greater than with a typical forecast.   But this is why we call it “Bonus Time”! This weekend has already been awesome with all the snow thats fallen, this is just the icing on the cake!

Enjoy, friends!

Just What the Doctor Ordered!

TLDR

A cold front moves through northern Utah this afternoon, with a period of heavy snowfall expected through the evening hours across mountain resorts.  Snow showers continue overnight through Monday morning. A brief lull in activity is expected Monday afternoon, before snow showers resume Tuesday morning into the afternoon.  Mostly sunny skies return Wednesday with cold temperatures.

Short Term Forecast

Our storm is currently beginning to push through northern Utah.  The surface cold front has pushed through the Salt Lake Valley and a band of moderate to heavy snowfall is positioned across far northern Utah.  The cold front will slowly move southward today, with a period of heavy snowfall expected across mountain resorts later this afternoon through the late evening hours.

GFSET_KSLC2018021812F084
GFS cross-section of wind, relative humidity, and freezing level (blue line). Courtesy of weather.utah.edu

Initially, snow ratios will start around 12:1 this afternoon and evening, but will increase to around 22:1 later tonight into tomorrow morning.  Right-side up snowfall indeed!  There will likely be a brief lull in shower activity around midnight tonight.  The upper level trough axis then swings through, with the flow turning out of the northwest.  High snowfall rates are expected in areas favored by northwest flow Monday morning.

Shower activity may briefly die off Monday afternoon, but is expected to pick up once again Tuesday morning.  Northwest flow picks up once again Tuesday morning allowing for orographic snow showers to develop.  Activity finally tappers of Tuesday evening into Wednesday morning.  Mostly sunny skies will return Wednesday with cold temperatures expected.

NAEFSPL_CLN2018021800F168

NAEFS ensemble snowfall forecast for the Upper Cottonwoods. Courtesy of weather.utah.edu

Snowfall Totals

This storm really comes down to the post-frontal orographic snow showers.  Areas favored by WNW-NW flow will likely see the larger snowfall totals with this storm.  With that in mind, here are my forecast totals!

  • Upper Cottonwoods: 20-30″
  • Park City Ski Resorts: 10-18″
  • Northern Wasatch Ski Resorts: 14-24″

-Alex

Let it snow, let it snow, let it snow

First of all, today was an amazing ski day for everyone who managed to get out there – let’s be honest, I’m always happy to see the tourists who make Utah their destination get rewarded by some fresh snow, bluebird skies, and a little extra pow to finish their vacation – we can’t have it *all* to ourselves and our average mediocre ski days are better than some get in an entire season (or lifetime!). Today was also a reminder that the late winter sun is getting strong… despite liberal applications of sunscreen, it did a number on me. A light crust was noticeable on south through west facing aspects, but north through northeast trees were fluffy as it should be!

Tom on Tom's Hil
Forecaster Tom on Tom’s Hil Today

Not too much has changed since Trey’s post but I’ll focus in on some of the spatial and model differences for those that are interested. This is one of the broader troughs we’ve seen this season, at least of the ones that have pushed far enough south to move into northern Utah. Typically these wide troughs are much slower to progress eastward and allow for prolonged periods of snow as we are expecting (versus the fast-moving narrow troughs we have been working with so far this season). Second, once the trough axis moves through and off to the east, the result is flow from, roughly, the northwest. The position of the trough will allow sufficient cold air to stick around through Monday and Tuesday (and perhaps beyond), though the air is cold enough and of continental origin – typically much drier. That said, the models do keep precip firing throughout the day on Monday with the possibility for snow showers to linger into Tuesday morning.

500 mb heights as the trough moves through Sunday night indicating the broad nature and (finally!) more southerly push
500 mb heights as the trough moves through Sunday night indicating the broad nature and (finally!) more southerly push

I’m going to ride with Trey’s totals previously posted but am sharing the NAEFS from three different locations below. First, the Cottonwoods are generally big winners in NW flow, especially Little. Minimum storm totals around 15″ with the mean near 25″ by the end of snow shower activity mid-week. There’s a good mix of CMCE and GEFS members at both the high and low end which gives added confidence in the mean verifying. With ample cold air, Park City area (and the Salt Lake Valley!) should finally see a significant storm, and similar totals are expected for the Snowbasin area. Worth noting… Jackson takes the jackpot on this storm again, but let’s just be happy with what we have, eh?

NAEFS Plumes showing minimum, maximum, and mean solutions through mid-week with a healthy spread around the mean giving added confidence in storm totals near the mean
NAEFS Plumes showing minimum, maximum, and mean solutions through mid-week with a healthy spread around the mean giving added confidence in storm totals near the mean

For those skiing at the resorts – if terrain stays closed longer than you’d like, just be patient and know that the avalanche problems this year are tough to mitigate. I wouldn’t be surprised to see the more hazardous zones stay closed till midday Monday. For those in the backcountry, keep up with the Utah Avalanche Center’s forecasts and recent reports and be smart and safe out there!

Winter’s Return

After a lovely bluebird Friday, Saturday should once again have great weather for skiing any leftover pow stashes. Temperatures will be a bit milder with highs in the 30s for most resorts. Without wasting any time I’ll get down to what everyone’s anxiously awaiting – our next storm!

Finally, a long awaited real storm will impact the Wasatch the tail end of this holiday weekend. In terms of clear weather for skiing I’d say Saturday is your best bet. Sunday shouldn’t be too stormy early, but by afternoon winds will increase and snow will move in as the trough approaches from the west. Overall, I’m not expecting too much precipitation with the pre-frontal period highlighted by the blue circle in the time-height below (Also important to note that time goes from right to left. The main event should begin with frontal passage (black circled area).

Screen Shot 2018-02-17 at 12.34.45 AM

Sunday night is when the big show begins – a cold front will slowly sag southward associated with an intensifying trough. A frontal band of precipitation will provide an initial burst of snow as 700 mb temperatures rapidly drop to -16 – -12 C, a very favorable range for dendritic growth. Also, the cold temperatures will means snowfall ratios near 20:1 after frontal passage – this will allow totals to stack up quickly and a return of Utah blower pow! Another factor in favor of significant snowfall is the speed of the trough itself. Because it’s expected to slowly traverse Northern Utah over a 24-48 hour period, the slow movement itself will provide ample opportunity for snowfall accumulation. I’d expect 6-12 inches by Monday morning and this is likely a conservative first stab.

ECMWF accumulated QPF through Tuesday night
ECMWF accumulated QPF through Tuesday night

Additional snow showers early Monday and into Tuesday are the other big wildcard. The period highlighted in purple (time height cross section above) features a fairly moist NW’ly flow regime. One potentially negative factor for significant accumulations is the relatively weak flow (albeit of a favorable trajectory) and temperatures may also be a little too cold for higher elevation areas. This could potentially put the benches – mid canyon in the most favorable regime given the extremely cold 700 mb temperatures and weak flow. Overall I’d expect at least an additional 4-8 inches in the period (though this could also be conservative). This is something that will certainly have to be monitored and refined in additional updates. The other big story will brutally cold temperatures below 0 on slopes at times Monday – Wednesday.  Regardless, early next week should have great powder days!

A Deep Day

If you didn’t decide to take a sick day today to go skiing or you didn’t see all the usual instagram posts of people plowing through powder with their GoPros mounted on a ski pole…today was a surprisingly deep powder day. Snowfall totals were generally 12-18″ in the Cottonwoods, 6-12″ on the Park City side, and ~6″ at Snowbasin. A nice little sample of the action:

Short Term

It was a coldddd one today (ridgetop temp in the single digits), and it will gradually warm up Friday and Saturday with the sun coming out and warmer air working into the region. Expect partly sunny skies both days, with the wind increasing on Saturday. Sunday the winds increase further and the clouds thicken as our next storm moves in.

Screen Shot 2018-02-15 at 10.26.04 PM
Time-height cross section from the GFS model for Salt Lake City. Note the warmup over the weekend, with the cold storm moving in early next week!

Long Term

The storm looks like it will impact us sometime on Sunday, lasting into late Monday or early Tuesday. Too early for snowfall totals but the temperatures look to be as cold or colder than today’s storm, which would be quite chilly.

A Valentine’s Day Snow!

Happy Valentine’s Day to all you skiers and snowboarders who love Utah snow just as much as we do! We are thankful for all our readers and we think you are going to LOVE the forecast I get to share with you!

TLDR:
Warm temperatures and southerly winds will give way to a frontal passage and precipitation this evening, into the overnight hours. Look for orographically-enhanced snowfall during the post-frontal NW flow regime through tomorrow mid-day.  It’s gonna snow, y’all!

Current Conditions and Synoptic Environment:
Currently, the Salt Lake valley is enjoying the typical pre-frontal warmth and strong southerlies. At KSLC, the temperature has already reached 54 degrees (Climatological normal high for today is only 43).  Several thousand feet up in the mountains, conditions are less pleasant.  Currently, light snow is falling and winds are gusting up to 66 mph at the top of Hidden Peak.  This is unsurprising given the low- to mid-level instability that was seen in the KSLC 12 UTC sounding from this morning.

KSLC 12 UTC Sounding; spc.noaa.gov
KSLC 12 UTC Sounding; spc.noaa.gov

These local atmospheric processes are a result of the large-scale atmospheric pattern.  Currently, there are two areas of low pressure that will effect the state at some point today: 1) A cut-off low near southern California and 2) A digging trough currently situated over the Pacific Northwest.

HREF 500 mb heights and wind spc.noaa.gov/exper/href/
HREF 500 mb heights and wind valid this morning;  spc.noaa.gov/exper/href/

The cut-off low is what is currently supplying moisture to southern Utah and the strong south-southwesterly flow to the entire state. This southerly flow will dominate until it is undercut by the much colder, denser air associated with the PNW trough.  The PNW trough is the stronger of the two (notice the wind speed max on the back side of the trough), and will be the main forcing mechanism for our orographic enhancement we see in the post-frontal flow regime early tomorrow.

The Forecast:
We expect this shift from southerly to west-northwesterly flow to occur in the early evening hours. Precipitation will begin scattered and convective-like and then become stratiform after the frontal passage. This is shown well by the HRRR’s forecasted composite reflectivity. (Composite reflectivity selects the highest reflectivity value from all radar tilts)

HRRR simulated composite reflectivity models.weatherbell.com
HRRR simulated composite reflectivity models.weatherbell.com

This storm looks promising for the entire North-South extent of the Wasatch range, with totals increasing as you move south.  I would expect places like Sundance to fair relatively well in this storm given the possibility of snowfall within both pre- and post-frontal flow regimes.
I feel comfortable forecasting 4-7″ for the entire Wasatch front with locally higher amounts (5-10″) in areas favored by NW flow (i.e. Snowbird, Alta) and even possibly Sundance (going out on a limb here).  These totals are a mix of guidance from the NAM, GFS, ECMWF, and just my own gut feelings.

Long Term:
Things are finally looking better for the intermountain west. A pattern shift will result in a more active coming week and cooler temperatures for the Wasatch front.
The next chance of snow is this Sunday into the Presidents Day holiday on Monday.

GFS 500 mb valid Sunday
GFS 500 mb valid Sunday; models.weatherbell.com

A deep, meridional trough will dive into the area Sunday afternoon, bringing cold temperatures and more precip.  The forecasts will be refined in the next few days as the weekend approaches.  For now, enjoying the day celebrating what we all love, SNOW!

 

Small Storm and Signs of a More Active Pattern

From what I’ve heard, the skiing was pretty good today.  Monday’s little storm exceeded expectation in the Upper Cottonwoods, dropping 6-8 inches.

Southwesterly winds will pick up tonight and tomorrow morning out ahead of an approaching storm system.  Precipitation associated with a cold front will break out across the state midday tomorrow and continue on and off until Thursday midday.  Temperature wise, this should be a fairly typical storm, with 15:1 ratios and snow levels generally below 6k ft.

The NAEFS output below for the Upper Cottonwoods is in agreement with the NAM-12km (not shown).

NAEFSPL_CLN2018021312F168

This system will once again favor southern areas of the state.  For totals, I’m going with 3-5 inches in the northern Wasatch, 4-7 in the Cottonwoods, and 5-8 in the southern mountains.

The rest of the workweek will consist of on and off mountain snow showers will minimal accumulations expected.  The long range is looking more optimistic.  500mb heights from the GFS show the ridge that has been just off  the coast further west, which should allow storms and moisture to more easily enter Utah.

gfs_z500aNorm_wus_fh48-384

More Snow This Week!

Clouds broke late this afternoon and precipitation is over after a day of fluffy snowfall for most resorts today. While minor accumulations today did not do much to bump up our snow water for the season, I heard it was a dream to ski in! Collins plot at Alta measured 0.33″ of water while reporting 9″ of snow over the course of the day (this seems high, as the Snowbird snowcam shows maybe 4″ accumulated through the day). Nevertheless, it appears that the Cottonwoods were the clear winners today due to their high elevation even though it was snowing at most resorts for the majority of the day.

Big flakes falling at Mid-Gad Restaurant at Snowbird today.
Big flakes falling near Mid-Gad Restaurant at Snowbird midday Monday, Feb. 12th.
Clouds breaking at 3:45pm after a day of low visibility and fluffy snowfall! http://prismcam.com/demos/snowbird-peaks/
Clouds breaking at 3:45pm after a day of low visibility and fluffy snowfall! (http://prismcam.com/demos/snowbird-peaks/)

A clearer, drier day is in store for Tuesday, but Northern Utah can expect another round of snow heading into the middle part of the week. The closed low centered over Nevada that brought some precipitation today looks to migrate southwest toward the southern California coast on Tuesday before it’s pulled back to the northeast as another trough approaches from the Gulf of Alaska on Wednesday. Wednesday’s system looks to have a strong northerly component with a trajectory along the Pacific Coast of SW British Columbia. While it will bring snow to northern Utah, a juicy moisture tap from the warmer waters of the Pacific Ocean will be absent, thus limiting large amounts of moisture that we really want and need!

So, how much more snow can we expect from our next storm? Recent runs of the NAM 12km and GFS have prefrontal precipitation starting on Wednesday afternoon/evening. Then, a cold frontal passage looks like it will move through northern Utah closer to midnight. Currently, NAEFS plume forecasts from weather.utah.edu have many members in the 2-5″ range as well as many in the 6-10″ range for the upper Cottonwoods. For northern Wasatch resorts, the range is large as well, from 2″ to 10″. So, we will have to keep watching the model runs as they come out tomorrow to pin down amounts! The good news is that it WILL snow more this week, but the details are still forthcoming.

Beyond Wednesday and Thursday, it looks to remain somewhat active for the next several days with some weak systems moving through every couple days.

GFS Ensemble spaghetti plot showing chances for precipitation and cooler temps over the next several days!
GFS Ensemble spaghetti plot showing chances for precipitation and cooler temps over the next several days! (http://www.wetterzentrale.de/en/)

Look forward to tomorrow’s post on more details regarding snow on Wednesday and Thursday and as always pray for snow!