Friday, November 30, 2012

Wet and Sloppy

Before talking about the the potential for snow the next few days, I'd like to remind everyone that this blog isn't a forecast service and many days we don't discuss the forecast.  Thus, if you need a forecast for the Wasatch, you can always check out, run by some really talented students here at the U.

Now that's out of the way, let's talk briefly about the next few days.  Everyone is salivating for powder, but we're not going to be seeing any.  We have two quick hitting storms moving through.  The first is tonight:

And the second is Sunday night:

The storms are going to be wet and sloppy.  In the Cottonwoods, snow levels in each storm will start out in each storm near 8000 ft.  Temperatures and snow levels fall during each storm, but only marginally.  Accumulations below 8000 ft are likely to be minimal.  Above that level, the snow is going to be a high density variety.  Given the quick hitting nature of each storm, I suspect 2-4" is likely in each storm, 3-6" if we're lucky.  Your best bet is to ski as high as possible.  I'm referring to elevation here.  The Wasatch Weather Weanies do not condone skiing under the influence!

Another storm is possible later next week.  Right now, that also looks like a quick hitter, but we'll see how it looks in a few days.

Incredible Cloud Gallery

Some spectacular clouds could be found over the Salt Lake Valley this morning.  First, we have a marvelous example of an orographic cloud over Lone Peak.  It's been sitting there since yesterday and is produced by southerly and southwesterly flow being forced up and over Lone Peak and the high divide that separates Little Cottonwood and American Fork Canyons.

Even better are examples of Kelvin Helmholtz Billows, referred to by meteorologists as simply KH.  KH billows look like waves breaking on the beach.

Photo: Peter Veals
Water waves break because friction slows the wave more at the ocean floor than near the ocean surface.  This causes the wave to steepen and eventually break.

KH waves in the atmosphere are produced by strong vertical wind shear.  In the photo above, the flow at the top of the wave is stronger than the flow at the bottom.  This leads to wave breaking much like occurs in the ocean.  Note that wave breaking is evident in the altostratus cloud near the top of the photo, but also near the top of the orographic cloud that is parked over Lone Peak.

The morning sounding from the Salt Lake City airport shows regions where the wind speed increases rapidly with height.

The first is from the surface to about 775 mb (~2200 m MSL).  This is associated with a strong southerly low-level jet produced by flow channeling in the Salt Lake Valley.  While there could be wave breaking in this layer, there are no clouds, so you can't see it (but you might feel it if you were on a plane).

The second begins just above 700 mb (~3000 m MSL).  This is likely contributing to the wave breaking with the orographic cloud.  One of the shear layers above this level is responsible for the wave breaking with the altostratus cloud.

Thursday, November 29, 2012

Is a US Snowfall Record in Jeopardy?

From the Weather Channel today, an article entitled "Mt. Shasta: Is U.S. Snowstorm Record in Jeopardy?

To quote the article, "The Thursday morning National Weather Service summit forecast for Shasta predicted an incredible 33 to 39 inches of snow -- just for Thursday alone...Add up the high end of the numbers and you get a forecast maximum of 218 inches of snow in four days!"

Unfortunately, this is an example of extrapolation and sensationalism run amok.  The world record single snowstorm accumulation of 189 inches was set from Feb 13-19, 1959 at Mount Shasta ski bowl. The ski bowl is going to get a pounding over the next few days, but some of the precipitation is going to fall as rain.  Snow levels are quite high in this storm.  Here's what the base looked like at noon today.

What about higher up on the mountain?  Well, the 218 inch figure noted above is for the summit.  Surely it will snow a ton there?  

Unfortunately, precipitation can't always increase with elevation, as I think was assumed for these forecast numbers, especially on a big mountain like Shasta.  Typically on such huge mountains, the heaviest precipitation falls at mid elevations, near 8000-9000 ft.  There are many reasons for this, but one that is evident at times over the next few days is that storms don't always extend to the summit.  For example, during some periods during the next few days, the storm is capped at about 700 mb, or 10,000 feet.

It is also illustrative to consider the circumstances during the 1959 storm.  During that event, there were prolific snows not only on the mountain, but also in the lower elevations.  Mt. Shasta City, at ~3600 ft. had a reported 33 inches of snow during the first day of the storm.  Unlike the current storm, that was a cold storm, and I suspect the snow that fell at the Mt. Shasta snow bowl was somewhat drier than average.  This helps to yield larger accumulations.

So, the answer to the Weather Channels question is no.  This will be an impressive storm at elevations perhaps in the 8000-10000 ft band on Mt. Shasta, but records will not fall.  Maybe one of you can go up and measure for me to confirm this.

Cold Pools, Cold Puddles, and Lake Breezes

During inversions, meteorologists frequently call the airmass beneath an inversion a cold pool.  The name seems appropriate as the dense air, when it is full of pollution or topped by clouds, behaves in much the same way as a pool of water.

In some instances, however, the cold pool is incredibly shallow.  As such, it might be better labeled a cold puddle.  One could observe lingering pollution in such a cold puddle yesterday afternoon over the Great Salt Lake and and lower elevations of the northern Salt Lake Valley.

Pollution in an extremely shallow cold pool (a.k.a. cold puddle) over the
Great Salt Lake and lower elevations of the northern Salt Lake Valley at
about 5 PM MST 28 Nov 2012 (click to enlarge)
That cold puddle represents the last remnants of our latest inversion event, which was extremely persistent over the Great Salt Lake.  One can see the cold puddle pretty well in the surface analysis from 5 PM MST yesterday.  Check out the incredible 12ºF temperature contrast between the two sites that are less than a mile apart at the Salt Lake Airport.  This contrast represents the boundary between the cold puddle and warmer air.

Source: MesoWest
For most of the day, the Salt Lake City airport was in the warm air, but the temperature dropped abruptly about 14ºF as the cold puddle pushed in.

What is happening here is that an extremely shallow puddle of cold air remained entrenched over the Great Salt Lake.  That cold air eventually pushed southward and eastward into the Salt Lake Valley with the Great Salt Lake breeze yesterday afternoon.  The temperature contrast accompanying the Great Salt Lake breeze was greatly concentrated thanks to the warm southerly flow ahead of it.

The Salt Lake City Airport and areas to the west can sometimes feel like another planet compared to the University of Utah and the east bench, and that was the case late yesterday afternoon.

Wednesday, November 28, 2012

Intricacies of Inversions

Looking out over the northern Salt Lake Valley and southern Great
Salt Lake from the Avenues Foothills yesterday @ 430 PM MST
Although the past few days seem pretty boring weather wise, they are simply fascinating for a micrometeorologist.  The contrasts in surface temperatures in northern Utah have been astounding.  Let's take yesterday afternoon as an example.

At 2200 UTC (300 PM MST), it was a balmy 56ºF on the University of Utah campus and 58ºF just up the hill at the Utah Museum of Natural History.  However, at the Salt Lake City International Airport, which is about 500 feet lower, it was only 50–52ºF.

Source: MesoWest
This reflects the incredibly shallow nature of the inversion.  However, it gets even more interesting if you look out over the Tooele Valley where temperatures were only in the 40s.  During many inversions, especially those without snowcover, afternoon temperatures over the lake are often much colder than those over the surrounding land.  The Tooele Valley more "vulnerable" to this lake influence that the Salt Lake Valley, and is often much cooler under these conditions.

The situation this morning is also fascinating.  The morning sounding from the Salt Lake City airport shows that the inversion"\ is extremely shallow and actually consists of two distinct inversion layers, one that is based right at the surface (and is confined to the lowest part of the valley), and another that is just above it.  You can just make out a break between these two layers at 850 mb.

One can literally see the surface-based inversion this morning from the Avenues.  Look at the smog layer that is hugging the valley floor.

Looking west from the Avenues @ 845 am MST
When you have a shallow inversion like this, there can be strong contrasts in air quality in the Salt Lake Valley.  The situation in the lowest elevations can be markedly worse than on the benches.

Tuesday, November 27, 2012

My Science Is Sexier Than Yours

How many of you scientists out there can say that it is a Hollywood starlet's lifelong dream to do your job?  Scarlett Johansson fulfilled that dream this morning when she did the weather on the Today show.

Of course, most meteorologists don't work in television broadcasting, and most television weather reporters aren't meteorologists (Al Roker's degree appears to be in Communications), so ScarJo isn't really doing what most meteorologists do.  Nevertheless, we're more than happy to be so appealing to one of the 100 sexiests actresses of all time.  Perhaps Channing Tatum will have a go next.

Monday, November 26, 2012

Turkey Leftovers!

Not much has changed.  The pre-thanksgiving forecast was a turkey, and so is the post-thanksgiving forecast.

The GFS still calls for the storm track to remain to our north.  Here's the accumulated precipitation for the 192-hour period ending at 0600 UTC 4 December.  Depressing.  We get just a couple of weak brush-by systems.

The European Center forecast is a bit more optimistic as it sags the jet a bit further south.  Thus, it's a bit wetter, with a system coming through Friday and Saturday.  Let's hope so.  We could use the snow.  A dietary change is desperately needed.

Tuesday, November 20, 2012

This Forecast Is a Turkey

The prospects for a deep-powder day for the holiday weekend are not zero, but are fairly low.  The latest computer model forecasts keep the action largely to our north.  The total accumulated precipitation forecast by the GFS between 1200 UTC this morning and 2100 UTC Sunday afternoon shows heavy precipitation over the northwest, and dry conditions over the southwest.  The Wasatch sit just to the south of the goods.

Two weak systems graze northern Utah during this period, one Wednesday night, the other late Saturday and Sunday.  We'll have to hope these storms are more productive than currently forecast if we're to get a good freshening up during the holiday weekend.  Yes, it's a turkey of a forecast, but there is something to be thankful for.  The snowpack SWE at Snowbird is 140% of average.  At upper-elevations in the central Wasatch, we will have an above average snowpack for this time of year.  

Source: NOAA/NWS

Monday, November 19, 2012

Blessings of Altitude

It goes without saying that altitude can be a blessing, especially during a warm period in the shoulder season.  While the higher elevations of the Wasatch picked up a gain in snowpack this weekend, the lower elevations, specifically those below the snow line, suffered.

John Paul Gondola Base (8800 ft)
Strawberry Gondola Base (6800 ft)
What a shame to lose all that natural low-elevation snow in the northern Wasatch from a couple of weeks ago.

While this event is simply the result of a relatively warm period and storm, it does provide a glimpse of what we will likely see more of in the coming decades—a greater fraction of precipitation falling as rain at the lower elevations, where the snowpack will also see more frequent cool-season melt events (several studies suggest this is already happening).  On the other hand, the upper-elevations have some insurance against the initial wave of warming given their colder temperatures.  Thus, the contrast between the lower-elevation and upper-elevation snowpack climate will likely increase over the next few decades, and upper-elevation ski terrain will become an increasingly precious commodity.

Sunday, November 18, 2012

Settlement and Recovery

Early morning snow at Alta
Last weekend's lake-effect snow was relatively low density, and thus underwent substantial settlement and compaction this week.  The Alta-Collins 7 am snow depth dropped from a maximum of 42 inches on October 11 to a minimum of 24 inches yesterday.

Notice, however, the uptick to 29 inches this morning.  The dribs and drabs of wet snow yesterday and overnight are adding up.  And it is high density base builder.  Over the past 24 hours, Alta-Collins has observed 8 inches of snow with 1.16 inches of SWE.  That's 14.5% water content.  The Utah Avalanche Center suggests the storm is producing quite a bit of graupel.  If it's white, it's good, and if it's graupel, better yet.

Friday, November 16, 2012

Snowfall Records

Looking for a way to blow some time at work today?  Peruse the National Climatic Data Center interactive map for record 1-, 2-, and 3-day snowfall by station.

Yup, this is it.  The history of record snowfalls at your fingertips.  Alta's records for 1-, 2-, and 3-day snowfalls are 34, 52, and 70 inches respectively.  Highmarket, NY on the Tug Hill Plateau east of Lake Ontario can top that with 43.5, 63.8, and 84.2 inches.  And of course, there is Thompson Pass, Alaska, with 62, 120.6, and 147 inches.  That's crazy!

A few caveats.  This map is based solely on data provided by National Weather Service cooperative observers.  Snow depth is typically measured once a day at the same time each day.  Thus, these are daily and not 24-hour records.  Alta's 24-hour record is 55.5 inches.  I suspect that storm cross the daily measurement time and thus was split into two days (I suspect the measurement wasn't made by the cooperative observer either - there are several groups that measure snowfall in upper Little Cottonwood).  In addition, keep in mind that this data is warty and that the period of record varies from station to station.  As I like to say, all observations are bad, but some are useful...

Thursday, November 15, 2012

Blessings and Curses

Early season snow is of course a blessing for the mountains, but it can be a curse here in the valley.

Valley snow leads to stronger and more persistent cold pools (a.k.a. inversions).  The buildup of pollution over the past couple of days is quite evident looking south over the Salt Lake Valley this morning.

The morning sounding from the Salt Lake City airport shows a stable, near isothermal (i.e., constant temperature) airmass extends from the valley floor to about 750 mb, or about 1000 m above the valley floor.  We're pretty much cutoff from the clean air above.

Fortunately this will be a short-lived event as the flow aloft is expected to increase tonight and will probably be strong enough tomorrow to at least stir things up and keep the pollution levels from getting annoyingly high.

Wednesday, November 14, 2012

El Nino Is Dead–Long Live No Nino

The borderline El Nino event that was thought to be a possibility a couple of months ago (see Oct 5 and Sep 12 posts) appears to be toast.  The Climate Prediction Center officially cancelled the El Nino watch last week and expects ENSO-neutral conditions through the winter.  In other words, this is likely to be a No Nino winter.  Click here for the gory details.

And thank goodness for that, not because it means anything in terms of what to expect this winter, but because I won't have to hear people mindlessly blaming every weather event on El Nino.  I guess now they can blame it on the absence of El Nino.

Tuesday, November 13, 2012

Weather Risk Opportunities and Challenges

The New York Times recently published a couple of interesting articles in the wake of superfrankenstorm Sandy.  The first is related to the disaster-preparedness economy, or what the author appropriately calls Mad Max Capitalism (article access here).

The bottom line is that there is big money in disaster preparedness, and this is a growing segment of the economy.  My bet is that they will sell millions of generators in the NY metropolitan area in the coming years.  One of the people interviewed is from The Ready Store, which is based in Draper, Utah.  One of you enterprising meteorology students ought to give them a heads up before the next big storm.

The second discusses a neighborhood on Staten Island where there were unfortunately several fatalities (available here).  Relevant is how residents were lulled into complacency by false alarms or past storms that were not all that severe.  This is one of the challenges facing meteorologists and emergency management groups, especially since the margins of error are such that "overwarning" can be reduced but not completely eliminated.

Monday, November 12, 2012

American Fork Gets the Shaft!

We just received this morning's visible satellite image from MODIS.  This is the first visible image since the storm and, although there are some high clouds, they are thin enough that you really can't miss where it snowed and where it didn't.  Check out the lack of snow cover north of Utah Lake around Saratoga Springs and American Fork.

How Big Was the Lake Effect Event

I thought I'd spend a moment today to put the weekend storm into a climatological context, especially the lake-effect phase.  To do this, I'll be concentrating on data collected by the NRCS SNOTEL stations located at mid mountain at Snowbird.  Based on the climatology developed by Yeager et al. (2012, in press, but available here), this site receives more lake-effect precipitation than any other regularly reporting site in northern Utah (Note: Alta might receive more, but we lack the data to verify this, and there is a site in the northern Oquirrhs that is a very close second).  In addition, during the weekend storm, the Snowbird SNOTEL received more lake-effect precipitation than any other SNOTEL, although Parleys Summit was a close second. 

As can be seen in the meteogram below, there were two major phases of precipitation during the storm.  The first was during the cold frontal passage on Friday.  The second was during the lake-effect period, which began Friday night.  The times are in UTC.  Subtract 7 for local (MST) time.  I have drawn a hard boundary between the frontal and lake-effect periods, but in reality the transition was not necessarily abrupt.  Nevertheless, we'll go with 0700 UTC 10 Nov as the time of the onset of lake-effect (it was a bit earlier to the north).  

SNOTEL stations aren't perfect.  The measurement tends to fluctuate due to gauge contraction and expansion from daytime heating and nighttime cooling, and snow occasionally builds on the gauge walls and falls in.  The green line above shows the accumulated precipitation by hour and you can see some of these effects in the trace.  Note the decrease after a peak at the end of the lake-effect period, as well as a rapid increase when a huge one hour accumulation of 0.6 inches of snow water equivalent that may have been produced by a clump of snow falling from the sidewall or rim of the gauge to the bottom where it could be measured.  We will use a 2 inch increase from 4.6 to 6.6 inches of SWE for the total precipitation produced during the lake-effect portion of the storm.  

Converted to metric, that is a total lake-effect SWE of 51 mm.  During the 1998–2009 period examined by Yeager et al. (2012), there was only one period that generated more lake-effect precipitation.  That period was the 2nd lake-effect period of the the Thanksgiving 2001 Hundred Inch Storm and it is by far the largest lake-effect period of the past 15 years.  Note how the scale in the graph below jumps from 40 to 80 mm so we can fit it in.  

SWE produced during lake-effect periods from 1998–2009.
Source: Yeager et al. (2012)
Although this weekends storm wasn't the biggest lake-effect event, it was clearly #2, at least at Snowbird.  It might be the biggest at other sites, such as Parleys Summit, but I don't have that data at my fingertips.  

The bottom line: Consider yourself blessed.  

Sunday, November 11, 2012

Accumulations So Far

As reported to the National Weather Service.  Totals through time indicated.

Snowbird: 46" (8 am Sunday)
Alta: 45" (6 am Sunday)
Alta-Collins: 42" (8 am Sunday)
Spruces: 35" (6 am Sunday)
Bountiful Bench: 28.5" (9am Sunday)
Cottonwood Heights: 25" (7 am Sunday)
Upper Millcreek: 24.5" (8 am Sunday)
Sandy (4852 ft): 22.7" (7 am Sunday)
Centerville: 18.2" (7 am Sunday)
Upper Avenues: 17" (7 am Sunday)

I suspect many of these are settled snow depth measurements (I have 15" at my house at 4800 ft in the Avenues).  Measurements taken every 24 or 12 hours and added would be larger.  These totals include snow from the frontal portion of the event on Friday.

And It Continues!

As noted in the previous post, this lake-effect storm is one of the best of the last 15 years or so, and it continues this morning.

Data from Alta-Collins shows quite well how the lake effect intensified each of the last two nights, as is common with the Great Salt Lake effect.  Note the ramp up in precipitation rate, with a peak Saturday morning and then another peak on Sunday.

Source: NWS
The automated snow-depth sensor at Alta-Collins busted through the 40" mark this morning.  I always consider that to be the start of decent early season skiing (my standards are high).  It's tough to say whether or not we'll be able to hang above 40" once things start to settle after the storm, but this is a really good start regardless.

We are going to continue to see lake-effect this morning.  The storm will wind down after noon.  There should be some great views once the clouds start to break up.  Enjoy!

Saturday, November 10, 2012

A Remarkable Storm

Wow, what an event.  After a bit of an afternoon lull, the lake-effect is raging once again.

Source: NCAR/RAL
We are now up to 1.1" (28 mm) of SWE at the Snowbird Snotel since 0700 UTC 10 Nov, when this lake-effect period began.  For the 1998–2009 period examined by Yeager et al. (2012), there were only a handful of lake-effect periods that produced more precipitation.

SWE produced at he Snowbird SNOTEL during lake-effect periods 1998–2009
Source: Yeager et al. (2012)
We have a long ways to go to get into the top three, but we are now in the top five.  Valley accumulations are also impressive.  It is spectacularly beautiful with the dendrites stacked deep in the Salt Lake Valley.  

Lake Effect Transition

The lake-effect event continues to rage.  This morning, the event has slowly transitioned into a more banded structure, as is now apparent in the radar image below.

We don't really understand these structural transitions, but I think in this case it might be related to a gradual veering of the large scale flow at ~700 mb (roughtly crest level) from westerly to northwesterly.     This means the large-scale flow is transitioning from primarily across the surface convergence zone (see previous posts) to along it.

I really should be skiing.

Great Radar Loop and Big Accumulations

Non-banded lake-effect events don't get much better than this one.  What a beautiful radar loop below.

Can it hang on?  Let's hope so.  Looks like heavy precipitation now from Little Cottonwood through the Bountiful area mountains.  It appears that Alta-Collins is getting creamed with very high snowfall rates.  The automated total snow depth is squirrelly, but if you ignore the false 240 numbers, it looks like they got 10" since 4 am.  The interval board was wiped twice during this period.  Looks like 10" through yesterday afternoon, then 13" through 9 am this morning, then another 3" as of 10 am.  Yes!

My impression is that this is one of the better lake-effect events we have had in some time, and it ain't over yet.

Lake Effect!

Overnight we had a nice transition to lake-effect snow, which has been concentrated over the northern Wasatch Front and eastern Salt Lake County.

0707–1454 UTC 10 Nov 2012 KMTX Radar Loop 
As can be seen in the loop above, the event thus far has been what we call "non banded" in that there is a broad area of lake-effect precipitation rather than a narrow, isolated band.

MesoWest observations show what we often see during lake-effect events with strong westerly flow over the western half of the Great Salt Lake converging with a stagnant and cooler airmass along the Wasatch Front and over the eastern half of the Great Salt Lake.

This convergence serves as the trigger for lake-effect convection, with precipitation falling downstream to the east and southeast.

During the October lake-effect event, we discussed how lake effect tends to weaken during the day (click here).  This effect is greatest in the fall and spring and weakest during the winter.  It will be interesting to see if that happens today.  There is extensive snow cover around the lake thanks to yesterdays storm, and the sun angle is lower, both of which suggest the daytime heating will be limited. Perhaps we'll see some weakening this afternoon, but not a total demise.  In any event, it looks like periods of snow showers for the Wasatch Front and Mountains through tomorrow morning.  Let it snow!

Friday, November 9, 2012

Where Is the Orographic Enhancement?

This has been a very impressive precipitation event thusfar in the Salt Lake Valley.  As of 2 PM MST, 0.94 inches of precipitation (snow-water equivalent) has fallen at the Salt Lake Airport.

Most skiers typically expect that when it snows this much in the valley, it must be snowing a lot more in the mountains, but that is simply not the case so far today.  On average during the month of November, Alta receives about 5 times as much precipitation as the Salt Lake City airport, but that's the average.  Today, we're seeing very limited orographic enhancement of precipitation.  For example, Alta-Collins has received only 1.17 inches of precipitation (snow-water equivalent) thusfar, or only 1.25 times more than Salt Lake City Airport.

Why is the enhancement so small?  It's because the precipitation is being generated primarily by the front and typically the orographic enhancement of precipitation is smallest over the Wasatch Mountains during periods when large-scale processes, such as those associated with fronts, dominate the precipitation dynamics.  For example, during the event below, which occurred during the 2001 Hundred Inch Storm, the ratio of precipitation (snow water equivalent) at Alta to Salt Lake City was lowest during the frontal storm stage [apologies for the poor resolution, but you are getting this for free :-)].

Source: Steenburgh (2004)

A Nice Storm

I love it when a front decides to linger over the Wasatch Front.  Below you can see it slowly moving through northern Utah over the past several hours.

Looks like snow will continue for the better part of the day in the valley and mountains.  6 inches and counting in upper Little Cottonwood as I write this.

Winter Arrives with a Bang

A strong cold front passed through Salt Lake City at about 4 am MST this morning, as clearly shown by the meteogram from the Salt Lake International Airport.

Such a large and dramatic temperature fall is somewhat unusual in the early morning hours, but with strong prefrontal winds, there was little cooling at the surface overnight, so the full brunt of the front could be felt at the surface.

Winter arrived with a bang following the frontal passage as thunderrain turned to thundersnow with falling temperatures at the airport between about 6 and 7 am MST.

It will be interesting to see how much accumulates today in the Salt Lake Valley.  Temperatures are right at the margins for snow and the ground is very warm.  There should be dramatic contrasts in accumulations between the valley floor and the upper benches, and from surface to surface.

BTW, the leading edge of the front was very shallow.  At 7am it was 34ºF at the Salt Lake Airport, but still 31ºF at Alta-Collins with southwest winds at the top of Mount Baldy.

Thursday, November 8, 2012

Intermountain Cyclogenesis

We have an exciting stretch of weather ahead and it starts today with an Intermountain cyclogenesis event.

Cyclogenesis is the formation and development of a cyclone, known colloquially as a low pressure system.  Today we have a nice example of this happening over the Intermountain West.  Watch in the loop below, which includes both analyses from yesterday and last night and forecasts for today, how a cyclone digs southward along the Pacific Coast and decays as a new cyclone forms over the Intermountain West.

This sort of behavior is not uncommon in areas of complex terrain.  Cyclones have a difficult time penetrating through areas of high topography.  As a result, they often decay as they approach a mountain range (in this case, the Cascades and coastal mountains of the Pacific Northwest) and reform in the lee.  The Intermountain West is a favored region for cyclone formation because it lies downstream of the Sierra Nevada and Cascade Ranges.

Also contributing to the Intermountain cyclogenesis event is a frontal zone that pushed into the Intermountain West late yesterday.  The clouds that extend from northern California to Montana early in the loop below are associated with this frontal zone, which helps serve as a locus for the cyclone development.

All of this means that a very strong but slow moving cold front will develop along with the cyclone over Nevada.  The Salt Lake Valley will be ahead of this development cold front today, and experience warm windy weather.  Temperatures will likely reach the low 70s.

The cold front should push into the Salt Lake Valley late tonight or tomorrow morning.  The models still differ on the timing, but tomorrow should eventually feel like you've been transported to another planet as snow levels will be falling all the way to the valley floor.  The difference in temperature between this afternoon and tomorrow afternoon will probably be more than 30F.