An Uncertain Sunday

Forecast uncertainty doesn't always grow continuously with forecast lead time.  Sometimes there is an issue with the intensity and timing of a weather system that can cause uncertainty to increase temporarily and then decrease at longer lead times.

A good example is the forecast for northern Utah this weekend.   The models all bring in a strong cold front, but there are variations in the timing and intensity.

The GFS forecast valid 1200 UTC 13 September (0600 MDT Sunday) shows one scenario with the cold front through northern Utah, a deep trough at 500 mb centered over the central Idaho Mountains, and cold post-frontal flow over northern Utah.  700-mb temperatures in far northwest Utah are below -2°C.  

The ECMWF AIFS has different ideas.  The front is much slower and for the same time valid above (0600 MDT Sunday), the front is just getting to Salt Lake City and the upper-level trough is centered over northeast Oregon.  The 700-mb temperatures in northwest Utah are around +6°C, 8°C warmer than the GFS.  

Put these and a gazillion other forecasts into the National Weather Service blend of models and you get a lot of forecast spread for temperatures on Sunday.  Note how the spread of the box-and whisker plot of forecast maximum temperatures (red box-and-whisker with annotated temperatures) gets really large on Sunday.  The middle 50% of the forecasts like within the colored red box which has a range from 68° to 84°F!  

The middle 80% of the forecasts lie between the ends of the whiskers (the white lines that extend from the red box).  The numbers aren't annotated, but the range is between 64°F and 93°F.  And to think your TV meteorologist will have to pick one number to put in their forecast for Sunday afternoon!

Max temperatures on Sunday are as much of a crap shoot as you can imagine and a prime reason not to look at only one model.  This is a classic case of what meteorologists call anticyclonic Rossby wave breaking over the north Pacific and western North America, which introduces uncertainty in the strength and movement of the upper-level trough as it amplifies along the Pacific coast.  I'd check the forecasts in a couple of days if you are planning a weekend backpack to high elevations.  

Snow!

I'll just put these here for some high stoke, low probability snow possibilities.  There are some ensemble members producing snow in northern Utah late next week and weekend.    

OK, truth be told it's three ensemble members out of 82.  

I told you it was a low probability possibility.

RRFS and Utah Snow Ensemble Repairs

Both the RRFS and Utah Snow Ensemble have been down for a few weeks on weather.utah.edu.  These outages were due to changes in the formatting of model data provided the National Weather Service and ECMWF.  I didn't have the time to dig fully into it until today and at this point I think I've got things repaired.  We will see if the automatic processing works as we move forward.  

I noticed there are a few members of the Utah Snow Ensemble producing snow at Alta Collins in several days.  

There's always hope lol.  

RRFS to Become Operational August 31, 2026

The Rapid Refresh Forecast System (RRFS) and RRFS Ensemble Forecast System (REFS) is scheduled to become operational with the 1200 UTC run on August 31, 2026.  The RRFS ensemble has been intermittently available on weather.utah.edu now for a couple of years (yes, I know it hasn't been available in a few weeks).  It's been a long slog for the National Weather Service to get the RRFS operational, so let's hope this proves to be a productive upgrade.

The RRFS and REFS will replace the NAM, HREF, SREF, and HiresW operational modling systems, if you happen to use those.  These will all be retired on the same day the RRFS and REFS become operational, along with their derived products.  I won't be sad to see any of these go.  

As is often the case, they have made the acronyms and ensemble model configurations as complicated as possible.  The so-called deterministic RRFS will run out to 18 hours hourly and out to 84 hours for the 0000, 0600, 1200, and 1800 UTC cycles.  It will cover the North America, including Alaska, at 3 km grid spacing.  There will also be a relocatable 1.5 km fire weather run. 

The RRFS will also produce forecasts from five ensemble members out to 60 hours for the 0000, 0600, 1200, and 1800 UTC cycles.  These members will involve a mix of differing initial conditions, lateral boundary conditions, and model physics.  The REFS is based on a combination of the deterministic and five ensemble members from the most recent and prior RRFS runs.  It is thus a time-lagged ensemble.  

I'm not sure to what degree I'll use the time-lagged REFS or its products.  I may stick with the six-member "RRFS ensemble" as we have been doing just because it is easier and I lack the time and mind to deal with complex things.  

The full announcent is available at https://www.weather.gov/media/notification/pdf_2026/scn26-48_RRFS_and_REFS_Implementation.pdf, if you are interested in some of the details.  

As I mentioned, I hope this upgrade proves productive.  The RRFS development has had many problems and is greatly delayed.  My time in Austria, with access to many modeling systems and ensembles that are run at higher resolution and with more members than the RRFS and the RRFS ensemble, has shown me that the US is now well behind Europe in operational numerical weather prediction (see I Have Seen the Future).  The RRFS won't fully close the gap to where we could be, but we will all hopefuly benefit from an advance in operational modeling capabilities.  

I Have Seen the Future

One of the great things about coming to Europe to work is getting exposed to the latest and greatest modeling systems for operational weather prediction.  

Modeling systems for operational weather prediction in the United States has stagnated now for several years.  The last major upgrade was when the Global Forecast System (GFS) upgraded to the Finite–Volume Cubed Sphere (FV3) dynamical core in 2021.  Beyond that, upgrades have been  incremental, with no major changes to the grid spacing of the GFS (13-km) or the HRRR (3-km).  The GFS Ensemble (GEFS), Short-Range Ensemble Forecast System (SREF), and High Resolution Ensemble Forecast system (HREF) have aged and are no longer cutting edge. 

Meanwhile in Europe, both numerical and artificial intelligence weather prediction systems (NWP and AIWP respectively) are advancing rapidly.  Readers of this blog are likely well aware that the European Center for Medium-range Weather Forecasting (ECMWF) ensemble has the highest resolution (9 km), most members (51), best data assimilation, and best statistical performance of any operational, global, numerical modeling system in the world.  ECMWF is also also at the forefront of AIWP and now has their Artificial Intelligence Forecast System (AIFS) ensemble running four times a day.  

But European countries are also pushing the frontiers of limited-area modeling systems that forecast for a specific region.  For example, Meteo Swiss runs an operational, 11-member, 1-km ensemble eight times a day with forecasts out to 33 hours.  They also run a 21-member, 2.1-km ensemble four times a day with forecasts out to 120 hours (see https://www.meteoswiss.admin.ch/weather/warning-and-forecasting-systems/icon-forecasting-systems.html). These forecasts are produced using the ICON model, which was originally developed at the Max Planck Institute for Meteorology in Germany.  The ICON is also used by the German Weather Service.

Here at the University of Innsbruck, I have access to an experimental version of the ICON model run by the Deutscher Wetterdienst (DWD; German Weather Service) at 500-meter grid spacing.  NWP models run at such grid spacings are sometimes called large-eddy simulations (LES) rather than mesoscale simulations because they are beginning to resolve the large eddies that are found in the boundary layer, the portion of the atmosphere that interacts directly with the Earth's surface.  A model run at 500-meter grid spacing also better resolves the fine-scale terrain in mountains regions, which is particularly important in the Alps where glacier-carved mountain valleys are quite narrow.  

Let's look at last night's 6-hour forecast from the 500-m ICON valid at 0600 UTC or 8 AM local time this morning.  The plot below shows the wind (vectors with color fill for speed in meters per second) at 2000 m elevation (relative to sea level).  Terrain elevation above 2000 m is indicated by grey shading. The pattern is characteristic of what are known here as föhn, a strong wind that affects the northern Alps during southerly flow.  In the Innsbruck area, the föhn acclerates as it moves northward through Brenner Pass and down the Wipp Valley.  At this 2000 m elevation, that strong flow eventually moves over Innsbruck and encounters the Karwendel Alps, leading to flow splitting on their southern (windward) side and a wake on their northern (leeward) side.  Locally strong föhn can also be seen in and north of other Alpine Valleys in the region.  

Source: University of Innsbruck

A cross-section from the ICON taken from south (left) to north (right) down the Inn Valley illustrates the vertical structure of the föhn in this forecast.  Locations identified in the cross section include Brenner Pass (BRE) and Innsbruck (IBK).  Note in particular that the strongest föhn flow becomes elevated just upstream of Innsbruck (near EUR) and ultimately rises rapidly whe it encounters the Nordkette ridge of the Karwendal Alps to the north of Innsbruck.  

Source: University of Innsbruck

The cause for the detatchment of the föhn flow from the surface as it approaches Innsbruck is the formation of a nighttime old pool over the Inn Valley.  At night and in the morning, the föhn often rises over this cold pool, although there are times it can "break into" the cold pool, resulting in strong south winds at the surface in Innsbruck.  This is an important forecast problem for the region, including for the local airport, as it affects runway flow direction and the elevation of föhn related turbulence.

How did that forecast verify?  Quite well.  Below is a time-height section of winds over Innsbruck observed with a wind lidar.  The time-height section is for a 24-hour period (time increases to the right).  I've added a red line corresponding to the time of the forecast above.  Note how in the left half of the diagram, the föhn frequently extended to the ground.  Then, just prior to and after 0000 UTC (0200 local time), winds over Innsbruck weakened.  However, by 0600 UTC the southerlies aloft increased once again, resulting in a structure similar to that above with light flow at low levels but strong flow aloft.  

Source: University of Innsbruck

Readers of this blog with a strong interest in snow might also be interested in seeing the corresponding 500-m precipitation forecast.  Validating this is a bit more difficult given the poor radar coverage in the Alps, so I provide it simply for entertainment purposes.  

Source: University of Innsbruck

Enjoy a look at the future.

Waiting for Snow, Still

Not much change on the weather front.  A weak system will come through tomorrow afternoon and evening.  Some models generate squat.  Others an inch or two.  A game changer it ain't.

A look at last nights Utah snow ensemble shows that storm around 00z 29 Jan with a few of the members producing modest accumulation but the vast majority at 2" or less.  A few ensemble members call for something around 00Z 3 Feb, but most are producing paltry amounts.  

It's only one model forecast, but the ECMWF HRES from this morning has a dreaded Rex block (high pressure "over" low pressure) along the west coast later next week.  

Hope something slips through the net or that the model guidance is just out to lunch.  Even a few inches would be nice.

An Upward Trend

 Despite recent posts grumbling about warmth and a lack of snow at low elevations, the reality is that the skiing at upper elevations has been incrementally improving and all elevations should see gains in snowpack over the next several days.  

The upward trend began on Christmas Eve, which was likely the worst day of skiing I've ever had in the Wasatch.  Simply an abomination.  I've been out 3 days since, all at Alta, and each day things have improved.  Groomers today were just fine and we should be happy about that given where we were several days ago.  

And the forecast for the coming work week looks pretty good.  Mean Utah Snow Ensemble SWE for Alta Collins through 12Z 10 January (5 AM MST Saturday) is a around 3" and snow close to 40".  The driest ensemble member is about 1.5" of water an 17" of snow.  

More importantly, temperatures are falling.  Tomorrow remains unseasonably mild, but temperatures (and snow levels) decline gradually Sunday night and Monday.  During the day Monday, snow levels look to fall to near bench levels and remain near or below that level through the work week.  

Let's hope Mother Nature bings further improvement to ski and snowpack conditions.

A Rainy Night for Santa

A warm storm is on tap for the Night Before Christmas, one that will not make Santa or his reindeer happy.   

To illustrate this, let's take a look at the forecast from the High Resolution Rapid Refresh (HRRR) for Little Cottonwood Canyon (click to enlarge).  The HRRR calls for periods of precipitation overnight (green box below) adding up to 1.5" of snow water equivalent at Alta-Collins through 7 AM Christmas morning.  

That's the good news.  The bad news is that the overnight period is remarkably warm, with the wet-bulb-zero level, the altitude where the wet-bulb temperature reaches 0ºC and roughly the top of the melting layer, reaching as high as 10,700 feet (the snow line is usually several hundred feet below the wet bulb-zero level).  Our algorithms suggest this period, highlighted with green shading above, may produce rain even at the 9600 foot altitude of Alta-Collins.  

Snow during other periods at Alta-Collins adds up to 8.4" by 7 AM, although we don't account for losses due to rain, so that might be optimistic.  That 8.4" will probably be wet and dense.  Even by 7 am tomorrow, the HRRR has the wet-bulb-zero level at 9300 feet, which suggests that the precipitation will probably be all rain below 8000 feet overnight.  

The HRRR is a relatively wet model.  Others, such as the RRFS ensemble below, are calling for less precipitation.  Through 7 AM tomorrow (14z 25 Feb), the RRFS members produce 0.45 to 1.2" of water.  Some of those members also produce rain to near the Alta-Collins level during the warmest part of the storm.  Snowfall is in the 3-8" range by 7 am, with amounts varying depending on water equivalent, snow level, and snow-to-liquid ratio.  

So, Santa will likely be delivering presents in the rain below 8000 feet.  He might also encounter rain or a rain-snow mix up to 9500 feet or even a bit higher depending on his delivery schedule.  Christmas skiers probably won't find The Greatest Snow on Earth under the tree tomorrow morning, but perhaps 4-8" of wet, dense snow at 9500 feet. Expect a strong gradient in snowfall amount with altitude between about 8500 and 10000 feet and the most snow above 10000 feet.  

This is one forecast that I hope is totally wrong or out to lunch.  There is a wide range of forecast water equivalent being produced by the models, so maybe we can get lucky and we can have the storm come in colder than anticipated and produce a lot of water, with more substantial accumulations over 8000 ft.  It is Christmas after all.  

There will be a cooling trend over the next few days with some snowshowers on the 25th and 26th and a snowstorm Friday night and Saturday.  

Welcome to Mordor

Wind and warmth continue to dominate the weather here in Mordor, with the fires of Mt. Doom casting their glow over the Wasatch this morning.  

The average temperature since November 1 at the Salt Lake City International Airport of 46.3°F is a remarkable 2.4°F higher than any prior November 1 – December 21 period (note: the graph below includes data from the downtown weather bureau office prior to 1928).  

For the first 3 weeks of December (i.e., December 1–21) the mean temperature (43.3°F) is also the highest on record, although the gap to #2 (42.6°F in 1889) is not as large.  

Frodo and Samwise Gamgee continue to their quest to destroy the One Ring and break Sauron's evil grip on the weather of Utah, but remain well short of their goal.  

Hopes for the cover of precipitation increase around 0000 UTC 25 December (5 PM MST Christmas Eve) as southerly flow and an atmospheric river penetrate inland into Utah in advance of the very persistent upper-level trough that has been hanging off the west coast the past few days.  

The 82 members of the Utah Snow Ensemble have various ideas on the timing and intensity of the various bits and pieces of the storm, including the structure of the trough has it moves through Utah, but for the 3-day period from 0000 UTC 25 December to 0000 UTC 28 December (red-box below), 77 of the 82 members are producing 1–2.5" of water equivalent at Alta-Collins and 74 of the 82 members are producing 10–22" of snowfall.  

Most members are also calling for a cooling trend during that 3-day period, although it should be noted that at the start (i.e., 0000 UTC 25 December), median wet-bulb 0.5°C levels, which roughly denote the top of the melting layer, are at 10,000 feet.  This is a storm cycle that is going to start out very warm, perhaps with rain at the base of Park City on the evening of Christmas Eve.  By Christmas morning perhaps snow levels will be down to the base, but that's a touch-and-go forecast right now.  Monitor forecasts for this 3-day period if you are interested in details.  

Whether or not this modest storm cycle will enable Frodo and Samwise to reach Mt. Doom, destroy the ring, and loosen Sauron's grip on Utah weather remains unclear.  

What are the Prospects for a Christmas Miracle?

Based on last night's SNOTEL observations, Snowbird sits at 6" of water (record low for December 20th at that site is 4.4"), Brighton 3.9" (record low 3.2"), Mill D North 3.7" (record low 2.0"), Thaynes Canyon 4.4" (record low 2.9").  

So, technically in the central Wasatch, we're not at record low levels, but we're also not far above those records and remain below a reasonable natural snowpack for proper skiing.

But is there hope of a Christmas Miracle?  

Through Christmas Eve day we'll continue to see warmth and some periods of low-to-mid elevation rain and mid-to-high elevation snow at times.  There's no "big" storm, but perhaps we can get add another 0.75–1.5" of water to the high elevation snowpack in Little Cottonwood from the bits and pieces through 5 PM MST on Christmas Eve.   

But what about the night before Christmas and Christmas?  Is there hope for a Christmas Miracle?

Well the GFS has a menacing trough off the west coast and a boatload of moisture moving into the western US at 2100 UTC 24 Dec (2 PM Christmas Eve).  

It's a slow moving trough, however, and is still off the coast by 1800 UTC 25 Dec (11 AM Christmas Day), so no cold air for Utah.

So, prospects for a white Christmas in the Salt Lake Valleys and other lowland areas of Utah are looking pretty grim.  The Utah Snow Ensemble plume for the Salt Lake City International airport shows some periods of precipitation late Christmas Eve and on Christmas, but the snow plume is flatlined through Christmas.  

Upper elevations may do better.  It's a warm storm, but notice the uptick in both water equivalent and snowfall at Alta-Collins that begins around 0000 Z 25 December (5 PM Christmas Eve).  

For what it's worth, the median 24-h water equivalent and snowfall forecast by the Utah Snow Ensemble for 5 PM Christmas Eve to 5 PM on Christmas at Alta-Collins are 0.87" and 6.9", equating to 12.5% water content Cascade Concrete.  I've spoken to Santa and he tells me that if you are nice and not naughty he will deliver more, possibly in the form of graupel.  If, however, you are naughty, he will bring less and push the snow level 9000 feet.  

Update on weather.utah.edu

I know that weather.utah.edu has been down quite a bit in recent weeks.  The most recent outage last week was a scheduled one as our Center for High Performance Computing takes down our systems for 1-3 days a couple of times a year to do updates and upgrades.  Prior to that, we had a number of unscheduled outages due to excessive loads.  A few changes were recently made that will hopefully help with that, but we will have to see how it goes.  

weather.utah.edu is a labor of love and a way to share our experimental forecast products with the world.  We do the best we can.  Thank you for understanding.  

Friday Morning Update

In the previous post (Windy Storm on Tap) we discussed an approaching storm system that would come in today (Friday), but really pick up Friday night as strong flow and an inland penetrating atmospheric river move into northern Utah. 

That forecast is still on track.  Overnight last night and today we are seeing the dribs and drabs at the leading edge of the storm system, as expected.  Overnight through 8 AM this morning Alta-Collins picked up about .16" of water and 2" of snow and Snowbasin-Boardwalk came in with 0.24" of water and 3" of snow.  

But the big story is not today but tonight when the precipitation efficiency looks to increase as an upper-level trough moves through and high integrated vapor transport (IVT) noses into northern Utah.  The GFS forecast valid 0600 UTC 6 Dec (11 PM MDT Friday) shows heavy precipitation over the mountains of northern Utah (or better put what the GFS thinks is the mountains of northern Utah) as the trough (dashed line below) as the trough moves through.  

Our HRRR-derived forecast for upper Little Cottonwood (click to enlarge) shows relatively light periods of precipitation through 5 PM today (top left), afterwhich hourly liquid-precipitation equivalent rates really pick up as the upper-level trough approaches.  Precipitation rates maximize at around 1 AM Saturday with periods of precipitation continuing through 7 AM tomorrow (Saturday) after which precipitation becomes widely scattered.  

This is a warm and windy storm.  Our forecast winds for Mt. Baldy peak at around 700 70 mph [Apologies for the typo! - Jim] at 4 AM Saturday.  Temperatures overnight are forecast to be around 27 F at Collins and 30 F at the base.  As a result, snow-to-liquid ratios are low and generally less than 10 for the period.  This keeps the HRRR-derived snowfall relatively low and around 13" including the dribs and drabs today.  That said, at this point with the need for base, Cascade Concrete is better than Cold Smoke. 

The overnight six-member RRFS ensemble shows a range of liquid precipitation equivalent of between about 1.1 and 2.3" and snowfall between about 13" and 26".  Thus, the HRRR is on the low end of the RRFS.  

My take is that 1.2-2.2" of water and 12-22" of snow from 7 AM this morning through 7 AM Saturday represent the most likely range of outcomes for Alta-Collins, with much of that coming this evening and tonight.  The water amounts are most important right now to build base.  Let's hope we can eclipse 2".

Looking to the north, the story at Snowbasin is much the same with the overnight period being the wettest and then things settling down towards morning.  Snow-to-liquid ratios are quite low at Boardwalk, which is lower than Alta-Collins and thus warmer in this storm.  I'm expecting this to be a very wet snow event up there.  

The HRRR Skew-T for Ogden shows a freezing level near 775 mb or about 7000 ft.  Conditions are saturated, so that also represents the wet-bulb zero level.  

If we zoom into the plot of wet-bulb zero height with time we see that it just about reaches the altitude of boardwal (~8000 ft) and after midnight the base is below that level.  This raises the possibility of a bit of rain or mixed rain and snow at the base depending on how things shake out.  

The extended forecast after this storm is not great for us, but maybe we can get something.  The GFS, for example, has a monster atmospheric river roaring across the northwest next week.  Batten down the hatches for the Cascades, and mountains of the Idaho Panhandle, Montana, and northwest Wyoming.  Goodness gracious that is a tempest of a forecast for them.  

We're to the south of most of the action.  Best case scenario is we get some storms to dip into our area and get some modest accumulations.  Worst case is we don't get much at all.  Odds favor below average precipitation next week, but if the storm track can dip a bit further south than currently forecast, we could get something.

Windy Storm on Tap

Batten down the hatches because we have storm that might have everything but the kitchen sink in it for the Wasatch Range.

Right now Thursday looks dry, but the leading edge of the storm looks to move in on Friday with some mountain snow, mainly in the northern Wasatch, but probably tickling the central Wasatch some too.

Then Friday night things really start to get rolling.  The GFS forecast valid 0300 UTC 6 Dec (8 PM MST Friday) call for very strong flow (red ovals) to move over a low-amplitude ridge that is centered west of SoCal.  This leads to the inland penetration of an atmospheric river, as indicated by the filament of high integrated water vapor transport (IVT) that extends from southern Oregon to northern Utah (red arrow).  

This general pattern persists until Sunday morning, although flow, IVT, and precipitation intensity weaken late Saturday (if forecasts hold).  

The Utah Snow Ensemble forecast below focuses on the 24-hour period ending 0000 UTC 7 December (5 PM MST Saturday).  That is probably the wettest part of the the storm.  The ensemble mean for that period is 1.0" at Snowbasin and 1.2" at Alta-Collins (upper right panel).  

The Alta-Collins plumes show a bit of precip on Friday, but things really picking up Friday night.  and persisting until Sunday morning or later in a few members.  

The GEFS ensemble is more bullish on precipitation than the European (ENS).  As I said in the previous post, it's important to be rooting for America and that continues to be the case in this forecast.  

The median water and snow forecast by the ensemble from 5 AM Friday to 5 AM Sunday is 1.5" and 16.2" respectively.  Perhaps a reasonable estimate for snowfall totals during that period is 10-20", although the distribution above skews to higher values so the odds of more is probably greater than the odds of less.  A lot will depend on details that are hard to reliably anticipate this far ahead.

I suspect we will also see wind and rime.  New lifties for riming-prone lifts may have a real initiation Saturday morning.  Good luck. 

I'll see if I have time for a closer look on Friday. 

All Elevation Snow Possible Sunday

Thanksgiving weekend looks to conclude with a storm that will likely produce some snowflakes at all elevations in northern Utah. It's not a big storm, but being the first that might bring winter driving conditions to some areas so far this season, at the end of Thanksgiving weekend, it's worth monitoring if  you will be traveling.  

The storm will be produced by an upper-level trough and cold front that will drop into Utah on Sunday from the northwest.  Below is the GFS forecast valid 1800 UTC 30 November (11 AM Sunday) showing the trough extending across northern Utah and Nevada.  

Below is the HRRR forecast sounding for the Salt Lake City International Airport valid 1800 UTC 30 November (11 AM Sunday).  It shows saturated conditions down to the valley floor with temperatures just above 0°C.  

The HRRR keeps surface temps just a smidge above freezing as the front moves through.  If that were to verify, the most likely outcome would be snow for the benches and wet-snow for the lowest elevations near the Great Salt Lake during the passage of the system.  If it were a bit warmer, then perhaps it would be a rain/snow mix at those lowest elevations.

 Below is our HRRR-derived snowfall guidance which suggests 1.6" at the airport, 2.6" at Cottonwood Heights, and 8.4" at Alta-Collins.  This product does not, however, consider on-the-ground melt, which could be an issue on the valley floor and might limit actual accumulations there.  A lot will depend on the snowfall rate during the passage of the system. 

We can also have a look at the 6-member RRFS ensemble.  It appears to be a smidge warmer than the HRRR as most members are producing 0.2" of water or more at the airport, but snowfall is scant with one member getting up to a bit under an inch.    

For Alta-Collins, five of the six members are coming in between about 3.5 and 8", but there is one very optimistic member going for close to 18.  There is always hope. 

So to summarize, a trough and frontal passage will be bringing precipitation to northern Utah on Sunday.  Snow is expected and bench and mountain locations.  At the lowest elevations, temperatures are such that we could see wet snow or a rain/snow mix.  It's worth monitoring the weather and road conditions if you need to travel on Sunday.  

Overexuberant Starting Dates and Splitting Storms

Delays in starting dates for ski areas are in the news.  Brianhead was scheduled to open on November 7 and has pushed their starting date back to November 21.  Solitude was scheduled to open on on Friday (Nov 14), but has pushed it's starting date back to next Wednesday (see this Trib article).  

In my view, this is much ado about nothing.  November is a fickle month.  Sometimes resorts can open, even as early as late October with natural snow as Brighton did in October 2004.  Sometimes we get a cold spell that enables sufficient snowmaking to get some terrain open with limited natural snow.  And sometimes we get a nothing burger.  We're getting the latter this year.  If you get a warm, dry stretch in February, you get a suntan while doing groomer laps.  When one happens in November, you get a delay to the start of the ski season.  

It is true that temperatures so far this November have been warm, with an an average for November 1-12 of 51.7°F at the Salt Lake City airport.  That is the 2nd warmest on record, but sometimes a ranking hides subtleties.  If we look at records since 1929 when observations were first collected at the airport, there have been 8 other Novembers with average temperatures at or above 50°F.  So, this year is warm, but to some degree it is cooked into the cake of weather variability.  Warm dry stretches in November can happen.  

The plot above also shows a great deal of variability as one might expect for a relatively short 12-day period in the late fall.  The coldest November 1-12 was in 2000 when the mean temperature was 32.6°F.  Holy cold surge Batman!  

The linear trend line is consistent with a warming trend as we might expect.  We will see more warm spells in the future and the resorts will find it more and more difficult to open early season terrain with current snowmaking capabilities. Opening a resort in Utah in early November has always been a crap shoot, but the odds will be decling in the future without advances in snowmaking capabilities.  

Looking to the future, the pattern over the next several days is dominated by splitting storms.  Split is a four letter word around here (yes my math is bad), but the reality is that many of our storms split.  The analysis below shows the average 300-mb (jet-stream level) winds during winter in the Northern Hemisphere.  On average, the Pacific jet is strongest in the western North Pacific.  The western United States is at the end of the Pacific jet in what metorologists call the "jet exit region".  On average, the jet level flow over the western. United States is actually relatively weak and this is consistent with the jet-level flow decelerating and splitting.  This is essentially a consequence of the distribution of continents and oceans in the Northern Hemisphere, the distribution of sea-surface temperatures in the North and Tropical Pacific, and the topography of western North America, among other factors.

So, many of our storms split.  The Wasatch Range gets a lot of snow because northern Utah still manages to get some snow from splitting systems, the split sometimes weakens and storms are able to penetrate directly into Utah, and the topography around here, especially around Little Cottonwood Canyon is just damn good at squeezing every dendrite out of winter storms.  

A textbook case of splitting storms is on tap for the next several days.  The GFS analysis for late yesterday morning [1800 UTC 12 November (11 AM MST Wednesday)] shows a full-latitude trough off the west coast (upper left panel) with and accompanying cyclone centered off the coast of Oregon and California (upper right panel).  

Instead of progressing to Utah, the upper-level trough amplifies through 1200 UTC 14 November (5 AM MST Friday), resulting in split flow with one branch of the jet moving across southwest Canada and the other taking a circuitous route around the upper level trough and into southern California (upper left panel).  As a result, the precipitation system moves into western North America in two pieces, one over central and southern California, the other near the Canadian Border (upper right).  

But the GFS forecast calls for things to get worse, at least temporarily for Utah. By 1200 UTC 15 November (5 AM MST Saturday), the southern storm has continued to dig southward.  SoCal is getting the goods, but we're left high and dry.  

Whether or not all is lost with this storm depends a lot on what it does as it drifts downstream and moves across the interior west.  By 0600 UTC 16 November (11 PM MST Saturday), remnants of the system are moving into Utah.  

Forecasts out to 10 days show a lot of splitting storms.  Our snowfall future depends strongly on the track of these storms and their remnants.  Sometimes we can really get a lot of snow from upper-level patterns that meteorologists from other regions think are fairly innocuous.  However, such details are hard to predict and this is why the Utah Snow Ensemble is a junk show for Alta (and northern Utah locations) with enormous spread in total water equivalent and snowfall over the next 10 days.  And that spread is not because there are one or two extremely high or extremely low outliers.  That's actually a fairly even distribution of members producing a total accumulated snow total through 0000 UTC 23 November between 15 and 50 inches.  

So, a lot of uncertainty, but we might frame that a little differently.  75% of the members produce 1.93" of water and 16" of snow through that time and 50% produce 2.5" of water and 32" of snow, the latter on the cusp of rock-ski skiability (I know some of you go out with less).  

So one way to think about this is there's a 50/50 chance we'll have marginal early season skiing next weekend.  I'll let you decide if you want to be a pessimist or optimist about which side we will land on. 

And if you are wondering, yes, this is one of those blog posts that I start and when I get to the end I realize I bit off far more than I can chew!

Update on Weekend Changes

On Monday we discussed the possibility of big changes this weekend with the potential for a significant snowfall event (see Big Changes Next Weekend).  Changes are still coming, but right now it appears that the pattern will not be quite as favorable for mountain snow, although there will still be some.  

The latest GFS is still bringing a front through northern Utah this weekend.  Below is the forecast valid 0000 UTC 26 Oct (6 PM MDT Saturday) with the front pushing into northwest Utah.  It's still looking like we will have a frontal passage Saturday night with Sunday significantly cooler.  

That said, the moisture and precipitation with the front isn't quite as robust as advertised a few days ago.  There's still a decent chance of valley showers and mountain snow, but amounts are not as high. 

Then, instead of the trough digging through the western US, it lifts off to the northeast.  We get a bit more precipitation Sunday and Sunday night as the atmospheric river and jet stream behind the front move through, but we never get into the deep, unstable, cold air.  Sigh.  

The net result is that the water and snow numbers for Collins are on the low end, with all but two members under a 10" total for the storm cycle and half the members under 5.5 inches.  

We'll see how things shake out, but this is looking like a good time to keep expectations low and hope for the best.

Big Changes Next Weekend

Although this week will be mainly quiet with the exception of a weak monsoon trough that will move across southern Utah Wednesday night and Thursday, next weekend looks exciting.

The latest GFS is forecasting a strong cold front to be moving across northern Utah late Saturday.  Behind the front, a strong jet extends across the Pacific and into the western United States.  

The European is on board with this general pattern shift, but is faster with the front, which it forecasts to be in eastern Utah by late Saturday.  

Regardless of timing, the frontal passage should bring another round of precipitation with it to add to the 4.95" October record at the Salt Lake City International Airport.  Additionally, it also looks to bring mountain snow and even the possibility of valley flakes, although much with regards to that will depend on what happens in the wake of the front.  

The Utah Snow Ensemble forecast for Alta-Collins has a few ENS (European Ensemble) members producing a bit with of snow with the monsoon trough Thursday, although most keep us dry.  However, during and following the frontal passage, many members are keen on a significant snowfall event.  Most are generating something in the 8 to 22 inch range.  

I think it's a bit early to be worried about numbers as this is a pattern in which the details are hard to forecast with precision at such lead times.  It is, however, worthy paying attention to.  We'll see how things evolve over the next couple of days.