Wasatch Weather Weenies

Yesterday (Tuesday) morning, the Salt Lake City International Airport observing site, which is located at the south boundary of the airport just north of I-80, observed as rogue of a rogue shower as you will ever see.  The storm produced rain at the observing site from about 0725–0755 MDT, generating 0.16" according to the rain gauge.   KSLC Time Series 0725–0755 MDT 6 Oct 2026. Source: NWS. The radar at 1317 UTC (0717 MDT) showed the rogue cell moving over the airport as it intensified.  The cell was perhaps 5 km across and developed pretty much over or just upstream of the southeast corner of the airport.     The weather cam image at the top of this post, taken looking west from the University of Utah, shows just the narrow area of falling precipitation associated with the cell.  What conspired to make such an isolated precipitation shaft is known only to Mother Nature.   Radar-estimated precipitation from the National Severe Storms La...

The models are advertising a significant pattern change to start October, one that will curl the smiles of snow-safety teams in the Wasatch Range.   Over the past several weeks, the large-scale pattern has been characterized by persistent troughing along the Pacific coast and ridging over the south central United States, as shown by the mean 30-day 500-mb heights for the period from 31 August to September 29.  Source: PSD Maproom This general pattern is consistent with the North American Monsoon, but these two major circulation features were stronger than on average.  In other words, the Pacific trough was deeper and the ridge over the south central United States were stronger than observed.  This "opened the door" for frequent monsoon surges into northern Utah and occasional severe convective storms due to the stronger flow and wind shear between the two circulation features.   The pattern is changing, however, for October.  The ECMWF AIFS analys...

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...

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.

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.  

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...

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) ensemb...

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.

 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) ...

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...

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-l...

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 tro...

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 li...

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...

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 s...