Wasatch Weather Weenies

The warning flags have been raised and the National Weather Service has issued a high wind watch for late tonight through Thursday evening for the Salt Lake and Tooele Valleys and northern Wasatch Front for strong and potentially damaging downslope winds . As we have discussed in earlier posts, there is good reason for issuing such a warning.  The key large-scale ingredients for a downslope windstorm have been anticipated by earlier computer model forecasts and are evident in the latest forecast produced by the NAM model.  These key ingredients are strong easterly to northeasterly flow, a stable layer near crest level, and a level aloft with reverse shear (i.e., winds weakening with height). NAM model forecast valid 8 AM MST Thu 1 Dec 2011 However, although our computer models today can predict the environment in which a downslope windstorm is likely, they provide us with little useful information with regards to just how strong the peak winds will be. The National W...

As we discussed yesterday , the atmosphere is in the process of going into outlier mode, and the next few days should prove quite interesting for weather. Our explosively deepening cyclone is now just south of the Aleutian Islands.  As expected, another low has formed downstream and is just off the Queen Charlotte Islands.  Those of you who are lovers of cyclones will be pleased to know that there is also a third cyclone over the Sea of Okhotsk.  This is what meteorologists call a polar low , because of it's small scale and formation in cold air over a warm body of water. 1500 UTC (0800 MST) 29 Nov 2011 IR satellite image and sea level pressure analysis The cyclone near the Queen Charlotte Islands is expected to dig southeastward into Washington State.  Although it will fill at low levels, the upper-level low is expected to be centered near Las Vegas by 1200 UTC (5 AM MST) 31 Nov (Thursday morning). GFS forecast valid 1200 UTC (5 AM MST) 31 Nov 2011 At...

Yup, I admit it.  A couple of weeks ago I declared the fall single track season over .  There was too much snow, too much mud, and too little sun angle to make the trails rideable again this year.  Well, several days of mild, windy, dry weather have laid that forecast to waste.  The Bonneville Shoreline Trail was in pretty good shape today with just a few muddy spots.  In fact, it was downright FAST in places. In addition to being a decent substitute for crappy skiing, it's also nice to exercise above the smog.  Ick.

The atmosphere is about to go into outlier mode over the western United States, and the foundation was laid upstream over the north Pacific last night.  As shown in the satellite image below, at 11 PM MST, a weak cyclone (note the comma cloud) was just south of the western Aleutian Islands.   0600 UTC 28 Nov 2011 GFS Analysis and IR satellite image The surface analysis from the Ocean Prediction Center showed a central pressure of 1000 mb, with two ominous labels near the low center: Rapidly Intensifying and Developing Hurricane Force .   Just six hours later, at 1200 UTC, the cyclone central pressure was 989 mb, an 11 mb drop in 6 hours.   Thus, this cyclone is well on it's way to meet the criteria for explosive cyclogenesis , which requires an average deepening rate of 1 mb per hour for 24 hours.  Meteorologists sometimes refer to such rapidly deepening cyclones as "bombs" ( Sanders and Gyakum 1980 ).  A cyclone like this ha...

Compared with last winter's snowpack, we're dealing with a far more insidious beast this year.  We have already had one avalanche fatality and natural and human triggered avalanches are still being reported in the backcountry .  Brett Kobernik summarized the situation quite well in today's avalanche advisory (my emphasis added below). Our main concern remains triggering an avalanche that breaks into old faceted snow. As I see it, we are in a holding pattern right now where I have not seen any significant improvement with the weak layer over the last seven days. Faceted snow is a type of snow characterized by angular crystals.  Facets can be small, but when they reach large size with steps and striations on their surfaces, they are called  depth hoar  (see below). Source: zacstracks.com Faceted snow is weak, lacks cohesion, and forms where there is a large temperature gradient in the snowpack.  A temperature gradient is a measure of how quickly the...

It's snowing lightly in the mountains this morning, but not enough to get excited about.  I was just taking a look at the medium range forecast and it, like the forecast for this holiday weekend, is a turkey for skiers too. The medium range forecasts being produced by the National Weather Service and European Center for Medium-range Weather Forecasts are dominated by a ridge over the western United States for the next 5-7 days, with only a couple of weak systems pushing into the ridge, the strongest on Wednesday, which right now the computer models suggest will give us a dry cold-frontal passage. Global Forecast System (GFS) forecast valid 1200 UTC (0500 MST) Wednesday 30 November). The bottom line is that it looks mainly dry through the middle to end of next week.  Having a thin snowpack sit around for so long is simply not good for avalanche conditions.  The buried facets from October's early snow are not healing (see today's Utah Avalanche Center  advisor...

We've gotten off to a decent start for the ski season, but conditions remain marginal.  The latest forecasts suggest that our best chance for snow this holiday weekend will be Friday when a weak short-wave trough brushes by us to the north.  As things stand now, one computer model thinks it will be a weak event, the other a non event. Global Forecast System (GFS) forecast valid 11 AM MST Friday 25 Nov 2011. North American Mesoscale (NAM) model forecast valid 11 AM MST Friday 25 Nov 2011. After the weak event on Friday, a high-amplitude ridge builds over Utah. GFS forecast valid 11 AM MST Sunday 27 Nov 2011. That means it will be sunny and warm in the mountains.  In other words, beautiful weather and great travel conditions, but I'd like to have some fresh powder for which to give thanks this weekend.

Southwest winds picked up in the mountains overnight, bringing in much warmer temperatures.  It is presently in the 30s at most locations, including the top of Mount Baldy (11,000 ft) where it is 31F. 1425 UTC (0725 MST) 23 Nov 2011 temperature and wind observations in the Cottonwood Canyons. The coldest temperatures are presently at the Spruces Campground in Big Cottonwood Canyon where it is 21F.  The area around the Spruces is the refrigerator of the Wasatch as it is a flat basin in which strong cold pools can form.  That is certainly the case this morning.  In fact, it is 19F warmer at the top of the Moonbeam lift at Solitude.  Now that's what I call an inversion. The cold air pool should scour out this morning, and temperatures at the Spruces will rocket to near 40F.  Be sure to dress in layers!

A nice article appeared on the Salt Lake Tribune web site this evening about our activities with the DOW.  I especially liked that our graduate students were prominently featured as they are the real brains behind the operation and they took full advantage of every opportunity this past month.  Weather never sleeps and, on a few nights, neither did they.  This past month with the DOW was easily the best teaching experience of my career. Peering into Wasatch Range and Little Cottonwood Canyon with the DOW

1500 UTC (0800 MST) 22 Nov 2011 IR Image That is Hurricane Kenneth, a category 4 hurricane that is now the strongest late season eastern North Pacific hurricane on record. It is perhaps a sick and demented dream of mine to have a surge of hurricane-related moisture into Utah in November.  Imagine the high-density, heavily rimed snow and graupel that would result in the upper elevations, just what is needed to build a snowpack. Alas, the moisture from Kenneth is presently forecast by the Global Forecast System (GFS) to surge up through western Mexico and then into New Mexico. GFS sea level pressure (contours) and integrated water vapor (color fill) for 0600 UTC 22 Nov – 0600 UTC 25 Nov 2011 Close, but not quite close enough, although this does bear watching to see if the moisture can creep up into the four corners area.  And, in case you are wondering, hurricanes have produced high-mountain snow over the southwest, including the infamous Hurricane Lester in Augus...

The folks from the Center for Severe Weather took the Doppler on Wheels away this afternoon. However, I didn't let it leave without a fight!

Here's a sneak peak at some of the Doppler on Wheels data we gathered Friday night.  Below are vertical scans taken looking up Little Cottonwood Canyon from Daybreak.  The reds are where we are getting strong returns from the terrain, which means it's ground clutter and not precipitation.  The oranges are areas where the precipitation rates are the greatest.  At this time, the frontal band is right over Little Cottonwood and the Salt Lake Valley and it is snowing hard everywhere.   That being said, we see some of the same features that we saw during the storm the previous weekend .  In particular, the peak depth of string radar reflectivities (organge colors) occurs at about mid canyon.  Farther up canyon, the storm shallows. Later, after the frontal band moves through, this structure persists.   In particular, note how the strongest/deepest returns are mid canyon.  In this instance, precipitation rates are probably greatest...

Tomorrow marks the 10th anniversary of the start of the 2001 Hundred Inch Storm , a multiday storm cycle that laid down 108 inches of snow at Alta, including 100 inches during a 100 hour period.  If memory serves me correctly, there was little snow leading up to Thanksgiving weekend that year, so the snow answered the prayers of desperate Utah skiers who were burning their rock skis as a sacrifice to Ullr to bring snow. As described in Steenburgh ( 2003 , 2004 ), the Hundred Inch Storm provides a great example of what Mother Nature can do when the atmosphere and Great Salt Lake are in outlier mode.  It was produced by two storm systems that were strongly augmented by the Great Salt Lake Effect.  Each storm system featured a period of stable, pre-frontal precipitation, a period of unstable pre-frontal precipitation that followed the surge of cold, dry air aloft, heavy frontal precipitation accompanying the cold front, and then intense lake-effect snowfall. Radar imag...

After spending much of the last month storm chasing, I was finally able to get out and sample the early season snowpack myself yesterday.  The meteorologist inside of me said that this is a good start to the ski season, but on the climb through the aspens, my tibias were screaming that I'd better keep my tips up on the descent. Let's look at some numbers.  Data from the Natural Resources Conservation Service (NRCS) SNOTEL stations show that on a basin-wide scale, northern Utah is sitting about 110–125% of average snowpack snow-water equivalent (SWE). Not too shabby.  At the Snowbird SNOTEL, it appears we are running just a shade behind average and   where we were on this date last year. That being said, during the early season, we deal a bit with the so-called statistics of small numbers.   The average this time of year is quite low and the difference between a good or bad early season is really just a reflection of whether or not we get a storm...

Our Doppler on Wheels activities for the night have concluded, bringing an end to the eighth intensive observing period (IOP8) of the Storm Chasing Utah Style Study (SCHUSS).  Our overnight crew tells me they shut down around 4 am.  What does a storm-chasing crew do at that time of morning?  Head to Denny's of course... Today will be the first Saturday in 3 weeks that I've had off.  I'm going to relax and head up for a short backcountry ski tour in the afternoon to check out the snowpack and start getting into shape for the winter.  

It was quite a pounding of snow this evening when the frontal band came through.  Alta-Collins picked up 6" of snow with .27" of water in 3 hours, including a 4" uptick on the snow interval stake from 9-10 PM. Things are looking interesting for later tonight.  The precipitation to the west has some embedded stronger cells. We're hoping we might see some deeper orographic convection over the mountains once this comes in.  We will be adjusting our radar scanning strategies more heavily on the Cottonwood Canyons area to allow for more frequent scanning if this turns out to be the case.  Keep your fingers crossed.

It's nuking out there and we are seeing some incredible stuff with the Doppler on Wheels (DOW) including the highest radar reflectivities of the entire field campaign.  I just heard one of the people in the cab say, "we are the kings of stratiform snow."  The screen shot below shows a vertical scan across Lone Peak.  Check out the waves at the top of the precipitation band.  More later, if we can find the time...

The Doppler on Wheels (DOW) should be getting setup as I type this.  Everything thusfar is proceeding according to plan.  The shallow surface front has pushed through the Salt Lake Valley, but the heaviest precipitation remains to the north where the front is deeper.  Things are, however, beginning to fill in and I suspect things will start to get exciting by perhaps 7-8 PM. I am attaching a guestimated terrain-clutter map from our last observing period.  This one is oriented so that west is up, east is down, and our the red line, which indicates the position of one of our vertical radar slices (i.e., RHI) cuts directly up Little Cottonwood Canyon and as close as we can get to over the snow-crystal imager and vertically pointing radar that Tim Garrett and Sandy Yuter have installed at Alta.  The purple line approximates the canyon floor. We'll be scanning this area extensively to examine the mountain effects during the storm.  Keep your fingers cr...

This is it for Utah storm chasers, our last weekend with the Doppler on Wheels before it returns to the Center for Severe Weather Research.  We will be out in the storm tonight and may opt to go down and look at Mt. Timpanogos on Sunday. The latest models suggest a strong frontal precipitation band will develop over northern Utah between 5 and 8 PM tonight.   The event then transitions into an event where mountain enhancement plays an increasingly important role during the late night hours.   We will be deployed where we can examine the frontal precipitation processes and orographic enhancement in and around the Cottonwood Canyons.  So looking forward to it. I figure tonight might be our last dance, but the latest model runs are calling for some precipitation to develop in southwesterly flow on Sunday afternoon.   If this forecast holds, we may head down to Utah County to examine enhancement on the 7000 foot southwest face...

One of my students, Jon Rutz, is working to better understand the inland penetration and impacts of atmospheric rivers over the interior western United States.  Atmospheric rivers are corridors of moisture transport that contribute to a large fraction of the flooding events in California and appear to play a role in major precipitation events over the interior, as we have discussed in previous posts . Mike Dettinger, Marty Ralph, Paul Neiman, and several compadres have done a great job illustrating the importance of atmospheric rivers in the weather and climate of the west coast.  In Dettinger et al. (2011)  they present a fantastic analysis of the contribution of atmospheric rivers to the hydroclimate of the western United States. Contribution of precipitation on the day of and day following atmospheric river landfall on the west coast of the United States to the wet season (Nov–Apr) precipitaiton. From Dettinger et al. (2011). Jon and I were both surprised th...

I have this dream in which we have the Doppler on Wheels, but all the precipitation falls during the day and early evening and we're able to sleep at night.  I don't think that will be the case tomorrow. But, we should be thankful that we do have a storm on tap.  The latest forecast from the North American Mesoscale (NAM) model calls for a front to develop and intensify over northern Utah tomorrow.  By late tomorrow, the forecast front is sitting pretty much over the Wasatch Front, but precipitation is still confined to the northern Wasatch. The NAM calls for the frontal precipitation to fill in nicely tomorrow evening, with the front sitting right over the Salt Lake Valley at 11 pm. The flow gradually veers to northwesterly as the front moves downstream, with precipitation continuing overnight over the Wasatch Range. Thus, it looks like an all-nighter is in store for the Doppler on Wheels, but also that there will be some freshies for skiers on Saturday ...

Last November, University of Utah Atmospheric Sciences graduate student Kyle Tietze passed away suddenly in his sleep.  Kyle was a popular graduate student, well known for his love of travel, passion for science, and skills as a brewer.  There are two empty bottles of his Synoptic Stout and Forecaster's Friend High CAPE Beer that I keep in my office as his home-made labels were perfect for this Wasatch Weather Weenie.  He was also an exceptional athlete and skier.   Kyle's family recently established a development fund in the Department of Atmospheric Sciences to support travel expenses for student exchanges between the University of Utah and institutions in other countries.  Kyle worked at the University of Lille in France prior to his passing.   Donations can be made by clicking here.   Simply note that the gift is in honor of Kyle Tietze and add a special instruction that it is for the Tietze fund.  

We are finally getting a chance to look at some of the data we collected during Sunday's storm.  We haven't had a chance to georeference it, so I need to hand wave a bit in this discussion. On Sunday, we were taking vertical slices up Little Cottonwood Canyon from our observing site near Daybreak.  An approximate position of one of these vertical slices is shown below.  It is oriented up the canyon and crosses over Snowbird and Alta.  Keep in mind that the radar beam spreads with distance from the radar, so the beam is actually somewhat wider than indicated by the red line. Below is the radar reflectivity from this slice.  Warm colors indicate higher radar reflectivities that likely indicate greater concentrations or sizes of ice paticles and snowflakes.  The bright red stuff near the bottom is ground clutter.  I've indicated where I believe we are getting returns produced by the Baldy Shoulder (separates Alta from Snowbird), High Greeley (the r...

It was a terrible day in the Wasatch backcountry yesterday.  The Utah Avalanche Center reports there were about 10 human triggered avalanches, one leading to the death of Jamie Pierre .  Our thoughts are with the victim's family and friends.  Get well wishes to others who were injured. In late September, we discussed how early snow usually becomes weak snow .  This is what has happened to the mid-October snowfall on northerly aspects during the past couple of weeks, leaving a weak foundation for the snow that came this weekend.  In fact, the weekend snowstorms put down more than 1.8 inches of snow-water equivalent at Alta-Collins, with the heaviest precipitation rates early Sunday morning as people were venturing out.  Even more water weight would have been added to the snowpack in wind-deposited areas. I'm thankful I was busy with the Doppler on Wheels as the temptations of powder fever must have been great.  It's early season (we're stoked...