Wasatch Weather Weenies

Courtesy John Lawson, University of Utah.

My Samsung Galaxy S does the job.  Large graupel falling at 5:03 PM immediately following the front. For those of you wondering, yes, graupel is fully recyclable.  Surely you've heard of the water cycle! These heavily rimed snow crystals form in strong updrafts, which we certainly had at the leading edge of the surface cold front.  I suspect we'll see a transition to big fat aggregates (multiple snowflakes stuck together) soon.

Some photos looking west from the Avenues showing the penetration of the front into the Salt Lake Valley at 448 PM and 451 PM MST.   Batten down the hatches!

It will be snowing and blowing soon.  This is a commuter special.

There is a very strong pressure gradient ahead of the approaching cold front that is driving strong southerly along-valley flow in many of the valleys of northern Utah including the Salt Lake and Tooele Valleys.  The strong pressure gradient is evident in the 1800 UTC (1100 MST) sea-level pressure analysis below. Source: NCAR/RAL It has been fairly windy in the Salt Lake Valley this morning.  In fact, the wind gusts on the valley floor are nearly as high as at some mountain site.  For example, at 1100 MST, winds at Salt Lake City International Airport were gusting to 43 mph, while at the top of Mount Baldy in upper Little Cottonwood, an extremely exposed ridge-top site, they were only reaching 50 mph.  Looking at the gusts in the map below (red text), you can see a number of valley sites with gusts comparable to or higher than observed at many upper-elevation sites in the Wasatch Mountains (ignore the 59 mph gust in Sandy which appears erroneous). Source: NO...

We've been waiting all season for this, but we're finally in the midst of an active storm cycle where storms come in rapid succession.  In fact, it is already snowing some this morning in the mountains. Source: NCAR/RAL That's just an appetizer as we have a cold front moving through northern Utah later today and this evening. And the pattern will likely remain active with periods of snow in the mountains through Friday morning.  Even the valleys will get something out of this. When all is said and done, this will be our stormiest week so far this season.  Finally!

I use 10" as the minimum amount of snow required for a deep powder day.  We haven't had many days with that much snow this season (2 if I remember right), but we have one today.  The Alta-Collins stake hit the 10" mark at 8 am. Snowfall overnight was remarkably uniform in the central Wasatch with Alta, Snowbird, Park City, Deer Valley, and Solitude all reporting 7" as of about 5:30 am this morning.  Northern areas like Powder Mountain and Snowbasin reported only 2".   As discussed yesterday , this was a situation where precipitation was going to be spotty and the flow was easterly for part of the night, which enabled the Park City side to get in on the action and create a more uniform snowfall.   That won't be the case this morning as the flow has now transitioned to west-northwesterly.  The radar imagery shows quite nicely the precipitation enhancement over the Wasatch Mountains and shadowing to the west.  The plus indicates the posit...

I like a storm that starts like this one.  Check out the view from the Avenues this evening.  The Wasatch are obscured (which means it is snowing) and the Salt Lake Valley is filled with mammatus clouds . Click to enlarge Numerous mechanisms have been proposed to explain the formation of these clouds.  Here in Utah, they seem to be frequent visitors when moisture moves in at mid levels above a dry low-level airmass.  There's a good discussion, and even more fantastic pictures of these clouds, at wikipedia , which draws heavily from an excellent review article by Schultz et al. (2006) .

Source: USDA Forest Service Fellow University of Utah Professor Tim Garrett and I will be online this Thursday at 1 PM MST to talk about snow, winter storms, and avalanches as part of a live chat hosted by ScienceNOW , the daily news site of the journal Science .  We'll be talking in general about the stuff that you weather and snow geeks love so much, but also some of our National Science Foundation (NSF) sponsored research on lake-effect storms and snow crystals, including Tim's cool Multi-Angle Snowflake Camera (MASC), which we discussed in a post last week .  For more information, see this NSF press release . To participate in the chat, go to the Science chat page on Thursday from 1–2 PM MST.

The forecast models call for a broad upper-level trough to swing into the interior southwest United States today, with the trough axis upstream of Utah by 2300 MST tonight. I think the forecast for the Wasatch Mountains tonight is difficult for a few reasons.  First, there some subtle but potentially important differences in the track of the upper-level and surface lows in the NAM and GFS models (not shown).  Second, the forecast precipitation ahead of the trough is scattered in nature.  For example, check out the 3-h accumulated precipitation produced by the NAM from 2000–2300 MST tonight. Note the lack of organization in the precipitation pattern.  If you could run this forecast 100 different times with 100 slightly different initial conditions, you'd probably see quite a bit of variability in where the precipitation falls.  Forecasting with spatial and temporal precision in such a pattern is difficult. Another interesting aspect of the forecast is...

Actually the Pic of Saturday.  Nice MODIS image below of post-frontal dust plumes over the playa south of I-80 at 1030 MST.  Click to enlarge. 1030 MST Sat 25 Feb 2012 Modis Image Dust deposited on the Wasatch snowpack during this event was subsequently buried in fresh snow, but will surely reappear during the spring melt.  Climatologically, the peak month for dust in northern Utah is April, so more events are likely unless the spring proves to be dead with regards to strong winds associated with fronts and cyclones.  When on or near the surface, dust increases the amount of sunlight absorbed by the snow, resulting in a faster spring melt and decreased snow-cover duration.

Today was one of those days when the sun shines right through you and touches your soul.  From a weather perspective, it was a 10. Then, I came hope, took a look at the computer models, and my mood lifted even further.  We haven't had much action at all this year with regards to winter storms, but the GFS is bringing not one but two troughs through Utah this week. The first comes in late tomorrow through Tuesday.  It has a somewhat southern track, but unlike many of the troughs we've seen this year, lifts northeastward after crossing southern California and should give us some snow.  I've learned not to be picky this year. Trough #2 slides in during the 2nd half of the work week.  It's too soon to speculate about amounts, but the models suggest that between the two troughs we may push the Alta-Collins stake over the 100" barrier (it presently sits at 84"). Time to channel those positive thoughts.  Strike the word split  from your vocabula...

There's going to be dust in the air today.  The latest satellite image shows a broad area of dust behind the front over the Salt Flats, Dugway Proving Ground and the Great Salt Lake.  If you squint, you can see a tail that extends back into Nevada to the Carson Sink, although much of the dust over Utah in this instance may be of local origin. Add this to the "Plagues of Utah" that have tortured us this ski season, although dust is often in the air here, especially in the spring.

It's always difficult for a meteorologist to recover after a blown forecast.  It takes time to get your Mojo back.  Perhaps this is why I'm in research instead of operational forecasting! But, at some point you have to get back in the saddle.  I've been watching the medium-range weather forecasts and we have a couple opportunities for snow over the next few days.  The first is tomorrow and tomorrow night, although this now looks like a quick hitter event that may be fairly windy. The second is a deeper trough that moves into Utah on Monday.  Details remain uncertain, but I'm going to keep an eye on it.    Maybe we'll get lucky for once and the models will underpredict the storm tomorrow and tomorrow night and come through big time on Monday and Tuesday.  Until I get my Mojo back, I may as well be wrong in a way that yields more powder.  

Looks like 1.09" of water overnight at Alta-Collins produced only 6" of snow.  That's a water content > 18%. The Utah Avalanche Center suggests dense graupel fell with the frontal passage.  Further, there was a 105 mile per hour gust on Mount Baldy at 5 am this morning.  Pity any dendrites that fell late in the storm.

While aesthetically appealing and offering a striking subject for photography, the fact is that most ice crystals are defective and irregular in shape to varying degrees - Bailey and Hallet (2009) When most of us think of snowflakes, we think of beautiful, symmetrical crystals.  Indeed, it is possible to grow such snowflakes in a lab or, with effort, to find them in nature.  Nobody does a better job of this than Ken Libbrecht at Caltech.  Some samples from his spectacular snowcrystals.com web site are below.   Source: snowcrystals.com However, as suggested by the quote above, most natural snowflakes are defective or, if I may use a scientific phrase, "beat to hell."  In addition, there's an unbelievable variety of snowflakes in any winter storm.   One of my colleagues at the University of Utah, Professor Tim Garrett, is leading the development of an truly incredible Multi-Angle Snowflake Camera (MASC).  Other University of Uta...

I'm not willing to call this a pattern change, but I am encouraged by what I'm seeing in the medium-range forecast models, which suggests that we may continue to see some periods of snow over the next several days. For example, the European Center for Medium Range Weather Forecasting (ECMWF) model brings two major upper-level troughs through Utah, one over the weekend, the other later next week. Source: Penn State E-Wall The GFS forecast for 1100 MST Saturday shows a cold front moving into northern Utah with abundant post-frontal moisture upstream. It's too soon to get excited, but we've had so little action this year, that even a modestly active pattern would be nice.  Let's see how things play out in the coming days.

In 1938 the "Utah Interconnect" involved taking a train to Park City and backcountry skiing through Guardsman and Catharine Passes to Alta via Brighton.  Ah, the good old days.  James E. Gurr pictured.  Source: Salt Lake Tribune and Special Collections, J. Willard Marriott Library. Digging through the historical archives and a nice summary article by  Kalitowski (1988 ), I came across this quote by Wasatch National Forest supervisor James E. Gurr (pictured above) about avalanche hazards in Little Cottonwood Canyon: " Winter sports enthusiasts should appreciate the fact that there is some hazard connected with the use of snow-clad slopes and should consistently practice such safety measures as are necessary to minimize these hazards. If they will do this and will cooperate in following out suggested safety measures, we can and will continue to use our outstanding and valuable winter sports areas. The probability of snow movement is forecast on the basis ...

Go ahead, make my day . Source: wikipedia.org With a ridge to our west this morning, one would normally expect nice weather.  That's conventional wisdom, but some ridges are dirty.  A dirty ridge is typically low in amplitude, enabling moisture, clouds, and precipitation to spill over to its downstream side, especially when a short-wave trough moves downstream of the ridge axis. In addition, the ridge presently to our west has a nice connection to the subtropics on its upstream side.  As a result, there is a plume of subtropical moisture originating to the northwest of Hawaii that is spilling over the ridge axis into the Pacific Northwest.  1500 UTC 21 Feb 2012 IR satellite image and GFS analysis of precipitable water (contours every 5 mm) and 925 mb wind (vectors). This should yield a couple of days of cloudy weather with some periods snow in the Wasatch Range. Precipitation will be greater, however, further to the north which will be more direct...

Today our search for powder took us west to the Oquirrh Mountains.  I didn't have the courage to show my face in the Wasatch Mountains after my busted forecast and, since it didn't snow much, I wanted to go somewhere where we wouldn't be skiing over tracks in the old snow. We found a completely "unadulterated" snowpack with a couple of inches of low-density fluff on top of settled powder.  It was our best day of the year. Neil Lareau Yours truly In addition to great skiing, we had the entire range to ourselves as we didn't see a soul the entire day. Physically, the tour went well thanks to a new, highly scientific dietary strategy based on Trader Joe's chocolate covered potato chips. If these don't get you to the top, nothing will.

Source: http://joshywashington.wordpress.com The frontal band came overnight, but was much weaker than I expected. Source: NCAR/RAL As of 6 am, only .18" of SWE and 2" of snow at Alta-Collins.  Maybe another inch or two out of the frontal band this morning and then we'll have to hope for the post-frontal stuff to get going.  All in all, my worst forecast of the year as I was counting on Mother Nature to be more productive overnight. That being said, given good forecast model consistency over the past couple of days, I'm not sure I would have gone for such low accumulations.  Sometimes you live by the models and die by the models. The only way to recover from such a beating is to head out anyway, in search of powder...

Source: http://www.consumertraveler.com Some forecast situations are fairly predictable with the tools we have today, some aren't.  Today's computer forecast models do a fairly good job simulating cold-frontal passages over northern Utah.  Thus, while we have a beautiful day today in the Salt Lake Valley and Wasatch Mountains, we know that change is coming tonight and that the Cottonwoods will see a pretty good burst of snow tonight .  There are uncertainties with regards to the distribution, intensity, and amount of snow, but the basic idea that there will be a snowstorm tonight is fairly predictable.  That wasn't the case 10 years ago when forecast models were nowhere near as good as they are today. In contrast, the post-frontal environment tomorrow is more of a crapshoot when it comes to snowfall.  There are a number of reasons for this: Post-frontal precipitation is produced by shallow convective clouds that are small in scale and typically initiated...

President's weekend is upon us.  Aspects of the forecast are easy.  There will be tourists, traffic, and crowds in the Cottonwoods.  How about powder? The latest GFS forecast brings a cold front into northern Utah Saturday night.  We should get a period of widespread snowfall in the mountains and the valleys as the front moves through. If the timing of the GFS forecasts is accurate, snowfall rates in the Cottonwood Canyons will be highest late Saturday and Sunday morning. This looks to be a right-side-up storm, with decreasing snow water contents over time, as often occurs with frontal passages.  Our snow water content algorithms, when directly applied to the GFS output, suggest an initial snow water content of ~8% at Alta, falling to ~4% later in the storm. When applied to the liquid precipitation forecast from the GFS, this yields an accumulation of about 8" of snow at Alta.  However, the GFS does not fully account for local orographic effec...

Yes indeed, we might just get a frontal passage in northern Utah this weekend.  The latest GFS puts a bonafide cold front over the Salt Lake Valley at 1200 UTC (0500 MST) Sunday morning. Wouldn't that be grand?  We'll take a closer look tomorrow at how the system is coming together and whether or not this will be another quick hitter or a bigger storm.

It has taken quite a while, but I'm pleased to announced that a new monograph entitled Mountain Weather Research and Forecasting will be published by Springer and available this summer. The monograph is an outgrowth of a workshop held in Whistler, BC during the summer of 2008 and includes chapters on thermally driven flows, orographic precipitation, numerical weather prediction in complex terrain, downslope winds, etc.  It will also include a chapter on numerical weather prediction and weather forecasting in complex terrain.  Chapter contributors from the University of Utah include Dave Whiteman and myself.  Dave and I will be using it as the textbook for the graduate level mountain meteorology course we will teach this coming fall semester.  

Las Vegas averages only 4.14" of rain per year, although February is the "wettest" month climatologically with an average precipitation of a whopping 0.57".  For comparison, the Salt Lake International Airport averages 15.66" annually. However, a surface cyclone is moving over Vegas this afternoon. And radar shows some showers just to their west. Source: NCAR/RAL So, perhaps a few drops on The Strip.  Of course, what happens in Vegas, stays in Vegas, right?  I suspect the folks in western Arizona, where this storm is heading, won't be saying that tonight or tomorrow.

An editorial in today's New York Times asks this question , and it's a good one.  We live in an increasingly complex world, yet in the US Congress we have only one physicist, one chemist, one microbiologist, and six engineers.  There are some doctors and nurses too, but not many (about two dozen). There's no guarantee that a scientist or engineer will be a good leader or politician, but having more people in Congress who are capable of analysis and reason strikes me as being a good thing. Bill Hooke, Senior Policy Fellow for the American Meteorological Society, runs a summer colloquium  for graduate students and professionals with a strong interest in atmospheric policy.   The registration deadline for this summer is 1 March .  I attended several years ago and it is an incredible opportunity.  One morning during the colloquium, I had breakfast with Neil Lane, former science advisor for Bill Clinton.  We had dinner with Vernon Ehlers, then a republi...

Pull up an elementary textbook description of the jet stream and you are bound to see something like the image below, which includes a northern "polar jet stream" and a southern "subtropical jet stream." Source: NC State , NASA Such images give the false impression that the jet stream is a narrow, coherent corridor of flowing air that completely encircles the pole and that two jet streams are always present.  In reality, the upper-level flow is more complicated. Let's have a look at the north Pacific basin today.  On the image below, I've included contours of 300-mb wind speed at 10 m/s intervals, beginning at 30 m/s (warmer colors indicate larger wind speeds) and have annotated an analysis of the jet streams in blue. Note how there are two regions of strong winds over China.  Most meteorologists would call the southern most wind maximum the subtropical jet, and the northern most the polar jet.  These two jets do not remain distinct, however.  ...

A somewhat unusual occurrence that becomes more common in Spring is the development of the so-called Tonopah or Nevada Low ( http://www.navair.navy.mil/nawcwd/weather/chinalake/fcstrhndbk/Sect2.htm ). These aptly named systems tend to form in the lee of the Sierra Nevada mountains, in the vicinity of Tonopah, NV. These systems can produce heavy precipitation on the east-facing slopes of the Sierra and in other regions that experience the typical rain shadow associated with approaching Pacific storms. The document linked above states that the development of these systems is typically preceded by the flow of cold air from Canada towards a warmer airmass over the Great Basin, creating unstable conditions. Indeed, The 18z GFS indicates a pronounced flow of cold air at 850mb from British Columbia into Nevada in the wake of an upper-level trough. The same page goes on to list three other conditions that may contribute to the strengthening of the Tonopah Low: 1. A wave on a west-east oriented...