Friday, October 31, 2014

Not So Scary Weather

As of 11:30 AM this halloween, it's already 68ºF at the Salt Lake City Airport.  The record high for the date is 76ºF and it's looking like we will make a serious run at that.

Other than the fact that it may be windy later today, you can't ask for better Halloween weather.  That's great news for trick-or-treaters who won't have to cover up their costumes with bulky layers to keep warm.

Tomorrow looks to be an exciting weather day with the potential for some thunderstorms, strong winds, and a vigorous frontal passage.  After that, much depends on the details of the postfrontal flows and the whims of the lake.  I still see a lot of spread in the model forecasts, although most are leaning towards periods of snow beginning tomorrow afternoon through Monday.  My most likely accumulation for the central Wasatch is 4 to 8 inches, less if the NAM wins (drier post frontal environment),  more of the GFS wins (wtter post frontal environment) and we also get the lake going.

Thursday, October 30, 2014

Some Things We Know, Some Things We Don't

One of the most important papers in the atmospheric sciences was published by Ed Lorenz, the Father of Chaos Theory, in the journal Tellus in 1969.

The key finding of the paper is summarized in the second paragraph of the abstract:
It is found that each scale of motion possesses an intrinsic finite range of predictability..."cumulus scale" motions can be predicted about one hour, "synoptic-scale" motions a few days, and the largest scales a few weeks in advance.
Although we have learned that in some instances the predictability limits for atmospheric phenomenon may be longer than suggested by Lorenz in that paper, the general result that larger-scale weather phenomenon (e.g., cyclones, upper-level waves) can be predicted with greater lead time than mesoscale weather phenomenon (e.g., fronts and mountain waves) and especially smaller scale phenomenon (e.g., precipitation generated by convection) is critical to consider in weather forecasting.

A great example is provided by the forecast for this weekend.  We have known for a couple of days that an upper-level trough will be moving through Utah this weekend and that this would be accompanied by a dramatic airmass change and cooler weather.  Both the ECMWF and GEFS ensemble forecast systems have shown this for the past couple of days and continue to show it today, as illustrated by the GEFS forecast panels below.

The lower right-hand panel, in particular, is known as a spaghetti diagram.  It shows contours of 500-mb height from all 21 GEFS forecasts.  Where the lines are close, there is good agreement.  Where you see spaghetti, there is lower agreement.  All members call for a trough to be approaching northern Utah on noon Saturday, but the spaghetti is indicative of a range of forecasts for the position and intensity of the trough.

So, this is an illustration of Lorenz's theory in action.  The large-scale characteristics are relatively predictable, but the smaller-scale characteristics are less predictable.

Things get even more problematic if we ask how much precipitation will fall?  The precipitation forecast is dependent not only on the trough structure, but also the frontal structure and dynamics (a smaller scale process), the associated cloud processes, and interactions with the topography.  These smaller scale processes have a shorter predictability horizon than the large-scale trough.

This is why we can now anticipate a large-scale airmass change many days in advance, and indicate that precipitation is likely, but nailing down rainfall and snowfall timing and amounts is more problematic.  In addition, many storms in Utah are very small in scale.  As a result, the predictability horizon for rainfall and snowfall is even shorter here than found in other parts of the country where cool-season storms are larger in scale, especially the eastern United States.

This case is especially problematic since the various models and their ensembles have yet to tell a consistent story with regards to the gory details.  My best guess is that the mountains are going to see a few inches late Saturday and Sunday, but it won't be a huge event and it will probably leave us in hiker and skier Purgatory when the ridge builds back in next week.  

Wednesday, October 29, 2014

Slipping Further Behind

My graduate advisor, Cliff Mass, provides yet another sobering assessment of U.S. numerical weather prediction in his blog today.  Be sure to give it a read.  Many of you are well aware that the European Center for Medium Range Weather Forecasting (ECMWF) is currently the gold standard for numerical weather prediction.  There are a host of reasons for this, but inadequate computer power for operational numerical weather prediction in the U.S. is one of the more significant.  Further, while other nations are plowing forward with major computer hardware investments, the U.S. has failed to even purchase a computer with the $25 million that was provided to NOAA by Congress a year and a half ago.


U.S. National Centers for Environmental Prediction
OK, those images exaggerate the situation, but this is serious business since advances in computer power and modeling capabilities offer significant potential to protect lives and property in the United States.  Other countries aren't simply throwing money at the problem for national pride. They recognize the economic advantages of advances in weather forecasting, not to mention better anticipation of a good powder day.

Announcement: Porter Fox Utah Talks

Porter Fox, Powder Magazine Editor and author of Deep: The Story of Skiing and the Future of Snow, will be giving three talks in Utah next week.

  • 12:00 PM 4 November, Weber State University, Shepherd Union Building, Wildcat Theater
  • 11:30 AM 5 November, Utah State University, Taggart Student Center
  • 7:00 PM 6 November, Westminster College, Vive Gore Auditorium
I believe all three talks are free and open to the public.

Tuesday, October 28, 2014

Snowstorm Possibilities Through the Weekend

One storm is currently "raging" in the Wasatch, with another one possible this weekend.

The storm presently underway is of the artificial variety as the resorts lay down a base of artificial snow in preparation for the coming ski season.  Below is a view of Alta this morning.

I'm guessing someone will try to ski the white ribbon of death in the near future, if they haven't already.

The second storm is fortunately of the natural variety.  Most of the medium range ensemble model forecasts are calling for an upper-level trough and surface front passage this weekend.  This is true of the GEFS ensemble below, as well as the gold-standard ECMWF ensemble.
Source: NWS
There is, however, some variability and timing and amount.  Some forecasts are calling for the action to get going early Saturday, others later Saturday.  Some suggest a few inches for the mountains, others a more significant event.  We've passed the so called predictability horizon with regards to the big picture (i.e., there will be a trough/front passage this weekend), but not for the gory details.  We'll see how things come together in the coming days.

Monday, October 27, 2014

Orographic Convection

Looking southeast at orographic convection over the central Wasatch @ 7:45 AM this morning
There's a lot to be learned by observing the weather during periods that are relatively benign.  Big storms are great, but you can't always peer into them and see the underlying processes that are contributing to precipitation generation.   Weak events, however, enable you to see some of the phenomena that ultimately contribute to big events.

Early this morning provided such an example.  We had weakly unstable northwesterly flow impinging on the central Wasatch.  This is led to the development of orographic convection over the central Wasatch and adjoining Traverse Range (see photo above).  Orographic convection features strong updrafts that are initiated as unstable or potentially unstable flow is forced over a mountain range.  Typically the intensity, depth, frequency, and or spatial coverage of the updrafts is greater over the mountains than the upstream lowlands, resulting in more widespread and deeper clouds.  

In some instances, such convection produces or enhances precipitation rates over the mountains, sometimes resulting in heavy snowfall or rainfall.  Today, however, the airmass is relatively dry, so for the most part we are seeing non-precipitating cumulus clouds developing and persisting over the mountains, with just a few showers at times.

Here are a couple of views, the first looking southward from near Red Butte Canyon.

And a second looking eastward from the western Salt Lake Valley.

Note in particular the greater depth and persistence of cumulus clouds over the Wasatch Mountains compared to the upstream lowlands.

This provides a weak example of what often happens in unstable, post-frontal, northwesterly flow over northern Utah.  Lifting by the mountains helps to initiate or intensify orographic convection, enabling storms to rage on.

Sunday, October 26, 2014

A Nearly Snow Free October

Although we will see a few snow showers today and tonight in the high country, perhaps enough to coat the ground in places, it appears that October will go into the books nearly snow free as the rest of the week through Halloween looks dry.

For those of you looking to make turns, Gunsight currently has a 0-2.5 cm base.  I'm using metric for marketing purposes.

The metric base builder can be found elsewhere in the Alta–Snowbird high country...

Most of this skiff of snow consists of large graupel, ice pellets, or small hail that fell during Tuesday's frontal passage.  I never know what to call precipitation that looks like this.  In honor of The Princess Bride, perhaps we should call it "graupel of unusual size."  This mass collected in a local pit of despair.

Elsewhere in the Wasatch, Lake Mary (left) is looking forward to a recharge this winter.  I don't know what the typical "spillway" elevation of Lake Mary is in October, but it surely can't get much lower than it is this year.  Note the dry dam at upper left.

On the plus side, unless today and tonight surprise me with more snow than expected, we should end October largely facet free.  Hopefully Mother Nature will eventually turn on the spigot in a big way so that we can avoid the deep instabilities that have plagued backcountry travel in recent years.

Saturday, October 25, 2014

High-Elevation Tornadoes

There's a nice article in the latest Monthly Weather Review examining what is now the highest-elevation tornado documented in the United States (see Monteverdi et al. 2014, access to the full article may be paywalled to those without a subscription).

The tornado occurred in the Rockwell Pass area of Sequoia National Park at an elevation of about 12,000 feet on 7 July 2004.  Impressive photos of the storm were taken by Scott Newton, a backpacker in the area.

Source: Monteverdi et al. (2014)
Source: Monteverdi et al. (2014)
Documented tornadoes at such high elevations are quite rare.  The most famous is the F4-rated Teton tornado of 1987 (see Teton Tornado 25 Years Ago by U Alum and retired Storm Prediction Center forecaster Jack Hales).

No tornadoes for Utah today, but the NWS has a wind advisory out for much of western Utah including the Salt Lake Valley for this afternoon and evening.

Source: NWS

Friday, October 24, 2014

USAW Workshop and Book Signing

The 2014 Utah Snow and Avalanche Workshop (USAW) will be held on Saturday, November 1, at the Southtown Expo Center.  As is the case every year, an excellent schedule is on tap to help prepare you for safe recreating in the Wasatch backcountry this winter.  Click here to see the schedule and purchase tickets in advance (click the "Add to Cart" button at the bottom).

I'm pleased to be giving a talk during USAW on my book, Secrets of the Greatest Snow on Earth, which covers all the essentials of Wasatch weather and climate for skiers and backcountry recreationists. 

We've pulled some strings and Weller Book Works should be on hand with signed copies of the book for purchase, a few days ahead of their general availability.  They are also taking advance orders at their Trolley Square location.  Pre-release sales have been high, so don't wait!

Thursday, October 23, 2014

Seize the Next Three Days

Mother Nature will be treating us with mild fall weather through Saturday and, given the lack of snow in the high country, I encourage you to seize the opportunity to get in some hiking, running, or biking either in the valley or the mountains.

The NAM time-height section below pretty much tells the story.  We have some upper-level moisture moving through the area today, which will lead to some mid-and-high clouds at times.  After that, the warm, dry southerlies are in firm control through Saturday.  

By late October standards, temperatures will be mild through the period, with temperatures on the top of Mt. Baldy (11,000 ft) rising today and remaining in the low-to-mid 40s through Saturday.

High temperatures at the Salt Lake City airport today, Friday, and Saturday should be in the 70s. Temperatures on Friday and Saturday will likely be in the mid 70s and could approach the records for each day (78ºF in both instances).


Tuesday, October 21, 2014

Mountain Mass Transit in Innsbruck

I am back in Salt Lake City and there is some weather outside today, but I'm having difficulty thinking about it in the wake of my trip through Europe.

I've already done a post on Innsbruck (see The Foehn Giveth and Taketh Away), but wanted to share some more of our experiences as they bear some relevance to long-term transportation planning for the Wasatch Front and Mountains.

Innsbruck is a "small" city, with a population of 130,000, but like many cities in Europe, is relatively high density with a large concentration of restaurants, bakeries, cafes, and the like.

It also has a remarkable public and mountain cableway system that provides incredible access to the mountains around Innsbruck.  First, there is the Nordkettenbahn, comprised of the Hungerburgbahn funicular and Seegrubenbahn and Hafelekarbahn aerial trams, which take you 5500 vertical feet from downtown Innsbruck to the top of the Nordkette or "North Chain" of mountains.

As mentioned in my earlier post, the two aerial trams ascend a remarkably steep and continuous slope, as illustrated by the view from the top of the Hafelekarbahn.

Here's another perspective showing the classic European passive avalanche control infrastructure in an avalanche starting zone for a slide path that probably drops a vertical mile to neighborhoods above Innsbruck.

Not interested in the steeps, then you can instead get on light rail and travel to the village of Igls and the Patscherkofel ski area, site of the famous 1976 downhill in which Franz Klammer claimed the gold for Austria.

Love the old-school tram!

Or, take a different light-rail line to the Village of Mutters where you can catch the Mutteralmbahn.

If that's not too your liking, continue on the light rail to the Fulpmes.

Yup, there's another resort here.

Or, forget that.  Catch the bus from here and you can travel up the entire Stubai Valley to Mutterbergalm.

Basically, the entire Stubai Valley can be accessed by train, train and bus, or direct bus from Innsbruck. During summer, hiking trails abound with lots of options for point to point hikes linked by the valley bus.

Or, get on the heavy rail and travel to St. Anton, the Otztal Valley, or a number of other great spots in an hour and a half.  

Whether or not such a mass transit system would work for the Wasatch Front and Mountains remains to be seen.  There are a host of issues that need to be explored, from funding to ensuring adequate environmental protection.  Now is a good time to let your opinions be heard.  Public comments are now being collected by the Mountain Accord project, which seeks to develop a future plan for the central Wasatch Mountains.  

Monday, October 20, 2014

Winter Speculation: The Arctic Oscillation

Many of you powder hounds out there have heard the terms "El Niño" and "La Niña" thrown around quite a bit in the context of seasonal prediction, but these are not the only long-term atmospheric oscillations that are potentially useful for looking into an upcoming winter. Ever heard of the Arctic Oscillation?

In the 2nd installment of the series of posts giving the people what they want (speculation about the upcoming winter), we will take a brief look the Arctic Oscillation Index and its potential impact on monthly snowfall in the Wasatch.

First of all, what is the Arctic Oscillation? The AO takes into account the difference in sea-level pressure between the Arctic and the mid latitudes (i.e. the continental U.S.). When the pressure is relatively low in the Arctic and relatively high in the mid latitudes, this promotes a predominately east-west jet stream and a "bottling-up" of colder air in the high latitudes. This is a positive AO phase. When the opposite occurs (pressure is relatively high in the Arctic and relatively low in the mid latitudes), the jet stream may exhibit more "buckling" and north-south flow, allowing cold air to spill southward more readily. This is a negative AO phase, and the Central and Eastern U.S. often see significant outbreaks of cold air in this scenario.

So where does Utah fit into this? Let's take a look at the correlation of the monthly mean AO Index and monthly snowfall at the Snowbird SNOTEL site. Below is a figure plotting the AO Index versus total monthly SWE at Snowbird for the period 1991-2014. The red line is the best fit line.

The results are…well…not encouraging. Here are the R-squared values (a value of 1 indicates a perfect fit of the best fit line) for each month:
November: 0.03
December: 0.16
January: 0.01
February: 0.12
March: 0.00
April: 0.16

In other words, the AO Index has no correlation to snowfall at Snowbird in November, January, and March, and a very slight correlation the rest of the winter. It is interesting that December is the only month with a trend of greater snowfall for a lower AO Index…this makes me even more wary of drawing any conclusions from the slight “trends” observed. So, the AO is overall not of much use for predicting snowfall in the Wasatch on the monthly scale.

While medium-range weather forecasting (out to 10 days) has become increasingly skilled in the computer age, seasonal prediction is still in its infancy. Also, the Arctic Oscillation is also calculated over the entire Northern Hemisphere, and there are other climatic oscillations such as the Pacific Decadal Oscillation (PDO) that capture more of the conditions that impact western North America. So perhaps some of these other indices have a more useful correlation to Wasatch snowfall…we’ll explore this some other time. Until then, stick to the 7-day forecast and keep doing those snow dances.

Wednesday, October 15, 2014

Winter Speculation: Does a Dry October Mean a Dry Winter?

Before Jim left for his much deserved vacation to Europe, he asked his students to do occaisional posts. And since Jim is away I thought I would post about something he would never post about: a winter outlook based on current weather. The basic idea is that there are long term atmospheric connections that we do not yet understand, but we can still see their effects.

So does our current dry October offer any insight on our winter ahead? Below is the SWE plot from the 2004 - 2005 winter at the Snowbird Snotel. By November 1st a whopping 13.1 inches of precip had already fallen and the snowpack at Snowbird was already comparable to an average January 1st snowpack! This winter would go down as one of the snowiest since the snotel first started reporting in 1990.

Below is the SWE plot from the 1990 - 1991 winter. Total precip for October amounted to only 3.8 inches, 1 inch below normal, and the winter never recovered.

But how representative are these 2 winters? Below is a plot of October Precip versus the mean monthly precip for the following November - April. I slapped a best fit line over the data and the trend is up, but only with an r-squared value of .18 (1 means perfectly correlated, 0 means no correlation). This suggests that dry Octobers may increase the odds for a dry winter and vice versa, but keep in mind the sample size is small (24 winters), and the correlation is weak. For example if the outlier winter of 2004-2005 winter is removed, the trend is still up, but r-squared drops to 0.10.

Next I investigated the upper levels during winters after dry and wet Octobers. Winters ending in 2004, 2000, 2009, 1996, and 2013 had the 5 driest Octobers and below is the the mean 500 mb geopotential height anomalies for those 5 winters (Nov - Apr). There are above average height anomalies across the entire West suggusting ridging during those winters.

Next I looked at the winters after the 5 wettest Octobers which ended in 1995, 2005, 2007, 2008, and 2011. Although Utah has positive height anomalies, there are negative height anomalies over the Pacific northwest suggesting some upstream troughing.

Again these signals are very weak and may not pass significance tests, but it is interesting to see a signal. Why is there a signal? Perhaps seasonal to annual teleconnections, like ENSO, or something we haven't even discovered yet, weights the odds for above or below average precip during the winter and the signal begins in the fall. It's fun to speculate, but no one really knows the answer.

 So where do we stand currently? Thus far the Snowbird snotel has received 1.3 inches of precip for the month. If we do not get any more this winter would be tied for the 2nd driest October, but there is still a lot of month left. Looking at the long range, however, I find it unlikely that Snowbird receives the 4.8 inches of precip necessary for an average October, which may slightly weight the odds for a below average winter.

 Look for another post this week by another graduate student about the Arctic Oscillation and its role on our winter weather, and perhaps I will post again in November about how November precip is an even better indicator of December - April precip than October. Only if I am allowed of course.

 post by Jeff Massey

Tuesday, October 14, 2014

Eiger Dreams

Is there a better way to stimulate one's corneas than to take a train ride across Austria and Switzerland? 

I couldn't help but think about what it would be like to grow up in a picturesque village like the one below with huge mountains in all directions.  You've never heard of the village below or the mountain behind it, but that's just the point.  It's like this everywhere in the Alps.  So many mountains, so little time!

We passed through St. Anton, home to one of the best ski resorts in Europe.  In 2001, the Salt Lake Olympic Committee sent me to St. Anton to observe weather support for the 2001 Alpine World Championships.  I felt this was an unnecessary expense, but they insisted, so I went.  I remember reading an article before we left saying that it was a great expert resort with a hedonistic nightlife.  If they were going to send me there, I was going to have a good time.

I have a lot of good memories from that trip, but here's my favorite.  On the day of the SuperG, we had a couple of hours to kill and went to the neighboring resort of Lech for a few runs.  We shared a chair with a local ski instructor who asked us, "who is the big American?"  We responded, "Daron Rahlves," to which he replied, much as Arnold Schwarzenegger might in the Terminator, "never heard of him."

Later that day, we were in the finish area for the SuperG as the race unfolded.  The Austrians were placed 1-2-3, with the nearly unbeatable Stephan Eberharter and Hermann Maier 1-2 as Rahlves raced down the course.  There were probably 30,000 Austrians in the finish area that day and what a frenzy they were in.  When Rahlves crossed the finish line and -0.08 posted on the board, the crowd fell silent except for two obnoxious Americans yelling "NEVER HEARD OF HIM."  We clanked beer mugs with Daron that night.   What an experience.

But I digress.  We arrived in Bern today and got an amazing view of the Eiger, Monch, and Jungfrau in the distance.

 It has always been a dream of mine to visit the Jungfrau and see these behemoth giants up close. Work calls, however, as I'll be giving a talk and visiting with scientists at the University of Bern tomorrow.  Eiger dreams will remain unfulfilled this trip. 

Sunday, October 12, 2014

The Foehn Giveth and Taketh Away

The Foehn is a dry, downslope wind that occurs north of the Alps, although the name is sometimes used to describe similar winds in other regions.  The equivalent in North America is the Chinook wind that affects the high plains near the Rocky Mountains.

When it comes to finding clear skies, the Foehn can be your friend.  On our current trip to Europe, we opted not to make reservations for the mountain part of our trip, but instead made reservations after arriving based on the weather forecast.  One of the reasons that we ended up in Innsbruck was the likelihood of Foehn conditions and mostly clear skies today.

Innsbruck is in the northern Alps and the Karwendel Alps to its north can offer clear skies during the Foehn.  In addition, Innsbruck offers a lift system that makes the Snowbird tram look like a bunny lift.  This morning we ascended nearly 5500 vertical feet from downtown Innsbruck to the crest of the Karwendel Alps via a funicular and two aerial trams.

The view looking southward toward the Alps showed a classic Foehn pattern with clouds over the Alpine crest in the Brenner Pass area.  Clouds spilling over the high peaks near the Stubai Valley formed a cloud bank that is sometimes called the "Foehn Wall."

Thanks to the Foehn, we enjoyed some beautiful hiking along the Goetheweg trail high above Innsbruck.

Of course, what the Foehn giveth, the Foehn taketh away.  In the afternoon, we thought we would get a quick tram ride in on the south of Innsbruck to gape at our route.  South of Innsbruck, however, is closer to the main Alps and the strong winds associated with the Foehn.  When we arrived at the resort, their tram was closed due to strong winds!  

Saturday, October 11, 2014

Alpine Meteorology

Fall Break has begun and I've taken advantage by traveling to Europe where I'll be giving a talk at the University of Bern in Switzerland next week.

For a mountain meteorologist and outdoor enthusiast, visiting the Alps is an amazing experience.  The mountains are huge, the valleys deep, and the spatial contrasts in weather dramatic.

I'm currently in Innsbruck, which is located the Inn Valley, one of the longest and deepest in the Alps.

Source: Wikipedia Commons (Map data (c) OpenStreetMap (and) contributors, CC-BY-SA)
The mountains immediately north of Innsbruck rise more than 2000 m above the valley floor.  Today, Mother Nature really gave us a great view of those mountains with a beautiful double rainbow over the city.

Of course, being in Europe has other advantages, such as a beverage fountain that includes wine on tap.