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.  

Thursday, October 9, 2014

Utah Snow and Avalanche Workshop


The 7th annual Utah Snow and Avalanche Workshop (USAW) will be held at the Southtowne Expo Center on Saturday, November 1, 2014.  The USAW is always a fun event and a good way to prepare the mind for safe backcountry travel during the coming winter.  For more information, see http://utahavalanchecenter.org/event/2014-utah-snow-avalanche-workshop-public-session.

Tuesday, October 7, 2014

Use and Misuse of Water Vapor Imagery

Water vapor satellite images are frequently misused and misinterpreted.  Here's a very basic primer.

Water vapor images do not measure water vapor and they certainty do not measure water vapor in the lower atmosphere where it plays an important role in the development of precipitation systems.  Water vapor imagery is simply based on a band of infrared radiation that is absorbed and emitted by water vapor.  This contrasts with the band of infrared radiation sampled by conventional infrared satellite images which is largely unaffected by the presence of water vapor or other atmospheric gases.

As a result, water vapor imagery is strongly influenced by the distribution, temperature, and concentration of clouds and water vapor in the upper troposphere, typically at altitudes above 500 mb (5500 meters).  A prime example is the water vapor loop below, to which I've added contours of precipitable water (i.e., total integrated water vapor).  Note the northward spread of cirrus clouds and upper-level moisture from into Utah over the past two days.  As ominous as this looks, it is simply a very thin, cold layer of clouds and moisture.  The juicy air associated with tropical storm Simon remains well to the south, as indicated by the precipitable water contours, and is just beginning to push across the US–Mexico border.  


Even areas in red above, which many people interpret as "dry" can overlay areas of abundant low-level moisture.  Those are areas that are dry and warm in the upper atmosphere, but not necessarily in the lower atmosphere.  For example, in the wake of tropical storm Simon, the upper-levels are very dry and warm, but the precipitable water values are fairly high due to abundant low-level moisture.

One of the major advantages of water vapor imagery is the ability to track water vapor features in areas that are cloud free.  This is extremely useful for inferring upper-level winds when no clouds are present.  One can also identify smaller-scale upper level features such as short-wave troughs using water vapor imagery.  These are effective applications of water vapor imagery.  The use of water vapor imagery to infer low-level water vapor concentrations is, however, dubious and should be avoided.