Tuesday, November 16, 2010
As winds nuke in the Wasatch
Check out Alta Mount Baldy (AMB) winds ...... gusting to 96!! The sensor was rimed of course until recently.....apparently you don't need a heater if the winds are around 100mph.......
Proposed blog changes
It's pretty clear that the restricted access of this site is a pain for a number of students. Although I had some concerns that public access might restrict our ability to freelance, I'm not sure that really is the case. Thus, I'm considering making it open access. Please add a comment here and let me know your thoughts.
Monday, November 15, 2010
Welcome to the Cascades
Whatever happened to the Greatest Snow on Earth? The UAC is reporting that 10 inches of heavy dense graupel fell last night in LCC, with a water content of 20%! There were numerous reports of riming and drizzle in the Cottonwoods yesterday as well. Green light conditions are over in the backcountry.
To understand the 24 hours, we need to recognize that liquid water needs a "partner", known as an ice nuclei, to turn into ice, even at temperatures below freezing. Liquid water's preferred partner is ice, and if it comes in contact with ice, it will gladly freeze if the temperature is below 0C. On the otherhand, liquid water is more selective with other potential ice nuclei. If the water comes in contact with a particle that has a molecular structure similar to ice, it may freeze at relatively warm temperatures that are only a few degrees below freezing. On the otherhand, if the water comes in contact with a particle that is dissimilar to ice, it may not freeze until temperatures are well below freezing, perhaps -15 C or colder. There are not alot of ice nuclei floating around, so it can be hard to get a cloud to glaciate, especially if cloud top temperatures are not well below freezing.
During yesterdays riming event, we were dealing with a very stable cloud deck, with a base near 750 mb where the temperature was around -6C and a top near 675 mb where the temperature was -8C.
Under such a scenario, it is very hard to get water droplets to freeze because there are not alot of ice nuclei. As a result, you get alot of riming as cloud droplets freeze on contact with the ground, trees, your goggles, etc., and you get drizzle as the droplets grow through collision and coalescence. Sure there can be some snow, but you are dealing with a really messy mixed regime.
Major changes occurred, however, with the precipitation dynamics overnight as temperatures cooled aloft and the moisture deepened. By 12Z this morning, cloud top extended to 500 mb, where temperatures were below -20C, and lapse rates were moist-neutral through a deep layer.
In this scenario, getting particles to freeze and snowflakes to form in the upper-portions of the cloud is not so challenging. BUT, we have tons of supercooled water to play with near cloud base where temperatures are very near 0C. Given the near-neutral conditions, graupel is forming as these supercooled droplets freeze on contact with falling ice particles in the cloud. This is riming too, but it is leading to hydrometeor growth within the cloud.
These processes are very common in maritime climates such as the Cascades and Sierra Nevada, but less common here where are storms are typically colder, have more ice nuclei, and have less supercooled liquid water. For now, however, we are dealing with an environment that is more maritime than continental, so we get to enjoy Cascadian snow for a while. In my view, it's all good when you need base.
To understand the 24 hours, we need to recognize that liquid water needs a "partner", known as an ice nuclei, to turn into ice, even at temperatures below freezing. Liquid water's preferred partner is ice, and if it comes in contact with ice, it will gladly freeze if the temperature is below 0C. On the otherhand, liquid water is more selective with other potential ice nuclei. If the water comes in contact with a particle that has a molecular structure similar to ice, it may freeze at relatively warm temperatures that are only a few degrees below freezing. On the otherhand, if the water comes in contact with a particle that is dissimilar to ice, it may not freeze until temperatures are well below freezing, perhaps -15 C or colder. There are not alot of ice nuclei floating around, so it can be hard to get a cloud to glaciate, especially if cloud top temperatures are not well below freezing.
During yesterdays riming event, we were dealing with a very stable cloud deck, with a base near 750 mb where the temperature was around -6C and a top near 675 mb where the temperature was -8C.
Under such a scenario, it is very hard to get water droplets to freeze because there are not alot of ice nuclei. As a result, you get alot of riming as cloud droplets freeze on contact with the ground, trees, your goggles, etc., and you get drizzle as the droplets grow through collision and coalescence. Sure there can be some snow, but you are dealing with a really messy mixed regime.
Major changes occurred, however, with the precipitation dynamics overnight as temperatures cooled aloft and the moisture deepened. By 12Z this morning, cloud top extended to 500 mb, where temperatures were below -20C, and lapse rates were moist-neutral through a deep layer.
In this scenario, getting particles to freeze and snowflakes to form in the upper-portions of the cloud is not so challenging. BUT, we have tons of supercooled water to play with near cloud base where temperatures are very near 0C. Given the near-neutral conditions, graupel is forming as these supercooled droplets freeze on contact with falling ice particles in the cloud. This is riming too, but it is leading to hydrometeor growth within the cloud.
These processes are very common in maritime climates such as the Cascades and Sierra Nevada, but less common here where are storms are typically colder, have more ice nuclei, and have less supercooled liquid water. For now, however, we are dealing with an environment that is more maritime than continental, so we get to enjoy Cascadian snow for a while. In my view, it's all good when you need base.
Sunday, November 14, 2010
Computers, guns, and tequila
I happened to notice this morning that something is askew with regards to one of the place names on the Google map image behind the MesoWest plot below (click on it to make it bigger). Can you find it?
I'll post the answer in a couple of days if nobody figures it out, but backcountry skiers with a tendency to study topo maps and gape at big lines in Little Cottonwood Canyon should find it quickly.
This is a nice little reminder of the Mitch Ratcliffe quote that "a computer lets you make more mistakes faster than any invention in human history -- with the possible exception of handguns and tequila."
I'll post the answer in a couple of days if nobody figures it out, but backcountry skiers with a tendency to study topo maps and gape at big lines in Little Cottonwood Canyon should find it quickly.
This is a nice little reminder of the Mitch Ratcliffe quote that "a computer lets you make more mistakes faster than any invention in human history -- with the possible exception of handguns and tequila."
Saturday, November 13, 2010
Dirty ridge
With us teetering on the edge of really getting the ski season going, I've been looking at the guidance regularly hoping to see a glimmer of hope for the "big one." Nothing would please me more than to see us lay down another 2-3 feet of the white stuff, especially at lower elevations, in order to open up the backcountry fully.
At issue is whether or not the GFS and NAM are teasing me. I've been fairly surprised at just how wet they are for Monday. As shown below, we're downstream of a long-wave ridge, in NNW flow, and yet the GFS is going berserk for precip. The NAM is also fairly wet as well.
Experience suggests that we'll get some periods of snow out of a pattern like this, but not the behemoth dump I'm looking for. Sometimes in a pattern like this we get a strong riming event. Typically that happens if we're on the anticyclonic side of the jet so that we get a layer of altostratus with cloud-top temperatures that are fairly mild, say -5C. In that situation, it's hard to get ice nucleation going. Snowfall in that situation is more limited.
Keep your eye to the sky the next couple of days as this could be an interesting period to observe. Don't despair if the snow doesn't fly big time. The longer-range guidance suggests we'll have some opportunities further down the road.
Tuesday, November 9, 2010
SOLPEX IOP2 photos
Storm chasing Utah style. These photos are from Christy Wall and all but the first were taken at the east-side site near the Antelope Island Causeway.
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| Student-designed mobile mesonet unit |
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| Jeff by the Perry mercury observing trailer |
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| Balloon inflation |
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| Wait, come back! Just kidding |
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| Cozy spot...internet and all |
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