Wasatch Weather Weenies

Because of the presence of La Niña conditions in the tropical Pacific, La Niña is an easy target to blame for the wacky weather of the past month or two, but is it the real culprit?  Let's have a look.    La Niña is a component of the natural see-saw of oceanic and atmospheric conditions in the tropical Pacific characterized by anomalously cold ocean temperatures in the central and eastern tropical Pacific.  These anomalously cold temperatures are evident in sea surface temperature anomalies from earlier this month.  Note in particular, the tongue of anomalously cold water extending along the equator from South America to the dateline.  Source: Climate Prediction Center If one looks at composites (or averages) of La Niña winters, one finds patterns similar to those illustrated in the bottom panel below with high pressure over the central Pacific near about 150ºW, cold conditions over northwest North America, wet conditions in the Pacific Northwest, ...

Kory Davis sent me the great cloud photo below taken looking east yesterday at about 8:30 AM from Snowbasin. Photo courtesy Kory Davis This is a wonderful example of breaking waves produced by Kelvin-Helmholtz instability, named after physicists Lord Kelvin and Hermann von Helmholtz.  Such instabilities are produced by vertical wind shear, leading to breaking waves that are similar in appearance to waves breaking on a beach.  Such instabilities occur frequently in the atmosphere, and produce turbulence, but aren't always easily seen.  Moving on to today's weather, there's much to discuss.  First, how about our afternoon temperatures.  At 2242 UTC (3:42 PM MST), many sites along the east bench are running in the 50s, including a 56 at the University of Utah.  Alta is 43, Mountain Dell 51, and Kimball Junction 50.  THIS IS NO WAY TO RUN A WINTER.   If you look carefully, evidence of the valley inversion is apparent, with temepr...

It's been an interesting break.  After hemming and hawing about whether or not to get out of Dodge, we decided that there was enough snow and decent enough air quality that we'd gut out Christmas week at home.  By and large, I think it was a wise decision. The cross country skiing has been pretty decent and has provided a good cleansing of my aorta.  Back country skiing?  We got in a tour the day after Christmas.  I can't say the skiing was good, but it was an education for my son who had never been out on such a hair-trigger, high-hazard day before.  I made him suffer too, with a 2000 vertical foot climb through heavily brushed slopes to start the day.  It's important that youngsters recognize it's not all fun and games out there.  We went up for a couple of high-speed laps at Alta this morning.  It was only my 2nd day of lift served this year.  Conditions were surprisingly good for carving.  I'm always amazed that when cond...

The large-scale pattern has not changed.  I repeat, the large-scale pattern has not changed. Yes, we got a couple of miracle storms prior to Christmas, but on the hemispheric scale, we are still dealing with a highly perturbed, wavy, high-amplitude pattern.  Note, for example, the dynamic tropopause (jet-stream level) analysis from 0000 UTC 27 Dec (1700 MST Tuesday/Yesterday).  Deep trough over the eastern US.  Deep trough off the coast of Asia.  High amplitude ridge over the eastern Atlantic.  You want snow, go to the lee of the Great Lakes or western Japan.  Both have been getting pummeled.  And, there's no end in sight for the dry weather.  Forecasts below are from the 0000 UTC 27 December initialized ECMWF and GFS models through the end of the holiday period (0000 UTC 3 January/1700 MST 2 January).  Storm track to our north.  Dry southwest.  Source: weather.us Source: weather.us There are a few members ...

Christmas turned out to be a fascinating weather day.  The Christmas Eve warm front and precipitation left a shallow cold pool over the Salt Lake Valley with widespread fog and dense haze in the morning.  I noticed some strong gravity waves from my vantage point in the upper avenues, one of which is pictured below.  Note the bulge in the depth of the fog, similar to the crest of a wave on the water.  Although the fog burned off in many areas, a shallow lens of haze remained over much of the valley during the afternoon.  My thinking during the day was that this was probably predominantly natural haze as PM2.5 concentrations were quite low on Christmas Eve morning.  However, the PM2.5 observations from Hawthorne Elementary show we reached levels unhealthy for sensitive groups Christmas evening.  In fact, the increase from Christmas Eve morning is astounding.  Normally one sees an increase in PM2.5 during a developing and persistent inversi...

With a full-latitude, high-amplitude ridge parked over and just north of Alaska, Santa will have a much needed tailwind after taking off from the North Pole for Utah.  Just check out the strong northerly jet stream (green contours) that will rocket him southward from the North Pole and across much of western Canada tonight!  That tailwind is a godsend because the reindeer will need to be fresh when they arrive in northern Utah.  With clouds and precipitation along much of the Wasatch Front and in the Wasatch Mountains, they will have a difficult job, even with Rudolph leading the team.  Mountain snow will reduce visibility and, with temperatures climbing, Santa may encounter a rain/snow mix or even a bit of rain in the lower elevations, depending on the timing of his deliveries. Rumor has it that Santa is considering hanging around and skiing freshies tomorrow at Alta.  Apparently he was spotted yesterday.  It's rare for Santa to leave t...

Most ski reports and skiers tend to focus on snowfall amount as the measure of storm size, but for many applications, it is the water equivalent of the snowfall (i.e., how much water it contains) that is the most important measure.  After all, the water equivalent determines how much weight (and stress) you are adding to the snowpack, which is important for avalanches, and how much water you are adding to the snowpack for water resource purposes.   Really, Utah skiers should also be focusing on water equivalent right now instead of snowfall amount.  We need base, and base is a function of how much water is in the snowpack.  Six inches of 15% water content snow goes a lot farther as six inches of 5% for building up base since it contains three times as much water mass.   As I write this post at 7:15 AM, I'm encouraged by the current storm so far.  Storm-total water equivalents in the Wasatch so far include 0.9" at Ben Lomond Peak (through 6...

Based solely on the large-scale pattern setting up for tonight and Saturday, one might not be very enthused about our snow chances.  There's a huge, high-amplitude ridge centered over Alaska and a ridge upstream of Utah with a short-wave trough moving across Montana.  Show this and nothing else to 10 meteorologists and ask them what will happen in Utah and they probably would say not much. However, the Devil is in the details, and those details suggest this storm could surprise.  The pattern is highly unusual because of the size of the ridge over Alaska, and we end up in a situation in which two airmasses of dramatically different origin are coming together, one from the subtropics, the other from the high latitudes.  This leads to a strong mid-level front and plume of moisture that extends inland across Utah. By itself, that probably wouldn't do much, but we have something going for us, the Wasatch Range.  The GFS forecast above shows that the terrain...

It's a 2-for-1 day at the Wasatch Weather Weenies.  If you want to read about the overnight snowfall, proceed to the previous post .  If you want to read about dust, air quality, pollution, and other apocalyptic aspects of the storm, stay here. Yesterday morning, an extremely nasty plume of dust penetrated into the Salt Lake Valley, pushing air quality to unhealthy levels. Although Salt Lakers are aware of poor air quality during inversion events, yesterday we dealt with an entirely different beast.  During inversion events, emissions from the combustion of fossil fuels and wood, as well as a few other sources, build up within the Salt Lake Valley.  Winds are light and the strong atmospheric stability prevents the mixing of pollution vertically.  In contrast, yesterday the poor air quality occurred during strong, southerly, prefrontal winds. The graphs below show what happened at Neil Armstrong Academy in the Northwest Salt Lake Valley.  From Tuesday ...

The total snowfall through 7 am this morning on the Alta-Collins stake sits at 6".  With a snow water content of 0.36", that makes for a water content of 6%.  Perhaps not quite cold smoke, but close to it.  Alta continues to see some light snow.  This stuff is barely discernible in the radar loop where all one sees are some stronger returns over the high terrain that are ground clutter and some very light returns in a couple of bands that move from east to west across the Wasatch Range, consistent with precipitation in the "wrap around" part of the storm.  It's very difficult to determine precipitation rates at Alta and in other parts of the Wasatch Range during such conditions using radar.  There are a couple of reasons for this.  First, the precipitation is quite shallow and often the radar beam partially or totally overshoots the precipitation.  Source: Secrets of the Greatest Snow on Earth Second, snow scatters a lot less radar e...

If you have studied introductory meteorological text books, you've probably seen schematics of frontal precipitation based on the one below, which is from a seminar paper published in 1922 that synthesized existing knowledge on frontal cyclone evolution into a coherent depiction known as the Norwegian Cyclone Model due to it's development in Bergen, Norway. Source: Bjerknes and Solberg (1922) The cold front is depicted on the left, with a narrow band of precipitation forming where the leading edge of colder air is intruding into the warm airmass.  This band of precipitation is known today as a narrow cold-frontal rainband (or alternatively, snowband if cold enough).   Although, conceptually simple, not all cold fronts behave in this manner.  Sometimes a wide cold-frontal rainband exists upstream of the surface front, as depicted below.  Source: Matejka et al. (1980) In some instances, the wide cold-frontal rainband exists in isolation, with no n...

I've been thinking of hanging it up for the season.  Not skiing, but forecasting.  It's starting to get depressing. I needed to remind myself this morning what a decent storm looks like in the Wasatch.  Certainly over an inch of water in 24 hours.  Or, better yet, a good pasting and base builder, which would give more than two inches of water in 24 hours (maybe 3 at the upper end).  What I wouldn't give for that. We do have a storm on the horizon.  The GFS forecasts a cold front pushing through Utah tomorrow at 5 PM MST.  The cold front is really a thing of beauty, wonderfully continuous in terms of the wind shift, temperature gradient, and precipitation band from NW Wyoming all the way to the White Mountains.  That's a rarity. We look to get some mountain and valley snowfall with the front.  Following frontal passage, a strong surface cyclone forms in the four corners area.  Could be some nasty weather for the Canyonlands area....

Christmas is still a full week away, but that isn't preventing people from making specific forecasts for the big day.  This is a common issue when a major day or holiday approaches.  The desire to provide specifics far in advance.  10-day forecasts for trick-or-treating weather on halloween.  Guarantees of a white Christmas, etc.  Unfortunately, the existence of a holiday does not magically clear up the meteorological crystal ball or alter the fundamental chaotic nature of the atmosphere.  I saw one forecast this weekend for a brutally cold Christmas day with a high of 18ºF.  Presumably this was based on forecasts like the one below from yesterday morning's GFS which did indeed have some exceptionally cold air over northern Utah with 700-mb temperatures below -20ºC. However, last night's GFS paints a totally different picture with a ridge over the west and 700-mb temperatures of -4ºC over northern Utah.  For the ski areas, that's a swing ...

The European Center for Medium Range Weather Forecasting (ECMWF) produces the leading medium range forecast model and ensemble prediction system in the world.  However, their products are generally paywalled and I am unable to access them freely for real-time applications (Note: They do generously provide their products for research applications that are not real time, which we greatly appreciated).  As a result, weather weenies and hobbyists who want to examine the ECMWF forecasts have typically had to pay for a subscription.  However, wx.graphics is now providing access to ECMWF forecast graphics without such a subscription.  Below, for examples, is the 5 day forecast valid 000 UTC Friday 22 December.  Source: weather.us I don't know how long this jailbreak will last, so enjoy while you can. 

Over the past several weeks, we've had a parade of storms that, to steal a line from Howie at Alta, "stretch like taffy." This is a symptom of the large-scale patter that has dominated our weather during the period.  Upper-level troughs either move through or over the ridge over the eastern Pacific and western North America into an area characterized by strong deformation .  Deformation is a word that describes flow patterns that tend to "stretch" and change the shape of weather features.  A good analogy is what you do with silly putty.  Push it down on something like comics in the newspaper, pick it up, and stretch it.  The figures on the silly putty get stretched out and deformed.  In other words, deformation. An example is provided by the forecast for the next couple of days.  The loop below depicts the forecast evolution of the dynamic tropopause , basically a map of the upper-level pattern.  Troughs are blue, ridges are red, and the wind ...