Category Archives: Large-Scale Flow

The More Things Change, The More They Stay The Same

"Pattern change" is currently on my list of banned words and phrases for good reason as it was being thrown around repeatedly for weeks despite the fact that nobody really knows what it means. 

As I've been watching the large-scale pattern for the last several weeks, there has certainly been variability.  Ridges and troughs have formed and dissipated.  There have been some major cyclogenesis events.  However, one thing has remained constant.  The large-scale pattern has been very high amplitude, meaning a wavy jet, especially from the Pacific Ocean to Europe. 

That situation looks to continue for the foreseeable future.  Below is the 10-day GFS forecast for the northern hemisphere dynamic tropopause.  The dynamic tropopause separates the troposphere, or the lower atmosphere in which we all live and reside, from the stratosphere and basically sits at jet-stream level.  Note in particular the high-amplitude, wavy nature of the pattern, with strong ridges and anticyclones (high-pressure systems) forming in several areas including over the Behring Sea and North Atlantic.  Basically, the large-scale flow is highly disrupted. 


This is essentially what we have seen now for weeks.  High amplitude patterns like this can be good for snow if you are in the right place (check out the Alps), but we haven't.  The tendency in Utah has been for us to be under the influence of high-amplitude ridging or just to the south of the storm track. 

So, the more things change, the more they stay the same.  We get the occasional storm, but a real storm cycle is hard to come by.  Unless the storm track shifts southward more than currently predicted, that looks to be the case over the next seven days.  Our best bet for snow, as indicated by the NAEFS forecast plume below is Thursday and maybe Thursday night, with maybe a bit here or there thereafter. 

The NAEFS plume above may even be a bit optimistic for Thursday and Thursday night as the water equivalents advertised by the NAM, GFS, and Euro fall in the low end.  Most members of our downscaled SREF are generating only .1 to .5 inches of water equivalent.  The optimistic Canadian model (CMCE members in the plot above) appears to be an outlier. 

As usual, keep expectations low and hope for the best.  A small storm will be appreciated, but recognize that I have yet to see the whites of the eyes of a real pattern change.  However, my crystal ball only sees out about 7 to 10 days.  Let's hope February is better. 

The More Things Change, The More They Stay The Same

"Pattern change" is currently on my list of banned words and phrases for good reason as it was being thrown around repeatedly for weeks despite the fact that nobody really knows what it means. 

As I've been watching the large-scale pattern for the last several weeks, there has certainly been variability.  Ridges and troughs have formed and dissipated.  There have been some major cyclogenesis events.  However, one thing has remained constant.  The large-scale pattern has been very high amplitude, meaning a wavy jet, especially from the Pacific Ocean to Europe. 

That situation looks to continue for the foreseeable future.  Below is the 10-day GFS forecast for the northern hemisphere dynamic tropopause.  The dynamic tropopause separates the troposphere, or the lower atmosphere in which we all live and reside, from the stratosphere and basically sits at jet-stream level.  Note in particular the high-amplitude, wavy nature of the pattern, with strong ridges and anticyclones (high-pressure systems) forming in several areas including over the Behring Sea and North Atlantic.  Basically, the large-scale flow is highly disrupted. 


This is essentially what we have seen now for weeks.  High amplitude patterns like this can be good for snow if you are in the right place (check out the Alps), but we haven't.  The tendency in Utah has been for us to be under the influence of high-amplitude ridging or just to the south of the storm track. 

So, the more things change, the more they stay the same.  We get the occasional storm, but a real storm cycle is hard to come by.  Unless the storm track shifts southward more than currently predicted, that looks to be the case over the next seven days.  Our best bet for snow, as indicated by the NAEFS forecast plume below is Thursday and maybe Thursday night, with maybe a bit here or there thereafter. 

The NAEFS plume above may even be a bit optimistic for Thursday and Thursday night as the water equivalents advertised by the NAM, GFS, and Euro fall in the low end.  Most members of our downscaled SREF are generating only .1 to .5 inches of water equivalent.  The optimistic Canadian model (CMCE members in the plot above) appears to be an outlier. 

As usual, keep expectations low and hope for the best.  A small storm will be appreciated, but recognize that I have yet to see the whites of the eyes of a real pattern change.  However, my crystal ball only sees out about 7 to 10 days.  Let's hope February is better. 

Cage Match: Nov-Dec 1976 vs. Nov-Dec 2017


By popular demand, we now compare Nov-Dec 2017 with the comparable start period of the "season that shalt not be named", the "drought year," or simply, 1976/1977.

The 1976/1977 season is the worst on record in the modern era (i.e., since WWII) in the Wasatch Range.  Records for Alta-Guard show a total seasonal snowfall (November through April of only 314.5 inches.  This is the second lowest on record next to 2014/15, when only 267.5" was recorded.

If 1976/77 was only the 2nd worst snow year at Alta, what makes it the worst ski season?  The lack of early season snowfall.  Nov-Dec 1976 produced only 30.5 inches of snow, 17.5 inches less than the second lowest comparable period on record, Nov-Dec 1962, and 102.5 inches less than Nov-Dec 2014.  In my book, a lack of early season snow is far worse than a lack of late season snow, mainly because you can't ski on dirt and the backcountry powder skiing is far less vulnerable to the sun during November and December than March and April. 

This season, Alta-Guard reported only 15 inches of snow in November.  I haven't seen their numbers for December, but Drew Hardesty of the Utah Avalanche Center notes in today's Salt Lake Tribune that Alta-Guard hasn't yet hit 50 inches for the season, and currently sits with the second leanest snowfall behind the 1976/77 season.  I think it will come in a shade under 50 inches.  Thus, in terms of snowfall, this season is bad, but not as bad as Nov-Dec 1976.

What about temperatures?  Nov-Dec 1976 had a mean temperature at Alta 28.8ºF, making it the 10th warmest such period on record.  This Nov-Dec it was 31.2ºF, good for fourth warmest.  One might be able to make an argument that this difference in warmth may have had some impact on melt and snowmaking.  In the case of the former, the loss of snow to melt on high-elevation north aspects is very small (or non-existent) this time of year when the sun angle is low.  Perhaps the difference in temperature has had some impact on snow losses down low during warmer periods (rain on snow, for example).  I'm going to guess that the impact is small, but stand to be corrected if someone can further than analysis with more data than I can look at in the short amount of time this morning.  I suspect that the situation on south aspects between the two seasons is a draw.  Near to nothing in both instances.  In the case of the latter, perhaps snowmaking conditions were a bit worse this Nov-Dec, but the argument is irrelevant since I don't think any resorts had snowmaking in 1976.  It would be interesting to go back and read some news reports from the 1976 holidays about what was happening at the resorts (alternatively, share your perspectives in the comments).  This Nov-Dec, we clearly have benefited from snowmaking in ways that were not possible in 1976 and, for resort skiers, that's probably a trump card surely making the start of this season better.

Now, getting to the meteorology.  If you are into El Niño and La Niña, you might be interested to know that weak El Niño conditions prevailed during Nov-Dec 1976, whereas weak La Niña conditions prevailed this Nov-Dec.  That's all I'll say about that.

The upper-level pattern during Nov and Dec 1976 was very high amplitude (i.e., wavy) across the Northern Hemisphere with a high amplitude ridge parked along the Pacific coast of North America and a deep trough over eastern North America.  This pattern kept much of the western US dry, but the eastern U.S. cold and snowy.
Source: ESRL

Source: ESRL

I was 9 years old at the time and living in upstate NY, and I still remember that as a very cold winter.  The extreme nature of the winter across the US sparked a good deal of research on climate and climate variability.  In what would have been a "rapid response" paper at the time, Henry Diaz and Robert Quayle published a paper in the October 1978 Monthly Weather Review arguing that January 1977 was probably the coldest month experienced in the eastern half of the U.S. in the last 200 years and that the 1976–77 winter set a new record for fuel demand due to the extreme cold in high population areas.

Source: Diaz and Quayle (1978)
This Nov-Dec was also characterized by a very high-amplitude pattern across the Northern Hemisphere.  However, the pattern over North America in November featured a ridge centered over the west-central U.S., rather than along the Pacific coast.

Source: ESRL
 This enabled storm activity in the Pacific Northwest, but kept the Southwest dry.  For northern Utah, the snowfall numbers for November 1976 and 2017 are nonetheless quite similar at Alta Guard, with 13.5 and 15 inches, respectively.   I haven't had a chance to dig into the water equivalent numbers to see how those compare and if there were any differences in the fraction of precipitation that fell as snow in the two years.

By December, the west coast ridge was dominant.  This is a pattern somewhat reminiscent of November and December 1976.  Alta-Guard, however, did a bit better for snow this December than in December 1976. 

Source: ESRL
It's not surprising that we see some similarities (and differences) between the two Nov-Dec periods.  Droughts in the west are frequently associated with ridging along the Pacific coast and that is a preferred area for ridge development.   Whether or not the remainder of this season evolves in a manner similar to the 1976/77 season remains to be seen, but my personal view is that analog forecasting based solely on local precipitation characteristics is not bound to be reliable over many cases.  My take is we just have to see how this will play out and hope that things shift for the better soon.

A few other thoughts:

1. The 1976/77 season was unbelievably bad in the southern Sierra Nevada.  Mammoth Mountains snowfall history (available here) shows a total seasonal snowfall of only 94" and no snowfall at all from October through December.  Four inches of that 94 fell before October.

2. Alta Ski Area's web site shows 74" in this Nov-Dec, but their observing site is higher up on the mountain.

3. I have not addressed the issue of observational representativeness and uncertainty in this post.  The Alta-Guard measurement site has changed over the years and this does affect snowfall measurements.  Similarly, I've never dug into the Alta site information to see if the location of the temperature measurements have changed, and that could affect the temperature comparison (there's a big difference depending on sun exposure, especially in December).

4. SNOTEL observations in the central Wasatch do not extend back to 1976.  It would be very interesting to utilize the manually collected snow course data to do a comparison.

Parade of "Synoptic Debris" Continues into 2018

The past two months have produced remarkable weather in Utah and many portions of the southwest United States. 

Remarkably bad that is, if you are a skier.

Often meteorologists use averaging to illustrate slowly evolving aspects of the upper-level pattern over long periods.  If we do this for November, one sees just a hint of a broad upper-level (500-mb) ridge over the southwest US, with westerly flow strongest just to our north across the US Pacific Northwest. 

Source: NOAA/ESRL
This was a pattern in which there was an active storm track just to our north, resulting in above average precipitation in many high-elevation areas of the Pacific Northwest, but below average precipitation for northern Utah and much of the southwest. 

Source: water.weather.gov
December's pattern was more "high amplitude" with strong ridging along the Pacific coast and deep troughing over eastern North America.
Source: ESRL
This resulted in drier conditions shifting northward into the Pacific Northwest, but "roll over" precipitation helped in portions of the Northwest interior. 

Source: water.weather.gov
The use of average conditions often obscures important aspects of the day-to day variability.  Thus, I put together a long loop of daily dynamic tropopause (jet level) analyses covering November and December.  The one thing to take away from this is how high amplitude (i.e., "wavy") the jet-stream pattern has been across the entire Northern Hemisphere.  We see some troughs moving across the western U.S., but they are often cut-off or strung out.  I call these troughs "synoptic debris."  Sometimes they can produce some snow for us, but this is a pattern that by and large is not one favoring frequent heavy snowfalls in northern Utah.  


Which brings us to the forecast.  Basically, more synoptic debris for western North America during the first 10 days of 2018, as advertised by the GFS. 


The next four days look dry in northern Utah, and then a piece of that synoptic debris, flirts with the area.  Some ensemble members give us some precipitation in the central Wasatch (Alta-Collins depicted below), although there are some members that keep snowfall totals to a minimum. 

Basically, this is business as usual for this winter.  Keep expectations low and hope for the best.  I'm debating whether or not to bring my rock skis in for a much needed tuneup, or save the money and just keep beating the hell out of them.  

Not Your "Average" La Niña Pattern

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, and dry conditions across the southern tier of the United States.  


Another way to look at this is in terms of hight anomalies at upper levels.  Areas in warm colors below correspond to anomalous ridging, and areas in cool colors anomalous troughing.  At upper-levels, the primary circulation features are an anomalous trough near Hawaii, ridging in the North Pacific, and troughing over northwest North America. 

Source: NOAA/ESRL
The pattern over the past month hasn't really looked like that.  Instead, we've had anomalous ridging along the west coast of North America. 

Source: NOAA/ESRL
In addition, while it has been dry across the southwest US and most of the southern US, it has also been dry in the Pacific Northwest.  The only areas of anomalously high precipitation is in the northwest U.S. Rockies and adjoining plains and in lake-effect areas.  


Thus, this is a pattern that doesn't fit the average La Niña pattern all that well.  That isn't to say La Niña isn't playing some role.  It could be playing an important role, with our use of relationships based on averaging past events the real problem.  On the other hand, it is also possible that we need to look at what is happening from a broader, global perspective.  Some discussion of this topic is provided by the California Weather Blog.  This is an area of active research, and one that will probably get even more attention after this winter, which has generated some remarkable weather extremes across the United States.  

Dismal Pattern Continues

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 of the NAEFS that drag the moisture down south enough to give us a little more action around later in the 7-day forecast period.  Thus there is a little hope, but I'm keeping my expectations low.  Plumes below are for Alta-Collins and show a small number of ensemble members giving us some action on or after the 30th of December.  Most generate no more than 4 inches of snow.  Sad!

Is this La Niña?  I'm not ready to endorse that viewpoint.  Yes, there are aspects of this pattern that are consistent with La Niña, but there are other aspects that are not.  Mechanisms affecting the large-scale circulation are multifaceted and complex.  Maybe we'll deal with this in a future post. 

Inversion Tidbits and Long-Range Prospects

Yesterday's satellite imagery summarized the ridge-dominated weather of western North America quite well with extensive fog found in the major basins, many of the valleys of British Columbia and the Northwest United States, and the Great Salt Lake Basin.  At the same time, smoke from the California Fires covered much of the offshore eastern Pacific Ocean.  If you look carefully, it appears that some of this smoke has been carried northward to the Queen Charlotte Islands.

Composite MODIS image from NASA.
Within the Salt Lake Valley, the pollution went into overdrive yesterday, with PM2.5 levels skyrocketing in the morning to unhealthy levels.  Unlike previous nights, when PM2.5 dropped considerably, levels declined only modestly overnight and remain unhealthy for sensitive groups. 

PM2.5 concentrations at Hawthorne Elementary.  Source: DAQ
Looking for a brightside?  The frosty trees make for a beautiful Christmassy scene.  


We are so desperate for weather that I feel the need to mention that there is actually a weak short-wave trough dropping down the back (eastern) side of the ridge and passing through our area Wednesday night.  


Yup, that's your weather for the week.  It will bring somewhat cooler temperatures to the mountains, perhaps helping with the snowmaking efforts and might stir the upper part of the inversion a bit.  Emphasis on might.  Low elevations will likely remained mired in pollution. 

I am a bit more optimistic that the trough on Saturday is strong enough to give us at least a partial mix out.  It's still soon to say if it will scour it all out.  Sometimes, the coldest, most polluted air at the lowest elevations can be quite stingy. 


Snowfall totals for the mountains presently look paltry.  About half the members in our downscaled NAEFS ensemble generate 2 inches or less.  A few members go for more.  A game changer is unlikely. 

The word "pattern change" is being thrown around a lot, but I bet you'll have a hard time finding anyone who can tell you what that means.  I have yet to see any indication from any ensembles that we are going to shift from the high-amplitude pattern that has dominated for weeks and in which there are very deep ridges and troughs at upper levels, to a more progressive pattern with stronger westerly flow.  Instead, there may be some shifts in the position of the ridges and troughs.  For example, some of the GEFS 10-day forecast members below have a ridge upstream of the west coast of North America, rather than near its present location along the west coast or just inland. 

Source: Penn State E-wall
Those shifts could be important if they lead to a slowly evolving but wet pattern for Utah.  However, looking at the GEFS solutions above, some might bring us some snow, others keep us dry.  Why waste time talking about this range of possibilities?  Like thermonuclear war, the best option is not to play.  


Thus, hope we get something from the trough on Saturday and at minimum hope it cracks the inversion.  It's the only slim hope we have for mountain snow over the next week.  After that, your guess is as good as mine. 

Heartbreak Ridge Tightening the Inversion Noose

Noontime smog yesterday, looking southwest from the Natural History Museum of Utah, University of Utah
Given that our last storm was winding down on Monday, I'll call today Day 4 of Heartbreak Ridge.

So far, the pollution buildup has been modest.  Because the center of the ridge has been along the Pacific Coast, we've been on the downstream side, temperatures aloft have been cool, and the inversion relatively weak and elevated.  This has enabled some vertical mixing of pollutants through a decent portion of the valley atmosphere.  As a result, the increase in pollution has been gradual and we've been fluctuating between good and moderate air quality.  

Source: Utah Division of Air Quality
However, Heartbreak Ridge is sliding eastward and the inversion is strengthening, as can be seen in the soundings from yesterday afternoon (top panel below) and this morning (bottom panel below).  


Source: University of Wyoming
Note in particular the warming in the layer between about 800 and 700 mb (6500–10000 feet), which equates to a strengthening of the "lid" over the valley atmosphere.  This morning, temperatures near the base of that layer increase about 5ºC through a depth of around 50 mb (1500 feet). 

The NAM sounding loop below (note: this is a skew-t diagram, not directly comparable to the diagrams above) shows further warming aloft over next two days, with temperatures aloft warming an additional 5ºC.  
Thus, the inversion will be strengthening and lowering through the weekend.  It appears we will be in the grips of the inversion at least through the next work week, unless a system stronger than presently advertised slides down the back side of the ridge and gives it a stir. 

Model Products Information

We have been having some problems with the server that hosts weather.utah.edu and it has been down intermittently the past two days.  Behind the scenes (and unrelated to the outages), I've been updating some of our products.  Options for the GFS now include global and regional plots from the 0.25 degree latitude-longitude grid (we've been using the old 0.5 degree grids), higher frequency (every 3-h to 240 hours), more regional sectors (e.g.,  Intermountain, Northwest, Southwest), and time-height section options that match the time period of the NAM for comparison.  Some little used plots are gone, such as the Indian Ocean sector.  




Heartbreak Ridge Provides One Blutarski of Precipitation Through Mid December

The Sunday Storm delivered at the upper end of expectations, which was great for skiers and storm chasers.  That's the good news.  The bad news is that Heartbreak Ridge is here, and maybe to stay, at least for a while.

The latest GFS dynamic tropopause (jet-stream level) forecast below ain't mobile friendly, but it tells it like it is.  A ginormous ridge is building over western North America this week, diverting the storm track into northwest Canada and Alaska.  Although that ridge eventually weakens and moves downstream, another builds behind it.


Total precipitation produced by the GFS in Utah over the next 10 days is precisely "one Blutarski."  In other words, zero-point-zero.


For those of you who don't know what a Blutarski is, watch this clip from Animal House and work harder to expand your educational horizons. 


Most medium-range ensemble members are similarly going for dry conditions over the area and nearly the entire mountain west.  Perhaps the ridge will be weaker than advertised, shift a bit westward allowing something to spill over the top, or go north enough for the southern branch of the jet to come into our area.  That's about all we can hope for.

I'm not one to extrapolate already medium-range forecasts even farther into the future.  Much can happen at long lead times.  Blocking patterns like this can be very persistent, but I'm inclined not to make forecasts for the 2nd half of December at this time. 

For Wasatch Front dwellers, now is the time to reduce driving, carpool, and take transit.  The inversion begins to develop today and the cold pool it isolates in the Salt Lake Valley and adjoining lowlands probably won't be going anywhere for a long time unless we can get some sort of dry cold front to slide down the back side of the ridge.  That's not impossible, but I wouldn't count on it.  Expect today's emissions to be tomorrow's smog.

Typhoon Lan Has It In for Utah Skiers

Typhoon Lan has been rampaging in the western Pacific, reaching a maximum intensity of category 4 on the Saffir-Simpson scale.  It made landfall early Monday morning (local time) in Japan, southwest of Tokyo.  Some spectacular photos of LAN were taken from the International Space Station.

Although half a world away, Lan will have some dramatic influences on the upper-level flow and unfortunately has it in for Utah skiers.

The image below shows the situation at 1200 UTC 21 October (0600 MDT Saturday) when LAN was still south of Japan.  Sea level pressure contours are colored (cooler colors indicate lower pressure) and 500 mb (upper-level) height contours black.  At this time, the upper-level flow over the mid-latitude north Pacific was primarily zonal, meaning from west to east, with a broad trough over the high-latitude North Pacific and Bering Sea. 


Lan struck its first blow for Utah skiers as it moved northward and across Japan.  During this period, the northward transport of tropical warmth and moisture, combined with condensational warming near and ahead of the system, built a ridge over the western pacific and perturbed the midlatitude flow, which quickly broke down across the entire Pacific basin.  At 0000 UTC 23 October (1800 MDT Sunday), a broad ridge was amplifying upstream of Utah, deflecting Pacific moisture to our north with just a few high clouds spilling across our area. 


Blow two comes as Lan undergoes extratropical transition and explosively develops as a midlaitude cyclone off the Kamchatka Peninsula.  This encourages further amplification of the large scale flow, which by 0600 UTC 24 October (0000 MDT Tuesday) features a high-amplitude trough along the entire US west coast. 


Thus, the beautiful fall weather we will experience in Utah this week comes from Russia with love.  Beware in California, however, as Diablo and Santa Ana winds are possible.

But, Lan isn't finished yet.  Although she weakens weakens, she continues to drift eastward across the Aleutians where the southward flow ahead of her can link up with that associated with a closed low further south and north of Hawaii. 


This ultimately leads to a new tap of tropical warmth and moisture that connects well into the tropics and reinforces the west coast ridge. 


Here's the whole thing in motion.


So, what does this all mean?  Well, it means we won't be seeing any significant snow around here through the end of October.  It means the start of ski season is officially on hold until November.  And it means you should get that bike tune up you've been putting off because you will be spinning instead of skinning. 

Is this unusual?  Nope.  Disruptions of the midlatitude flow by tropical cyclones are common in the fall.