Friday, February 23, 2018

Postfrontal Orographic Effects

I've had a busy morning with no time to write, which is a shame given the weather. 

I can share one quick observation from the storm today.  The radar is showing some orographic effects in the post-frontal northwester flow from 1738–2032 UTC (1038 AM – 132 PM MST).  Note, for example, the persistent echoes on the western (windward) sides of the Oquirrh and Wasatch Mountains, which contrasts with the shadowing seen over the southwest Salt Lake Valley. 


Clearly better skiing above the Kennecott Smelter than at the open pit mine. 

Thursday, February 22, 2018

When the Ridge Is in Its Happy Place

Over the past week and in forecasts for the next 10 days the overall pattern remains in some ways similar to what we have seen all winter.  The flow is very high amplitude, with strong upper-level ridges and troughs.  This can be seen in the dynamic tropopause analysis below, which is essentially a map of jet stream level winds with areas of locally low tropopause pressure (warm colors) indicating ridges and areas of locally high tropopause pressure (cool colors) indicating troughs. 


What has changed, however, is that the mean ridge position has shifted upstream to what I'll call its "happy place" over the central Pacific Ocean.  As a result, we will see several amplifying upper-level troughs digging into the western U.S. over the next 10 days.  This is a much colder pattern than we have seen all winter.

It is also a more "active" pattern.  Forecasts for the next 7 days show a series of weak but frequent storm systems moving through.  Total accumulated water equivalent produced by our downscaled NAEFS product for Alta ranges from 1 to 3 inches of water.  The former would be a bit below average, the latter almost double. 

Thus, beginning with last week, this looks to be the best stretch of winter weather we have had all season.  Anything close to average beats the previous 3 months. 

The Steenburgh Effect is in full force. 

Wednesday, February 21, 2018

Finally, GOLD!

In 66 years of women's cross country skiing, the US has never won a medal, let alone a gold medal. 

That just changed. 


Tuesday, February 20, 2018

Winter Storms from Salt Lake City to PyeongChang

Lake-effect snows added a bit of frosting to the President's weekend winter storm last night.  Alta is reporting a 22" storm total, but only 3" overnight.   In the end, I think the storm did a little better than anticipated through yesterday morning and a little worse than anticipated yesterday and last night.  Such is the post-frontal crap shoot. There are reports of more than 20 inches (through yesterday afternoon) in Sandy and Cottonwood Heights, so this was an event in which storm totals did not increase significantly with elevation up the canyon.  

Temperatures this morning are bone chilling in the mountains.  The latest from MesoWest shows predominantly teens in the Salt Lake Valley, which isn't all that bad, but above about 8500 feet, most stations are at or below zero, with a -12ºF at 11,000 feet.  

Source: MesoWest
Ski touring on days like these requires constant movement.  I recall doing a huge day several years ago in conditions like this.  The skiing was outstanding, but I was cold the entire day, despite being heavily layered.  There were no breaks.  Did I mention that the skiing was outstanding?  

Turning out attention westward, the schedule for some weather-sensitive events is being shuffled due to the weather forecast.  The fly in the ointment is a surface trough moving across the Yellow Sea and the Korean Peninsula from 0600-1500 UTC 22 Feb (1500-2100 KST Thursday).  




This trough then intensifies into a cyclone over the East Sea (Sea of Japan) and, along with a secondary trough to the west, drives strong winds across the Korean Peninsula on Friday, as illustrated by the forecast valid 0300 UTC 23 February (0900 KST Friday).  


As currently scheduled, the Women's Downhill is 1100 KST Wednesday (7 PM MST Tonight).  This is well in advance of the trough and the main concern will be the omnipresent gusty winds and perhaps some flat light from cloudiness.  I think they will get it in.  Later Wednesday are the Team Cross Country Sprints, which they should also get in.  The DVR will get a workout tonight for that as the finals aren't until 1900 KST (0300 AM MST Tonight).   

Thursday at 10 AM KST is the Men's Slalom Run 1, 1130 AM is the Women's Alpine Combined Downhill, 1330 is the Men's Slalom Run 2, and 1500 is the Women's Alpine Combined Slalom.   This covers a period from 0100-0600 UTC 22 February and as can be seen in the plots above, those events are scheduled to occur before any precipitation arrives, but also as pre-trough southerly flow is increasing.  Official forecasts for the top of the downhill show 5 m/s (10 knot) winds through 1200 KST, then increasing.  It's going to be close.  


Assuming it does go off, tomorrow night (MST) should be a great viewing for ski fans.  Helping in that quest, there's no figure skating scheduled.  Hooray!

Monday, February 19, 2018

Everybody Gets Some, Plus Tonight's Lake-Effect Intricacies

Finally, a great storm.  All elevations, all locations.  Some cherry picked storm totals so far based on reports to the NWS (time of measurement in parentheses):

Smithfield, Cache Valley (4 PM Sun): 12"
Ogden (5 PM Sun): 2"
West Valley City (6 AM Mon): 5.2"
Salt Lake Airport (5 AM Mon): 3.6"
Cedar Hills, Utah County (5 AM Mon): 9"
Powder Mountain (5 AM Mon): 12"
Brighton Crest (5 AM Mon): 16"
Alta-Collins (3 AM Mon): 14"
Spruces (4 AM Mon): 10"

Through 8 AM, Alta Collins is up to 18", blowing my 7-14" expected through 9 AM out of the water. 

With the KMTX radar up-and-down overnight (and currently down), getting a good handle on the action is more difficult than usual.  One thing that caught my attention is described in the tweet below, issued last night.  From 8-10, Alta-Collins recorded 6" of snow (3"/hr mean rate) and I saw some tweets of impressive accumulations near Alpine as well.  During this period, a very pronounced band extended across northern Utah County and far northwest Wasatch County, and stronger radar reflectivities also lingered over the upper Cottonwoods. 

One option when KMTX is down is to examine data from the Terminal Doppler Weather Radar (TDWR) operated near the east shore of the Great Salt Lake west of Farmington.  The primary purpose of this radar is to detect hazardous weather and wind shear over the airport.  It is blocked significantly by the surrounding topography, and provide little to know information about what is happening over the Wasatch and the broader region.  You can see, however, returns related to snow showers over portions of the Salt Lake Valley. 



Periods of snow look to continue today and tonight in the mountains and also in the valley.  The latest NAM forecast shows us transitioning into deeper northwesterly flow during the day today, with the flow transitioning to westerly overnight.


The situation for tonight is really interesting.  The latest forecasts show a pocket of remarkably cold air moving over northern Utah, with the latest NAM forcasting -22ºC over the Great Salt Lake at 1200 UTC.


In fact, the absolute minimum is an astounding -22.9ºC at 1500 UTC (8 AM).  That is a remarkably low 700-mb temperature.  It would not be a record for February (-25.9ºC is the all-time low), but we don't see too many days around here with temperatures that cold.

The Great Salt Lake is actually not that warm compared to climatology, but still, the average lake-surface temperature is almost 4ºC. 


As a result, the HRRR is fairly excited about a possible lake-effect event tonight.


Our statistical forecast system, based on the 6Z NAM, shows elevated lake-effect probabilities ovrenight tonight, peaking at 90% at 2 AM.   Note how the affected area shifts from the Cottonwoods to the northern Wasatch with the flow shift overnight. 


There are, however, three important issues to keep in mind.  The first is that wind directions beneath these upper-level troughs are tricky to forecast, so one can't count on that forecast precisely. 

The second is that we tend to fixate on lake effect, when we need to keep in mind that we could see post-frontal snow showers generated by other processes.

Finally, the third is the cold.  This is a remarkably cold airmass.  Temperatures at crest level are going to be so cold that instead of favoring dendrites, they will favor higher density crystals.  I've seen situations where this has put a damper on snow amounts in the past.  There aren't a lot of days at Alta that are this cold, but if you look at the snow-to-liquid ratios when the 650-hPa temperature is below -20ºC, there is a tendency for lower values. 


I'm thinking another 3-6" in the upper Cottonwoods through 6 PM this afternoon.  After that, I'm happy to sit in my ivory tower and watch this one play out.  Hopefully the radar will come up. 

Sunday, February 18, 2018

Six Questions to Answer When Forecasting

Exciting weather is happening and on the way, so it seems fitting to organize this post around the six questions to answer when forecasting

1. What has happened?

This "winter" has thus far been like 3.5 consecutive Novembers rather than a typical November, December, January, and February sequence.  The average temperature at the Salt Lake City International Airport for 1 December - 17 February was 37.8ºF.  That's just a shade lower than the November mean of about 40ºF.  As everyone knows, we're well below average for snowfall and snowpack, especially in the lowlands.  The photo below was taken this morning looking up City Creek Canyon and indeed it looks more like a scene you might see after a November snowstorm than one would expect in mid February. 

 
This context is important as I suspect most people are entirely unprepared for what is coming.  It will probably seem like the first storm of the year.

2. Why has it happened?

This is a good question and one that I can't answer satisfactorily.  The easy answer is that the warmth and snow drought reflects persistent high pressure and a storm track that has remained predominantly north of northern Utah.  Why that has been the case remains a subject of debate.

3. What is happening?

Wow, what a windy night.  Strong south winds at all elevations.  In the past six hours (ending at 9:20 AM MST), several sites in the northern Wasatch and Bear River Range have gusted over 70 mph and ridgelines in the central Wasatch have seen gusts as high as 71 mph.  I can find many sites in the mid elevations reporting gusts over 50 mph.  Sherwood Hills (5658 ft) near Sardine Canyon guested to 64 mph.   If there was much powder left over from yesterday's feast, I suspect it's been blown to Jackson Hole.  Peak gust at the Salt Lake Airport so far is 43 mph.

With these strong winds, we are seeing some dust.  Concentrations were especially high in the western Salt Lake Valley, which I suspect is due to emissions from the area west of Utah Lake as we have seen in recent events



4. Why is it happening?

The answer here is an approaching frontal trough that at 1500 UTC (0800 MST) was sagging southward into northern Utah.  This has created a strong pressure gradient to its south, with strong gusts at all elevations. 


5. What will happen?
6. Why will it happen?

Loaded questions!  I'll answer them together as it is easier.  As I write this, the surface front just passed Hill Air Force Base.  The HRRR shows it progressing slowly southward today, with frontal passage in the northern Salt Lake Valley around 2000 UTC (1300 MST).  Thus, expect to see a wind shift early this afternoon, if not sooner in the valley. 

Periods of snow are likely in the northern Wastach today and will develop in the central Wasatch later this afternoon.  It's a bit of an oddball situation as the latest NAM shows the frontal band over far northern Utah through 2100 UTC, but then rather than bringing it through continuously, redevelops it to the south tonight. 



Tomorrow brings the post-frontal crapshoot beneath the upper-level trough where much depends on flow direction, moisture, and instability.  The NAM forecast below isn't too bullish on snow, but the 6 Z GFS is more enthusiastic and keeps us in wrap-around moisture (not shown). 


It's worth a look at the 12-km NAM-derived forecast for Alta.  Measureable precipitation begins around 5 PM and is strongest from about 6 PM to 11 PM with the frontal forcing.  Periods of snow continue through 6 PM tomorrow in the unstable post-frontal period.  Total water equivalent is 0.6" with 10" of snow by 9 AM tomorrow and 12" by 7 PM tomorrow. 


Take a peak also at the temperatures for Mt. Baldy.  Keep in mind these are for 11,000 feet, a bit above the lift-served terrain, but this provides some idea of how cold the airmass will be.  It goes sub zero by noon tomorrow and down to -8ºF by 9 AM Tuesday.  I don't think we've seen air this cold yet this year.

To summarize, this looks to be an all elevation storm and you should be prepared for winter conditions.  We haven't had a stress test like this in some time. Thankfully, it is the President's Day Holiday, which will hopefully help with tomorrow's commute.  For Alta-Collins, I lean toward 7-14" by 9 AM tomorrow.  I have a bit more heartburn for totals after that given the variability I'm seeing in the models.  Some snow is likely, but the range of possibilities is large.  Hug a ski patroller or avalanche forecaster when you see them.  They will have a tough job the next few days. 

Finally, this is a high-impact, rapidly evolving situation.  Keep an eye on official forecasts at http://www.weather.gov/slc/. 

Friday, February 16, 2018

Powder Fever, Real Winter, Olympic Dreams

Much to talk about today.  I'll split this post into two parts, Powder Fever/Real Winter and Olympic Dreams.

Powder Fever/Real Winter


Wow, what a morning.  Yesterday's storm blew away my expectations for both snowfall amount and water equivalent.  The Utah Avalanche Center reports 12-18" of new snow in the Cottonwoods and along the Park City Ridgeline.  This morning is bluebird.  It's hard to imagine a better ski day after all the pain and suffering of the winter to date.  I suspect many dawn patrollers were out this morning and that it will be powder panic in and around the Cottonwoods this morning.   In the backcountry, the buried weak layers still give me heartburn.  Check the avy report and don't let powder fever cloud your decision making.

The models have also been shifting to higher totals for the storm sometime late Sunday to Monday, as evinced by the downscaled NAEFS plume for Alta. 
Totals currently being spit out by the Euro and the NAM are a bit lower.  Let's see how it comes together and keep our fingers crossed. 

One thing is for sure.  It is going to feel like winter early next week.  REAL WINTER.  The current GFS is dropping 700-mb temperatures to -21ºC by 11 AM Tuesday morning.  My 20/20 rule tells me that anything above 20ºC or below -20ºC is exceptionally warm or cold, respectively, for these parts.  You wanted winter.  You're going to get it.

Olympic Dreams

For me, the Winter Olympics have kicked into high gear now that the alpine skiing events are underway.  The compressed schedule might not be what the athletes want, but as far as I'm concerned, it's great for me.  Having the two tech event runs bracketed around a speed event means skiing dominates the broadcast, which makes me happy, although NBC still managed to skip Wendy Holdener's first slalom run yesterday, which was the fastest in the field.  I bet Austrian TV is smart enough not to skip the run by the skier ranked 4th in World Cup slalom points.  The DVR has also proven it's worth as I've been recording cross-country overnight and getting up early to watch before heading into work.

The schedule for tonight and the weekend is enticing.  Super-G 7PM MST tonight, Women's 4x5 km relay 2:30 AM MST Saturday, Men's GS 6:15 PM MST Saturday, and Men's 4x10 km relay 11:15 PM Saturday.  Throw in some freestyle skiing, and there's much to look forward to.  The main weather concern for these events would be wind, which hasn't been as bad in recent days, but still has shown its ugly face at times.  Hopefully all will go off without weather having a significant impact.

A few comments on the cross country.  I had the good fortune of attending both the Men's 4x10 km and Women's 4x5 km  during the Nagano Games in 1998.  The Men's 4x10 km is the Superbowl of Nordic skiing and at the time, the Norwegian and Italian ski teams had an incredible rivalry, that is well documented in Bud Greenspan's excellent Olympic documentaries.  The Italians upset Norway on their home snow during the Lilliehammer 1994 Olympics, with Silvio Fauner nipping Bjorn Daelie, the greatest male cross-country skier of all time, at the line by 0.4 seconds. 

In Nagano, the Norwegians changed strategy, putting Bjorn Daelie in the second or third leg (I forget which).  Below, Daelie is chasing down a competitor from the Italian team.


Instead they put Thomas Alsgaard, a better sprinter, in the anchor leg and he was able to take the win for Norway at the line by 0.2 seconds.  What a race!

An equally exciting race followed in 2002 in Salt Lake, with Alsgaard once again sprinting to victory.

I think the Norwegian team this year is overwhelming, but these team sprints are often closer than expected and always worth watching. 

Which brings us to the women's 4x5 km relay.  In Nagano 20 years ago, the US team finished in 15th place, just ahead of last place Canada.  I attended the race with high mucky mucks from the US Ski Team and Salt Lake Olympic Committee, who talked at length about how to get better.  It was great to be a fly on the wall for that one. 

Fast forward to 2018 and the US women's team is one of the best in the world and Jessie Diggins has been knocking on the door for Olympic medals.   The US women have never had an Olympic cross country medal and the men haven't had one since 1976.  The 4x5 is in play, as well as the team sprint.  Let us hope that this is the year. 

Thursday, February 15, 2018

Ah, the Blessed Steenburgh Effect

Sidelined with a broken bone in my hand this week, you reap the benefits.

Alta Collins has recorded 0.49" of water and 8" of snow through 7 am this morning (the 18" snow interval depth is spurious in the data below, so it's unclear if we may have ticked up or down from the 8" at 6 am).

While not a big storm it's pushing toward my arbitrary "deep powder" threshold of ten inches.  It's also pushing the upper end of predictions.

The radar imagery shows we'll add more to that total, especially in the next hour or two.


Nice to see it snowing in the lowlands as well.  Campus was covered in a thin blanket of white at sunrise this morning.


Make a few turns for me.

Tuesday, February 13, 2018

The Dribs and Drabs Will Continue Until Morale Improves


In times like these, one learns to appreciate the smaller dumps in life.  My usual definition of a deep-powder day is a 24-hour snowfall of at least 10 inches, but we've only had one of those at Alta since December 3rd!

On the other hand, recent dribs and drabs have certainly helped the skiing some, even as we continue to lose ground to climatology for snowfall amount and snowpack water equivalent.  The 6" of quick snow Saturday afternoon and 7.5" yesterday did create some smiles.  Maybe 6" is the new deep powder day.

You'll be hearing some talk of a pattern shift probably in the coming days, and indeed there are some changes afoot.  The GFS forecast valid 5 AM MST next Tuesday, for example, has a trough over the northwest U.S. and a ridge over the east, something we haven't seen a lot of this winter.



Similarly, the ECMWF model has a trough in the west (with some differing details) as do most (but not all) GEFS ensemble members.

Penn State E-wall
However, the overall pattern is one that remains high amplitude.  Note, for example, the strong ridging over the eastern Pacific and the north Atlantic in the GFS forecast above.  Given the characteristics of this flow pattern over the eastern Pacific and western North America, I'm still not enthused about this pattern opening up the spigot from now through the President's weekend.

Instead, dribs and drabs are likely.  As shown in the NAEFS plume below for Alta, the next round of dribs and drabs looks to be late Wednesday through Thursday AM.  After that, there's a break and then a great range in the timing of possible dribs and drabs Saturday night through Monday.  As usual, there's a couple of more excited ensemble members, so my usual line of keep expectations low and hope for the best applies. 

There is one non-scientific reason for you to be optimistic.  I took a surprisingly hard fall skate skiing on Saturday and learned yesterday that I fractured a bone in my hand.  They tell me I can continue to ski with a splint, but this is likely to slow me down a bit more than usual.  Thus, there may be a partial Steenburgh Effect that increases the likelihood of a deep powder day, although perhaps not as much as when I'm out of town.  This effect, if it exists, will only last 6 weeks, so be ready.  

Monday, February 12, 2018

PyeongChang 2018: Cold, Wind, and Lessons for Salt Lake 2026/2030

You can always count on the Winter Olympics to serve up some good weather stories.  So far in PyeongChang, it's cold and wind.

Let's talk about the cold first.  The average temperature in PyeongChang during the Olympic Period is 22.1ºF, making its climate easily the coldest to host the Winter Olympics since Lilliehammer in 1994.  Note that the numbers below for sites other than PyeongChang are from Wikipedia and for the entire month of February.

PyeongChang 2018: -5.5ºC (22.1ºF)
Sochi 2014: 6.0ºC (42.8ºF)
Vancouver 2010: 5.5ºC (41.9ºF)
Turin 2006: 6.4ºC (43.5ºF)
Salt Lake City 2002: 3.6ºC (38.5ºF)
Nagano 1998: 0.0ºC (32.0ºF)
Lilliehammer 1994: -5.3ºC (22.5ºF)

Some of these sites have outdoor venues that are higher (and colder).  However, if you are a reporter returning to the host city each night, you are frequently experiencing a warmer climate.  There's no escape from the cold in PyeongChang.  Even in the Gangneung Coastal Cluster, near sea level, the average temperature is -0.5ºC, colder than all but Lilliehammer.

Thus, for people covering the games, even average temperatures are a big adjustment.  In addition, over the past two weeks, mean temperatures inferred from the maximum and minimum temperatures reported at Daegwallyeong in the Mountain cluster (the site used for the climatological PyeongChang discussed above temperature above) were below average except on Feb 9 and 10.
In addition, it has also been windy, resulting in low wind chills and affecting many of the outdoor competitions.  The Men's Downhill and Ladies Giant Slalom were postponed (I learned during my Olympic service that the word cancelled shall not be used under any circumstances) and watching events the past few days it was clear that wind was playing a role.

None of this is unexpected from a meteorological perspective.  The Korean Peninsula lies along the east coast of Asia, the largest continent.  During winter, dominant high pressure frequently drives cold, flow over the region.  The pre-Olympic Weather Report summarizing the climate of the region, issued in April 2017 by the Pyeongchang Organizing Committee, provides a summary of the main weather patterns that may affect the Games schedule, and explicitly states that:
Cold and dry air flow from the northwest...is the most dominant weather pattern during the Olympic and Paralympic Periods. The Siberian High brings cold and dry weather to the Korean Peninsula. When the air mass games strength, high winds and low windchill temperatures are the most influential factors in particular during the Olympic Period.
Thus, nobody should be surprised by this weather.  Climate is what you expect, and weather is what you get.

Which brings us to Salt Lake City's likely bid for the 2026 or 2030 games.  Should those games be awarded, it would be a mistake to assume either that: (1) the weather in 2026 or 2030 will be similar to that in 2002, or (2) we will have above average temperatures because of global warming.

If you remember back to the 2002 Games, Mother Nature blew out the air pollution just prior to the start of the Olympics and for the most part during the Games, the weather was great.  In fact, Pat Bagley featured it in one of his cartoons.



However, what happens in 2026 or 2030 is going to be very dependent on the whims of the Mother Nature.  February in Salt Lake is a fickle month and a lot can happen that can affect transportation, athlete and spectator safety, logistics, and competitions.  Persistent inversions with fog and air pollution.  Downslope windstorms.  Arctic intrusions with extreme cold.  Heavy snowfall in valleys or mountains.  Strong winds in the valleys or mountains.  Lightning.

Climatologically, Salt Lake has a great climate for the Olympics, but that doesn't mean the weather will necessarily be easy on us if we host the Olympics again.

Friday, February 9, 2018

Deep Dive: How Unusual Is Our Snowfall and Snowpack This Season?

Skate skiing on the "Greatest Snow on Earth" at the Utah Olympic Park late yesterday
left much to be desired.
Following up on the previous post, let's take a deep dive and see how unusual this year has been so far for snowfall and snowpack.

This is perhaps an even more challenging topic than temperature.  Measurements of snowfall and snowpack are spotty and continuous records going back to before 1990, when most SNOTEL stations were installed, are difficult to find.  In addition, snowpack is strongly influenced by changes in vegetation and human activity around observing sites, not to mention factors such as wind transport.  

For snowfall, our best option is the meticulous record kept by snow rangers and avalanche professionals at Alta Guard, which is being extended and maintained today by the UDOT Avalanche Safety Office in Little Cottonwood Canyon (big hat tip to them!).  Observations were collected at the Atwater study plot above the Town of Alta Municipal Offices through 1998, after which they have been collected at a site just west of Our Lady of the Snows.  These sites are about 400 or 500 meters apart.  

Snowfall at Alta Guard for the months of November through January (blue bars below) averages 249 inches, with significant variations from year to year.  Although a linear fit to this data shows no significant trend (blue dotted line) one can see some important variations on shorter time scales.  The late 50s and early 60s featured several poor snow years, whereas the 1980s and 1990s were generally fat, with Nov-Jan snowfall consistently above average.  Since 2000, we've seen an high frequency of seasons with below average Nov-Jan snowfall.  Similar trends are seen for liquid precipitation equivalent of snowfall (orange lines). 


The bars highlighted in red highlight Nov-Jan snowfalls that are below 170 inches, which is one standard deviation below the mean.  These represent especially poor starts to the snow season.  The worst on record is 1976/77, when only 81" was observed.  This season, 2017/18, 109" fell.  Not far behind are 1960/61 (116") and 1959/60 (121").  These are very close analogs for snowfall amount.  Five other seasons since 2000 fall into the poor start category, with 2002/03 being the next worse to this season with 128".

SNOTEL observations of snowpack are easy to access and provide daily data, but they start in the 1980s.  An unfortunate reality of my business is that the atmosphere exhibits a great deal of variability and 30-40 years provides a very short sample.  It's like rolling two dice a few times and hoping you get a good probability sample.

Another option is snow course observations, which are collected manually near the end of the month, using coring tubes, by the Natural Resources Conservation Service.

Observations at the end of January or early February were collected at a snow course site north of Parley's summit at an elevation of 7500 ft from 1952-2002.  Starting in 1979, a SNOTEL site was operated at a nearby, slightly higher location (7584 ft).  Data from these two sites is presented below.  One sees considerable variability, but curiously, there are ten seasons with lower snowpack water equivalent than the 6.8" observed this season on 1 February.  February 1977 is the big loser with only 2.8".  Also apparent is a paucity of "fat" late January/early February snowpacks since the late 1990s, consistent with the Alta snowfall record above.


Another option is the Mill D South snow course in Big Cottonwood Canyon (7400 ft).  Observations in late January and early February have been collected here since 1956, although a house built near the site in the early 2000s may influence measurements.

Here we also see considerable year-to-year variability in snowpack water equivalent.  Curiously, last season featured the highest value in the record, followed by this season's pathetic situation.  This season's late Jan/early February value of 5.3" is eclipsed only by 1977 (2.3") and 1981 (4.9").  Years only slightly better include 1961 (5.4"), 19060 (5.5"), 1963 (5.6"), 1992 (6.6"), 2003 (6.3"), 2007 (6.6"), and 2014 (6.8").


Finally, we have Brighton, where we can amalgamate observations from three sites, Silver Lake (with observations back to the 1930s!), Brighton Cabin (1961-present), and the Brighton SNOTEL (since 1986).  Again, significant variability from year to year.  Late January/Early February 1977 is still the big loser, with only 2.6" or 4.2" of water depending on measuring site.  Aforementioned years in the early 60s also look poor.  The Brighton SNOTEL (grey line) is prone to having lower values than the other sites, and this is quite apparent in low snow years.


Obviously, the picture one gets from this analysis is clear for some conclusions and muddy for others.  This reflects a number of factors, including the difficulty of snowfall and snowpack measurements, changes in site characteristics or sampling procedures, and the fact that snowfall and snowpack evolution feature tremendous spatial variability.

However, it is clear that if you are looking to crown the champion of crappy early (Nov-Jan) ski seasons, 1976/77 is the clear winner.  It is also clear that the 1980s and 1990s were very healthy for early season snow, and that the late 1950s and early 1960s, as well the first part of the 21st century, featured a high frequency of relatively poor early season snow and snowpack years.

Sorry kiddos, but your parents, shredding in the 80s and 90s, had it better than you.

Now for some words of caution.  Observations are often treated as "truth", but all observations have their errors and uncertainties.  I haven't dug deeply into these issues in this blog post.  Second, there is a difference between a trend and trend attribution.  Explaining why we have periods of poor or good early season snowfall is challenging.  Teasing out the influence of long-term global warming from climate variations in recent years is also challenging, as is possible contributions of dust-on-snow and other climate factors.  I am not tackling those issues here.  Finally, this analysis focuses on stations above 7000 ft.

In a future post, we may do an even deeper dive by examining what is happening at the end of the snow accumulation season.

Thursday, February 8, 2018

How Unusually Warm Has This Winter Been?

Answering that question is not as straightforward as it sounds.  It is probably most easily answered at the Salt Lake City International Airport where data records go back to 1928.  There, Dec-Jan came in with an average temperature of 36ºF, making it the 4th warmest Dec-Jan on record.

Source: NOAA Regional Climate Centers
But let's suppose you want to know what has happened in the mountains.  Here's where things get tricky.  One option is to look at data collected by National Weather Service Cooperative Observers.  If you pull up a map of the stations, it looks like there are many options. 

Source: Western Region Climate Center
However, there really isn't.  Those are all stations that provided any data for any period going back for many decades.  The Snyderville Basin site started in 1991.  The site near the Park City Golf Course started in 1986, which is great, but ended in 1991.  That sounds like a long time, but there's data for temperature on only 26% of the days in the period.  Alta is a favorite of yours truly, but has lots of data gaps, even in the post WWII period.  The site near Brighton has records back to 1937, but with data gaps and, unfortunately for today's post, the observations from this January haven't come in yet.  If one does tempt fate and looks at the Alta coop site, one finds that this Dec-Jan is rated as the third warmest (27.2ºF, no missing days) behind Dec 1985 - Jan 1986 (27.2ºF, 11 missing days) and Dec 1980 - Jan 1981 (30.8ºF, 1 missing day).  

Source: NOAA Regional Climate Centers
There are other observing sites in the Wasatch, including those operated by ski areas, as well as the NRCS SNOTEL stations.  Data records for these are also often limited and don't go back a long ways in time.  

One option is to use estimates for average temperature in the "Northern Mountains" Climate Division produced by the National Centers for Environmental Information (NCEI).  These estimates integrate the available observations and attempt to account for data gaps and other data warts and biases (see Rose et al. 2014 for gory details).  If we pull that data, we see that this Dec-Jan had an average temperature in the region of 27.8ºF, which is the 2nd highest on record, behind only Dec 1980–Jan 1981.  Several other periods were close to as warm, including Dec 1917 – Jan 1918.  

Source: NCEI
Unfortunately, the Northern Mountains Climate Division covers a pretty varied region in northeast Utah with pretty dramatic changes in climate.  Trends could vary dramatically within that region.

Source: NCEI
If we pull all of this together, we find that we can be confident that this Dec-Jan was unusually warm relative to the climate in the historical record.  It does not appear to be the warmest such period at most sites, but probably sits in the 5-10% warmest Dec-Jan periods since the early 20th century.  

All of this highlights the desperate need for improved monitoring of weather, climate, snowfall, and snowpack in the Wasatch Range if we are to better anticipate, observe, and understand future climate change and it's impact on our snow climate and water resources.  For the most part, weather, climate, and snow scientists must act like vultures and piece together what we can with datasets that are incomplete and have lots of warts.  We have developed many techniques to do this, but nothing beats a well-maintained monitoring network, preferably one that observes more than just temperature and snowfall, but also snowpack characteristics and important drivers of snowmelt (e.g., solar radiation).  Establishing such a network would be a wise investment that could be taken advantage of by the generations to come as they attempt to anticipate changes in snow and water resources in a rapidly changing climate.  

Wednesday, February 7, 2018

Curious Comparisons with Previous Snow Drought Years

After several days of cloudy weather, the 6 or so inches of recently new snow combined with bluebird skies this morning will probably make for one of the nicer ski days in about a week and a half.  I wish I was skiing, but I'm not, so I thought I'd dig into the archives for some curious comparisons of this year with previous snow drought year.

I will focus on SNOTEL observations from Snowbird, because they are convenient, although they only go back to the 1990 water year (the water year begins on 1 October and is denoted by the calendar year in which it ends) and changes in the site characteristics, exposure to wind transport, and other factors means that this isn't a perfect comparison.  Nevertheless, we shall plow forward.

At this site, we currently have 12.1 inches of snowpack water equivalent.  There are actually three other water years at or below the unlucky 13-inch mark on this date: 1992 (12.4"), 1994 (12.0"), and 2007 (11.2"). 



Of those water years, 1992 (mustard colored line) took a dramatically different path to sub-13" infamy.  It featured significant storminess in late October and November, reaching 10.4" of water equivalent on 3 December, which represents a robust early season snowpack.  Then the spigot turned off.  December and January were also only 1.4ºF warmer than the 20th century average in the northern mountains, so unlike this year, snowpack losses at lower elevations and on southern aspects were probably more limited compared to this year (although this is admittedly speculative). 

The 2007 water year also featured more early season snow than this year and it tracked near or just below median through mid December, when the spigot turned off.  Temperatures in December and January were 0.3ºC cooler than the 20th century average, so despite this being a poor snow year to date, the healthier holiday snowpack and cooler temperatures would have yielded better skiing overall than this year. 

So, if you are looking for an analog since 1990, 1994 is it.  That season tracked very close to this one, and featured intermittent storms separated by dry periods (note the sawtooth like pattern for both season).  It also was 2.9ºF warmer than the 20th century average temperature in December and January.  The National Centers for Environmental Information hasn't published the temperature numbers for January yet (they usually come around the 10th of the month), but one difference is that this year is probably going to be quite a bit warmer than that. 

A curious thing about the 1994 water year is that on January 5–6, Alta set the state record for 24-hour snowfall with 55.5" of snow.  Although the graph above is for Snowbird, this event is clearly evident in the trace.  The water content of that snow, based on measurements at Alta, was 3.2", for a water content of 5.8%.  In addition, that year featured a major storm cycle from Feb 8-12 when the snowpack water equivalent increased from 12.5 to 19 inches.  Several day's later, an avalanche fatality occurred on Peak 10420 near Brighton, with the run now named Lane's Leap after the victim.  I mention this as a reminder that even if we do get a game-changing storm cycle in the next few weeks, we are still probably going to be dealing with persistent, tricky avalanche conditions in the backcountry. 

As we look forward to the future, the NAEFS forecast plume shows nothing significant happening through the weekend from a precip perspective.  Maybe a few snow showers.  After that, perhaps a trough will flirt with us, although spread right now ranges from practically nothing to about an inch of water. 

Really, only 5 runs produce more than 0.6" of water and a foot of snow.  Thus, such a dump might not be impossible, but it is a low probability outcome.  As I've said many times this season, keep expectations low and hope for the best.  

Tuesday, February 6, 2018

Pre-Olympic Cold in Pyeongchang

It's currently just after midnight in Pyeongchang and data from the Korean Meteorological Agency (available at http://pc2018.kma.go.kr) shows a temperature of -18.4ºC (-1ºF) at the Pyeongchang Olympic Plaza and -20.9ºC (-6ºF) at the downhill start at the Jeongseon Alpine Center.  Brutally cold. 



Official training begins "today" (7 February KST) for some events (Biathalon, Luge, Ski Jumping) under what will be relatively cold conditions, but with temperatures above what I suspect are considered the minimum competition thresholds.  For example, the minimum temperature for holding an FIS World Cup Nordic event is -20ºC.  Forecast temperatures for the Biathalon center are -17ºC at 8 am, rising to -8ºC at noon. 

Training for the Men's Downhill starts "tomorrow" (8 February KST).  Temperatures, however, are expected to be warmer, but still crisp at -13ºC at 9AM and -10ºC at noon. 


The good news for opening ceremonies is that temperatures are expected to moderate over the next few days.  The situation at present [1500 UTC 6 February (0000 KST 7 Feb)] features a cold flow originating over interior Asia.  The 925-mb (about 750 m above sea level) temperature sits at about -16ºC, which explains the cold surface observations noted above. 


Over the next few days, temperatures warm gradually and by 1200 UTC 9 February (2100 KST 9 February), roughly an hour after the start of opening ceremonies, the 925-mb temperature sits at a far more tolerable -2ºC. 


The one issue in that forecast might be the westerly flow.  Currently, however, the Korean Meteorological Agency forecast is calling for light southwest winds (1 m/s equates to 2 knots). 


The opening and closing ceremonies sometimes feature displays or activities that are very weather sensitive.  Closing ceremonies for the Salt Lake City Games featured, for example, hot air balloons. 

Source: http://olympicgamesblog.blogspot.com/2005_04_01_archive.html
Thus, the wind forecast can be all important for the opening and closing ceremonies.  For the Salt Lake closing ceremonies, a cold front with strong post-frontal winds was bearing down on Salt Lake and was the cause of a great deal of forecaster heartburn.  Frontal passage and the strong winds held off, however, to just after the end of closing ceremonies, to the great relief of forecasters.  

I suspect the Pyeongchang forecast team will be keeping a close eye on the winds (as well as other weather parameters) as the opening ceremonies approach.