Wednesday, February 28, 2018

The Devil Is in the Details

Nothing gives me heartburn more than the hyping of winter storms days in advance in Utah.  The devil is in the details and snowfall at any given point in our state is strongly dependent on frontal position, wind direction, and the like. 

With those words of caution, let's take a quick look at forecasts for the storm later this week and this weekend.  As I mentioned yesterday, there will be a period of warm-frontal precipitation in southwesterly large-scale flow Thursday afternoon and evening that should some snow to the mountains.  Then, things get interesting.

The 6Z GFS forecast shows a developing trough and strong cold front over the Great Basin and northwest of Salt Lake City at 1500 UTC (8 AM MST) Friday.  We are in the strong southerly flow ahead of the front, with precipitation primarily lagging it. 

At 700-mb (roughly crest level), strong southwesterly flow reaching over 30 m/s (60 knots) covers much of western Utah. 

If happening in the afternoon, this would be a recipe for very strong southerly flow and wide-spread blowing dust.  At night and in the morning, it's a bit more of a crapshoot what will happen in the valleys as sometimes we are able to maintain a nocturnal stable layer or inversion that helps reduce the strength of the surface winds.  I'm inclined to think in this case we will see that inversion mix out and strong southerly winds will develop Thursday night and give us a good blow Friday morning ahead of the cold front. 

The models differ somewhat on the details of the frontal passage.  The 6Z GFS pushes the front through Salt Lake City around noon Friday, with an active zone of frontal precipitation draped over the region Friday afternoon.  Post-frontal precipitation would fall as snow at all elevations.

The GFS is positively bullish on frontal precipitation blanketing our area for much of Friday afternoon and Friday night.  Note the lack of movement from the forecast above, valid 2 PM MST Friday, to the forecast below, valid 11 PM MST Friday. 

The 12Z NAM has a remarkably different forecast as it stalls the front to our northwest, keeping us in prefrontal southerly flow Friday and even Friday evening.  This is a dramatically different forecast that will surely give forecasters heartburn. 

Eventually the NAM pushes the front through late Saturday and Saturday night.  Thus, we can have confidence we're going to have winter weather, but the timing and amounts vary dramatically between these two model forecasts. 

In situations like this, I tend to lean toward the GFS, at least for the gross large-scale details for the following reason.  The GFS is a global model with a later cutoff for ingesting weather observations because it runs later.  The NAM is a regional model, with an earlier cutoff, and it is driven on it's boundaries by the previous GFS forecast. 

Perhaps another reason to lean toward the GFS is that the Euro also favors a frontal passage on Friday and a solution that is more GFS-like than NAM like, at least as far as large-scale features are concerned.

That being said, in terms of the amount of precipitation produced, the GFS is a bit of an outlier and I consider it's precip amount forecast to be a lower-probability outcome.  NCEP has finally corrected a bug that was providing incorrect hourly precipitation amounts in the station output that we use for our model-derived upper cottonwoods forecast guidance (info here).  Thus, I've started processing that data again and as can be seen below, the total amount of water produced for the period, including the warm-front tomorrow, is 3 inches, with nearly 50 inches of snow due to relatively large snow-to liquid ratios. 

This is substantially higher than the Euro, which is producing a bit over an inch.  It is also higher than every member of our downscaled SREF product (Note that the SREF only goes to 0000 UTC 4 March/5 PM MST Saturday, although this still captures most of the storm). 

For the GFS to verify, we'll probably need everything possible to align just right.  Although not out of the realm of possibility, the odds favor water and snowfall totals in the upper Cottonwoods that are lower than forecast by the GFS. 

The bottom line is that we're still a couple of days out from this one and that much is going to depend on small-scale details including the timing and movement of the cold front.  Monitor official forecasts from the National Weather Service and be prepared for winter weather Friday and over the weekend. 

Tuesday, February 27, 2018

Potential Storminess Ahead

The models have been advertising a fairly exciting period of weather for this week and weekend the likes I'm not sure we've seen for some time. 

It's a complicated enough situation that I struggled with how to describe it in this post, and ultimately decided to simply use the GFS forecast time-height section for Salt Lake City for a summary (click here for information on time-height sections and remember time increases to the left). 

Through Wednesday, we're in the doldrums, but early Thursday we have a weak warm-frontal feature moving through northern Utah that might bring a bit of snow to the mountains.  Then things get interesting as a deep upper-level trough digs southward out of the Gulf of Alaska and parks itself along the Pacific Coast.  This leads to a period with strong southerly flow developing Thursday night and persisting into Friday.  Any snow available for transport at that time will surely go for a ride and we may see some dust as well. 

Right now, the GFS is advertising a frontal passage for mid-day Friday, with snow likely at all elevations.  A second cold front develops and moves across northern Utah late Saturday.  By and large, it looks like an active period.  It should be noted, however, that this is still a medium range forecast and much will depend on the evolution of the trough and it's interaction with the mountains of the western US (especially the Sierra Nevada).

The downscaled NAEFS mean is about 1.5" of water through 0000 UTC 4 March (5 PM MST Saturday), with a little falling with the warm front and most falling with the cold front after mid-day Friday (there are differences in timing).  This bodes well for a good powder day Saturday, provided the storm doesn't slow down (it happens). 

This is a storm worth watching and hoping that it stays together in a way consistent with recent model runs. 

Monday, February 26, 2018

Bad Ass Olympic Performances

The Winter Olympics have wound down, leaving only memories of great performances.  One thing that struck me about these games is that the women's events were equally or more compelling than the men's.  In fact, when I think about the most memorable performances I saw, which are admittedly heavily biased to alpine skiing, nordic skiing, and biathlon, they were all by women.  Thus, here's my list of top bad ass performances during the Olympics. 

  • Marit Bjoergen, women's 4x5 relay: Bjoergen appears 3 times in this list as she cemented her place as the greatest Winter Olympian of all time at these games.  She skied the anchor leg in this race, schooling the younger Stina Nilsson of Sweden.  
  • Marit Bjoergen, 30-km mass start: As far as endurance races go, this is about as dominating as you get.  Bjoergen pushed the pace from the start and was a locomotive for 30 km, winning by near 2 minutes.  The performance was the epitome of "a confident athlete is a fast athlete."  She knew she was the fastest and she knew her pace, and she just laid it out there for 90 minutes.  
  • Marit Bjoergen, everything: Five medals in 2018.  8 golds overall. 15 medals overall.  Insane.  Micheal Phelps gets well deserved accolades for his accomplishments, but he doesn't win everything from sprints to the 1500 meters.  Bjoergen won medals in these games in everything from the team sprint to the 30-km mass start.
  • Jessie Diggins/Kikkan Randall, Team sprint: I often grow tired of NBC's US-centric coverage of the games, but these two overcoming 66 years of frustration is a well deserving feel-good moment.  Plus, the race was AWESOME.  I knew the winner when I finally sat down and saw the replay and was still on the edge of my seat as Diggins slides back into 3rd place on the final downhill and somehow finds a way to thread the needle and win the sprint.  Heart of a champion.  

  • Ester Ledecka, anything on snow: I didn't even know there was anyone competing in both Alpine skiing and snowboarding, and then Ledecka comes along, wins a surprise gold in the Super-G, and then follows that up with a parallel GS victory.  She was a favorite for the latter, but the darkest of dark horses for the former.  Sadly, NBC had broken away from the Super-G and had to cut back to her surprise run. 
  • Anastasiya Kuzmina, Women's 12.5 km mass start: It's a wonder Biathlon isn't more popular in the U.S. given our fixation on guns.  The intensity of this sport is INSANE, but especially insane in mass start races where the top skiers enter the range at roughly the same time and shoot next to each other.  In this race, Kuzmina nailed 19 of 20 targets and 5 of 5 in her final round of shooting.  Talk about ice water in the veins.  Honorable mention for Laura Dahlmeier who won golds in the 7.5 km spring and 10-km pursuit.
There were certainly some great male performances during the games, including Aksel Lund Svindal and Kjetil Jansrud going 1-2 for Norway in the downhill, but I found none of these to be as exciting as those above.  A special shoutout for Norway, which dominated the games and seemed to do it with class, style, and sportsmanship.  

It's now 4 years until the next Winter Olympics, which will be held in Beijing, which has a climate that is not all that unlike Pyeongchang with cold, dry, windy winters.  The mountains get even less snow than those in Pyeongchang.  Of course, climate is what you expect and weather is what you get, but to all the reporters out there who called me about how cold it is in Pyongchang, bring a down coat and add a pollution mask to your suitcase.  

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 

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 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.