Saturday, October 21, 2017

Lessons from Orographic "Cumulus Patheticus"

After yesterday's dustpocalypse, the weather this morning seems relatively benign, but there's always something to be learned. 

Overnight and early this morning, orographically (i.e., mountain) forced cumulus clouds developed over the Wasatch Range. 

The unofficial name for such shallow cumulus clouds is "cumulus patheticus" as they are pretty wimpy compared to their cumulonimbus (towering clouds associated with rain and thunderstorms) brethren. 

Officially, they are stratocumulus clouds.  In this instance, lifting by the mountains appears to have been essential for their formation.  The GOES 16 satellite image for 1512 UTC (0912 MDT) showed the clouds were confined primarily to very near and downstream of the Wasatch Range, with lee waves generating wave-like clouds further downstream. 

This morning's satellite imagery shows that the clouds were confined to a layer between about 750 mb (about 8000 feet) and 550 mb (about 16,000 feet).  A pronounced stable layer with a base at 550 mb (16,000 feet) prevented penetration to greater heights. 

Source: SPC
The cumulus patheticus did produce some small snow pellets in the Avenues overnight.  I suspect there were a few snow showers in the central Wasatch as well.  

Shallow cumulus clouds like these can produce prolific mountain snowfalls under the right circumstances.  This morning, we appeared to be moisture limited given the large difference between the temperature and the dewpoint at low levels.  This, combined with the stable layer aloft, limited cloud depth and updraft strength.  More moisture at low levels would have likely enabled deeper clouds, stronger updrafts, and more rapid growth of ice crystals.   

Under such a scenario, snowfall rates of two ore three inches an hour are possible if the cloud exists at temperatures favoring the growth of dendrites, those wonderful 6-armed snowflakes that we all love.  

Orographic clouds do not necessarily need to be deep to be prolific snowfall producers, but they do need the right ingredients. 

Think of this the next time you're skiing, it's snowing hard, and yet you can make out the sun when you look up.  

Friday, October 20, 2017

Postfrontal Dustpocalypse!

A strong cold front raced across northwest Utah this morning, reaching Salt Lake City around noon bringing a blast of moderately strong pre- and post-frontal winds, the latter accompanied by blowing dust.

Dustpocalypse Now!
Observations collected every minute from the William Browning Building (WBB) on the University of Utah campus show a wind shift from SW to WNW from 1153 to 1155 MDT.  Winds continue to turn through NW at 1200 MDT.  From 1153 to 1200 MDT, temperatures fell 10.3ºF.  Pre-frontal wind gusts reached as high as 42 mph a couple hours ahead of the front and peaked at 49 mph at 1209 MDT, just behind the front.

Adding to the story was the post-frontal blowing dust.  At Wendover in far western Utah, the post-frontal visibility dropped to as low as 4 miles, likely due to blowing dust.  However, at the Salt Lake City International Airport, minimum visibilities reached 1 mile, suggesting that dust emissions from the area surrounding the Great Salt Lake and the west desert contributed.

The dust made the cold front very apparent as it entered the Salt Lake Valley (h/t to @UteWeather for tweeting the image below, taken facing from the U toward downtown Salt Lake City).  One can see the classic frontal "nose" to the left of the photo, with friction resulting in a slight forward tilt of the front with height in the lowest one or two hundred meters, above which the front slopes back over the cold air.

The post-frontal air was nasty.  PM2.5 concentrations spiked to 120 ug/m3 on campus immediately following frontal passage.

I guess if you're not going to have much snow, weather excitement like this is better than nothing.

Addendum @1235 MDT:

Shortly after writing this post, the PM2.5 at our mountain met lab topped out over 200 ug/m3 (note scale change from graph above). 

There's some uncertainty in these measurements, so perhaps we should be cautious about the absolute values.  That being said, the air was pretty nasty out there and remains so as I write this at 1235 MDT.

Thursday, October 19, 2017

Another Waste of a Trough

Ordinarily, a satellite image like this mornings (below) would get me excited.  There's a cold front over the Pacific Northwest, a deep upper-level trough over the eastern Pacific, and plenty of convection over the eastern Pacific, indicative of cold air. 

Unfortunately, the system has three things going against it.  One is it's moving into the ridge that is parked over the North American interior.  Two is that it's a fast moving system.  And third, there isn't much of a snowpack currently in the Wasatch, so a refresher doesn't do us much good. 

The loop below from the GFS summarizes the first two issues quite well.  Note the weakening of the trough as it moves into the western US and the associated precipitation falls apart and moves quickly across northern Utah. 

Our downscaled SREF forecasts for Alta show most members generating under 0.3" of water tomorrow (Friday) and tomorrow night.  0.7" is the upper end.  Most of this precipitation will fall as snow above 8000 feet, but that's still only an inch or two for about half the SREF members, with perhaps up to 6 or 7 inches for the wettest.  I suspect the wet members bring the trough in a little stronger and a bit further south. 

So, this will be another waste of a trough for the Wasatch, not providing enough for turns. 

If you need to feed the habit with a tour, the Grand Targhee SNOTEL appears to have the highest snowpack water equivalent of any SNOTEL site in the contiguous US with 5.4".  The base of the resort looks thin, but the summit web cam looks inviting.  They also look to do much better than us out of this storm.

Wednesday, October 18, 2017

Last Half of October Looking "Ridgy"

The period from mid September to mid October was relatively cool in northern Utah, ranking as the 12th coldest on record at the Salt Lake City International Airport and the coldest since 1986. 

Source: NOAA Regional Climate Centers
The period also brought a bit of snow to the mountains, which continues to linger on shady upper-elevation slopes.

However, the pattern is shifting for the latter half of October.  Although we have a cold front moving through the area on Friday, bringing a temporary cool down for the first half of the weekend, the extended range forecasts are strongly hinting that the next 10 days or more will be dominated by ridging over our area.  Below are GEFS forecasts valid 6 AM Monday and Wednesday mornings, showing the jet either to our north on Monday, raking the area along the US-Canadian Border, and high amplitude ridging over our area on Wednesday.  

Source: Penn State e-wall 
Source: Penn State e-wall 

A strong tendency for ridging is also suggested by most members of the GEFS for late next week. 

Source: Penn State e-wall 

By and large, this is not a recipe for October skiing.  We might get a little snow with the front on Friday, and it's possible that something could "slip through the net" over the next 10 days, but by and large, these are pretty pessimistic forecasts for those looking for October turns.

On the other hand, that's not necessarily a bad thing.  Early snow often turns into weak snow (as is happening on the shady aspects where snow lingers) and if we have our druthers, a season that comes on strong in early November is preferred to one that comes in with a bit here and there in October.  The key is for this pattern to change in November, preferably early.  Let's hope that happens.  

Tuesday, October 17, 2017

Perplexing Probabilities

There are a host of challenges posed in the forecast communications business.  One that I thought of this morning as I surveyed the ensemble forecasts is the low probability, high impact weather event.

Fair weather looks to predominate over northern through Thursday, but on Friday, an upper-level trough moves across the northwest U.S. with the trailing cold front racing across Utah.  The NAM calls for precipitation accompanying the front to be relatively light.  Perhaps some valley rain showers and mountain snow showers, but nothing for skiers to get excited about.  

If we look at our downscaled forecasts for Alta based on the Short Range Ensemble Forecast System (SREF) we find that most members are producing very light accumulations of 0.25" of water equivalent or less through 6 PM Friday (0000 UTC 21 October).  Again, nothing to get excited about.  However, 2 of the 26 members are going bigger and putting out about 0.7" of water or so.  
If we look at our downscaled NAEFS forecasts for Alta, most members producing light accumulations, a few in the 0.4" to 0.7" range, but then two outliers that go absolutely huge, generating about 2.5 inches of water and around 25 inches of snow.  Skiing anyone?

Such outliers are unusual, but not unheard.  However, I don't know of any studies that have attempted to look specifically at the reliability of such low probability, high impact forecasts.  The NAEFS forecast above, if taken literally, would yield about a 10% chance of 20" of snow or more on Friday, but a 90% chance of 7 inches or less.  Is that a reasonable forecast of the probabilities?  In addition, if that was a reasonable forecast of the possible outcomes, how best to communicate that to the public and forecast customers?  "Well, we think that there will be some snow showers.  Odds are it won't add up to much, but there's a slight chance of 20."  That should go over well.

I don't have answers for these questions.  We need better validation studies of our ensembles and, as ensembles improve, better ways to both extract and communicate probabilistic forecast information in a way that is useful to the end user.  

Monday, October 16, 2017

Impacts of Post-Tropical Ophelia on Ireland

Following up on yesterday's post, here's a few tweets from Ireland showing the impacts of Ophelia.

Sunday, October 15, 2017

Irish Eyes Aren't Smiling

Hurricane Ophelia has had an unusual life cycle in the northeastern Atlantic Ocean and as of 11 AM AST this morning, was still a category 1 hurricane off the coast of Portugal. 
Source: National Hurricane Center
Over the next 24 hours, Ophelia is expected to undergo what is known as extratropical transition, the transformation from a tropical cyclone into an extratropical cyclone.  It is expected to track northeastward and bring strong winds to Ireland and Scotland on Monday. 

The GFS sea-level pressure and wind speed (meters per second) forecast from the GFS is below and it shows the storm strengthening and broadening just southeast of Ireland, before weakening just a bit prior to landfall. 

Nevertheless, the system is quite strong at landfall.  The areas in yellow feature sustained winds of 28 m/s (56 knots) and orange around 35 m/s (70 knots), the latter are hurricane force.  These areas are found over water.  Winds are weaker over land, but still quite strong. 

The Irish Meteorological Service, Met Éireann, has issued a National Weather Warning and is expecting sustained winds of 80 km/h (43 knots) and gusts in excess of 130 km/h (70 knots) in the southern half of the country.

Source: Met Éireann, 9:30 MDT 15 Oct 2017
Much will depend on the precise track of the storm, but it looks like this will be a strong windstorm for Ireland, and perhaps Scotland and other portions of the UK. 

Saturday, October 14, 2017

The Waiting Game Begins

Last night's trough passage brought a couple inches of snow to the upper elevations of the central Wasatch.

Source: Snowbird
Even at my place, there was a trace of snow. 

The waiting game now begins for the start of the ski season.  As things stand now, the next five days look dry.  Although cold today, we should see marvelous fall weather beginning tomorrow through at least Wednesday and probably Thursday as well.  

After that, we shall see.  The good news is that the GEFS is calling for troughiness over the western US late next week.  

However, snowfall in the Wasatch is greatly dependent on all sorts of factors that cannot be nailed down so far in advance.  Some of those solutions would probably give us a pretty good dump, others next to nothing.  

Thus, at this stage, it's best not to buy into any click bait based on extended range forecasts. 

Need a Recommendation

I've discovered some minor damage to my carbon fiber mountain bike frame.  Recommendations for affordable repair shops or individuals greatly appreciated. 

Friday, October 13, 2017

Abrupt Changes This Weekend

Mid October arrives on Sunday, meaning that I begin to take a closer interest in potential storms that could bring the start of ski season.  

The trough moving through tonight and tomorrow won't bring more than some light accumulations to the central Wasatch, so the ski watch continues, but it will bring some rapid changes in upper-elevation temperatures.

While we have fall-like weather today, by 1200 UTC  (6 AM) tomorrow morning, a fast moving upper-level trough ushers in some legitimately winter-like air, with 700-mb (10,000 ft) temperatures at or below -10ºC by tomorrow morning.  That's pretty frigid for October.

But by 1200 UTC (6 AM) Sunday morning, we've rebounded nicely to +2ºC. 

Here's the yo-yo as illustrated by our automated temperature forecast derived from the NAM for the summit of Mt. Baldy (11,000 feet).  Temperatures today in the low to mid 20s (the station currently shows 25ºF), but plummeting overnight to 8ºF by 8 AM.  Temperatures climb, however, as the trough moves out and the ridge moves in and by Sunday morning, they are pushing 40ºF.  

Bottom line: Tomorrow is good for sleeping in, enjoying brunch, and shopping for skis.  Save higher altitude adventures for Sunday.  Those adventures, however, won't involve skiing, at least in the central Wasatch.  

Tuesday, October 10, 2017

Sad Reminder that Early Snow Is Not Necessarily Safe Snow

It's very early in the ski season, yet a backcountry skier died in an avalanche on Imp Peak in the Madison Range of Montana on Saturday.

Source: Friends of the Gallatin National Forest Avalanche Center
Some basic information is available in this article from the Bozeman Daily Chronicle.

This is a sad reminder that early snow is not necessarily safe snow.  The central Wasatch has had early season fatalities in the past, including within resort terrain, which is de facto backcountry during the preseason.  Keep this in mind when we start to see snow piling up again.  

Saturday, October 7, 2017

Cold Blast to Start Fall Break Week

Don't be fooled by today's mild temperatures.  A blast of cold air will move into Utah tomorrow and yield some unseasonably cool temperatures on Monday for the start of the U's Fall Break week. 

The NAM forecasts the dry surface front to be pushing through northern Utah early tomorrow morning, so tomorrow is a day during which temperatures will struggle to rise. 

By Monday morning, the upper level trough is centered near Vernal and 700-mb temperatures are dow to around -7ºC. 

Such a temperature wouldn't be a record based on historical upper-air soundings, but is well below average. 

And the NWS forecast shows how the bottom drops out after today. 

Monday looks to be a below average temperature day statewide.  Pity this system looks to only produce some snow showers and perhaps an inch or two of snow in the central Wasatch.  

Thursday, October 5, 2017

Is High North Snow Here to Stay?

I'm traveling today to climates far from snow and wondering how much of the snow that currently sits at high elevations, mainly on aspects facing the northern half of the compass, is here to stay. 

In Utah, most of the energy for melting snow comes from the sun.  We are now in October, beyond the fall equinox.  Those north facing slopes are not receiving much solar radiation anymore.  If we got a warm storm, perhaps long-wave radiation from clouds and condensational warming could eat some snow, but such storms become increasingly rare as we move through October.  Finally, temperatures just aren't very high this time of year, so even on warm days, the flux of energy from the atmosphere into the snowpack is relatively modest.  There's even a cold front coming in Sundayish to help with the effort. 

Your thoughts? Is the snow here to stay? 

Wednesday, October 4, 2017

Storm Chasing Doppler on Wheels Radar Coming to Utah!

A storm-chasing Doppler on Wheels (DOW) radar will be coming to the University of Utah in November for the Outreach and Radar Education in Orography (OREO) field program.  

The visit of the DOW, operated by the Center for Severe Weather Research and supported by the National Science Foundation, will give University of Utah students a hands-on education in radar operations and interpretation, mountain and lake-effect precipitation processes, and the use of mobile observing platforms for field research. 

The DOW last visited campus in fall of 2011.  We had a field day, observing everything from intense fronts pushing through the Salt Lake Valley to lake-effect bands pushing into the Wasatch Range. 

During the visit, atmospheric sciences graduate students will plan and lead several DOW field deployments and educational activities for majors and non majors.  We are also planning a major public display of the DOW.

More information on these activities will be forthcoming in the next couple of weeks.  Stay tuned!

Tuesday, October 3, 2017

Frank Brown: Friend and Mentor

Frank Brown, professor of Geology and Geophysics and Dean Emeritus of the College of Mines and Earth Sciences at the University of Utah died suddenly of a heart attack on Saturday.  It is impossible to put into words the impact that he has had on my college, the University of Utah, and my career, but I'll make an effort here. 

If you are or have been a student in the College of Mines and Earth Sciences, Frank fought tooth and nail to make your education as high quality and cost effective as possible.  I know this first hand because I was chair of the Department of Atmospheric Sciences for six years.  I watched Frank tirelessly fundraise for scholarships, attempt each year to find scholarship support for every student in the college with a GPA of 3.0 or higher (and bemoan the fact he couldn't provide more, as well as something for students below that bar), and question every aspect of my budget to ensure money was being spent effectively. 

In 2001, Frank won the Rosenblatt Prize for Excellence, the highest award for faculty at the University of Utah.  It came with a check for $40,000.  He had every reason to keep that award.  He had worked tirelessly as a professor and dean.  He was probably the lowest paid dean on campus.  He drove a beat-up old pick up (to my knowledge he drove that truck until the day he died).  Instead, he donated every cent of it back to the University to help students. 

When I arrived at the University of Utah, I was as green as grass, 28 years old, and commonly assumed to be the student representative at faculty committee meetings.  Frank provided unwavering support right from my arrival.  Perhaps he was more than glad to have a young faculty member deal with issues he'd rather avoid (computer support and management you know who you are), but it is now clear that he had an agenda.  I distinctly remember him telling me once, when I had only been at the U for a few years, that I would not only be a professor, but also a chair and a dean.  He was right on 2/3, at least so far.   His strategy was one of the self-fulfilling prophecy.  Tell good people very directly what they are capable of achieving and there's a pretty good chance it will happen.  He was also famous for confidence building quips like "you'll do fine" when people enter unknown and stressful circumstances.  It doesn't sound like much, but Frank had a way of saying it that inspired confidence.

The wonderful Continuum cover above calls Frank a "Hominid Extraordinaire."  The tendency when one sees a line like that is to think about professional achievement and in that regard, Frank was a Hominid Extraordinaire.  Indeed, Frank met that bar. How many Deans still taught a full teaching load every year?  Actually, I think he may have taught beyond that.  He was a world-class paleontologist.  He was a passionate and dedicated administrator. 

But those aren't the reasons why Frank was a Hominid Extraordinaire.  The reasons are Frank's generosity and goodness.  He did much to help people who were sick and disadvantaged.  I don't know how he found the time.  I almost always found out about these efforts when we were working late or on a weekend and he'd mention that he has to go and lend someone a hand.  He traveled to Africa every summer for field work and, as discussed in the Continuum article, spoke several native languages.  Our meetings were frequently interrupted by a phone call from Africa.  Frank would pick up and cluck away in some impressive dialect.  When the call was done, he would proceed to tell me with great concern about the personal or regional challenges that the caller was facing.  I have no idea how he juggled so many balls.

Frank Brown was my friend and mentor.  I will miss him, and so will the U.

Monday, October 2, 2017

Snow over Utahrado

I found it tough writing this morning, but I felt it best to do something positive, even if my thoughts are elsewhere.

From a snow perspective, there's a great deal going on across the Utahrado nation.  A slow moving, digging upper-level trough has spawned a quasi-stationary band of precipitation that extends across central Utah and northern Colorado.  It is also producing a little lake-effect precipitation southeast of the Great Salt Lake.

These features are apparent in this morning's GOES-16 imagery.  

The lake-effect is just a little meteorological eye candy, but the frontal band is delivering big time at upper elevations.  Here's a shot from Steamboat.  Quite a pasting at 10,000 feet.  

Further, the snow there is likely to continue through the day today.  I suspect there will be some good skiing on the upper mountain later today and tomorrow.

Sunday, October 1, 2017

Cloud Scraping on Mt. Ogden

My knee is still talking to me on descents, and I'm sick of hiking up Snowbird, so I elected to go up to Snowbasin today, bag Mt. Ogden, and take advantage of the Needles gondola for a good portion of the descent.

It's been about 15 years since I've been on Mt. Ogden.  It's quite a peak, with a stupendous view, so I wonder what took me so long for a return visit.

Mt. Ogden from the lower Snowbasin slopes
The morning weather at Snowbasin was better than it was over the Salt Lake Valley and central Wasatch where it was raining when I left.  Nevertheless, there were some scattered showers, which made for some picturesque virga shafts.

My timing for summiting wasn't great as it was about as cloudy as it would be all day, but I have always liked being on narrow alpine ridges when there is a cool orographic cloud with the base right near the summit.  It creates a cool scene with the clearer skies upwind. 

The summit was socked in an frigid.  25ºF with winds gusting to 40 mph according to MesoWest.  I had enough layers for my torso, but could have used a thicker pair of gloves.

As soon as I began to descend off the summit, the skies began to break up a bit.  Here's a view looking southward along the Wasatch spine. 

Next weekend is the last for summer gondola rides.  They don't seem to be charging for the descent, but it's $14 for the up, not that I took advantage.

Saturday, September 30, 2017

Changing of the Seasons

Below average temperatures in northern Utah have been few and far between the past few months, but the latter half of September has delivered the cool goods.  Since the 14th, we've only had three days with an above average maximum, and even most of the minima have been below average as well.  Simply splendid!

Source: National Weather Service
Leaves are starting to go now.  The cell-phone photo below doesn't do them justice as some there are some reds and yellows out there that are really starting to pop.  

With snow on the mountains, the feel has been more of October than September, but I'm not complainin'