Tuesday, August 31, 2021

Caldor Fire

The Caldor Fire continues its relentless march eastward and northeastward.  The latest on #Firemappers shows the fire has crossed route 89 and is now pushing into the Carson Range.  Many homes and cabins are threatened and there was a mass exodus from South Lake Tahoe yesterday when evacuation orders were issued.  You can add Heavenly to the list of ski areas threatened.  

Source: Firemappers, 8 am MDT 31 Aug 2021

To the south, Kirkwood is now under direct threat.  

Source: Firemappers, 8 am MDT 31 Aug 2021

My son and I ski toured a closed Kirkwood with a dwindling snowpack on May 9th.  It's a beautiful area and we were very impressed by the trees.  Enough so to take the photo below.

I have no strong connection to the area other than that day, which was the first time I had been through Carson Pass.  I am hoping for a miracle for everyone and the forests effected.  

Meanwhile to the north, the monstrous Dixie Fire has now surpassed 800,000 acres burned, including a significant fraction of Lassen National Park.  The map below provides some perspective.

Source: Firemappers, 8 am MDT 31 Aug 2021

According to fire.ca.gov, Dixie is the 2nd largest wildfire in California history, behind only the August Complex last year at 1,032,648 acres.  

Snow can't come soon enough this fall. 

Monday, August 30, 2021

Summer Is Ending with Hazards Aplenty

Tomorrow (Tuesday) is the last day of meteorological summer.  September is almost here!  Celebrate with Earth, Wind, and Fire.

On the other hand, there's not much to celebrate this morning as summer is ending with hazards aplenty.


The children's song goes "What does Idaho, she hoes her Maryland," but yesterday, Ida raked Louisiana, coming ashore after rapidly intensifying into a ferocious category 4 hurricane.  

Ida at Landfall.  Source: NCAR/RAL.

The track and intensity forecasts for Ida were quite good, as pointed out by Sam Lillo below.  

Still, it is a devastating event and one with compound hazards from wind, storm surge, precipitation-related flooding, and COVID-19.  The phrase "it's over" doesn't really apply today in southeast Louisiana.

Caldor Fire

Fires continue to rage in California, with the Caldor Fire now an immediate threat for the Tahoe basin and ski areas.  

The latest mapping at FireMappers shows the fire perimeter has pushed past Sierra-at-Tahoe ski area with hot spots at Echo Summit.  Kirkwood is also in the cross hairs further south.  

Source: #Firemappers

Photos from the ski resort below from @ABCliz.

I'll call the forecast "not good" with an upper-level trough moving across the Pacific Northwest producing   dry, southwesterly flow in the Tahoe area through Thursday morning.  Below is the GFS time-height section for south Lake Tahoe showing very low relative humidity and SW winds at low levels of 20-30 knots through Thursday morning.  

Western Air Quality

Air quality in northern Utah has been intermittently poor this summer, although it's nothing compared to the smoke-filled communities in northern California.  The latest from PurpleAir shows hazardous air quality conditions at some locations near fires. 

Source: PurpleAir

Really, the air quality near the fires should be called "haute category," "hors catégorie" a French phrase meaning "beyond category" that is used to classify the most extreme climbs in road cycling.  The threshold for hazardous air quality is 250 μg/m3. Purple air sensors suggest values well over 300 μg/m3 and in some areas over even 700 μg/m3 near South Lake Tahoe.

Source: PurpleAir

For comparison, concentrations reported by Purple Air in the Salt Lake Valley at 9 AM this morning are generally in the 35-55 μg/m3 range, about 1/10th that in South Lake Tahoe.

Salt Lake City Summer Temperatures

We conclude with a quick look at the race for hottest summer in the history of Salt Lake City.  With two days to go, this summer has an average temperature of 81.0˚F, just barely ahead of 2017 for hottest on record.  

Source: xmacis

Based on last night's minimum and forecasts for this afternoon and tomorrow, we may hang on to the record, but it's going to be close.  

Friday, August 27, 2021

Climate Nonstationarity

Changes in the statistics of climate and climate variables is sometimes referred to as climate nonstationarity.  It makes climate "normals" and other statistics based on past data increasingly irrelevant as the climate changes. 

A good example is provided by the mean summer (June, July, August) temperatures in Salt Lake City. The graph below shows the mean summer temperatures in the Salt Lake City area from 1875-2021 (blue;the latter year included with a few days missing), the 30-year running mean temperature (red), and the 1991-2020 average temperature (orange).  

Data source: http://xmacis.rcc-acis.org/

Prior to approximately 1965, temperatures in the Salt Lake City area fluctuated without a major trend, but after that time, temperatures began to climb.  The average summer temperature for the 30-year period from 1936-1965 was 72.9˚F, but for the 30-year period from 1991-2020 it was 76.4˚F, an increase of 3.5˚F.  

The 30-year averages are sometimes referred to as "climate normals."  However, when the climate is nonstationary and warming rapidly, they really represent the climate of the past not the climate of the present.  From 2006-2020, the latter half of the most recent 30-year climate normal period, 12 of the 15 years had average temperatures above the 30-year average and the average temperature for that period was 77.6˚F.  

One challenge, however, in using a 15-year period is that shorter periods are more strongly influenced by climate variability.  One can see how such variability caused some periods or relatively warmer or cooler climate prior to 1965 in the graph above.  This is a significant issue in the fall, winter, and spring when weather variability in northern Utah is quite large.  It's smaller during the summer months (especially July), but still a factor to consider.  

This is an issue that we will be facing in the coming decades as climate change continues and accelerates.  Temperature is an important variable, but precipitation extremes will be even more challenging to anticipate and plan for and will require better modeling and tools than we have today to provide guidance for future infrastructure and adaptation efforts.  

Note from Jim:

In preparing this post, I noticed that the 30-year averages I was obtaining both on the xmacis site and using summer averaged temperature data from that site were about 1˚F lower than the National Center for Environmental Information (NCEI) climate normals.  I have not been able to reconcile these differences in the short time that I have, but opted to not use the latter in this analysis so that the graph above was based on a consistent dataset.  

Wednesday, August 25, 2021

You Can Help Improve Snowfall Forecasts

My University of Utah Atmospheric Sciences colleague Dr. Timothy Garrett and his team are embarking on a citizen science project to classify snowflakes and train computer algorithms to improve snowfall prediction.  Tim provides a summary of this effort, including how you can participate, below.

Snowflake ID

A British expression for a phony excuse is “the wrong kind of snow”, a phrase originally coined by British Railways to justify winter train delays. For residents of Utah, such dry humor might be lost — snowflake type affects our enjoyment of wintertime sports. The key distinction that is usually made is between fluffy “aggregates”, or assemblages of pristine six-sided snow crystals, and denser “graupel”, small hail-like pellets that grow when a single snowflake collides with millions of tiny cloud droplets as it falls, and these freeze on its surface. Studies have shown that determining which type of snow forms in clouds is crucial for accurate weather and climate prediction. Because graupel tends to fall faster than aggregates, getting the difference right affects forecasts of where geographically snow will land first as well as the speed of the water cycle.  

To help add insights into this difficult problem, Dr. Tim Garrett and his team at the University of Utah have launched a project that recruits citizen scientists to help build a snowflake classification algorithm.The Multi Angle Snowflake Camera or MASC is a new meteorological instrument that was developed at the University of Utah to automatically photograph snowflakes in freefall from three different angles. 

Examples of snowflake images captured by the Multi-Angle Snowflake Camera (MASC)

Because the MASC has subsequently been sold to research teams around the world, hundreds of millions of snowflake images have been collected in locations as far flung as Greenland, the Antarctic, the Alps, South Korea and right here in Utah at Alta Ski Area. The issue now is one of so many snowflakes to classify, so little time. To help automate the classification process, about 5000 snowflake images have been uploaded to Zooniverse.org, a citizen science web portal owned and operated by the Citizen Science Alliance. The Zooniverse Snowflake ID webpage first educates users in snowflake identification and then allows users to classify as many snowflakes as they feel up to. The classification process is designed so that anyone aged 8 and up can participate, learning more about snowflakes in the process. 

The goal of the project is to “teach” an artificial intelligence computer algorithm to be able to automatically classify any snowflake it is presented. Scientists in the US and internationally can then use this sophisticated tool to accurately classify the millions of snowflakes images that they have been collecting, supporting their studies into the weather conditions that affect snow development. Some day, with refined weather and climate models, it may be possible to better predict “the right kind of snow” 

You can check out the project and learn how to contribute at https://www.zooniverse.org/projects/fitch09/snowflake-id

Friday, August 20, 2021

New Careers in Atmospheric Sciences

It's a little known fact that the U.S. Bureau of Labor Statistics projects an above average job outlook for the atmospheric sciences from 2019-2029.  

The field is small, but growing with broadening career opportunities.  When most people think about meteorologists, they think of television or National Weather Service meteorologists, but the reality is that most of our students work in other areas.  

As examples of emerging opportunities, Amazon currently has 5 weather-related openings to expand their group of weather professionals.  These openings are:

  • Principal HPC Solutions Architect for Weather Modeling, AWS: Craft cloud-based weather and climate modeling solutions for AWS customers.
  • Weather Research Scientist, Modeling and Optimization: Model weather’s impact on various aspects of Amazon's business, supply chain, and transportation network.
  • Software Development Engineer, Modeling and Optimization: Build software systems that can help Amazon predict and manage the impact of weather on its businesses.
  • Software development Engineer, Prime Air (drones):  Development and deploy weather observation and forecasting services for drone delivery, and implementation of weather models into our flight simulator.
  • Senior Applied Scientist, AWS: Build forecasting models to help manage our global renewable energy and storage resources using weather data as input.
These openings illustrate the importance meteorological, forecasting, data science, programming, and instrumentation skills.  Additionally, candidates must have strong verbal and written communication skills and the ability to work with and across a variety of internal and external teams at Amazon.  

I expect more positions like these to be coming down the pike.  Numerical modeling and machine learning are transforming forecast capabilities and services in ways that will greatly benefit private industry.  Over the past several years, we have passed a tipping point where the usefulness and reliability of forecasting systems can make this happen. Of my 5 most recent PhD students, three are working in the private sector.  This is an exciting transformation for students in or interested in the atmospheric sciences. 

Thursday, August 19, 2021

Time to Build an Ark

What a deluge.  Impressive totals around northern Utah and it's still raining hard this morning in some areas, including the University of Utah.

Below are estimated rain totals for the 24-hour period ending at 1200 UTC (0600 MDT) this morning from the National Weather Service.  Nearly all of Utah saw measurable precipitation, with a large coverage of > 0.5 inches.  

Source: NWS

That analysis probably has some uncertainty in it due to spatial resolution and the datasets and algorithms used.  Below are some station reports for the 24-hour period ending around 1500 UTC (0900 MDT).  There are a few sites in the Salt Lake Valley with > 2" and in the Uinta Mountains reaching 2.7".  

Source: MesoWest/Synoptic Data

Some of that precipitation in the Uintas certainly fell as snow, although I suspect accumulations are limited due to the mild air and ground temperatures.  The soil temperature measured by the SNOTEL site at Chepeta (12,120 ft) in the eastern Uintas, for example, is still 45˚F this morning.  

Radar at 1518 UTC (0918 MDT) shows heavy precipitation associated with what meteorologists might call a mesoscale circulation center over the Great Salt Lake and Wasatch Front.  Some strong cells extend along the east bench of the Salt Lake Valley, explaining the downpour at the University of Utah. 

Precipitation to the north of Salt Lake City may continue for much of the day if the HRRR model forecast below (valid 2200 UTC/1600 MDT) verifies.

For the Salt Lake Valley, we're likely to see some showers and thunderstorms, but there will be breaks.  Keep an eye to the sky and move indoors if you hear thunder.  

This weather has destroyed my post-vacation mountain bike reconditioning plans.  I suspect that the trails are going to need a couple of days to recover and are likely to be quite muddy in places today and tomorrow.  Hoping to maybe ride on pavement or the Ensign fire road later today, if there's a break.   

If there isn't, I'm going to start building an Ark.

Wednesday, August 18, 2021

Loving this Weather!

After a summer of heat, enjoy the weather this week.  We are in a magical place meteorologically with a deep midlatitude trough at upper levels and monsoon moisture at low levels.  Overnight (0900 UTC; 3 AM MDT) GFS forecasts show the upper-level trough centered just west of Boise (black contours) with monsoon moisture, indicated by the color precipitable water contours, streaming northward at low levels through Utah.  

This gives us instability, but also wind shear and large-scale forcing to help with precipitation generation and convective storm development.  

Additionally, there's also a surface front somewhere out there, although there's so much convection and precipitation out there, it's pretty chewed up and not easy to precisely locate.  

As I write this, the 1410 UTC (0810 MDT) radar shows a broad area of precipitation over Salt Lake, Summit, and Wasatch Counties, with scattered showers and thunderstorms elsewhere.  

You don't see many soundings around here like the one from the airport this morning.  We see many "inverted V" soundings around here in which cloud bases are elevated and below them the sounding features an inverted V with an increasing difference between the temperature and dewpoint as you go down to the ground.  Today, instead, we have a moist mixed layer at low levels and drier air at mid levels.  This is the type of sounding one sees more commonly in the eastern US as a cold-front approaches.

Due to the threat of heavy rainfall and potential for flash flooding, the National Weather Service has issued a Flash Flood Watch for much of Utah.  They also issued a hazardous weather outlook that emphasizes the potential for heavy rainfall, flash flooding, hail, and gusty winds near storms.  And, just for fun, you might like this:

"Elevations above around 10,000 feet may see a changeover to snow for a time tonight behind a cold front."  

Music to my ears.

Monitor forecasts, warnings, special weather statements and the like at https://www.weather.gov/slc/.  

Sunday, August 15, 2021

Checking In

I've been out of town for the past week and it sounds like it has been an eventful one in Salt Lake City.

Yesterday marked the 21st day with a maximum temperature of 100˚F or higher, tying the all-time record.  There was also that incredible fire in Parley's Canyon, which due to heroics by fire crews and a remarkable aerial assault, may have been tamed.  I hope that is the case.

I've been visiting family and spending some time enjoying the Adirondack Mountains.  It has been a fun return to the homeland, although it has been quite humid, making for some sweaty hikes.  

Any trip to these parts is a walk down memory lane for me.  I last hiked Cascade Mountain, one of the Adirondack "High Peaks" with my father in 1979 in an October snowstorm. 

Forty-two years later, Andrea and I ascended the trail, which other than being snow-free this time, was still rocky and rugged.

IThe weather on top was better this time and we could linger and enjoy the view.  Below is a photo of the high peaks region from the summit, with Mt. Marcy, the highest peak in New York, near the center.   

For the skiers out there, we made a quick stop at Whiteface, which has the most lift-served vertical (nearly 3200 feet) and some of the better fall line skiing in the east.  It is also known as "iceface" due to the cold temperatures and hard snow.  

The fun and games are, however, almost over.  I return to Salt Lake tomorrow to prepare for what looks to be a very challenging fall semester.  

Thursday, August 5, 2021

Help Us Stop the Spread

If you have some anxiety about the start of classes at the University of Utah on August 23rd, you are not alone.  I have been working on campus since sometime in April.  It's been pretty quiet, everyone I interact with is vaccinated, and until a few week ago, case counts were quite low.  In May and even June I wasn't very concerned about requirements imposed on us by the State Legislature to teach 75% in person, not require vaccinations, and not mandate masks.  I was hopeful for a return to something close to normal, if we weren't thrown a curve ball.

However, that curve ball has come in the form of a significant population that has elected not to get vaccinated and the more contagious delta variant.  Earlier this week, Dr. Micheal Good, CEO of University of Utah Health and acting President of the University of Utah, provided the update below, illustrating some of the trends in COVID-19 cases, hospitalizations, and deaths. 

I have been developing some classroom hesitancy as the start of classes approaches.  The classroom I teach in will be fully subscribed with students, who will be sitting elbow to elbow in a poorly ventilated interior room.  

I recognize that my vaccination status greatly reduces the risk of serious illness, but I wonder what might be coming down the pike for future variants and I'm concerned about students in my class who may have a greater health risk than I.  

The reality is that we are all in this together.  As emphasized by University of Utah leadership in their message to campus community a few days ago, we need your help to stop the spread.  

Get a COVID-19 vaccination if you have not already done so.  If you are not vaccinated, get weekly asymptomatic coronavirus tests.  Please follow CDC guidelines regarding face masks, which now call for everyone to wear face masks indoors.  Although I had given up on mask wearing a few weeks ago, I am back in the habit again. 

We have all the tools needed to make this a safe semester.  Let's make it happen!

Wednesday, August 4, 2021

Red Sky at Night Ain't No Delight

Smoke has returned to northern Utah and with it degraded air quality and reddish sunrises and sunsets.  Below is last night's sunset showing a deep orange sun and the reddish hue of the smoke.  

Many people believe that the sun is yellow, but in reality, the sun is white.  It emits all visible wavelengths of light at sufficient intensities that the sun in space appears white.  

NASA photo of the sun and International Space Station in May 2011

So, it is a myth that Superman's powers derive from the yellow sun.  It's a good story, but the sun really isn't yellow.

On the other hand, to those of us on the Earth's surface, it certainly appears yellow or, in some instances, orange or red.  This is because of the selective scattering of light by the Earth's atmosphere and constituents, especially aerosols. 

Molecules in the Earth's atmosphere scatter shorter wavelength light, such as blues and violets, more readily than longer wavelength light like reds, oranges, and yellows.  As a result, as sunlight moves through the atmosphere, it shifts from white to yellow if the skies are relatively clear.  If there are additional particles such as smoke aerosols, the scattering is more intense and the shift stronger, resulting in the sun appearing orange or red.  

This process also is why the sky appears blue.  The blue hue results from the preferential scattering of shorter wavelength light in all directions by the atmosphere.  For more gory details, see this Scientific American article.

Perhaps the best situation for spectacular sunsets are situations in which there are aerosols aloft in the atmosphere, but not near the surface.  In such instances, the sunset is redder, but you can breath clean air.  We are not in such a situation right now.  We have smoke at the surface, and it, some degradation of air quality.  

Thus, red sky at night, ain't no delight and red sky at morning is an air quality warning.

Monday, August 2, 2021

Last Night's Deluge

Thunderstorms with heavy rain, frequent lightning, and nearly continuous thunder move north-northwestward into the Salt Lake Valley from the Wasatch Mountains, resulting in a number of issues related to flash flooding. Portions of the northern Wasatch Front were also affected.  

The system that affected the northeastern Salt Lake Valley, including Mill Creek, Sugarhouse, St. Mary's, the University of Utah, Downtown, and the Avenues began to develope over the Wasatch Mountains just before 0000 UTC (6 PM) yesterday evening.  At 2352 UTC (5:52 PM MDT), the first strong cell appeared over Big Cottonwood Canyon.

This cell exploded in intensity and coverage over the next 20 minutes.  Anyone recreating in Big Cottonwood or Mill Creek Canyon would have been quickly overwhelmed by heavy rainfall, and possibly small hail.  A second cell began to develop at this time on the Alpine Ridge south of Little Cottonwood. 

At this point, all hell began to break loose as more thunderstorms developed along the northern Wasatch Mountains as far north as Francis Peak.  

These heavy storms persisted over the Wasatch for some time as the National Weather Service began to issue severe thunderstorm and flood advisories.  By 0107 UTC (0707 PM MDT), heavy rainfall, lightning and thunder, and probably a few areas of small ail extended from Lone Peak nearly to Francis Peak. 

At 7:14 PM, I took the photo below looking southeastward toward the central Wasatch.  It shows heavy precipitation over Olympic Cove and Mill Creek Canyon.  

After this time, the system began to move and build westward, and by 0152 UTC (0752 MDT), heavy rainfall with pockets of small hail covered much of the Salt Lake Valley east of I-15, with the heaviest precipitation north of I-80.

Radar estimated precipitation for the 3-hour period ending at 0307 UTC (0907 PM MDT) shows the heaviest precipitation int two regions.  The first is in the high terrain between Big Cottonwood and Mill Creek Canyons where radar-estimates reach above 3".  The second is in the mountains east of the University of Utah northeastward into the Session Mountains east of Bountiful. 

Pacificorp has a weather station at 6600 ft along the Big Cottonwood Canyon highway, very close to the radar-estimated precipitation maximum.  As illustrated in the graphic below, it observed over 3" of rain in less than 2 hours and a peak 10-min accumulation of more than 0.7".  

At the University of Utah, almost 1.5" fell, but precipitation rates around 0800 PM MDT were really intense with 1.4 inches falling in less than an hour.  

For the area around Big Cottonwood Canyon, 3" in 2 hours has an average recurrence interval of more than 200 years.  For the University of Utah, 1.4"/hr has an average recurrence interval of 50 years.  There are a number of issues at play with the interpretation of these recurrence intervals, so we should be cautious making statements like this was a one-in-50 year storm.  In particular, such intervals are for specific points, not areas, and the local nature of convective storms means that the average recurrence interval for a storm of such magnitude somewhere in the Salt Lake Valley or somewhere in the Wasatch Mountains is shorter (for some discussion of this and other issues interpreting recurrence intervals, see our previous post Misconceptions of a 200 Year Recurrence Interval).  Nevertheless, this was a pretty good downpour.  

This morning, it's raining again.  I rode my bike into the office this morning like I used to in Seattle in full rain gear.  I found about a foot of standing water on 11th Avenue, which was closed and I was trying to sneak through on my bike.  Now we need it to stop.