Pressure and Altitude

Atmospheric pressure, sometimes referred to as barometric pressure, is a measure the total weight (or mass) of the atmosphere.  It decreases with elevation and varies with time due to the passage of high- and low-pressure systems and other atmospheric phenomenon.

Pressure was once measured using a device known as a Torricellian barometer, which was invented by Evangelista Torricelli in the 1600s.  As illustrated below, a tube with a sealed end was filled with mercury and placed upside down in a bowl filled with mercury.  The pressure of the atmosphere thus affects the mercury in the bowl, but not the tube.  As a result, the mercury in the tube would rise until the weight per unit area of the mercury in the tube equaled the weight per unit area of the atmosphere and mercury out of the tube.

Source: https://www.explainthatstuff.com/barometers.html.

Mercury is of course poisonous, but had the advantage of being very dense.  At sea level, the mercury in a well-constructed Torricellian barometer would rise 760 mm (29.92 inches) above the height of the mercury in the bowl.  This is why pressure is sometimes reported in inches of mercury in the US.

If instead you built a barometer out of water, it would need to be over 30 feet tall.  That's quite impractical.  Imagine your local meteorologist reporting a sea level pressure of 33.9 feet of water.

Pressure Units

The preferred scientific unit of pressure is the pascal, defined as one newton per square meter (the "US" equivalent would be pounds per square inch or PSI).  For atmospheric pressure, hectopascals are typically used with 1 hectopascal equal to 100 pascals.  A hectopascal is also equivalent to a millibar, which is used by many US meteorologists.

In conversation, I prefer millibar (abbreviated mb) because it rolls of the tongue much more easily than hectopascal (abbreviated hPa).  Millibar is also recognized by more Americans.  However, for scientific publications, I use hectopascals, which is the preferred unit.

Pressure and Altitude

Pressure decreases with elevation, so if you were to carefully hike up Little Cottonwood Canyon while carrying a Torricellian barometer, the mercury in the tube would gradually lower.  Conversely, the mercury in the tube would rise as you hike down the canyon.

The figure below is patterned off a a similar figure that was produced by Greg West at the University of British Columbia.  The base and top elevations of five US ski areas are presented, as well as two international ski areas and Mt. St. Elias is Alaska.

This is a double y-axis plot with elevation on the left and pressure on the right.  Pressure is based on what is known as the U.S. Standard Atmosphere, which is a model of how temperature, density, and pressure change with altitude.  Notice that the change of pressure with altitude is not constant, but decreases as you move higher in the atmosphere since the density decreases.  Below 3000 meters, pressure decreases about 100 mb/1000 meters or 100 mb/kilometer which is an easy number to remember.  Higher up, the values are lower.  For convenience, I've done some rounding of the pressure values on the right to numbers that are easier to remember.

Alyeska in Alaska is the lowest major ski resort in the western U.S., with a base elevation of 90 meters and a top lift elevation of 840 meters.  Based on a U.S. standard atmosphere, this equates to pressures of 1004 and 917 mb, respectively.  As you move to higher elevations, the pressures at ski areas like Snoqualmie Pass, Squaw Valley, and Snowbird decreases.  At Snowbird, the base and summit pressures are around 760 and 670 mb, respectively.  Average sea level pressure is 1013.25 mb, so at the top of the tram, the air pressure is about 66% of that at sea level.  

The greatest lift-served vertical in the world is in Chamonix, although my understanding is it requires a guide.  If you ski the full vertical trop at Chamonix, the pressure increases from 629 to 895 mb, or 266 mb.  Relative to the pressure at the top, this is a 42% increase.  

What about the highest ski resort in the world?  Apparently it is Jade Dragon/Snow Mountain in China.  I found a few different reports of the top lift elevation and went with the highest, which is 4700 meters (15,420 feet in US units).  There, you're down to a pressure of 562 mb.  

Finally, there is Mt. St. Elias in Alaska.  Theoretically, you could ski the longest ski descent in the world from its 5,488 meter (18,808) ft summit to sea level.  Based on a U.S. standard atmosphere, the pressure on the summit of Mt. St. Elias is 506 mb, which is almost exactly half of the pressure sea level (1013.25 mb).  Thus, on the summit, half of the mass of the atmosphere is above you and half is below.  If you could ski the full vertical, you would thus descend through half of the mass of the atmosphere.  

I don't think that anyone has skied continuously from summit to sea on Mt. St. Elias.  An Austrian team apparently skied it, but in pieces on two separate expeditions.  Some of the challenges are described in the video below based on an expedition by Mark and Janelle Smiley. 

A Bad Omen for the Future?

A 3 acre wildfire above Farmington. Source: Fox13.

Yesterday I did something extremely unusual for April in Utah.

I ran my sprinklers.

My yard has a south aspect and the grass was already brown and crunchy.  Some of the perennials also looked to be suffering.  

It was only Monday of last week that I mentioned that "normal" spring would continue.  At the time, I commented that the airport had received only 0.26 inches of rain, which was below average, but the month thus far had seen typical temperatures.  I also anticipated we would get some rain that coming Thursday, which turned out to be a bust.  

So now we sit here with only 0.26" in what, for the Salt Lake Valley, is typically one of the wettest months of the year.  Additionally, we will see well-above-average temperatures.  

And if you are wondering, 0.26" would equate to the driest April on record in Salt Lake City.  The current record holder is 0.45" in 1981 and 1934.  

The photo above illustrates a small wildfire that started yesterday afternoon, apparently by a downed power line above Farmington.  

Is it a bad omen for the future?  

Well, I'm not a big fan of ranking or predicting fire seasons.  There's no such thing as a good fire season.  Instead, some fire season are worse than others.  Being prepared for fire simply makes sense in our part of the world, so I look at the fire above not as a bad omen, but as a reminder that if you live the wildland-urban interface, be prepared. 

Responding to threats like wildfire will likely be more challenging this summer than others due to the coronavirus.  Let us hope that Mother Nature has no tricks up her sleeve this fire season.

More Reading Recommendations

Washing, distancing, and masking.  These continue to be our most valuable weapons against COVID-19.  Don't let down your guard as the beast has not been slain.

While distancing, here are a couple more books to read.  First, is Avalanche Busters by Linda Bonar.  

The cover page is a bit ho hum, but I found the book to be a fun read with a lot more in it than memoirs of the Snowbird and Alta Ski Patrols.  There's some history of Little Cottonwood Canyon and Alta Ski Area, an quite a bit on the birth and development of Snowbird.  I really enjoyed the chapter on the December 1973 avalanche cycle and the history of Snowbird was also more compelling that you might expect.  She did a good job of bringing that history back to life.  I was less interested in the Author's autobiographically focused chapters, but those are pretty limited.  If you are wondering, Linda is the sister of Bob Bonar, who served in many capacities at Snowbird from its inception, including President and CEO, but was the first of the two of them to move to Little Cottonwood Canyon.  

The second is The Fifth Risk by Michael Lewis.  

I'm surprised I didn't think of this book when I made book recommendations a couple of weeks ago as I enjoyed it a great deal and it is very relevant for the coronavirus debacle.  Those of you who believe the government should and must play an important role in preparing and navigating major risks will probably like the book.  Others may not, but should read it anyway.  Lewis recently did an interview for Vox based on the book and his perspectives on how the Trump administration is handling the coronavirus response that you might have a look at after completing the book.  

Stay safe and healthy.

Solar Angles, Aspects, and Topographic Shading

Motivated by the previous post, I thought we would dig a bit more deeply into solar angles, terrain aspects, and topographic shading, which are critical for understanding mountain meteorology and microclimates.

Although Fox News might argue differently, the Earth is round (technically it is an oblate spheroid), orbits the sun, and has a axis of rotation that is presently at about a 23.5˚ angle relative to its orbital plane.  Its orbit is not perfectly circular, but is slightly eccentric, so that the distance from the Sun to the Earth varies by about 3% (5 million kilometers) during the year.  All of these affect the path of the sun through sky and/or the amount of solar energy received by the Earth's surface.  Although nearly constant for the recent past or immediate future, slow variations in the orbital characteristics and angle of rotation have caused large variations in the Earth's climate, including cycles from ice age to interglacial periods (see this NASA article).

Because the Earth is nearly round, we use spherical geometry to deal with calculations related to sun angle.  Representing these spherical perspectives in two dimensions is challenging!

First, let's talk about how the sun's angle changes during the day and during the year.  The graphic below was developed for Atlantic City, New Jersey, but works reasonably well for Salt Lake because they are nearly the same latitude (subtract a degree for Salt Lake City - see addendum at end of this post discussing how the solar paths in this image should be parallel).  On January 1st, shortly after the winter solstice, the sun rises just south of east and sets just south of west, reaching a maximum elevation of 28 degrees relative to the horizon at solar noon.  As we move through the first part of the calendar year, sunrise and sunset shift northward and the maximum elevation angle increases.

Source: pressofatlanticcity.com

Ignore the shading in the image above, which is fixed.  In reality, shadows change during the day but also during the year.  At our latitude, your shadow is longer at solar noon in January than in June.

The amount of solar energy received by the Earth's surface depends on the location of the sun in the sky, the aspect of the terrain, the steepness of the terrain, and the surrounding topography.  At our latitude at solar noon on a clear day, a south aspect that is illuminated by the sun receives more solar radiation per unit area than a north aspect that is illuminated by the sun since the sunlight hits the north aspect more obliquely, as illustrated below.

Source: https://www.eoas.ubc.ca/courses/atsc113/snow/met_concepts/07-met_concepts/07h-aspect-effects/

At the extreme, if the sun angle is low or the terrain is steep, the north aspect might not receive any direct sunlight.  Ski High Rustler at Alta on noon on a clear day in late December and you know exactly what I mean.  It's in the shade.  In contrast, in April at noon, High Rustler receives direct sunlight.  At that time, however, the slopes across the canyon that face south receive far more solar energy per unit area than High Rustler.  This is true for most (but not all) of the day, which is the primary reason why south facing slopes at our latitude melt faster than north facing slopes.

Much depends, however, on latitude, time of day, time of year, and slope angle.  In Utah in June, just after sunrise and just before sunset, a north aspect actually receives more radiation per unit area than a south aspect.  There can be a brief period during which High Rustler receives more solar energy per unit area than the slopes on the other side of the canyon.  But integrated throughout the day, it receives less, regardless of time of year.

Elsewhere, your mileage may vary.  If you were on a mountain near the equator, the north slopes receive more energy per unit area than the south slopes in June, but less in December.

Aspect is great, but there is another concern and that is topographic shading.  Topography can cast shadows.  Extreme examples are created by high peaks, such as the triangular shadow cast by K2 pictured below.

Source: https://i.imgur.com/1mAzNUY.jpg?

 If one does not consider this effect, then a solar radiation calculation in the shadowed area would be incorrect.  Both aspect and topographic shading often need to be considered in areas of complex terrain.

With a little playing around, one can examine what sites are exposed to the sun or shadowed at caltopo.com.  Below is an example for upper Lake Blanche Fork in the central Wasatch at 3PM in December.  The drop-down menu at upper-right allows you to specify sun exposure, along with month and time of day.  I'm not sure if we're looking at a first of month or middle of month calculation, but for our purposes, two weeks or so is good enough.  I do think they are considering topographic shading.  For instance, you can see the shadow cast by Sundial Peak extends up the southwest facing aspect on the other side of the canyon to its northeast.

Let's test my comments about High Rustler above.  Top image below is the sun exposure at noon in January and the bottom is noon in April.  Bingo!  In fact, very little at Alta is in the shade at noon in April.

We tend to think about how all of this affects snow, but it also affect soil moisture and vegetation.  At our latitude, south aspects receive a great deal more solar energy than north aspects.  This leads to greater water stress on south aspects than north aspects and resulting contrasts in vegetation.  You'll notice these even when the snow is gone.

Addendum

Professor Phil Dennison of the University of Utah Geography Department pointed out to me that the solar paths in the top figure above for Atlantic City are angled and not parallel.  He provided the schematic below showing the solar paths over Salt Lake City on the solstices and the equinoxes (middle path) to illustrate the correct paths.

Courtesy Dr. Phil Dennison

Bringing Light to the Darkness

In these difficult times, it's important to bring light to the darkness, and Mother Nature is doing that for many parts of the Wasatch Range that are in the shade for much of the winter.

One of the more striking changes that occurs from February through April is how the early morning sun begins to lightup the Coalpit Headwall.  The Coalpit Headwall is a north-northeast facing slope to the north of North Thunder Mountain.  This morning, as shown in the picture below (inside circle), it was illuminated well by the sun.

The sun angle is pretty low early in the morning, so in part this reflects altitude, aspect, and the fact that the sun rises north of west east, which allows it to kiss the north-northeast slope early in the morning.

Below is a comparison of the sun exposure in the Coalpit Headwall area (inside circle) at about noon in January (left) versus 7 AM in April.  In January, the Coalpit Headwall is a shady place (indicated by purple).  Even at noon, it's in the shade and in fact, there is no time of day in January when the Coalpit Headwall is directly illuminated by the sun.  That's great for powder preservation, but also growing facets if the snowpack is thin.

Sun exposed (yellow) and shady (purple) areas based on analysis by caltopo.com

In April, however, the Coalpit Headwall sees the sun.  In fact, it gets the first rays of sun in the morning (right image above) and the sun is high enough in April that it gets sun during the day as well, although shadows begin to creep across its face after mid afternoon, as illustrated by the photo below, which I believe was taken a bit earlier in late March.

These changes in sun exposure are important to recognize if you travel in the backcountry or even ski at a resort. At a resort, however, it's pretty easy to move to a different aspect.  If you are ski touring, however, the timing of sun exposure or shadowing can make or break your adventure depending on the snow (powder or corn) and avalanche conditions.  

"Normal" Spring to Continue

As far as Aprils go, this one hasn't been too exciting or unusual from a weather standpoint.  For the first 19 days of the month, the average temperature was 48.9˚F, which would rate as the 46th warmest or 45th coolest out of 92 years of record keeping at the Salt Lake City International Airport. 

Source: NOAA Regional Climate Centers

In other words, we are right at the median, or the middle of the distribution of past Aprils.  I don't say this much, but that's "normal" or as close to it as you can get. 

If one were to quibble, it might be with regards to precipitation as the Airport has only had 0.26 inches of rain so far, which would be below average.  Still, I would rate this April as fairly typical and not all that unusual. 

The short-range forecast also looks like typical spring.  Highs in the 60s today over northern Utah with some showers and thunderstorms in central and southern Utah.  Tomorrow looks like more of the same, then a dry Wednesday before we have a spring front move in to give us some precipitation Wednesday night and Thursday with valley rain and upper elevation snow.  Below is the GFS forecast valid 1200 UTC (0600 MDT) Thursday showing the system as it moves through northern Utah.  700-mb (crest-level) temperatures are near -2˚C, which means fairly high snow levels with high-density snow at upper elevations. 

We normally look at forecast plumes for Alta-Collins, but we shift today for the gardeners out there and look at rainfall amounts for the Salt Lake City airport.  Our downscaled SREF product generates  from 0.05 to 0.5" of precipitation, with an average of 0.15."

I'm hoping for 0.4".  After a few dry days, a good soak would be nice.  

Lies, Damned Lies, Statistics, and the Importance of Domain Experts

As a teacher, I like pithy quotes.  A short, memorable, and forceful quote can help students avoid pitfalls or take advantage of opportunities throughout their lives and careers.

Mark Twain's quote above is one of my favorites.

Along a similar vein is the book How to Lie with Statistics, which was published in 1954, curiously written by a journalist rather than a statistician, but, despite being dated, provides a number of good cautionary tales about the use and interpretation of statistics.

I share the information above not because I am anti-statistics.  Like all scientists, statistics are integral to the work that my group does and are often critical for improving forecasts.

Instead, I share it because we are seeing a lot of statistics being used in media reports and social media blurbs about COVID-19.  Numbers based on statistical analysis are quite compelling, but it often takes domain experts, people who are authorities in the subject area, to identify underlying issues in sampling or analysis and provide proper context and interpretation.

Additionally, there are people using statistics in nefarious ways to push their agendas and it is very difficult for the lay reader, including trained scientists outside of the subject area, to smell a rat.

I have seen this in the weather and climate business for many years.  Time series of temperature, solar output, CO2, and other variables have been cherry picked and manipulated in all sorts of ways to justify every hypothesis "under the sun" (pun intended).

At this critical juncture it is important that we cautiously examine media and social media reports, move forward with the best-available information from domain experts (not just in health, but other disciplines critical for economic recovery and societal resiliency), and encourage our leaders to do the same.

Higher Ed Under Pressure

The COVID-19 crises poses incredible challenges for higher education and the University of Utah, as discussed in an article in today's New York Times. 

We've never gone through anything like this.  Although budgets were slashed during the great recession, we didn't deal with an instant transition from classroom to on-line instruction, the loss of students from dorms, and the potential for a prolonged period of online instruction that could extend beyond summer.  This has some severe impacts.  Although some teaching activities can be transferred reasonably to online instruction, many can't.  How do you replicate large-group design projects and lab experiments online, or the programing of data loggers and the assembly of environmental observational systems? 

Additionally, campus is essentially closed.  Scientists and graduate students are unable to access their labs and do research.  We are not even allowed at the moment to visit field sites.  Research is happening, but not at the pace it did before.  In addition to slowing graduate student education and the advancement of knowledge, this will have ripple effects on the innovation economy. 

We don't know what state budget cuts the University of Utah is facing, but it is difficult to imagine they will not be extreme, perhaps as big or bigger than those during the Great Recession.  There is also lost revenue from dorm refunds and the specter of lost revenue from endowments and tuition, the latter if enrollment decreases.

University of Utah administration is already preparing for the inevitable and summarizes what departments may do to deal with budget cuts at https://www.hr.utah.edu/coronavirus/.  This includes leave donations, reassignments, early and phased retirements, furloughs, etc.  I suspect all these tools will be used before we're out of this one.

I have no doubt that the COVID-19 crisis will cause more harm than good for higher ed, but let's not "waste a good crisis." That phrase sounds harsh, but we should look for opportunities and strive to transform what we do and invent a new future.  We should plan to come out of this better equipped to educate students and move the world and our local communities forward during the 21st century.

More Cold Air

Afternoon highs on Sunday and Monday were 49˚F and 47˚F respectively, with a stiff breeze blowing.  Under the circumstances, when it would be nice to lie outside in the warm sun to soothe the soul, this is weather fit for neither man nor beast!  If you are wondering, the average high this time of year is about 60˚F, so we are unseasonably cool.

Today we'll make it to perhaps the low 50's before another we begin the transition with the next cold surge tomorrow.  The setup for this cold blast is the high amplitude upper-level pattern over the North Pacific and North America with an upper-level ridge over the Gulf of Alaska and a deep trough over central North America.  A short-wave trough (dashed brown line) that was over the Aleutians at 1200 UTC (0600 MDT) 12 April moved over the ridge and across Alaska on the 14th and will dive southward in the large-scale northerly flow today. 

Preceding this trough will be mountain snow showers and a few valley rain showers on Wednesday, and eventually the cold air Wednesday night.  Below shows the NAM forecast for 2100 UTC (3 PM MDT) Wednesday with mountain snow showers in the westerly crest-level flow and then the colder, post-frontal northwesterly flow at 1200 UTC (6 AM MDT) Thursday. 

This is a relatively dry system, so mountain accumulations will likely be limited.  The downscaled SREF mean for Alta is around 6 inches by Thursday morning (16/12Z in the plume diagram below), but the spread is fairly large with some members producing little and others generating 10 inches or more. 

My view is that this will probably not get to the 10 inch threshold, although there's a low probability that could happen if tomorrow ends up being more productive than advertised.  Personally, given the stay at home orders, I'd prefer it to be about 15 degrees warmer so that it was more enjoyable in the valley.  Let's save the cold air for next season when we can put it to better use.

Anecdotal Evidence and Wishful Thinking

Today's exhibit A in the belief in anecdotal evidence and wishful thinking is a Utah pharmacist who has stockpiled enough ingredients for hydroxychloroquine, the antimalarial drug promoted previously by President Trump (Salt Lake Tribune article here). 

Source: Salt Lake Tribune

Most disturbing in this case is that it appears to have caught the attention of the Utah Health Department and State Senate President Stuart Adams.  This despite the recommendation of the American Medical Association, American Pharmacists Association, and American Society of Health System Pharmacists discouraging hospitals and pharmacies from stockpiling the drugs and stating that there is "no incontrovertible evidence to support off-label use of medications for COVID-19.”  

Further, that recommendation explicitly cautions against the hoarding of such medication. "Stockpiling these medications—or depleting supplies with excessive, anticipatory orders—can have grave consequences for patients with conditions such as lupus or rheumatoid arthritis if the drugs are not available in the community."

I have a cautionary tale for those who wish to push treatments based on anecdotal evidence and wishful thinking.  In March of 1989, two University of Utah scientists, Stanley Pons and Martin Fleischmann, announced that they had produced cold fusion.  This was an exciting finding, one that could revolutionize energy production, but it had not been validated by the scientific process.

This morning I read a few news articles from that period and they are quite illuminating.  New York Times archives include an AP article published on August 8, 1989 entitled Utah Votes $4.5 Million for Cold Fusion Studies.  The vote was cast by the Fusion-Energy Advisory Council, which controlled $5 million appropriated by the State Legislature in April for fusion research.  With $500,000 released for patent lawyers' fees, in August 1989, the council voted to release $4.5 million for research on cold fusion at the University of Utah.  The vote was 7 to 1, with one abstention and one vote opposed, which was cast by Karen Morse, the Provost at Utah state who said "We can only have verification when a full understanding of the science is in."  

At the time, the cold fusion finding was already being questioned by scientists, although it should be noted that there were some scientists at the University of Utah and elsewhere who were promoters.  Ultimately, the cold-fusion debacle was a stain for the University of Utah and contributed to the retirement of University of Utah president Chase Peterson.  

Cold fusion provides an example of the dangers of circumventing the scientific process and rushing to support findings that have not been carefully vetted.  Perhaps we will learn that hydroxychloroquine and related drugs have some positive benefits for treatment, and I hope that's the case, but the cautious approach being expressed by the medical and pharmacy communities should be heeded until more evidence is in. 

Blocking Pattern Will Bring a Chill to Northern Utah

I confess that given the stay at home order, my desire for warm weather is unusually high.  In addition, my preference is to have ridging over Utah in April and May, which means comfortable weather, than June, July, and August, which means uncomfortable weather. 

Mother Nature will not be cooperating, however, over the next few days.

Instead, she is producing a highly amplified pattern at jet-stream level, which means persistent upper-level flow originating from the high latitudes.  Below is the 500-mb geopotential height forecast valid 0000 UTC 13 April (6 PM Sunday MDT) showing a high-amplitude ridge upstream of the Pacific coast of North America and a deep trough over central North America.

The transition to this pattern begins in earnest tomorrow (Saturday), with cooler air and showers moving in during the afternoon.  Colder air continues to move in Saturday night.  Sunday will likely feature high temperatures in the high 40s, with a slow recovering during the "work week" (whatever that means these days).  Below is the National Weather Service Forecast for downtown Salt Lake to illustrate the change.

Source: NWS

If you are planning a walk, hike, bike, or ski Saturday, I get a weather forecast update from the National Weather Service tonight and tomorrow morning as how early showers (and upper-elevation snow) develop tomorrow afternoon is still a bit uncertain.  Meteorologists are not supposed to "wishcast," but I'm hoping it will be as late in the day as possible.

Despite the cold air, right now this doesn't look like a big snow producer for the mountains.  Below is the SREF plume for Alta-Collins, with the snowiest member generating just under six inches.  Some members produce under an inch.  Think dust on crust. 

The Dangers of Shortcutting the Scientific Process

The spread of coronavirus through our society has greatly increased pressure to find treatments, a cure, and a vaccine quickly.  There is a great desire to understand who is at risk and who isn't.  However, we need to be very cautious as a public about interpreting results from scientific studies that are very recent and haven't been vetted by peer review or further scientific analysis.

Yesterday, a breaking story came out reporting that new research linked air pollution to higher coronavirus death rates.  Here's an example of the story from the New York Times.

They even go so far to claim under the top photo that Atlanta is likely to suffer more deaths than the adjacent Douglas County due to this effect. 

I have not had time to read and digest the study.  It could be a good one.  It might be important.  However, when I went to the web site for the paper, I noted that there is a disclaimer immediately under the title that says "This article is a preprint and has not been certified by peer review.  It reports new medical research that has yet to be evaluated and so should not be used to guide clinical practice" [my italics].

https://www.medrxiv.org/content/10.1101/2020.04.05.20054502v1

Peer review is a process whereby fellow scientists evaluate the professional work of others in their field.  Typically 2 to 3 reviewers are selected by a journal editor and those reviewers evaluate papers like the one above.  They can make any number of recommendations.  The paper could be rejected if deemed of low quality or poorly written.  Low quality could mean the scientific advances are minimal, or there are critical errors in the data and methods or interpretation.  More commonly revisions are recommended to clarify certain points, require additional work to support key findings, or improve interpretation.  Peer review is not perfect.  Sometimes papers get published that have errors and sometimes high-quality papers are rejected, but it is an initial check to help ensure the quality and importance of scientific research.

Peer review has been criticized for many reasons, most commonly is the slowness of the process.  This is particularly problematic during crises like the coronavirus pandemic, when we want to accelerate the race to understanding and solutions.  

It is probably essential that scientists share pre-peer-reviewed results in a transparent way at this time.  In fact, this is not entirely unusual.  Trained scientists have the capacity to evaluate papers and determine their strengths, weaknesses, and utility.  No paper is perfect, so the reality is that we are constantly doing this as part of our research efforts.  

What is concerning currently, however, is the sharing of pre-peer-reviewed results and other observations publicly.  This has the potential to do serious harm as people look for treatments based on anecdotal findings or understanding based on papers that may contain flaws or misinterpretations.  

There was a time when I was taught that one should not publicize results prior to peer review.  If you read science articles regularly, you will often see statements like, "in a paper published today in Science", which at least tells you that the paper has been through some level of peer review.  It may not have been scrutinized by the broader scientific community, but it has had an initial check.

The paper above might be very good and important.  It might be good, but need some changes in interpretation.  Perhaps it will be rejected.  I don't know.  I have some capacity to evaluate portions of the paper, but I don't work with the sorts of datasets that are used for this type of research, so that's an area where I'm blind.  I consider my expertise to be specialized and limited when I examine results in other fields.  

As we move forward through this crisis, I encourage you to consider the status and significance of stories about scientific findings very carefully.  Treat those based on anecdotal evidence with extreme caution and those based on pre-peer-reviewed results with at least some additional checking.  For published results, consider that the nuances are often not reported.   Look to experts who have sifted through the full spectrum of scientific results and have domain knowledge for information.  The scientific process isn't perfect, but this helps you separate the wheat from the chaff and enables you to move forward with the best available information.  

Projections vs. Forecasts

Source: https://www.lacan.upc.edu/admoreWeb/2018/05/all-models-are-wrong-but-some-are-useful-george-e-p-box/

Buried somewhat in today's Salt Lake Tribune is a great interview by Robert Gehrke with University of Utah Professor Lindsay Keegan, an epidemiologist in the Department for Internal Medicine.  Dr. Keegan makes a number of important points, including one that I could relate to as a meteorologist.  She immediately stated that what she is doing in collaboration with others is creating scenario-based projections.  I put that in italics because there is a difference between a projection and a forecast and that distinction is important, not well recognized, and important for how we interpret model results.

Projections vs. Forecasts

Although they are sometimes used interchangeably, there is a difference between a forecast and a projection.  As noted by MacCracken (2001), a projection is a statement of what will happen in the future if certain conditions develop.  In the study of climate, projections are used extensively.  We use models to produce estimates of future climate under selected emissions pathways.  For example, the graph below illustrates multi-model average changes in global mean surface temperature under four future greenhouse-gas emissions scenarios, including "low" (blue) and "high" (red) scenarios.  These are projections rather than forecasts because each assumes a future pathway for key forcing agents.

Source: http://www.ipcc.ch/report/ar5/wg1/

In contrast, a forecast is a prediction of what will happen in the future based on what is known today.  MacCracken (2001) actually distinguishes between a prediction and a forecast, but we won't get into those semantics here.  In a forecast, one does a best estimate of present conditions (and possibly future conditions) and then forecasts what will happen in the future.  This what is done every day in the weather forecasting business, including by our forecast models.

In her interview, Dr. Keegan correctly emphasizes that they are doing projections because they are making assumptions about what interventions or choices we might take to address the virus.  This is often swept under the rug in news articles which simply state that "the model from <insert credible group here> shows this."

My mom lives in Florida and when there is a hurricane forecast to affect the region I tell her repeatedly to monitor official forecasts and heed the recommendations of local emergency management officials.  I tell her to ignore the tweet that says model X says you will fine or another that says model Y says you will be wiped out.  Your best course of action is to listen to people who can bring their expertise to bear on the problem and do so in a collaborative fashion after examining all of the evidence and models.

Similarly, it's probably best if we non-experts don't read too much into the results of what Dr. Keegan describes as "public facing models."  Let's focus on what those in the know tell us to do.

The Power of Data Assimilation

Data assimilation is the process of determining the best initial estimate of the state of the atmosphere, ocean, and land using prior forecasts and observations.  It is an absolutely essential first step in numerical weather prediction since weather forecasting is what scientists would call an initial value problem.

The best data assimilation system in the world is the European Center for Medium Range Weather Forecasting (ECMWF) 4DVAR system.  4DVAR stands for four-dimensional variational assimilation.

4DVAR at ECMWF is an incredible marvel.  According to their web site, ECMWF processes and uses 40 million weather observations daily, most from satellites.  Incredibly, they have a web site where you can actually see the observations going into each forecast cycle.  The slides below summarize everything that went into the 0600 UTC 3 April initialized ECMWF forecast cycle.  You can click to enlarge, although for the purposes of this discussion, the details aren't important.  The slides are mainly to provide a glimpse at the incredible collection and processing of data that occurs 24/7 to produce a global weather forecast.

The video below provides a glimpse at the past, present, and future of the ECMWF 4DVAR system.

An interesting thing about data assimilation is that all observations are not created equal.  Some have a bigger impact than others and in some cases, bringing together multiple observation types gives more bang for the buck than if you added up the impact of each observing type independently. 

We are currently running an inadvertent experiment on the value of aircraft observations, which have declined significantly in the past month due to COVID-19 travel restrictions and reductions.  Below is the trendline for Europe through 24 March.    

Source: https://www.ecmwf.int/en/about/media-centre/news/2020/drop-aircraft-observations-could-have-impact-weather-forecasts

As of 23 March, the ECMWF reported a 65% reduction in European aircraft weather observations and a 42$ global reduction.  

Based on early studies, the ECMWF suggests that removing all aircraft observations from their data assimilation system results in a degradation of short-range temperature and wind forecasts at jet-stream level of 15% and surface pressure forecasts of 3%.  The former illustrates why it is advantageous for aviation companies to provide such observations for weather prediction, since the improvement in forecast skill reduces fuel consumption through better route planning and may also improve passenger comfort through better turbulence forecasts.  

Modern data assimilation truly is an incredible scientific marvel.  Without it, numerical weather prediction would not be possible and any great global forecast system has a great data assimilation system. 

The Seeder-Feeder Effect

There was a great visual example of the seeder-feeder effect this morning over the central Wasatch.  The seeder-feeder effect involves the fallout of precipitation from seeder cloud aloft into a lower-level cloud generated by flow over a mountain barrier.  This can result in the growth of ice crystals that originated in the seeder cloud as they fall through the feeder cloud, leading to precipitation enhancement over the mountains, as illustrated schematically below.

Source: Secrets of the Greatest Snow on Earth

Below is a photo I took about 7:10 AM MDT this morning.  Thin, mid level "seeder" clouds were producing falling ice crystals aloft.  These crystals then fell into a feeder cloud associated with orographic lift over the central Wasatch. 

At this time, precipitation rates were very like and I suspect if you were on, for example, Lone Peak you probably would have noticed just a few flakes.  Nevertheless, this is a nice illustration of what happens during seeder-feeder, which during precipitation events often can't be "seen" without the use of a radar.

Buds are Breaking

We are at the start of a dramatic transformation of the Salt Lake Valley as the "urban forest" that covers much of the Salt Lake Valley undergoes leaf out.

The urban forest is especially dense over the older neighborhoods of the northeast Salt Lake Valley, including the Avenues, Sugarhouse, Mill Creek, and environs.  This morning, that forest still looks brown as most trees are just beginning to bud. 

The view will, however, change dramatically in the next two weeks as buds break and the trees sprout leaves.  Signs of spring are definitely evident.  One example is that my apricot tree is beginning to bloom.

Take a few moments to enjoy the clear skies, gaze at an early season bloom, inhale the clean air, and ponder the words of Alexander Pope:

“Hope springs eternal in the human breast;

Man never Is, but always To be blest.

The soul, uneasy, and confin'd from home,

Rests and expatiates in a life to come.”