Wasatch Weather Weenies

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 ...

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" i...

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 fr...

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...

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 no...

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 ...

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 identi...

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...

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 r...

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 t he 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 grav...

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...

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 i...

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 conditi...

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 detail...

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 ha...

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.”