Wasatch Weather Weenies

It sure can get exciting around here when monsoon (and tropical storm remnants) can interact with a mid-latitude trough.  This morning in the Salt Lake Valley has been incredible with round after round of heavy rain and thunder.  These are not those high-based "virga storms" that we sometimes get around here, but the real deal with pretty good downpours and loud, crashing thunder.  Love it. We discussed the ingredients for today's rain in the post from a couple of days ago entitled An Unusual Moisture Pathway .  Those ingredients included the remnants of tropical storm Iselle and a front that was expected to develop over central Nevada.  Indeed these ingredients came together ahead of a deepening trough along the Pacific Northwest coast.  The front is especially apparent at 700 mb (lower left panel below) where there is temperature contrast and wind shift between southern Utah and northern Nevada and Utah.  The large-scale wind pattern is one that mete...

I'll just put these here for some high stoke, low probability snow possibilities.  There are some ensemble members producing snow in northern Utah late next week and weekend.     OK, truth be told it's three ensemble members out of 82.   I told you it was a low probability possibility.

The remnants of Tropical Storm Iselle are taking an unusual pathway into the western US interior and will be visiting northern Utah this weekend.   Yesterday morning (1200 UTC 26 August), Iselle's remnants were to the west of the Baja Peninsula.  The color contours below are precipitable water in millimeters with warmer colors indicating higher values.  Precipitable water is a measure of the total water vapor in the atmosphere expressed as the depth of water if all of that water vapor were to condense and fall out.  Iselle's remnants were associated with a maximum in precipitable water above 65 mm.   Iselle's remnants moved northwestward yesterday and last night.  As this happened, they began to interact with the southwest flow ahead of an upper-level trough off the Pacific Coast, resulting in a plume of high precipitable water movign northeastward toward California.  That plume spreads eastward and ultimately serves as the locus for precipit...

The last few days have brought regular afternoon and evening thunderstorms to the Salt Lake Valley.  It's worth taking a closer look at the drivers for the storms and who has gotten the rain.   On average, the 500-mb heights in August are characterized by  a ridge that is centered roughly over west Texas and a trough over or just to the west of the Pacific coast.  This pattern yields mean easterly flow at 500-mb over central Mexico which turns clockwise (cyclonically in meteorology speak) near Baja California before moving into Utah.   Source: climatereanalyzer.org The pattern above is characteristic of the so-called North American Monsoon.  This monsoonal pattern has been amplified the past several days.  As an example, below are the 500-mb height anomalies (departures from average) for today.  Positive height anomalies over the western US and Mexico are strongest over west Texas and the Mexican border area to the west, right where the ...

Forecasts from the ECMWF Artificial Intelligence/Integrated Forecast System (AIFS) are now available on weather.utah.edu.  Look for ECMWF AIFS in the left-hand nav bar.  An example forecast is below.  Based on the data available, most of our favored four-panel variables are available, but due to limitations in the data provided, there is no forecast of outgoing longwave radiation (used for a forecast infrared satellite image) in the upper-right panel and the precipitation is six hourly, which is a longer accumulation period than many of our products.   As illustrated in the link at the top of this post, AIFS forecast skill at 500 mb is roughly the equivalent of the ECMWF IFS (called HRES on weather.utah.edu) through about day four. At longer lead times, it exhibits somewhat better skill.  The AIFS forecasts after 9 days are about as good as the IFS at 8.5 days, so they are basically giving you an extra half day of skill at longer lead times.  That's ...

Classes start at the University of Utah this coming Monday, August 24.  Campus is getting busier and energy levels are rising.  The start of a new school year is coming! I was on sabbatical last academic year and although I did teach for a full semester at the University of Innsbruck, it feels like higher ed has changed dramatically since the last time I taught at the U in spring 2025.  One reason for this is the rapid advancement of AI, including weather forecasting models and generative AI assistants like ChatGPT. My approach to teaching has been one that has brought new tech into the classroom.  The weather analysis and forecasting classes I teach today use tools and techniques that did not exist when I started as a professor and in some cases even a couple of years ago.   As we go into the new semester, I've been thinking a lot about how to utilize AI in the classroom but also how to ensure that students are using AI tools responsibly.  The lowest-...

Following up on the post from August 8th ( The Death of Summer Skiing ), as reported over the weekend by weathertoski , the last operating ski area in the Alps, Passo Stelvio in Italy, closed on Saturday, August 15th.  There are no summer skiing options left in the Alps.   They suggest this may be the first time there's no (lift served) summer skiing operations in the Alps.  It's likely that applies to the Northern Hemisphere.  Mt. Gassan (Japan) appears to have closed in early July.  Timberline on Mt. Hood appears to have closed on July 19.   I believe late operating resorts in Norway are also closed.   2026.  The year that summer skiing died. 

Monsoon thunderstorms developed over the Salt Lake Valley this afternoon and brought heavy rainfall to the northeast corner of the Salt Lake Valley, especially the University of Utah.  The event started with the development of a cell over or just downstream of the Salt Lake International Airport.  This one moved off over North Salt Lake.  Shortly therafter, two cells formed just to the south of the track of the first cell and pounded the Avenues and Avenues Foothills.   Then things got interesting as a cell exploded west of Murray and moved northeastward to the University of Utah.  This was the beginning of a series of training storms that pounded the area around the U before things settled down.  The full sequence is below.  I'm hoping the video will upload properly as I'm working with some limitations currently.   Storm total Radar precipitation estimates through 2200 UTC (1600 MDT), which does not quite capture the entire storm period...

The National Weather Service Climate Prediction Center (CPC) issued their monthly El Niño/Southern Oscillation (ENSO) Diagnostic Discussion today and El Niño is looking like a lock for this winter.  They give a 90% chance of a very strong El Nino during Northern Hemisphere fall and winter.   By most definitions, a strong El Niño is already in place over the Tropical Pacific Ocean.  Sea surface temperatures more than 1°C above average already extend westward along the equator to nearly 180° with areas more than 3°C above average near the coast of South America.  Anomalously warm sea surface temperatures also extend poleward to the west of North and South America.   ENSO strength probabilities from CPC are near or above 90% for September-November through November to January.   The odds of a strong event decline later in the winter, although the odds of El Niño conditions persisting remain high.   El Niño is a tropical climate phenomen...

August is off to a blistering start.  Seven out of ten days to start the month with high temperatures above 100. Six days with low temperatures 70 or above including an 81 on August 9.  The average temperature for the first 10 days of August at the Salt Lake City International Airport was 85.2°F, the second highest on record behind only 2024 (86.3°F). Relief is coming, however, due to a subtle change in the large-scale pattern.  The upper-level ridge that has been over us the past few days is weakening and sliding eastward slowly while troughing is developing along the Pacific Coast.  The GFS forecast for 0000 UTC 14 August (1800 MDT Thursday) shows the trough along the Pacific Coast (red dashed line) with a plume of elevated integrated vapor transport streaming up the lower Colorado River Valley and into Utah (red arrow).  A weak trough is also evident at 700 mb over central Nevada and far northwest Utah.   The net impact of these changes will be a de...

Summer skiing used to be a thing in the climate system of the 20th century.  In North America, there used to be skiing on the Palmer Snowfield of Mt. Hood deep into summer.  When I lived in Seattle, we skied there on Labor Day weekend in early September calling it the "Opening Day of Ski Season" since the next winter was coming.  There also used to be skiing deep into July on the Horstman Glacier at Blackcomb in Whistler.   In the Alps, summer skiing became a thing in the 1970s and by 1985 there were 32 operating glacier skiing resorts.  These didn't necessarily operate all summer, but they did offer warm-season skiing.  As recently as a few years ago there were resorts that operated year round or very late in the summer [Hintertux (Austria), Zermatt (Switzerland), Saas Fee (Switzerland), Passo Stelvio (Italy)] or into portions of July and/or August [Kitzsteinhorn (Austria), Mölltal (Austria), Les 2 Alpes (France), Tignes (France), Val d'Isere (France)...

An article published yesterday in the Salt Lake Tribune discusses eight ways proposed by professors at Utah State to improve wintertime pollution for the 2034 Olympic Winter Games.  Fraser Bullock who is leading the Utah 2034 effort is quoted as saying a few years ago that:  " Air scared the heck out of me. It scares the heck out of me because we got so lucky last time because we had an inversion the day before [the 2002 Olympic Winter Games].  And the morning of Opening Ceremonies, in comes a storm, blows it all up [and] we had really great weather. " I was involved in weather support for the 2002 Olympic Winter Games and remember the pre-Olympic inversion well.  Prior to the Olympics, there are a lot of press from all over the world looking for stories to write.  I remember participating in a press conference in which speakers would get up, discuss something about the Olympics, and then answer press questions.  I had discuss Olympic Weather and somehow g...

During winter, the Salt Lake Valley often sees pollution episodes with elevated particulate matter due to the presence of low-elevation cold pools that persist due to the limited solar heating.  This enables particulate matter that forms from the emissions from automobiles, industry, home heating, and other sources build up within the cold pools, resulting in poor air quality.  This poor air quality is reflected in elevated levels of particulate matter with a diameter of 2.5 micrometers or less, or PM2.5.  Such events are known colloquially as inversions. Because the PM2.5 is typically trapped in the cold pool, one can usually find clean air by moving to higher elevations.  The depth of the pollution varies from event to event and sometimes from hour to hour as the cold pool sloshes around in the valley.  At times, the benches may be in the clear air.  At other times, elevated PM2.5 can extend higher.   An example, from December 15, 2025, is shown...

It felt almost pleasant this morning as the the low temperature was 70 or possibly 69 at the Salt Lake City Airport.  70 is actually the average low at the airport, which just goes to show how insane summer has become around here that it feels cool and refreshing when we finally have an average low.  Average in this case is based on 1991-2020, so if we went back further, we're probably still running above the 20th century average.   Countering the coolness was the smoke, which thickened overnight.  PM2.5 concentrations at Hawthorne Elementary climbed substantially after midnight and are now above 40 ug/m3, in the unhealthy for sensitive groups category.   Source: MesoWest Yesterday's MODIS imagery shows several major sources of smoke in the Great Basin and Pacific Northwest including fires on the eastern slopes of the Cascades and in northeast Washington that exploded over the weekend, sadly causing serious losses of homes and structures in Spokane....

Fire is on the minds of many of us who live in Utah and the western United States.  Conditions favorable for explosive wildfire spread are increasing in severity and frequency.   More and more I realize that my "instincts" about wildfire risk in my region, neighborhood, and home probably do not match reality.  I encourage everyone to take a look at an article written by Tom Cova, a Professor in the University of Utah's School of Environment, Society, and Sustainability, that was published in today's Salt Lake Tribune .    The article emphasizes the importance of being ready to evacuate given the fact that "fast-moving fires compress every step of an evacuation."  As Eisenhower said, "Plans are nothing, planning is everything."  This is especially true during extreme wildfire spread.