Wasatch Weather Weenies

The numbers yesterday from the Salt Lake City airport were absolutely astounding.  With a maximum temperature of 98˚F and minimum of 76˚F, the average temperature was 87˚F, the highest ever observed in May at the airport.  The graph below shows the highest daily average temperature observed each May in Salt Lake City based on downtown-area observations prior to 1928 and airport observations thereafter.  There are two clear outliers in this record, 2003 and 2020.  They are only Mays in the instrumented record with at least one day with an average temperature above even 80˚F.  Source: NOAA Regional Climate Centers Late May of 2003 was blisteringly hot on the 28th, 29th, and 30th with maximum temperatures of 99˚F, 99˚F, and 97˚F, respectively.  Minimums were 62˚F, 71˚F, and 73˚F, respectively, yielding averages of 80.5˚F, 85˚F, and 85˚F, respectively. Late May of 2020 was blisteringly hot on the 29th and 30th with highs of 96˚F and 98˚F, but minima ...

As an atmospheric scientist with some background in aerosols and cloud microphysics, I've found discussions of the transmission of SARS-CoV-2 in the media to be lacking.  I've had a lot of questions about how the 6-foot rule for distancing came about and what it was based on, how such a general guideline should be adapted to differing environmental circumstances, how indoor and outdoor transmission potential differ, how masks work, etc.  A perspective article in Science Magazine this week goes into these issues in depth.  The lead author is Kim Prather, an Atmospheric Chemist who holds multiple appointments in Atmospheric Chemistry, Chemistry, and Biochemistry at the Scripps Institution of Oceanography and UC San Diego with Coauthors from institutions in Taiwan, China, and UC San Diego. The article is entitled Reducing Transmission of SARS-CoV-2 and can be freely accessed .  The article reviews the transmission of respiratory diseases in general and COVID-19 in p...

This morning's sunrise I woke up this morning, saw a red sky, and felt the warm breeze.  My first thought was that the remnants of our snowpack are doomed. Most Wasatch and western Uinta Snotels are now below 30% of median snow water equivalent for the date and crashing toward zero.  An exception is Snowbird, which sits at 42%, a number that is still not great.   If only we could bend the coronavirus curve like Mother Nature is bending the snow water equivalent curve.  The crash of the spring snowpack this year has been quite remarkable and persistent since late April, with just a brief and temporary slowing last weekend and earlier this week due to a trough passage. Over the past two days, the Snowbird SNOTEL has lost 3.5 inches of water.  With 13.3 inches remaining, the snow will be gone in four days at that rate.  That will be about 2 weeks ahead of median.  Such a shame. 

Ah, the good old days.  Source:  https://www.gsecclesfoundation.org/ The Salt Lake Tribune recently reported that there will be students on Utah System of Higher Education campuses this fall, including the University of Utah.  This has been discussed in numerous faculty meetings I've attended via zoom in recent weeks, so it is no surprise.  The devil is in the details, however, and those details remain murky as I've yet to see a detailed announcement from the University of Utah administration.  In an article in today's Salt Lake Tribune , they reported that: Each school should prepare to monitor outbreaks, be able to contain them, and have a shutdown plan There won't be large auditorium classes Class sizes will be kept small Some classes will remain online for those at higher risk of infection, including both students and professors A few classes will be hybrid where half a class may meet in the room and half may join via video conference or half of...

USS Muskeget (formerly USS YAG-9) On September 9, 1942, the US Coastguard Cutter Muskeget was torpedoed by a German U-boat killing all on board.  At the time, the Muskeget was collecting weather observations in the North Atlantic.  Included in the crew were four civilian National Weather Service Meteorologists: Lester S. Fordor of Cleveland, Ohio; George F. Kubach of Sandusky, Ohio; Edward Weber of New York, New York, and Luther H. Brady of Atlanta, Georgia.  In 2015, 70 years after the end of World War II, these four meteorologists were awarded the Purple Heart .  It was the first time that National Weather Service personnel were awarded this award.  Today we remember these four meteorologists and all who died while serving the United States, including more than 400,000 members of the Greatest Generation who made the ultimate sacrifice during World War II.

Pileus is a latin word for a felt cap.  In modern English, it refers to the cap of a mushroom.  In meteorology, it refers to a cap or lenticular cloud that forms on top of a cumulus or cumulonimbus cloud.  There were a plethora of them forming over the cumulus clouds above the Wasatch Range this morning.  Below is an example. The basic formation mechanism involves the pushing up of air aloft as air within the cumulus cloud ascends.  If the air is close to saturation, this leads to the formation of a layered cloud that resembles the cap or lenticular clouds that are generated by mountain waves as the air that flows through the ascending layer aloft follows a path similar to that generated by topography.  I have tried to illustrate this below, although the perspective was such that I've probably oversimplified things. There are some good examples in the time lapse below.   The cumulus cloud can punch through the pileus layer if it has enou...

At around 1700-1800 MDT yesterday afternoon, a brief but violent dust storm or haboob swept through the Salt Lake Valley, degrading air quality and uprooting trees. As described in the Glossary of Meteorology , the term haboob was first used to describe sand and dust storms in Sudan.  It is now commonly used to describe such storms in arid and semiarid regions around the world.  It is often used for dust storms in the American southwest, especially Arizona.  Below is an example from storm chaser Reed Timmer. While there are many types of dust storms, haboob is typically applied to those with sharp leading edges caused by a density current or front.  It is often clear ahead of the density current, with opaque dust loading behind it.   I first noticed yesterday's haboob at about 1730 MDT when it had spread into the northwest Salt Lake Valley.  Looking toward the southwest at that time, a shallow layer of dust was evident at low levels and c...

Forecasts are looking good for a few tenths of an inch of soaking rain tonight. The latest 12Z NAM forecast valid 6 PM MDT (0000 UTC) this afternoon shows the surface cold front pushing into the Salt Lake Valley.  If this forecast holds, the surface front, marked by the abrupt wind shift in the image below, will precede the precipitation band, so the frontal passage will be dry. However, the lagging frontal precipitation band slides in over the next few hours.  The period from 2100-0000 MDT (0300-0600 UTC) looks to feature a good soaking rain, with the NAM producing more than 0.25 inches at the airport for the three hour period.  Gardens rejoice! Rain will then taper off to showers by morning.  In total, the 12Z NAM pumps out 0.69 inches of precipitation for the airport, and what a godsend that would be for our crusty soils.  The 6Z GFS (the 12Z isn't in yet) is a bit less bullish on precipitatoin, but still produces 0.42".  A look at the SREF s...

After 33 consecutive days without measurable precipitation, the Salt Lake City International Airport recorded 0.05" of rainfall yesterday. Hooray! "Yesterday", however, is defined as the standard-time calendar day.  The reality is that the airport received no measurable precipitation during the day yesterday and the .05" actually fell at just before midnight last night standard time. It appears another .02" fell after midnight and will count toward the total for May 21. Two days in a row of measurable rain.  Will miracles never cease? Some preliminary precipitation reports through yesterday evening are below and show up to 0.19" in the Salt Lake Valley through 7 PM.  That observation was from our mountain meteorology lab facility at the mouth of Red Butte Canyon on the University of Utah campus. Source: NWS Overnight rain brought the total at that site to 0.25".  I wish it was more, but that's better than nothing. For the Salt La...

Yesterday's southerly winds wreaked havoc in the West Desert with peak winds along I-80 topping 70 mph.  The public intormation statement below from the National Weather Service shows numerous stations with peak wind gusts above 50 mph in the Great Salt Lake Desert and Mountains, including 78 mph at I-80 milepost 29 and 73 mph at another I-80 site. Source: NWS A look at the meteograms for I-80 milepost 29 shows that yesterday morning at 0800 MDT the flow was north-northwesterly.  This is consistent with the passage of the weak front discussed in yesterday's post.  The flow then veered (turned clockwise) over the next four hours, becoming persistently southerly and sustained between 25 and 40 mph from 1400–1900 MDT when the winds began to veer to southwesterly in advance of the front, which passed at just after 2000 MDT and was marked by an abrupt drop in temperature and dewpoint. Source: MesoWest The time of peak gust was 1710 MDT.  A look at the sustaine...

The meteograms below from the University of Utah shows the persistent, gusty, southerly flow that has dominated the weather around Salt Lake City since about noon on Sunday.  However, two things happened overnight.  First, winds died down in the evening, enabling overnight temperatures to drop to lower levels than Sunday night.  Second, a weak front pushed into the northern Salt Lake Valley, resulting in a further decrease in wind speed and a shift in the wind.  Observations from across northern Utah show northerly flow penetrating southward across the west desert and northern Great Salt Lake.  Winds over the southern Great Salt Lake are more variable in wind direction, but northwesterly flow near and north of the Salt Lake City International Airport suggests that the weak front has made it into the northern Salt Lake Valley.  Is it here to stay?  Probably not.  The models emphatically show a return of southerly flow today.  An exam...

Former KSL meteorologist Mark Eubank used to call it the HATU wind (Utah spelled backwards).  I lean toward the Great Basin Sirocco, a nod to the hot and sometimes dusty wind that blows to southern Europe from north Africa.  In any event, it's been a hot, dry, and sometimes dusty 24 hours, with strong flow expected to continue today and possibly extend into Tuesday.  The setup for this is a slow moving and digging upper-level trough off the Pacific coast.  In the southwesterly flow ahead of that  upper-level trough, a southwest to northeast oriented surface trough has developed downstream of the Sierra, resulting in strong southerly flow across much of western and northern Utah, as illustrated at 1800 MDT yesterday afternoon (0000 UTC 18 May) below.  The pattern is quite typical for springtime when southwesterly flow interacts with the Sierra Nevada.  There is typically flow splitting around the high Sierra, confluent flow downstream of the high...

On average, April and May are the wettest month's of the year in Salt Lake City, averaging 2.02 and 2.09 inches of precipitation, respectively. So, the period from mid April to mid May is the heart of our "wet season," yet we have gone nearly a month now without measurable rain at the airport.  The last measurable rain we received was 0.17 inches on April 16. Anecdotally, the foothills seem like they never got as green as usual this year and the grass growth seems stunted on south aspects.  I haven't been able to find a web site with a good comparison of fuel moisture this year compared to previous, but the National Weather Service tweeted this morning that fine and medium size fuels are near record low dryness for this time of year. Very warm temps, low RH, and strong winds will combine Sunday and Monday elevating fire wx danger The strong south winds will peak in most areas Monday. Due to recent absence of rain, fine and medium size fuels are nearing record ...

In 1989 when I started graduate school, the importance of public communication was far from my mind.  As a young scientist, I, like many others, was overwhelmed simply trying to acquire knowledge in my field, learn how to create knowledge as a researcher, and communicate it to my peers.   In 1989 also received my first e-mail account.  "Cloud computing" involved logging into a Cray Y-MP at the National Center for Atmospheric Research, a "supercomputer" that at the time was lightning fast, but provided about as many computations per second as today's smart phones.  There was no Facebook, Twitter, or Instagram.  The newspaper was still a thing.  There was no Fox News.  That bears repeating.  There was no Fox News .  The Immigration Act of 1990, which resulted in more immigrants being admitted to the U.S. in the 1990s than any single prior decade, passed with bipartisan support in the Senate 89-9 and in the house 264-118.  ...

Flash flooding in Little Wildhorse Canyon sadly took the lives of two young girls on Monday.  The situation was one that is common on the Colorado Plateau with precipitation from an afternoon thunderstorm funneled into a narrow slot canyon.  The tweet thread below from University of Utah graduate student Tom Gowan, who was in the area, describe the situation. I was up Little Wild Horse Canyon (where this occurred) with @tayloragowan and a friend during this freak incident. We knew the chance of heavy rain producing thunderstorms was low, but when we heard thunder, we turned around and got out of the slots. (thread) https://t.co/tkKjsHyhAv — Tom Gowan (@tommgowan) May 12, 2020 After we found a high, sheltered spot, all hell broke lose. Heavy rain turned into the heaviest nickel-sized hail I've ever seen. After several minutes, we noticed a debris flow coming down Bell's Canyon. Video (warning: language): pic.twitter.com/o4hH4DQnjQ — Tom Gowan (@tommgowan) May 12, 2...

Yesterday, hazardous convective storms affected locations in Utah, resulting in at least one fatality. Northern Utah In northern Utah, convective storms produced strong microburst winds in several areas, resulting in a few downed tree branches and a lot of blowing dust and pollen.  The tweet below includes a video showing dust and probably pollen kicked up by microburst winds moving through downtown Salt Lake City. Updated loop of afternoon microburst in Salt Lake City. Watch how dust/pollen/or whatever cloud moves through downtown. Initiated early in loop by virga near Oquirrh Mts. Possible reinforcement west of downtown. #utwx pic.twitter.com/d6GTQAJU7p — Jim Steenburgh (@ProfessorPowder) May 12, 2020 There were some downed tree branches reported near Liberty Park according to NWS reports. Microbursts are produced by strong downdrafts that fan out when they contact the ground, as depicted below. Source: Fujita (1981) Yesterday's was a traveling microburst simi...