Friday, July 31, 2020

July Enters Cold, Leaves Hot

On July 1st, the low and high temperatures at the Salt Lake City International Airport were 53˚F and 88˚F, quite comfortable by northern Utah standards.

In contrast, overnight minimum on this last day of July was only 73-75˚F (the official minimum won't be reported until noon) and the forecast high for this afternoon is 100˚F.  


I've mentioned in several previous posts that this July hasn't seemed too bad (i.e., hot) compared to recent standards, but that it has been hot by 20th century standards, and that appears where it will end up at the close of business today.

With one day left in the month, the average temperature has been 80.8˚F, which ranks as the 16th warmest all time. 

Source: NOAA Regional Climate Centers

There are only three July's ahead of it that occurred during the 20th century, 1988 (80.9˚F), 1989 (81.1˚F), and 1960 (81.2˚F).  There's a chance we'll move up ahead of 1988 today.  I'm not sure we can catch 1989 or 1960.  In any event, this July would have ranked at least in the top 4 during the 20th century.

However, many of the 21st century July's were hotter including (in order of increasing average temperature): 2014, 2008, 2002, 2019, 2012, 2006, 2016, 2018, 2003, 2007, 2013, and 2017. 

So basically, the "baseline" for July in Salt Lake City has shifted.  This July didn't seem too bad by 21st century standards, but it was quite hot by 20th century standards.

Scientists sometimes refer to this as climate nonstationarity.  This is a phrase you will hear more of in the coming years as past climate normals become irrelevant for future climate normals.

The National Weather Service uses 30-year averages for climate normals.  These are used, for example, for the "normal" high and low temperatures reported on the news.  They are updated every 10 years, so right now, the climate normals reported on the news are based on the 1981-2010 average, but as can be seen in the chart above, that was a period of increasing temperatures during July with the decade of that period relatively cold and the last decade relatively hot.  

Those averages are no longer relevant normals for July in 2020.  Year to year variations are not bouncing around that average, but a higher one.  

The National Weather Service will issue new climate normals after 2020, based on the 1991-2020 averages.  These will also become obsolete, probably even quicker than the 1981-2010 normals.  


Keep cool and carry on.  

Wednesday, July 22, 2020


It was great to go for a hike early this morning and see some showers in the area.

I even got sprinkled on, which was greatly appreciated.

If you are keeping score at home, we have had no measurable precipitation at the Salt Lake City airport so far in July.  Our last measurable precipitation was on June 30, so we've now gone 21 days without rain.  That's not unusual or exceptional (Salt Lake has gone 50 or more consecutive days without rain 11 times), but still I miss it.

Showers and thunderstorms will be possible today across much of Utah and are also possible through and the first part of the overnight hours in northern Utah.  The HRRR forecast valid at 3 PM MDT is below.  Don't take it literally for location and intensity as convection is too chaotic for a single model run to predict precisely, but hopefully we will see some action, although I can't guarantee it at your residence. 

Late tonight and tomorrow, the Salt Lake Valley may, unfortunately, be "dry slotted."  The dry slot is an area of dry air that sometimes wraps around an upper-level trough.  You can see it in the lower left NAM forecast panel below (valid at 6 PM MDT tomorrow) as an area of orange-yellow shading indicative of low relative humidity in the lower and middle atmosphere. 

Thus, the forecast for tomorrow is for isolated thunderstorms in our area. 

Bottom line: Safely enjoy anything we get today. 

Monday, July 20, 2020

Some Thunderstorms This Week

Slow and subtle changes in the large-scale circulation will cause some changes in the weather of northern Utah early this week.  The situation at 1800 MDT yesterday (0000 UTC 20 July) showed some scattered convection across Arizona, Utah, and Nevada with relatively weak radar echoes.  Precipitation was limited and the main influence of the convection was to produce some gusty winds. 

One measure of the amount of water vapor in the atmosphere is precipitable water, which is the depth of water you would have if you condensed all of the water vapor out of the atmosphere.  Yesterday, values across much of Nevada and Utah were less than 15 mm and in some cases less than 10 mm (see color contours in image above).  For the Great Basin in July, this isn't much to play with unless you have a deep trough over the area, which we don't.

Over the next few days, however, precipitable water values will be slowly increasing as a weak trough (emphasis on weak) approaches from the west.  The NAM forecast for 1800 MDT Tuesday (0000 UTC 22 July) shows values across most of Nevada and Utah > 15 mm and in some areas > 20 mm. 

By 1800 MDT Wednesday (0000 UTC 23 July), values near 25 mm are moving through northern Utah, with drier air that has wrapped around the weak trough moving into central Nevada. 

That's enough to increase the thunderstorm threat, but this is not a strong monsoon surge. Thunderstorms in northern Utah will probably be isolated tomorrow and scattered Wednesday, but if you happen to be near one, there will be a threat of lightning, gusty winds, and precipitation.  It will be worth keeping an eye to the sky.  When thunder roars, head indoors. 

Friday, July 17, 2020

Evidence of Snow in July

Astute observers can find evidence of falling snow in July over northern Utah, even in this heat, but you need to know where to look. 

I took the photo below on Monday morning when altocumulus clouds were rolling across northern Utah.  In the center is one of these altocumulus clouds, which features a ragged cloud base with streaks extending diagonally toward the Earths' surface.  The poorly defined cloud base and streaks are produced by falling snow crystals (or snow flakes) that have grown in the cloud.  Due to the dry airmass at low levels, these snowflakes do not reach the Earth's surface, but instead sublimate or melt and evaporate before reaching the ground. 

Below is another photo I took of this process that morning.  In the upper right-hand corner there's what we refer to as a mixed-phase cloud, which means the cloud consists of both liquid water and ice particles.  The liquid water particles are supercooled, meaning that they are colder than 0˚C, but still remain in a liquid state. 

In such a cloud, the ice particles grow faster than the water droplets, and they ultimately become large enough to fall out as snow crystals or snow flakes.  One can see these snow crystals trailing below and behind the cloud in the photo above.  This trailing tail of snow crystals is sometimes called a Mare's Tail. 

If there were no flow or no change in wind speed or direction with height, the snow crystals would just fall straight to the Earth's surface and you would not see a curving Mare's Tail.  The shape of the Mare's Tail depends on the wind shear (changes in wind speed or direction with height), the fall speed of the snow crystals, and the perspective of the observer.

Take some solace in the fact that it was indeed snowing this week aloft, even if it wasn't reaching the ground.  This is particularly important today (Friday) when the forecast high at the Salt Lake City airport is 100˚F. 

Blogging Update

It's been a challenging time for blogging as my workload this summer has been unusually high and my mind has been occupied by many things besides the atmosphere.  This has curtailed my time and creativity, which has reduced post frequency.  It's likely that I will continue to limp along, with potentially some longer breaks.  Apologies, but you do get what you pay for with this blog :-).

Thursday, July 9, 2020

Brief Flirtation with Nuclear Summer

The first 8 days of July are in the record books and as anticipated, they were hot by 20th century standards, but not too bad by early 21st century standards.

The average temperature for those 8 days was 78.1˚F, which is a bit higher than the average July temperature in the 20th century (77˚F), but quite a bit lower than the average July from 2010–2018 (81.6˚F).  That period also clocks in as the 3rd coolest since 2010, behind 2010 and 2019.  

Source: NOAA Regional Climate Centers
So, hot for for your grandparents, but cool for your kids. 

It looks, however, like we will see a trend toward misery through Saturday, although the worst of the heat may be short lived. 

This morning, the GFS shows us in fairly weak west-southwesterly large-scale flow with three major large-scale flow features at 500-mb.  The first is a trough over the Gulf of Alaska.  The second is a weaker trough just off the Pacific northwest coast.  And the third is a weak ridge over Texas.

Through Saturday, the trough just off the Pacific Northwest coast progresses downstream across the northwest US, while the Gulf of Alaska trough amplifies.  Meanwhile, over the southwest US, the ridge that was previously over Texas migrates westward and amplifies.  By Saturday morning, if is centered over New Mexico. 

During this period, all of Utah will see increasing temperatures.  NWS forecast highs for the Salt Lake City International Airport today, Friday, and Saturday are 93, 96, and 98 respectively. 

That flirtation with what I like to call "nuclear summer", the hottest and most miserable part of the year for heat and sun intolerant snow lovers like me, looks like it will moderate in northern Utah, however, as the Gulf of Alaska trough progresses downstream into the Pacific Northwest and the ridge weakens through Monday. 

Thus, highs relax to 97 and 93 on Sunday and Monday, respectively.  Additionally, the forecast highs for Tuesday and Wednesday in the wake of the trough are 90 and 88.  A quick look at the ECMWF shows similar trends. 

Thus Saturday looks to be the warmest of the next five.  There is some risk we will make a run toward 100.  I dread thinking about it, but take some solace that we should cool off a bit early next week.

Tuesday, July 7, 2020

The Economic Benefits of Foreign Students

Yesterday, US Immigration and Customs Enforcement, more commonly known as ICE, announced changes to the temporary exemptions being provided for nonimmigrant students taking online courses due to the pandemic during Fall Semester 2020.  As described at, M-1 and F-1 visas will not be issued for students to enter the United States if they are enrolled at a school or program that is fully online.  Students currently in the United States on F-1 and M-1 visa who are enrolled in such a school or program must leave the country or transfer to a school with in-person instruction. 

This is a cruel and xenophobic policy that also makes very little sense economically.  The United States benefits greatly from attracting the world's greatest minds, but also, these students pay tuition and spend money in the United States.  Detailed information about the economic benefits of foreign students is avialable from NAFSA: Associations of International Educators (see  In Utah, for example, there are almost 8,000 foreign students, providing cumulative economic benefits of over $200 million by paying tuition, renting apartments, dining out, making retail purchases, etc. 

Source: NAFSA

Monday, July 6, 2020

I See Your Fireworks

It was an unusual Fourth of July holiday this year due to COVID-19 restrictions.  Public fireworks displays were limited, with none in Salt Lake County, but a few displays in Tooele and Utah Counties (see 

However, individual displays were plentiful, and one can "see" these fireworks in PM2.5 measurements collected by the Utah Division of Air Quality.  PM2.5 spikes were occurred on either the night of the 3rd or 4th or both, indicating degraded air quality. 

Cache County gets the reliable patriotism award for producing spikes on both the night of July 3rd (times below local) and July 4. 
Cache County PM2.5 concentrations.  Source: Utah Division of Air Quality.
Utah County gets the extreme patriotism award for producing the highest PM2.5 concentrations measured by one of the DAQ's real-time sensors, with values reaching over 160 ug/m3 on the night of the 4th.  Technically, they could have pipped Cache County for the persistent patriotism award too since they also produced a spike on the night of the 3rd, but in this contest, everyone gets only one award. 
Utah County PM2.5 concentrations.  Source: Utah Division of Air Quality.
Davis County gets the extreme patriotism honorable mention award for also pushing PM2.5 to relatively high levels (> 100 ug/m3), but falling shy of Utah County's effort.  Nice try.  Maybe next year. 
Utah County PM2.5 concentrations.  Source: Utah Division of Air Quality.
Finally, Salt Lake County gets the participation award.  Nothing on the night of the 3rd with a pulse on the 4th that barely gets to 40 ug/m3.  On a population-adjusted basis, that's pretty pathetic, although many of us were happy to breath easy. 
Salt Lake County PM2.5 concentrations.  Source: Utah Division of Air Quality.
These are single point measurements though and there was probably a great deal of spatial variability that one might explore using the PurpleAir network, although I have work to do to get my classes ready for fall....

Saturday, July 4, 2020

July Enters "Like a Lamb"

July is climatologically the hottest month of the year in Salt Lake City, but so far, the first three days of July have been relatively pleasant.  One might even say that July has entered like a lamb.

It's worth a look at July from a historical perspective.  July is not only the hottest month in Salt Lake, but it also features relatively little variability from year to year.  The range in average temperature from July to July is around 5˚F, with a few exceptions (e.g, 1993). 

Source: NOAA Regional Climate Centers
One can also clearly see that recent July's have been quite warm.  During the 20th century (1901-200), the average July temperature in Salt Lake City was 77˚F.  We have not had a July below that average since 1997 (75˚F) and since 2010 the average temperature in July has been a miserable 81.6˚F, more than 4˚F above the 20th century average.  Further, since 2010, even the coolest July, 2015 (77.4˚F) was warmer than the 20th century average.  

So, on this 4th of July, we should thank our lucky stars that the first three days of July were relatively pleasant.  On the 1st, the minimum and maximum temperatures were 53˚F and 88˚F, both below average (average here based on 1981-2010).  On the second, they were 59˚F and 90˚F, below and at average, respectively.  And then on the 3rd, we reached 68˚F and 95˚F, which are above average, but I've learned not to complain about 95 in July.

By and large, the forecast for 4th of July weekend looks great, with the only blemish being a possible isolated shower or thunderstorm, mainly in the mountains of central and eastern Utah, as noted by the National Weather Service graphic below.

Additionally, the extended forecast ain't awful, with highs in the low-to-mid 90s through next Friday.  

Based on those forecast temperatures, the average temperature for the week would be 78.5˚F.  Hot and higher than the 20th century average temperature, but a bit lower than the average for Julys since 2010. 

Thus, I'll take it and will hope that we will continue to keep it at or below 95.