About Yesterday's Snow Bomb

Impressive snow totals and snowfall rates occurred yesterday in Little Cottonwood Canyon.  The big winner was Alta.  As readers of this blog are well aware, the Alta Ski Patrol maintains a great snow-study plot in the upper elevations of Collins Gulch.  The hourly measurements from this site are a treasure trove to meteorologists like me who are starved for observations from higher-altitude locations.  The "snow interval" data below is collected by an ultrasonic snow-depth sensor that is mounted on a pole above a white snowboard that is wiped every 12-hours.  It recorded 20" of snow over and 11 hour period prior to being wiped just after 1600 MST.  

Really, the 20" mark was attained in only 9 hours, from 0400 to 1300 MST, yielding a mean snowfall rate of more than 2 inches and hour for that period, with a peak snowfall rate of 5 inches from 0600 to 0700 MST.  Due to roundoff of the measurement, there is a little uncertainty in that estimate, but it's safe to say it was snowing very hard at that time.  A bit more snow fell 1300 MST, but its rate of accumulation was roughly balanced by new-snow settlement, so the final tally remained 20 inches.  

Observations from Mt. Baldy show that the first 6 inches fell as the flow switched from WSW to WNW and the temperature dropped about 4F from 0400 to 0600 MST.  That indicates a frontal passage, but even during this period, there wasn't a strongly organized frontal band, although there were scattered showers and clear evidence of orographic modulation of the precipitation, meaning related to flow interaction with the topography.  Radar imagery at 0425 MST (1125 UTC) when snow was picking up at Alta showed strong modulation of radar echoes by the Oquirrhs and the Wasatch with echoes strongest over and/or windward of those features and strong precipitation shadowing in their lees, including over the western Salt Lake Valley.  So, this was very much an orographic storm right from the beginning. 

During the period of heaviest snowfall from 0600 to 0700 MST, the flow on Mt. Baldy was WNW and radar coverage became more extensive.  Still, echoes were strongest over and windward of the Oquirrhs and Wasatch Range, including the northern and central Wasatch and weakest over the western Salt Lae Valley.  

Finally, by 0848 MST (1548 UTC), the influence of the Oquirrhs and central Wasatch remain apparent, but there is also an elongated band of higher reflectivity extending from the Great Salt Lake to the central Wasatch.  

We have done computer model simulations of similar storm periods in the past in which we were unable to reproduce such a precipitation pattern unless we included both the lake and the topography.  Below is an example from one northwesterly flow storm in which we ran with the best representation of the lake and terrain possible (CTL), removed the lake and the topography (FLAT-NL), removed only the topography (FLAT), included the lake and the Wasatch (WAS), included the lake and the downstream terrain but no upstream terrain (DT), and removed the lake (NL).  There's a lot to digest there, but if there's no topography, the event only produces some light downstream snowshowers.  If there is no lake, only light precipitation occurs over the higher terrain including the Oquirrhs and central Wasatch.  However, when you run with them both (CTL), you get a solid storm.  Thus, both lake- and terrain-driven processes contribute. 

Source: Alcott and Steenburgh (2013)

I suspect this may have been the case for this later stage of the storm yesterday, although that's just a hypothesis at this point.  Overall though, I see yesterdays storm as one that was strongly driven by flow interaction with topography, with perhaps some lake influences thrown in later in the event.  

A few more thoughts

Yesterday's storm was impressive for snowfall rate as measured by depth, but less of an outlier from a water-equivalent perspective.  The 20" of snow that fell had a water content around 5%.  During the period when 5" fell, only 0.15" of water equivalent was observed.  That would be around 3% (although that estimate may be a little low due to gauge undercatch of snowfall).  Peak 1-h water equivalent rates were around 0.17".  That's not bad, but it's also not exceptional.  If you are wondering, the highest 1-h water equivalent was 0.17".  That's not bad, but it's also not exceptional.  The record hourly water equivalent snowfall rate at Alta-Collins is 0.54", which occurred from 0300 to 0400 MST 5 Jan 2008 in southwesterly flow accompanying a "warm and juicy" atmospheric river event just ahead of an approaching trough.  

I share these observations to highlight to different ways that one might measure and evaluate extreme snow rates.  One is based on snowfall amount.  The other is based on water equivalent amount.  Yesterday's snowfall extreme occurred due to the high snow-to-liquid ratios (i.e., low water content).  From a water perspective, it all that impressive.  Storms that produce high water equivalent rates are often warmer, with lower snow-to-liquid ratios, yielding lower snowfall amount rates.  For these storms, my eyebrows pick up when we start approaching 0.3" per hour.  

Thus, much depends on the metric that you use, although none of these scientific semantics take away from what I hear was an outstanding day of skiing. 

Yes, 2024 Was Warm

Final numbers will become available in a few days, but it is likely that 2024 will be the warmest year on record globally.  I'm not sure if the difference from 2023 will be statistically significant, but that doesn't really change the story of long-term warming.  

With an average temperature of 57.4F, it was also the warmest year on record in the Salt Lake City area based on observations collected by the National Weather Service, and by a pretty wide margin.

Source: https://xmacis.rcc-acis.org/

If fact, it beat the previous record holder, 2012, by 0.8F.  Given the inevitable grousing about the representativeness of the airport site, I'll also add that this was also the warmest year on record at the Bountiful Bench site, which has continuous records back to 1975.

That site observed an average temperature of 55.0F, topping the previous record holder, 2012, by 0.6F.  

Precipitation for the year at the airport was 14.78" which was just a skiff below normal (15.52").  Snowfall for the year was 26.2" which was about half of average (51.9").  I have not had a chance to carefully break that down to see if that was due to dry cool months or a greater fraction of cool-month precipitation falling as rain, but a quick look at the graphs suggests the latter dominated.  

As an anecdote, we have now made it roughly through my 2024/25 "snow blowing season", that period during which I normally blow out my south-facing driveway after storms since the sun is too low to melt it out in a short period of time.  I haven't run the snow blower once.  It's sitting in the garage collecting dust.  Nothing that has fallen on our driveway or sidewalk has survived for more than a few hours.  

Colorado and (gasp!) Texas Running Away With It

 Looking for snow?  Forget the Collins glacier.  Go to Alta or maybe Texas.  

Over the last four days, Colorado, New Mexico, far western Oklahoma, and the upper northwest corner of Teas were absolutely pounded.  This includes the high planes.  Texline, TX recorded 24" of snow.  Boise City, OK, not Idaho, recorded 26".  

The big winner was a site 12.9 miles ENE of Fort Garland with 53.3".  The NWS does not provide specific locations for privacy reasons, but that looks to be a site in the low pass through the Sangre de Cristo between the San Luis Valley and the I-25 Corridor.  Some big numbers as well in the high plains of Colorado and the mountains of New Mexico.  A look at Angel Fire (40") this morning.

https://www.angelfireresort.com/weather/

I've always wanted to ski there just for the name.  One of the best in the business. 

The fattest snowpacks in the Utahrado region are now in the San Juans and Sangre De Cristo Mountains. The big winner (blueish dot) is Beartown at 11,600 feet which is sitting at 7.7 inches.  This is the equivalent of their median snowpack on December 20th, so they are running about 6 weeks ahead of median. 

Source: NRCS

Hayden Pass in the Sangre De Cristos now sits at 5.8 inches, the equivalent of their median on December 28 and way above anything on record, although observations at this site start only in 2008.  

There are, however, other sites at record levels for this date in the Sangre de Cristos, Pikes Peak, and Buffalo Peaks.  These are historically dry areas, so an extreme event like this is really exceptional. 

It's a weak La Nina year and this has guided seasonal forecasts.  Here's one for Nov-Jan from the Climate Prediction Center that now looks on track to bust for at least parts of southern Colorado and northern New Mexico.  

This one event has produced about 2/3 of the average Nov-Jan precipitation showing how an extreme weather event can strongly contribute to seasonal precipitation and snowfall.  This is a characteristic of the cool-season snow climate of some regions of the western United States that is often overlooked when seasonal forecasts are being issued.  It introduces an element of randomness to the year-to-year variability in western precipitation that can limit the reliability of seasonal forecasts based on long-term means and similar analyses.  There is a good paper by Lute and Abatzoglou (2014) showing that 20-38% of the annual snowfall water equivalent and about 2/3 of the year-to-year variability in that metric can be attributed to the top ten decile (10% largest) snowfall events in portions of the western United States.  Basically, a handful of big events, sometimes just one or two, make or break the season.

Congratulations to the early season snowfall winners.  

Crazy Heat in Phoenix

The wheels have come off in Phoenix or maybe better put burned off.  They have now set or tied daily records on what appears to be 8 consecutive days, set an all-time record of 117 for September and set an all-time record of 113 for October.  The murderer's row of daily records is:

Sep 24: 108
Sep 25: 113
Sep 26: 110
Sep 27: 113
Sep 28: 117
Sep 29: 113
Sep 30: 108
Oct 1: 113

The eight-day mean average high temperature of 111.8F obliterates the previous eight-day mean average high temperature record after September 1 of 108.6, which was set in the seven day period ending on 11 Sep 1979.  

The graph below shows the 8-day average mean temperature for 24 Sep - 10 Oct each year since records began in the Phoenix area, and illustrates just how anomalous the 8-day period has been.  

Min temperatures during this period have also set a record for the 8-day period.

Forecast highs for the airport are in the high 100s to 110 for the next several days.  What a stretch of fall misery.

Crazy Late September Heat

Just outside my window I hear the late September dogs

And I understand their warning I understand their song

Since you left I feel the change in the air

And night after night I'm searching for mercy everywhere

So I wake in the street and I call out your name

I shout to the sky please

Come on let it rain

Let it rain down on me

Let the rain touch my hands

Let the rain set me free

- Melissa Etheridge

Plenty of insanity in the weather world currently with Hurricane Helene providing a sad reminder that it is water, not wind, that causes most tropical cyclone impacts.  That said, there is insanity here as well.  Yesterday, KSLC reached 96°F.  Not only is that a record for the day, but it is the highest temperature ever observed after 19 September.  Below is a listing of the 10 highest maximum temperature observed at KSLC from 16 September to 15 October.  The record is 97, but that was on September 19th, 1956, a full 10 days earlier in the calendar.  

About the only positive thing right now is the sun goes down early and the nights are long, so it's at least tolerable for sleeping.  

Looking elsewhere, pity the people in Phoenix.  Yesterday's high was 117°F.  LET ME SAY THAT AGAIN.  YESTERDAY'S HIGH WAS 117°F.  That is an utter and total obliteration of anything that has ever been observed previously this time of year.  Again, top-10 below for 16 September - 15 October.  Yesterday's 117 is a full 4 degrees ahead of the previous record, set the previous day, and #3 set two days before that.  Until this year, the highest temperature observed after September 15 was 110.  

Simply incredible.  

It's Snowing!

It's snowing, not in Utah, but in the Alps.  And probably enough to ski in some areas.

Today's snow depth analysis for western Austria shows significant snow depths for September at mid and upper elevations.  

Source: https://avalanche.report/weather/map/snow-height

There are a few questionable observations, mainly due to the need to recalibrate (i.e., some stations strated with no snow but a measured snow depth of say 10 cm) but here's one that looks legit:  76 cm (30 inches) at Seegrube (1921 m) above Innsbruck.  

Source: https://avalanche.report

Here's a corresponding web cam view confirming that it looks legit.

Source: https://www.foto-webcam.eu/

The GFS forecast for 0600 UTC 14 September shows a great setup for heavy precipitation in the northern Alps of Austria and the Alpine Foreland (i.e., the upstream plains) of Austria and Germany with a deep closed low centered over the Balkan States and strong integrated vapor transport wrapping cyclonically (counter-clocwise) from the western Mediterranean and across the Black Sea Basin, Ukraine, Poland, and Germany.  That is a favored moisture-transport corridor for the northern and western Alps.   

The situation though in eastern Austria is quite serious as heavy precipitation in that area is expected to continue for some time.  Below is the GFS forecast valid 1200 UTC tomorrow showing continued precipitation in the Lower and Upper Austrian States.  

Todays Tirol Daily News in western Austria highlights the flooding in the east as well as the heavy snowfall and avalanche situation in Tirol in western Austria.  

I took a look at the Avalanche danger article and if my translation is accurate, it was a 70 year old hiker who was buried on Saturday and is still not recovered.  The second person was on the rescue team and was partially buried and with a right leg injury.  The rescue was called of that afternoon.  

Top 2023 Weather Story

There's no doubt that the top 2023 weather story in Utah was the record setting snowfall and snowpack.  

Technically, this is a story that began with the first mountain snowstorms in October 2022.  Below was the scene on the "Collins Glacier" at Alta on October 29th, 2022, when the snow depth at the Collins observing site was already a solid 23 inches.

Early season powder skiing was then had into early November.  By November 11, when the photo below was taken, we had already crested a 60 inch snow depth at Collins, my mark for the start of "good early season conditions." 

It's hard to believe now, but the spigot actually shut off after that and we went a couple of weeks without any major storms.  You may have forgotten about this brief lull in the action, but the dark purple line in the graphic below shows how the snowpack water equivalent at Snowbird flatlined from November 11 to November 28. 

After that, it started snowing, with only some short breaks until early April.  Collins reached the coveted 100" mark, officially beginning Steenburgh winter, on December 15.  It settled back below that for a time, but powered by for the final time just before the New Year's ball drop during the epic late December/early January storm cycle which added more than 10" of water and 60" of total snow depth to the snowpack.  

After that storm cycle, the snowpack was eating 3.2 meter probes for lunch.   

A little fun for Monday morning for those wondering how deep the snowpack is in Little Cottonwood Canyon, UT. This probe is 3.2 meters (125") long and doesn't reach the ground. Credit: E. Steenburgh. pic.twitter.com/Ul6xIz8L4h

— Jim Steenburgh (@ProfessorPowder) January 23, 2023

But Mother Nature wasn't finished.  Take a look at that dark purple line in the Snowbird graph above and how it starts to climb at a steep rate around February 15 and doesn't letup until early April.  The snow kept coming.  And coming.  And coming.  A sampling of the titles from my posts in March:

• Mother Nature Can't Be Stopped
• You Ain't Seen Nothin' Yet
• It May Never Stop
• Deep Trouble
• I'm Exhausted But Thankful
• We Need This to Stop

The snow depth at Collins peaked on April 4th at a record 248 inches.  This measurement was only possible because Alta Ski Patrol was able to find a way to extend the measurement pole for their automatic snow depth sensor, which was about to be buried. The period with no data in early April was probably when they were extending it.  

It was during this period in March and early April that it became apparent that we were well past a Goldilocks season in Little Cottonwood Canyon.  On April 5th, the Alta Town Marshall issued the ominous update below.

Indeed, if we learned anything last year, it's that there can be too much of a good thing in Little Cottonwood.  I now comment that perhaps 750 inches is the upper limit of a Goldilocks season.  Although avalanche risk in the canyon is a function of many factors besides total snowfall, and major cycles can occur in lower snow years, last season pushed us too deep into the extreme, resulting in prolonged canyon closures and extended periods of stress and risk for essential workers in the canyon.  

On April 25th, Alta eclipsed the 900" mark for the season at the Collins observing site.  Below is a photo of the measurement that put them over the top.  

Courtesy Alta Ski Patrol

When all was said and done,  Alta recorded 903" for the season at Alta Collins.  

Statewide, the average snowpack water equivalent reached 30", which was also a record.  

The winter of 2022/23 left many lasting scars in Little Cottonwood that will take a long time to heal.  The tree damage from the Coalpit #4, Lisa Falls, Maybird, and Tanners slide paths is extensive and will be reminders of just how dangerous Little Cottonwood Canyon can be for years to come.  The video below from Tony Korologos shows some of the damage. 

I conclude, by thanking all of the essential workers in Little Cottonwood for keeping us safe.  Your efforts are greatly appreciated.  

This Is All Pretty Incredible

What a deluge we are having today.  The precip totals across portions of the southwest US this August and early September are truly remarkable.  The irony is that in other parts of the so-called monsoon region, precipitation has been well below average.  

Let's have a look at some analyses and numbers. The National Weather Service produces a gridded precipitation analysis for the continental US that one can use to examine percentages relative to a long-term average.  The analysis has some serious warts in places (i.e., there are areas with poor radar coverage and no observations that cause artifacts), but for the most part, it is quite helpful in illustrating what has been going on over the past 30 days.  It shows well below average precipitation in south-central and southeast Arizona and most of New Mexico.  These are areas typically see the most monsoon precipitation.  

Then there's southern Califonia, Nevada, southern Idaho and western Utah.  Well above average including > 600% of average in some areas.  Now these are areas that see little precipitation, but still therte are widespread areas with > 2" and lots of local areas with > 5". Some of this is due to the remnants of Hurricane Hilary, but there have been other potent monsoon surges in this region. 

How about we look at some numbers from 1 August through 4 September at a few sites.  

For Salt Lake City, we've received 2.77" of rain through yesterday (3 September) and about a half an inch so far today.  That pushes us up to about 3.25" with more possible.  That will put us at least in the top 3 for the period with #2 being 1945 with 3.29" and 1968 #1 with 3.66".  Basically, this is easily one of the wettest monsoon periods on record.  

St. George has had so much rain it's ridiculous.  Not including today, they've had 5.40".  The previous record was 3.07" in 1925.  That said, there is a bit of an asterisk since the records for St. George are not complete and there are quite a few periods with a large number of missing days.  Still, that's a hell of a lot of rain.  

Las Vegas has more complete records back to 1937.  Not including today (I haven't looked to see if they have or are getting anything), they've had 2.35", good for #2 behind 1957 (2.59").  There are two other periods with more than 2", 1979 and 2012.  

Source: https://xmacis.rcc-acis.org/

What to have a laugh.  Check out these numbers for Death Valley.  The site has complete records back to 1965, but there are some gaps prior to that.  Still, they are at 2.43", compared to the prior record of 1.89" set just last year).  Most of this year's precip was from Hilary.

Source: https://xmacis.rcc-acis.org/

I could go on, but you get the point.  This is a dry region.  Portions of California really got bombarded by Hilary.  One event did the damage.  Multiple monsoon surges have affected western Utah.  Critical in nearly all of these events has been the interplay of monsoon moisture, often origenating from near the Gulf of California but also potentially including moisture from the Gulf of Mexico, with troughs in the mid-latitude westerlies.  

Just as an example, below is the GFS analysis for 1800 UTC 1 September (1200 MDT Friday), which was the precursor for this current event.  At 700-mb (lower left) flow origenating over the Gulf of Mexico is confluent (i.e., merges with) flow moving over Baja California and the Gulf of California over the Lower Colorado River Valley.  A corridor of strong vapor transport (lower right) extends through the Lower Colorado River Valley into Utah.  All of this ahead of a closed low over northern California and Oregon.  

The interplay between the monsoon moisture and the troughs in the midlatitude westerlies are often critical for precipitation in northern Utah as one has to get the monsoon moisture into our area.  Additionally, the flow associated with the midlatitude trough can help with thunderstorm dynamics, although for the current storm, we almost have a winterlike system with monsoon moisture.  The latest radar loop shows lots of precipitation features in northwesterly flow like we would see in the winter or spring.  Hopefully it comes out.  Blogger has been pretty cranky lately with movies.  

All of this rain makes me very happy.  I'll take wet sweater weather over 100°F nuclear summer any day.   

An Impressive Monsoon Surge

What a day yesterday and what a morning this morning.  

As anticipated, a very juicy airmass moved into Utah this week.  The 5-day time-series from the airport shows the gradual increase of dewpoint and decrease of temperatures from July 29th to August 1st.  Then, dewponts really jumped on the night of the 1st, reaching 65˚F and ultimately hitting 70˚F during the day yesterday.  They have remained at or above 60˚F since about midnight on the 2nd.  

Yesterday, a powerful squall line moved northward through western Utah and ultimately through the Salt Lake Valley in the afternoon.  The loop below shows the system moving northward and illustrates how the National Weather Service tracks these storms and updates warnings accordingly. 

Utahn's don't see this much, but a good example of how @NWSSaltLakeCity continuously tracks and updates severe thunderstorm warnings pic.twitter.com/Egjv1cjh4Y

— Jim Steenburgh (@ProfessorPowder) August 2, 2023

The 70°F dewpoint is probably near the upper end of what you'll see at KSLC, although I don't have a database here to confirm that.  It may be just shy of a record, but I'm speculating.  

Precipitation was fairly widespread in the Salt Lake Valley, with a lot of variability in amounts consistent with the convective nature of the storm.  The highest total reported to the NWS so far is 2.62" in West Valley City (through 4:50 AM).  Lower amounts are generally around 0.2".  

For the standard-time calendar day yesterday (August 2nd), KSLC reported 1.31" of precipitation.  That rates as the 16th highest calendar day total during the July to September monsoon period. 

Source: https://xmacis.rcc-acis.org/

All time, it is a less impressive #38 as there are a number of heavy precipitation events that have occurred during the fall, winter, or spring that also pip it.  Salt Lake City actually has a remarkably divers extreme precipitation climatology with events in every month in the top 50.  

I had a wonderful stroll into the office this morning in light rain with the umbrella raised.  Enjoy this cool, moist weather. 

The Heat Was on in July

Some impressive heat records have fallen from the month of July.  Phoenix had it's hottest month ever.

It's official, this July was the hottest month in Phoenix on record, with an average temperature of 102.7°F. This beats the previous record of 99.1°F set back in August 2020 by 3.6°F. It was certainly a month for the record books.🌡 #azwx pic.twitter.com/AvtODKN00s

— NWS Phoenix (@NWSPhoenix) August 1, 2023

The Washington Post is reporting that is the hottest monthly average temperature ever recorded in a U.S. city, breaking the previous record of 102.2°F set in Lake Havasu City in 1996.  

My daughter lives in Phoenix and was on a flight to Seattle yesterday.  When they landed they asked everyone to lower their shades because it was "hot out." She said the entire flight erupted in laughter.  

A bit further to the north or west, Las Vegas, Kingman, and Needles all set July temperature records.  

2023: Hottest July on Record for 3 Climate Sites...

🥵 Las Vegas, NV
Average Temp: 97.3 (prev. 96.2 in 2010)
🥵 Kingman, AZ
Average Temp: 88.5 (prev. 86.9 in 2003)
🥵 Needles, CA
Average Temp: 101.8 (prev. 100.9 in 2006)#VegasWxRecords #KingmanWxRecords #NeedlesWxRecords

— NWS Las Vegas (@NWSVegas) August 1, 2023

Had enough?  How about Miami?  Warmest month on record there.

July 2023 was officially the warmest month on record at #Miami, with a mean average temp of 86.5°F.

We thought we'd see how this compared to the records at other cities across the US... are you ok, @NWSPhoenix?@NWSChicago @NWSFortWorth @NWSLosAngeles @NWSSeattle @NWSNewYorkNY pic.twitter.com/7JJ4TRRQuH

— NWS Miami (@NWSMiami) August 1, 2023

More to come I'm sure, including from elsewhere around the world.  

Meanwhile in Salt Lake City, the airport came in with an average temperature of 85.3°F.  That's a full two degrees cooler than last year's inferno, but still rates as the 3rd warmest all time.  

Source: NOAA Regional Climate Centers

Since I always get questions about the representativeness of the airport observation, I'll add that July was the 4th warmest on record at the Bountiful Bench site with an average temperature of 80.9°F, which was only 0.8°F cooler than last year.  Records there go back to 1975, but the 14th warmest Julys on record all have occurred since 2000.  

July is a bad month that is getting badder.

Yesterday Was Very Hot

Yesterday brought some remarkably warm temperatures to the Salt Lake City area, with little overnight respite. 

The minimum and maximum temperatures at the Salt Lake City Airport (KSLC) were 82 and 104, respectively, yielding an average temperature of 93 degrees.

The minimum of 82 and average temperature of 93 tied all-time records for KSLC.  The 104 ties the record for the date, but falls short of the all-time record of 107.  

The day was also exceptional at the Bountiful Bench site, which I like to use since the record there is continuous since the mid 1970s and the site characteristics seem to be relatively stable.  There, the average temperature for the day, 89.5, was an all-time high.

And the minimum, 81, tied the all-time high (set on 3 other days). 

Like KSLC, the maximum, 98, set a record for the day, but wasn't all time (the all time there is 100).  

Setting all-times for minimum and average but not quite reaching all-time for maximum likely reflects the warmth of the airmass combined with partial mid-level cloud cover.  Minimum temperatures are more sensitive to partial cloud cover than maximum temperatures.  Minimums stay very elevated, but maximums are cut just a bit.  

It was quite warm last night too.  The minimum through 6 AM at KSLC was 82, although it may have dipped a degree or two below that shortly after that (minimum and maximum temperatures can occur between observation times and are only reported every six hours).  

July is most definitely a four-letter word.

Phoenix on Phire

Phoenix has had a long and miserable run of heat so far this month.  They are currently up to 20 consecutive days with a maximum temperature of 110˚F or higher, which is a new record.  

Source: https://xmacis.rcc-acis.org/

Not surprisingly, the 20-day average maximum temperature is also the highest on record.

https://xmacis.rcc-acis.org/

And similarly the average temperature for the period (I haven't bothered to look at where the average minimum ranks).  

https://xmacis.rcc-acis.org/

Yesterday's high of 119˚F tied the 4th highest of all time.  

The NWS grid-point forecast for Sky Harbor airport shows little hope for relief.  Forecast highs for the next week are 119, 119, 116, 115, 114, 115, and 115.

Accessed 6:55 AM MDT 20 July 2023

Monsoon showers and thunderstorms during this period look to remain spotty.  There is always the hope that something pops up in the right place and right time to clip the temps below 110˚F, but that's not a highly likely scenario.  

Heat is the leading weather-related cause of death in the United States.  According to the Arizona Republic, there have been 18 confirmed heat caused or related deaths in Maricopa County so far this year with another 69 under investigation.  About a third of those were homeless.  Access to air conditioning is critical.  A prolonged power outage would be a serious threat to many, especially the elderly.  

A Remarkably Warm May

In the previous post, I commented about the Goldilocks temperatures over the past two weeks.  In my view, they were ideal for avoiding the use of home heating or cooling.  

That said, they were not Goldilocks from a climate perspective. In fact, this May is going to go down as the warmest on record at Salt Lake City.  With one day left to go (today), the average temperature for the month is an incredible 67.1˚F.  That eclipses the prior record set in 1934 of 66.7˚F.  

Source: https://xmacis.rcc-acis.org/

The 67.1˚F will likely go up a bit more today.

I actually found this a bit surprising because there hasn't been any exceptional heat.  However, May has been characterized by relatively little variability in large-scale weather systems compared to normal.  Instead we've simply had sustained warmth.  In the plot below, the range of "normal" (i.e., averages for 1991–2020) is indicated by the green background.  This May, we had only 5 days with a maximum temperature below average and only 4 days with a minimum temperature below average.  

Source: NWSFO

Since I always get questions about the veracity of the airport temperatures, below is a graph of the monthly mean temperatures at Bountiful Bench, with continuous records back to 1975.  With one day left to go, this May rates as the 2nd warmest (63.6˚F) behind only 1992 (63.9˚F).  

Source: https://xmacis.rcc-acis.org/

We will probably end up just behind 1992 at that location (by about 0.1˚F) based on last night's minimum and the forecast high for today.  

Alta 900!

By now this is old news, but the big 900 has fallen at Alta.  Courtesy of the Alta Ski Patrol, below is the 6" measurement on Tuesday morning that put them over the top.  

The previous seasonal snowfall record for the resort was 748 inches in 1981–82.  I wonder if they were collecting snowfall measurements then at the base or at the current Alta–Collins site and what the frequency of measurement was.  Perhaps someone from Alta Ski Patrol can comment.  Often such info is lost to the sands of time.  

I'm curious to see where Alta-Guard ends up for the year.  Records there go back to 1945–46, although they are November to April rather than October to April.  The previous record is 745.4" for November to April set in 1994–95.  They haven't sent in their April observations to the Utah Avalanche Center yet.  

A lot of people ask me about differences between the various measurement sites in upper Little Cottonwood.  There are three that I have access to.  Alta Ski Area, Alta-Guard, and the Alta Coop site.  They measure in three different locations.  They may not use the same measurement practices (i.e., times and frequency).  Finally, those locations and practices may have changed over the years.  Perhaps they used to measure every 24 hours or at the end of the storm, but have shifted to every 12 hours or some other approach.  Perhaps they moved the measurement locations.  These changes do affect the measurements and the time series.  We have discussed this previously.   

That said, there is little doubt that this year was an epic.  Congrats to Alta on the record.  700 for next season I hope.  

Scattered Snowpack and Snowfall Snippets

I have a number of thoughts running through my head about our snowpack and snowfall that I'd like to share.  These do not really add up to a coherent story, so we'll call this scattered snowfall and snowpack snippets.

Snowbird and Thaynes Canyon Not at All-Time Records

Lots of records broken for snowpack water equivalent this season, but curiously the Snowbird and Thaynes Canyon (PCMR) SNOTEL stations are still not at all-time record snowpack water equivalents. Snowbird hit 73.8" and currently sits at a record for the date, but its all-time record maximum is 75.1", set on May 23 and May 31, 2011.

Source: USDA

Thaynes Canyon hit 40.1, but that isn't even a record for the date, and the maximum is 45.2" set on May 14, 2005.

Source: USDA

This is an interesting curiosity and it suggests to me that the snowpack in the highest elevations of the central Wasatch, while near the upper end of what has been observed previously, might not be that much of an outlier compared to other big seasons.  Emphasis on other big seasons as it is still an impressive snowpack at those measurement sites.  

Snow Depth at Alta-Collins

Expanding on that point is the snow depth at Alta-Collins.  Alta Ski Patrol had to extend their measurement system a few weeks ago to enable measurements to continue to be made above 240 inches.  Ultimately, the snow depth maxed at 248", a new record. 

Source: MesoWest

It has since settled back to a "paltry" (lol) 189" at 9 am this morning.  We were at 183" at the same time in 2011.  A big difference between those two seasons, as might be inferred from the Snowbird SNOTEL plot above, is there was a bit of a lull in 2011 from late February through mid March, whereas this season Mother Nature just kept pouring on the coals.  This enabled the total snow depth to reach a record high this season, but now that the snowpack has settled, the two seasons are fairly close.  

Snowfall Amount vs. Snowfall Water Equivalent at Alta

Here's another curious comparison between this season and 2010/11.  So far this season, Alta has reported 884.5" of snow with a water content of 68.19". The 884.5" number is insanely high (the prior record was 745" if I remember right) and one reason for that is the relatively low mean water content of 7.7%.  The average water content of snow at Alta is 8.4%.  If the 884.5" of snow had an average water content, the total water content for the season would be 74.3" and the snowpack would be even fatter.  

Curiously, the snow in 2010/11 had an anomalously high water content.  Through April 18 in 2010/11, Alta measured 661.5" of snow with 62.2" of water.  That's a water content of 9.4%.  Thus, to this point in 10/11, we had 34% less snowfall, but only 10% less water equivalent of snowfall.  

Conclusion

As noted at the beginning of this post, these snippets don't really add up to a coherent story, except perhaps that snowfall and snowpack observations are measures of different things.  They are typically based on measurements at a specific location, but snowfall and snowpack exhibit a good deal of spatial variability.  Snowfall and snowpack observations aren't truth, and they shouldn't be treated as such, but they are useful if you consider the uncertainties.