Wednesday, May 31, 2023

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.  


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).  


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.  

Tuesday, May 30, 2023

Goldilocks Temperatures with Thunderstorms

Since about May 12th, we've been locked into what I'll call the large-scale doldrums with relatively weak flow at upper levels and a lack of strong synoptic systems and fronts.  The average 500-mb height analysis for May 12 to May 27 shows the pattern that has predominated quite well with a long-wave trough over the central Pacific, ridge over western North America, and trough over the Canadian maritimes.  

Image source: NOAA/PSL

At the same time, the pattern over Utah and indeed a good chunk of Nevada and the Sierra Nevada has been quite active from a thunderstorm perspective.  The reason for this is the weak short-wave trough that is embedded in the long-wave ridge (indicated by the dashed line above).  Systems have moved through this trough, modulating thunderstorm coverage and intensity, but it has refused to go away.  

As a result, we've seen lightning and thunder on a regular basis in the Salt Lake Valley.  Other than that, there hasn't been much in the way of weather variability, especially for May.  Since May 12 at the Salt Lake City International Airport, minimum temperatures have been at or above 50˚F and maximum temperatures have been at or below 88˚F. 


This is pretty much the Goldilocks zone for comfort in the valley, at least at my house where we haven't bothered running the heat or cooling system throughout this period.  If you like to exercise, it's tolerable in the morning and even in the afternoon.  One has just had to dodge the thunderstorms.  

Enjoy.  July will come eventually.  

Wednesday, May 24, 2023

Great Salt Lake Update

The Great Salt Lake at Saltair* rose 4.7 feet from 4188.7 feet on October 1st of last year to 4,193.4 feet on May 1st of this year.  That's a big increase, but it is still very low.  The graph below illustrates the lake elevations at Saltair based on data from the USGS.  The orange line indicates the 4193.4 ft level, showing that the current elevation is still below all but the low stand in the early 1960s, recent seasonal minimums in the fall, and the drawn out low period of the past couple of years.  

Lake elevation at Saltair since 1847 (USGS data)

You may have noticed the asterisk above.  Saltair provides long-term records for the south arm of the lake, but the rock-fill railroad causeway dividing the lake in half can cause elevation imbalances.  Additionally, the berm in a gap in the causeway was raised recently.  As a result, while the south arm receives most of the freshwater runoff and has risen a lot, the north arm has only climbed slightly to 4189.2 ft.

Lake elevation at Saline since 1966 (USGS data)

Landsat imagery from last May and this May shows more water in Farmington Bay, Ogden Bay, and the Bear River Bay.  However, large expanses of lake bed remain exposed in Farmington Bay and on the western side of the lake.  


We will probably see lake levels rise for a few more weeks.  Below is a bathymetric map of the lake that includes the 4188.7' (historical low), 4193.4' (current), 4195', 4198' (functional low), and 4211' (historical high) elevations.  Perhaps the south arm will get a bit above 4195', although that's really just a guess. on my part. 

Note that the map above assumes a level lake.  Lake elevation, coverage, and shorelines do fluctuate due to wind, inflows, and other effects.   

Anyone want to set the over/under for peak lake elevation at Saltair?

Sunday, May 21, 2023

That's a Wrap

It's never over until it's over, but yesterday was probably my last day of resort skiing for the season.  

It was an unusual last day, with smoked filled skies from the Canadian wildfires.  

Friday night lows at the top of Hidden Peak were only 39˚F, yet there was a solid freeze of the snow on the mountain thanks to clear skies and long-wave radiative cooling.  Regulator was "not recommended" first thing and I can confirm that the ski patrol was on point.  With early sun, Mineral offered up soft skiing quickly due to its easterly and southerly exposures, but I'm always happier when the steeper lines off the tram can be skied.  North Chute and the like with May morning sun exposure began to soften up and ski well around 10:30.  

It will be interesting to see if Snowbird can make July.  There is still an enormous amount of snow on the upper mountain.  Water equivalent at the SNOTEl site, although now well below where we were in 2010/11, is still in the top 10% of snowpacks on May 21 since 1990.  

That said, the warmth of this May has shed about 20 inches of water equivalent at the SNOTEL site, the snowpack is fully ripe, and it is extensively dust covered.  A shift to cooler weather would probably be helpful.  

Thursday, May 18, 2023

Great Salt Lake Bed Dust

 Yesterday evening, while out for a walk, I noticed a wall of dust over the western Salt Lake Valley.  

After returning home, I took a look at a video from the west-facing camera my department operates at the University of Utah and it showed a remarkable plume originating to the north and presumably from the exposed Great Salt Lake bed in what used to be Farmington Bay.

Much has been made about the snowpack, runoff, and rise of the lake.  Indeed, the lake elevation at Saltair Boat Harbor has increased over 4 feet from its record low last fall.  It currently sits at about 4193.3 feet, but that is still remarkably low as can be seen by the elevation graph below for the past 40 years.  

As a result, the lake area remains low and lake-bed is still exposed in many areas, including much of Farmington Bay (east of Antelope Island) which I suspect was the source of yesterday evening's dust (image below from May 15).  

About a month ago, it was anticipated that the lake would eventually rise to 4195 feet with this year's runoff.  That's a big increase, but it is still below what is viewed as the optimal lake zone between 4198 and 4205 feet.  

Friday, May 12, 2023

The Big Melt

Snow is melting and the decline in lower-to-mid elevation snowpack has been impressive.  

The lowest SNOTEL in the Wasatch Range is Ben Lomond Trail in the northern Wasatch (5972').  Snowpack water equivalent has dropped like a stone there from its all-time 47" peak (with records going back to 1981) to 17.1 inches yesterday.  It remains at an all-time high, ahead of 2011, 1984, and 1983.  Based on the forecast, I suspect it will probably make it about another 10 days before becoming snow free.

Source: NRCS

In City Creek Canyon, the low-elevation Louis Meadow site (6700') has also seen an incredible decline from 43.3 to 13.1 inches.  It's now behind where the snowpack was in 2010/11.  

Source: NRCS

A bit higher on Lookout Peak (8161'), the big melt has just begun and has been slower.  Although now behind the 2010/11 snowpack, 45" of water remains.  Streamflows in City Creek are forecast to increase in the coming days as this upper-elevation snowpack begins to melt in earnest.  

Source: NRCS

The Parley's summit snotel has a long period of record going back to 1979.  At 7,585', this site has shed a bit over half of its snowpack and it is behind 2011, 1984, and 1983.  It might have about 10 days of snow cover left.  

Source: NRCS

Finally we have the high elevation Snowbird snotel (9177 ft).  You may recall a blog post from a couple of weeks ago (Snowbird SNOTEL Measurement Oddities) in which I discussed how it strangely climbed and reached a new all-time high.  It appears the NRCS has corrected that provisional data, so the site now shows no record peak.  Melt has not begun in earnest yet, but it has shed a small amount of water and it currently sits behind 2011 and 2005.  Still there is a lot of water to come down from the upper elevations.  

Source: NRCS

By and large, I think the situation right now is perhaps the best we could have hoped for given the enormous snowpack that existed in April.  The runoff has produced some flooding and damage in places, but given the enormous snowpack, we have been able to shed a good fraction of the lower and mid-elevation snowpack while the upper-elevation snowpack on north aspects has been ripening but not releasing a lot of water.  In the Salt Lake area, the worst may be over in terms of snowpack runoff for Emigration Creek, which drains a lower elevation basin, but creeks draining higher elevation basins, like City Creek and the Cottonwoods, have big water to come.