Thursday, July 31, 2014

Something Unusual...

It's not uncommon to see cumulus clouds popping up over northern Utah in July, but there's something unusual about these, at least for our summertime climate.  If you know or would like to guess, leave a comment.  

Let's Do It Again?

There's some potential that we will see another major monsoon surge impacting the region on Sunday and Monday.

As presently forecast, the event would feature a nice interaction between systems in both the tropical easterlies and the midlatitude westerlies, specifically a tropical wave that is currently located over southern Baja (red line below) and the westerly flow and broad trough currently located off the coast of California (red arrow).

The upper panel below is what is known as a dynamic tropopause analysis.  It is basically a map of the jet-stream level flow.  If you look carefully, you can see how the tropical wave near Baja slowly moves northward and eventually induces an amplification of the broad trough off the coast of California.  The two features then merge and begin to move northward toward Utah.

This leads to another surge of moisture into the state on Sunday (currently forecast to be a late day arrival into the far northern portion of the state.

If this comes together, we'll have another round of rain and moist, cool weather.

Wednesday, July 30, 2014

The Juicy Aftermath

A blanket of stratus obscures the Wasatch in the aftermath of two days of monsoonal rains
What a great couple of days.  Cooler temperatures and high humidities have done wonders for my skin and my disposition.  Let's have a look at some of the more remarkable aspects of the event.

Integrated precipitable water reached nearly 1.4 inches.  Although not a record, this is beyond the 99th percentile for the month and more than 3 standard deviations above the mean.  

Source: NWS
Given that we live in a region that is typically fairly dry, but punctuated by occasional monsoon surges with high moisture contents, one needs to be cautious in interpreting these moisture statistics.  That being said, I think it is safe to conclude this was a fairly juicy event, but there's been juicier.  

Dewpoints at the Salt Lake City airport have been at or above 58ºF now for 36 hours, with peaks at 65ºF yesterday morning and this morning.  A couple more mornings like this and I'll save a fortune on skin cream. 

Source: MesoWest
Preliminary maximum storm accumulation reports by region include 0.71" in Logan (Cache Valley), 1.73" in Corinne (northern Wasatch Front), 1.37"in Sandy (Salt Lake Valley), 1.32" in Levan (southern Wasatch Front), .83" in Cedar Mountain (Western Deserts), 1.64" near Morgan (Wasatch Mountain Valleys), 1.81" at Red Spur (Wasatch Mountains north of I-80), .65" at Alta–Collins (Wasatch Mountains south of I-80), 1.23" at Norway (Uinta Mountains), .35" in Duschesne (Uinta Basin), .18" at the Carbon County Airport (Castle Country), 1.12" at San Pete Reservoir (San Pete/Sevier Valleys), 1.31" in Fillmore (west-central Utah), and Ok, that's enough!

Basically, this wasn't a hit or miss event.  There were wide-spread variations in accumulations, but nearly everyone got something and there weren't any outrageous accumulations, although it is possible that the gauges missed something.  For example, there was a strong, stationary cell near Eureka yesterday afternoon, as well as another northwest of Eagle Mountain in Utah County, that may have put down more than indicated in the observations above. There was some localized flooding in places, including Eagle Mountain, but for the most part, we were spared the really nasty stuff.  

Still a chance of some showers and thunderstorms today, although they should be more scattered.  

Tuesday, July 29, 2014

Let's Build an Ark!

The University of Utah @ 12:40 PM
The University of Utah is currently experiencing a nice soaking rain, but stronger downpours are occurring elsewhere and could affect us later in the day.

Rdar imagery shows a nice cyclonic (counterclockwise rotating) circulation center over the West Desert.  Although there is widespread shower activity across much of northern Utah, some very strong cells can be found in the Salt Lake Valley and the area around Eureka, not to mention coming off the high terrain in far northwest Utah.

The Oak Springs weather station northwest of Eagle Mountain in Utah County recorded 1.94 inches in the past three hours.  Quite a deluge.  Guess we can turn off the sprinklers for a few days.

Very Refreshing!

Some of yesterday's storm activity in the Wasatch Mountains
The juicy tap delivered a refreshing evening last night with widespread rain and thunderstorms along the Wasatch Front and across much of Utah.  Integrated precipitable water, the depth of water in an atmospheric column if it were all precipitated as rain, reached nearly 4 cm yesterday afternoon, which is fairly high for northern Utah.  Values remain high this morning.  
Observations from the Salt Lake City Airport show how temperatures dropped from a high of 92ºF early yesterday afternoon to about 68ºF with the onset of rain in the afternoon.

Source: MesoWest
Since then, temperatures remained nearly flatlined at 68ºF.  Further, dewpoints are currently sitting around 64ºF.  That's very high for northern Utah.  I don't know what the record dewpoint is for the Salt Lake City Airport, but I think the highest dewpoint I can remember seeing there since moving here in late 1995 is 68ºF.  Maybe an adventurous student out there can rifle through the records.

It looks like a cool, humid day (by Utah standards) is on tap today with some showers and thunderstorms.  How refreshing!

Monday, July 28, 2014

A Juicy Tap

Utah will be under the influence of a juicy tap of monsoon moisture today and tomorrow thanks to the amplification and eastward shift of an upper-level ridge over the interior western United States.

This has pretty much opened us up to southwesterly flow and a juicy tap from the southwest U.S. and northern Mexico.  Tropical Storm Hernan also lurks off the tip of Baja (see red box), but right now appears to be heading westward.

If you've had an eye to the sky the past couple of days, you already know that moisture levels have been on the rise.  Integrated precipitable water, the depth of water in an atmospheric column if it were all precipitated as rain, has climbed from about 0.6 inches Saturday afternoon to over an inch this morning.
Showers and thunderstorms are expected statewide today, with the potential for some heavier downpours and flashflooding, especially in southern and central Utah where the National Weather Service has issued a flash flood watch.

Source: NWS
All in all an exciting day.  Keep in mind that yesterday lightning from monsoonal thunderstorms killed 1 and injured 13 at Venice Beach, California.  Let's be careful out there.

Saturday, July 26, 2014

Long Lift Lines, But Worth It

Perhaps against better judgement, we travelled up to Alta this morning to sample the wildflowers, which are probably near peak in Albion Basin.  Being that it was the Wasatch Wildflower Festival this weekend, the Yogi Berra quote, "nobody goes there anymore it's too crowded" came to mind as we pulled into the parking lot.

Perhaps there was a capacity closure of the canyon as the lift lines were long and the slopes packed.

I don't think I've ever seen it busier during the summer at Alta.  That being said, it was good to see so many people, young and old, enjoying the the Wasatch Mountains.

East Greely looked like East Greenley today.  Spectacular.

The wildflowers higher up below the Castle weren't as spectacular as lower in the basin, but still nice.  There's still some snow patches for those of you desperate for turns (actually, there is remarkably little snow left for July).

It's always good to reacquaint with old friends.

If you head up tomorrow (Sunday), plan on walking from the Albion base as the lines for the shuttle are long.  The best flowers we saw all day were in the lower basin anyway.

Friday, July 25, 2014

The Southwest Drought

The New York Times occasionally runs a series of maps and charts examining a variety of issues, including their latest, Mapping the Spread of Drought Across the U.S.

Drought severity across the U.S. on July 22, 2014.  Source: New York Times.  
 Drought is an under appreciated natural disaster.  The onset and end are not typically sudden, but the costs can be quite high.  If you scan the list of billion dollar weather disasters since 1980, drought appears 18 times, with combined loses of almost $250 billion in current dollars.

Droughts are often through to be periods of abnormally low rain, but they are actually quite multifaceted with considerable geographic variability.  There's more to the story than precipitation as the conditions that lead to low soil moisture are also affected by temperature and other weather, climate, and soil factors.  Although there are many different ways to both define and determine the severity of drought, the most widely used index is the Palmer Drought Severity Index (PDSI), which attempts to account for a variety of factors that affect soil moisture.

Plots like the one above derive from the U.S. Drought Monitor, which blends a number of drought measures and expert judgement.

The Southwest is currently in the grips of widespread drought, with drought conditions rated as exceptional over portions of California and Nevada (the "more" region above).  To the first order, this drought reflects the influence of climate variability.  As concluded by Hoerling et al. (2013) in the Assessment of Climate Change in the Southwest United States:
"It is likely that most of the recent dryness over the Southwest is associated with natural, decadal coolness in tropical Pacific sea-surface temperatures, and is mostly unrelated to influences of increased greenhouse gases and aerosols." 
In other words, more persistent La Nina conditions have played an important role in the long-term drought conditions.  This is not to say that global warming has had no influence on the drought.  It is an exacerbating factor with higher temperatures, by contributing to soil drying, increasing in drought coverage and intensity.

Thus, we should be cautious in attributing the current drought to global warming.  On the other hand, we also shouldn't assume that all is well and good in the coming century.  The evidence suggests a decline in water resources over the Southwest over the long term.  As discussed by Gershunov et al. (2013) in that same Assessment of Climate Change in the Southwest United States:
"Drought, as expressed in Colorado River flow, is projected to become more frequent, more intense, and longer lasting, resulting in water deficits not seen during the instrumented record (high confidence)" 
"In terms of soil moisture, drought is expected to generally intensify in the dry season due to warming (high confidence)"

Thursday, July 24, 2014

Hot Stuff

Here's four hot stuff factoids for your Pioneer Day enjoyment:

  • Yesterday's high at the Salt Lake City International Airport was 103ºF, which is tied with July 14th for the hottest day of the year so far.
  • Climatologically, this is the hottest period of the year.  From 18 July to 2 August, the average high temperature at the Salt Lake City International Airport is 94ºF and the average low is 66ºF. 
  • The overnight (through 6 AM) minimum temperature at the Salt Lake City International Airport was only 80ºF, although temperatures did dip to 79ºF just after 7 AM.  I woke up in the middle of the night and heard the air conditioning cranking and thought, whoa, it must be hot!
  • Globally, June was the hottest recorded in the instrumented record.
Source: NCDC
The heat miser is winning.

Wednesday, July 23, 2014

Early Results: Perspectives on Daylight Savings Time

As some of you are aware, the Utah Legislature is presently investigating whether or not to put an end to daylight savings time, the setting of clocks forward in the spring so that the sun rises and sets at a hour of the day during the spring, summer, and fall months. I am a fan of the later sun rise and set relative to the local-time clock, but others out there may feel differently.

The Utah Governor's Office of Economic Development is currently conducting an online survey on views on daylight savings time that can be completed at by both Utah residents and non-residents (yes, the latter is important as we have a big tourism economy).  You can vote and add comments until August 15th.  I wonder if that means August 15 defined using UTC, MDT, or MST?

Results and comments through yesterday morning are now available on the GOED website and they show that the daylight time lovers are currently getting slaughtered.  With over 26,000 responses, a whopping 67% of the respondents wish to align with Arizona and stay on standard time all year.  Only 15% want to maintain current practice.  18% say stay on daylight savings time all year.

Of course, this is a voluntary survey, which tends to invoke response from those with the strongest opinions.  It would be interesting to see what the results would be of a random sample of Utah residents and non-residents.  Ultimately, the decision to could be put up for a vote, and that might be even more interesting.

For your entertainment purposes, more than 13,000 specific comments are available here.  Here are a few I've self selected just for fun.  I especially like the third and fourth.
"Changing time by legislation is so silly to me. Time should never change, it's a cosmic reality, not a law of men. Fooling ourselves about the real time of day is a bit insane." 
"Daylight Savings is silly for a country which calls itself free. If you want to get up an hour earlier for an hour more of sunlight, then do it; it is your prerogative. But it is a form of totalitarianism to force everyone to get up an hour earlier." 
"If DST was a face, I would punch it as hard as I could." 
"I have not changed my clocks in 4 years. I have hated daylight savings for years. What is the point. "
One thing is apparent from reading the comments, everyone hates the change twice a year.  At least we an agree on something!

Monday, July 21, 2014

Clear Views, Clean Air

After several days of smoke inundation, it was great to wake up this morning to clear views and clean air.

In addition to yesterday's storms, we've had a shift in the large-scale wind direction after several days of northwesterly flow, as evident in wind observations from the top of the Collins chair at Alta Ski Area.  The transition to southwesterly flow has resulted in a smoke-free airstream for the Wasatch Front.

Overnight PM2.5 observations from the University of Utah showed the lowest PM2.5 levels in a few days, with values sitting near 0.

Enjoy the clean air!

Sunday, July 20, 2014

The Pots o' Gold Are on Campus

A spectacular rainbow display could be seen looking toward the east bench this evening.  From my vantage point, the pots o' gold produced by the primary and secondary bows were on the University of Utah Campus, including one near Rice-Eccles Stadium.  No word on whether or not President Pershing was scouring the grounds hoping to add to the U's endowment.

The primary bow was spectacular and featured at least one and possibly two supernumerary bows, purple arcs on the inside of the bow. I've had to doctor-up the photo below to bring the most obvious supernumerary bow out.

Saturday, July 19, 2014

Coast to Coast Smoke

Smoke from the western fires of the U.S. and Canada has now spread coast-to-coast.  If you look closely, you can see it in the visible satellite image below over eastern Canada and Maine.
The National Environmental Satellite, Data and Information Service (NESDIS) provides a nice interactive map for examining fire and smoke hazards.  The screenshot below shows the active fires (red dots), areas with moderately dense smoke (yellow) and areas with thin smoke (green).  Coast to coast coverage is achieved thanks to a fire near the California coast and then large-scale transport of smoke from fires in the western U.S. and Canada across the continent.

Some views of the smoke from MODIS follow (source: NASA).

Smoke plumes over Oregon 
Dense smoke over the Columbia Basin
Smoke over the northern Plains (Lakes Superior and Michigan at right for reference)
Smoke over Labrador, Canada
Sadly, fires have destroyed an estimated 100 homes in north-central Washington.

Friday, July 18, 2014

Ask and You Shall Receive: Insights from a New Ozone Sensor

After belly aching in yesterday's post about the need for more real-time air quality monitoring stations in the Salt Lake Valley, I learned that my colleagues in the mountain meteorology group here at the University of Utah have just installed PM2.5 and ozone sensors at our mountain meteorology lab (MTMET) on upper campus (click here to access).  At an elevation of 4996 ft, this site should make for good comparisons with the DAQ sensors at Hawthorne Elementary near the valley floor and almost 700 feet lower.  MTMET is influenced by outflow from Red Butte Canyon, and this is already proving to be quite interesting.  

Data from the past 24 hours at MTMET (courtesy shows very nicely the gradual rise in temperature during the day yesterday, with a high just above 90ºF.  Just before 2000 (8 PM) MDT, temperatures dropped abruptly to 75ºF with the onset of easterly canyon outflow, after which temperatures held steady until about midnight when the temperatures jumped abruptly when the outflow weakened. The strength of the outflow varied for the rest of the night, with temperatures bottoming out in the low 70s just before 0800 (8 AM) MDT.   

Ozone for the period spiked briefly from 1300–1400 (1–2 PM) MDT yesterday, hitting ~80 parts per billion (ppb).  Ozone overnight, even with the supposedly "clean" canyon outflow, stayed near about 50 ppm until about 0800 (8 AM) MDT when the outflow weakened and winds gradually shifted to southwest. 

We can compare this data with that from Hawthorne, which thankfully is available online again.  It shows a similar spike in ozone in the early afternoon, but lower ozone concentrations than observed at MTMET overnight.  In other words, from the standpoint (solely) of ozone concentrations, the outflow from Red Butte was "dirtier" than the air at Hawthorne.  
Source: Utah Division of Air Quality
That may sound surprising, but it is likely the result of a curious oddity of meteorology and air chemistry.  Profiles of ozone in other regions (e.g., the Los Angeles Basin illustrated below) often show the highest ozone concentrations are aloft and not at the surface (note: this doesn't necessarily mean the air at the surface is "clean"!).  
Ozone concentrations over the Los Angeles Basin from 05-07 local time, 25 June 1987.  Source: Dayan and Koch (1996).  
This may seem strange since one expects the pollution to be worst near the ground where the emissions are, but ozone is a secondary pollutant and the complexities of ozone photochemistry and meteorological turbulence lead to the strange distribution.  Further, this effect is most pronounced at night and in the early morning.   The Los Angeles data above was collected from 5-7 AM local time when ozone concentrations were less than 50 ppb near the surface, but exceeded 250 ppb aloft.

So, one hypothesis for the higher ozone at MTMET last night is that the ozone levels dropped in the valley, but the outflow from Red Butte was tapping into the higher ozone air further aloft.  

Of course, this is an are educated guess.  Comprehensive observations of meteorology and atmospheric chemistry are needed to better understand these local characteristics of our pollution.  

Thursday, July 17, 2014

How Bad Is the Air?

Answer: We don't know.

Source: Utah Division of Air Quality
With the infusion of smoke over the Salt Lake Valley, I was curious about the air quality.  Sometimes with smoke in the summer, you get the double whammy of elevated PM2.5 and ozone at the same time.

Unfortunately, it appears that a computer network failure has resulted in a loss of real-time air quality data in Salt Lake County (see red box below).

Source: Utah Division of Air Quality
I suspect based on data from other counties that we're probably in a moderate air quality for PM2.5 and either moderate or unhealthy for sensitive groups for ozone in the afternoon.  I suspect the folks at the DAQ can access data from additional sensors, which informs the statement in the red box above, but unfortunately John and Jane Q. Public, can't.  

We've spoken previously about the need for more publicly available real-time air quality monitoring stations in the Salt Lake Valley (see Inversion Snippets).  Here's yet another reason to address this need.  The public deserves to know all they can about the air they breath.  

Wednesday, July 16, 2014

The Great Smokies

A smoky atmosphere is currently in place over the Salt Lake Valley with reports of a spectacular sunrise (I missed it!).  The central Wasatch look like the Great Smokies today.  

Satellite imagery from late yesterday afternoon shows extensive smoke across most of the Pacific Northwest including the Columbia Basin and the Snake River Plain.  

Some of this smoke originates from British Columbia, but there are also 21 major wildfires burning in Washington, Oregon, and Idaho.  Note the increase in large incidents just between yesterday and today. 
Some of the apparent clouds evident in satellite imagery are dense smoke and pyrocumulus clouds produced by these fires.  In the image below, I've outlined the dense smoke plume generated by the Whiskey Complex Fire in southwest Idaho.  Note how it fans out and eventually merges with the more diffuse smoke over the Snake River Plain.

Many of these fires were sparked by lightning.  Below shows the cloud-to-ground lightning strikes just from 1200 UTC 13 July through 1200 UTC 14 July, which was an active period across Oregon and western Idaho. 


Tuesday, July 15, 2014

Near or Above Average Temperatures Are an Easy Bet in July

Bloody hot out there again today.  At 1 PM, it was 95ºF at the Salt Lake City Airport, just 2ºF cooler than yesterday when we hit 103ºF.  Another 100 is likely.  Average high for today is 93ºF.  Wouldn't that feel wonderful.

If you are looking for a month to bet on for near or above average temperatures in Salt Lake City, July is your best option.  July features the smallest amount of year-to-year temperature variability of any month of the year.  This, combined with the gradual increase in global temperatures, means it's pretty hard to have July that is substantially below average unless something really exceptional happens.

Below is the average July temperature for Utah Climate Division 3, which covers the Wasatch Front.  One can see the overall warming trend since 1895, which reflects a surge of warming prior to about 1940 and then after the late 1970s.  These two warming surges are also apparent in globally average temperatures (not shown).  Year-to-year fluctuations are only about 3-4ºF on average.  The grey line is the 1981-2010 climate average and we haven't had a year significantly below it since 1997.  Ah, the good old days.

Source: NCDC
Now lets take a look at January.  January sees considerably more variability from year to year.  So much so that it's hard to see the longer-term warming trend (although it's there) and the two surges noted above.  The year-to-year variability in January is very large compared to July and about 10ºF (note that the scale has changed and covers more than double the range of temperature in the July plot).

Source: NCDC
In July, the storm track is usually to our north and the monsoon usually has a modest influence on the weather of northern Utah.  As a result, we see less variability from year to year.  The signal to noise ratio is small in July, so the long-term warming trend has a more obvious influence on regional temperatures.  In contrast, January is more at the whims of the jet stream and there is tremendous variability from year to year that obscures the large scale warming signal.  You can get a well-below average in January, leading everyone to ask what happened to global warming.  Getting a well-below average July is more difficult.

Of course, there is always the potential for a black swan event.  July 1993 is a good example as it is easily the coldest July in the instrumented record in northern Utah and a full 4ºF colder than any July since 1915.  Several factors came together in 1993 to give us an unusually cold summer.  The first was the eruption of Mt. Pinotubo, which dropped temperatures globally.  The second was a weaker-than normal circumpolar vortex, which enabled cooler air to spread more frequently from the high to the low latitudes.  The third was a strong negative phase of the PNA pattern, which put persistent troughing over the interior west.  See A Tale of Two Summers: 1993 vs. 2013 for more discussion.