Thursday, June 17, 2021

If June Is the New July, What Will July Be?

 

This blog post is brought to you by Panda Express, which along with the adjoining but depleted Union food court, appears to be the only place to eat on the University of Utah campus and provided me with the fortune above yesterday.  

Forget that.  

This June has been awful.  How awful?  Some statistics:

  • Although we just went through the climatologically coolest first half of June, if the month ended today, it would still rate as the warmest on record at the Salt Lake City International Airport (KSLC) by 1.4˚F.  
  • Likewise for Tooele.  So far 1.1˚F hotter than the hottest June on record (records back to 1896).
  • The average temperature at KSLC for June 1-16, 78.9˚F would rank in the top 25% hottest Julys.  More on July in a minute.
  • KSLC has had no measurable rain so far this month (they recorded a trace on June 5).
But what about the future? 

As it says at the gates of hell, Abandon Hope All Ye Who Enter Here.  

The GFS forecast through June 27 below is very much July-like. The storm track remains to our north.  Weak troughing at times near the west coast.  Maybe a brush-by slight cool down.  

This isn't a recipe for another 107˚F day, but it also isn't a recipe for a return to near average temperatures.  Temperature forecasts from the National Weather Service's National Blend of Models show we will likely see high temperatures near or above 90 for the period.  The best odds for below 90˚F are on Sunday and Monday when we may feel the effects of the bush by.  Still the majority of NBM members call for highs at or above 90˚F those days.  

Source: NWS

I'm not a fan of looking farther out, but I'll give you what you want.  The Climate Prediction Center 8-14 day outlook, covering the last week of June, shoes the odds stacked for above average temperatures.  

Source: CPC

Essentially, this June is the new July, with a large-scale pattern, temperatures, and precipitation characteristics more reminiscent of that typically hot, dry month than June.  

But what will July bring?

Really, I have no idea.  However, we can look at past Julys and think about what the climatological likelihoods are, doing some tweaking and educated guesses since our climate is changing. 

July is on average our hottest month, but it also exhibits the least amount of variability from year to year.  The coldest July on record occurred in 1993.  That was a black swan July with an average temperature of 69.9˚F, considerably cooler than we've had so far this June.  

Source: http://xmacis.rcc-acis.org/

However, July 1993 had two things going for it that we don't have today.  First, the planet was cooler in general.  Second, Mount Pinatubo, a volcano in the Philippines, erupted in June 1991, spewing particulates into the stratosphere and temporarily cooling the planet about 0.5˚C through 1993.  A repeat of July 1993 is highly unlikely.  

Perhaps a reasonable request would be something like July 2015, which was the coldest July in the past 20 years.  The average temperature was 77.4˚F, slightly cooler than we've seen so far this June.  My blog post from July 23, 2015 (Perspectives on Our Fantastic July) suggests that the month was "fantastic with tolerable temperatures and the occasional showers and thunderstorms to help moisten things up."  

On the other hand, since 2000, there have only been two Julys with an average temperature lower than the 78.9˚F we've had so far this June, 2011 (78.5) and the aforementioned 2015.  This is a small sample size (20 years), but our July climate has shifted so much that it's unclear how useful pre-1990 temperatures are for present day climate.  

My view is that it is looking pretty likely that the average temperature from here until the end of July will be comparable to or higher than what we've seen so far this June.  The odds that it is lower are probably less than 20%, and the odds that it is much lower (say more than 2˚F) are probably less than 5%.  

How's that for positive perspective? 

Tuesday, June 15, 2021

Heartless Rocky Mountain Power

A few days ago, a notice was hung on our door from Rocky Mountain Power that our power would be shut down tomorrow from 9 am to 3 pm.  


Given that today we are in an excessive heat warning and tomorrow a heat advisory, with a forecast high of 97˚F, this seems like an incredibly foolish time to shut down power.  We have options to leave the house during that period, but I wonder about neighbors and the notice warns that "unexpected difficulties may extend the outage."  

Although they claim that "poor weather may cause the work to be cancelled or postponed," this has not happened yet.  I checked with Rocky Mountain Power via Twitter last night and they are still planning on shutting down the power.  Their response..."sorry for the inconvenience."


I hope they will reconsider this shutdown as it is both reckless and foolhardy to have it this week.  It's not like they don't have the ability to monitor and adapt to the weather.  They have done power shutoffs for fire-weather conditions and, according to their press releases have a meteorologist and emergency management team to monitor evolving weather systems.  

Rocky Mountain Power has been slow to respond to climate change, has fought residential solar, and as of last year still got over 50% of their power from coal.  I guess I shouldn't be surprised.

Sunday, June 13, 2021

Lessons in Boundary Layer Mixing, Transport, and Dispersion

A three-alarm fire occurred last night in an office building in Sugarhouse.  Sixty firefighters fought the blaze, which stared around 2 AM and continued into the morning.  One firefighter was injured and we hope they have a speedy recovery.

I observed the smoke plume during a morning hike in the foothills.  At 8 AM, the behavior of the smoke plume was strongly affected by the stable cold pool that forms overnight in the Salt Lake Valley.  The smoke rose perhaps a couple hundred meters before settling back down and being transported by the local flows, as illustrated below.  

I've annotated several key features.  The heating of a fire results in warmer air than the surrounding airmass.  As a result, the air becomes positively buoyant and rises, resulting in an ascending smoke plume.  As it does so, it cools and, if the air is stable as is often the case in the morning near the Earth's surface, it will eventually reach a level where it has the same temperature of the surroundings.  At this level, which is known as the equilibrium level, the air is neutrally buoyant.  However, the air continues to rise because it has momentum, but begins to decelerate.  Eventually, the updraft dies, at the overshooting top.  Here, the air is colder than the environment, and settles back down to the equilibrium level.  

In the photo above, the local flow was westerly at the fire site, resulting in the transport of smoke eastward (the photo is taken looking south).  However, near the time of the photo, there was an eddy present, so the smoke turned northward and then westward.  If you look carefully, you can see some smoke further east, above where I've added the label "old transport and dispersion."  Earlier that morning, there was a pronounced smoke layer here, suggesting that the eddy had just recently developed.  

The behavior of the smoke changed rapidly, however, by 8:46 am.  Note how in the photo below the smoke rises vertically through a much deeper layer.  It is also being transported westward.  

The vertical rise could be related to the warming of the air near the earth's surface.  At the University of Utah, where we collect 1 minute observations, the surface temperature increased about 5˚F during this period.  Another possibility is that the heat related by the combustion increased.  Either of these would result in a a warmer smoke plume able to ascend to greater heights.  In a wildfire, these two effects can be closely related since changes in the ambient atmosphere affect the combustion process such that wildfire intensity often increases during the day.  

The shift in the orientation of the plume is more difficult to explain.  On short time scales of minutes to tens of minutes, turbulence in the atmosphere and other larger-scale eddies can cause smoke dispersion to be fickle.  The outflow from Parleys Canyon typically results in easterly flow (which would transport smoke to the west) in the morning in the Sugarhouse area.  However, this morning at one observing site there was a clear shift in the wind from easterly to southerly at about 8 AM (see the image below), when the flow was weak.  After that, the flow was S-SW.  


These observations don't correlate all that well with the plume evolution, which illustrates the fickle nature of smoke transport and the challenges of using sparse observations to anticipate smoke transport during light wind periods.  This is a major challenge for anticipating the transport of smoke, pollutants, and other hazardous materials produced by fires, accidents, or terrorist incidents, especially during periods of weak flow. 

Friday, June 11, 2021

Forecasting Maximum Temperatures

Next week looks hellish, with the National Weather Service currently predicting (as of 8:25 am Friday 11 June 2021) maximum temperatures for the Salt Lake City International Airport of 102˚F Monday, 103˚F Tuesday, 101˚F on Wednesday, and 100˚F on Thursday.  These are all near record highs for those dates.

How are maximum temperature forecasts produced?  The exact approach may vary depending on your source, but here are the basics.

Numerical weather prediction models form the backbone for weather forecasts.  These models solve the governing equations for the atmosphere, which are based on physical laws such as conservation of momentum, mass, and energy.  On example is the Global Forecast System, or GFS, which is the primary modeling system produced by the National Weather Service for medium-range forecasting.

Forecast models like the GFS have revolutionized weather forecasting.  In the middle of the 20th century, weather forecasting was based almost entirely on painstaking manual analysis of surface and upper level data, forecaster intuition, rules-of-thumb, and other ad hoc techniques.  Forecast models like the GFS have grounded the forecast process in science and greatly improved the accuracy of weather forecasts.  And, they continue to improve with increasing spatial resolution (enabling more detail), better accounting of physical processes related to clouds and radiation, and the assimilation of an increasing array of weather observations, especially those from satellites.

Models like the GFS, however, struggle predicting conditions very near the Earth's surface, including variables like temperature or maximum temperature.  There are a number of reasons for this, but in our part of the world, one of the biggest sources of error is the inability of models like the GFS to resolve the topography.  The GFS is comprised of grid cells that are about 13-km on a side.  As a result, does not account fully account for the topography of the Salt Lake Valley and surrounding ranges.  Since the elevations of the GFS do not match those in the real world, a GFS forecast for the Salt Lake City International Airport is strongly biased.  

This is where machine learning comes in. Around 1970, meteorologists began to train past forecasts with observations to develop techniques to produce better surface weather forecasts.  In a classic paper, Glahn and Lowry (1972) called this technique Model Output Statistics, or MOS.  MOS greatly improves upon direct model forecasts by adjusting for systematic biases and other effects.  For all intents and purposes, it was an early machine learning approach.  

The National Weather Service continues to call forecasts produced using such machine learning techniques MOS.  They also have a new system called the National Blend of Models (NBM) which uses many modeling systems to produce forecasts.  Private sector companies are also using machine learning techniques to produce forecasts, including many of those that you access on your phone.  The quality of such forecasts depends on several factors including the quality of the underlying model or models, length of the training period, and statistical techniques used.  

Where do humans enter the loop?  It depends.  Although machine learning can be quite automated, humans still are involved to some degree in the design of the approach and hopefully the testing an evaluation of the forecasts.  However, after that, most of the forecasts you get on your phone are probably generated automatically with no human intervention.  National Weather Service forecasts can, however, be adjusted by humans using software called the Graphical Forecast Editor.   A reminder here that we're talking strictly about temperature forecasts.  Humans play many essential roles in the forecast process including the issuing of watches and warnings and decision support activities.

All of this physics and statistics is wonderful, but when we have a potentially high-impact weather event, it's good to have some idea of context.  For this, I'm going to use the GFS forecast of 700-mb (about 10,000 feet above sea level) temperature.  This level is high enough that it is not strongly biased by the poor terrain representation, yet it is also strongly coupled to the surface during the summer when intense surface heating drives turbulence that strongly couples that level with the surface.  

The 0600 UTC initialized GFS forecasts 700-mb temperatures at the Salt Lake City International Airport of 17.7˚C on Monday afternoon, 19.4˚C on Tuesday afternoon, 18.0˚C on Wednesday afternoon, and 18.4˚C on Thursday afternoon.  These are exceptionally high relative to past upper-air observations.  The highest 700-mb temperature in the upper-air record at the airport is 20.2˚C on the afternoon of 13 July 2002 when Salt Lake City hit its all time record high of 107˚F.  The highest 700-mb temperature measured in June is 19.0˚C on the afternoon of 29 June 2013 when we set the June record of 105˚F (note: The prior day also hit 105˚F with a 700-mb temperature of 18.2˚C).  

Also catching my attention is that the airmass that will be in place early next week is remarkably dry and the low-level flow is southwesterly, as illustrated by the time height section below

These are also consistent with high maximum temperatures at the Salt Lake City Airport.  I took a quick look at the Euro and its numbers are close to the GFS.  On Tuesday afternoon, it has 700-mb temperatures of 19-20˚C over the Salt Lake Valley.  

We could also also take a look at an ensemble product.  Below is the NBM guidance from the National Weather Service based on many ensemble modeling systems.  Box-and-Whisker plots for maximum and minimum temperature are on the left and a graph of the median hourly temperature and dewpoint forecast is on the right.  We'll focus on the former.  The median forecast maximum temperature for Tuesday afternoon is 105˚F.  The interquartile range, or middle 50% of forecasts, lie between 103˚F and 106˚F.  The extremes look to be about 100˚F and 107˚F.  

A temperature of 105˚F would be unprecedented for so early in the season.  The earliest 104˚F was recorded on June 21, 1961 and the earliest 105˚F was recorded on June 28, 2013.  I suspect the duration of heat next week will probably make the average maximum temperature for the period the highest on record for that period. 

Thursday, June 10, 2021

Uncharted Meteorological Territory and the Evolving Hot Drought

 Don't let today's cool weather fool you, this June has been and will continue to be a disaster meteorologically, further exacerbating extreme to exceptional drought and fire weather conditions across the State of Utah.

In the previous post, we discussed the remarkable heat of the first 6 days of June.  Here's an update.  The average temperature at the Salt Lake City International Airport for the first 9 days of the month was an incredible 79.8˚F.  This is the warmest start to any June on record.

Source: http://xmacis.rcc-acis.org/

Let's take a closer look at the graph above.  Until 2016, the highest average June 1-9 temperature was 73.6˚F (1977).  We were 6.2˚F warmer than that!  In Salt Lake City, the urban heat island may be a local contributor, but even Alta had an average June 1-9 temperature of 59.3˚F, which is its highest on record.  Ah but the records there are spottier and only go back to the early 1970s.  How about we look at Tooele.  Records back to 1896.  Even there, June 1-9 has never been hotter.  

Source: http://xmacis.rcc-acis.org/

We are in uncharted meteorological territory.  

Today's cold frontal passage will bring pleasant temperatures to northern Utah, but this is a brief respite.  The computer model forecasts call for us to return quickly to exceptional warmth.  For example, look at the GFS forecast below for 0000 UTC 14 June (6 PM Sunday).  Deep trough off the west coast, high amplitude ridge over the upper plains, and Utah in the intermediate hot, dry southwesterly flow.  


The NWS forecast is as ugly as it gets.  One day of cool weather today.  By Friday, we're already back to a near average 81˚F.  After that, 92, 98, 100, 101, 99....

Source: NWS.  Downloaded 8 am MDT 10 June 2021.

This is the epitome of "hot drought" in which aridity is exacerbated by high temperatures, which increases evaporation and transpiration and the demand for water for irrigation.  It is estimated that approximately 1/3 of the decline in Colorado River runoff in recent years is due to higher temperatures.  

This has been anticipated for some time.  The Blue Ribbon Advisory Council on Climate Change Report to Governor Jon Huntsman, Jr. published on October 3, 2007 (available here) includes a chapter prepared by several Utah climate scientists including myself.  Amongst our conclusions:
  •  "Utah is projected to warm more than the average for the entire globe and the expected consequences of this warming are fewer frost days, longer growing seasons, and more heat waves."
  • "Ongoing greenhouse gas emissions at or above current levels will likely result in a decline in Utah's mountain snowpack and the threat of severe and prolonged episodic drought in Utah is real."
For city residents, the effects of drought are not always readily apparent, but they are severe and costly.  The National Integrated Drought Information System estimates that since 1980, 26 major national droughts have cost the U.S. at least $249 billion.  Amongst natural disasters, only hurricanes have caused more damage in that period (see https://www.drought.gov/news/high-cost-drought).  

This drought is not an act of God.  It is a reflection of weather and climate variability supercharged by anthropogenic climate change.  The climate of the 20th century is over.  This is a new world of change.  

Monday, June 7, 2021

Real Cooling Is Coming

The start of June has, in my view, sucked meteorologically.

High temperatures at the Salt Lake City Airport for the first six days of the month were 88, 91, 97, 100, 97, and 92.  

This is off the charts hot.  The average maximum temperature for the 6-day period was 94.2˚F, 3.2˚F warmer than that of any prior year on record.  In fact, there are only two other such periods with an average maximum temparature above 90: 2016 (90.5˚F) and 2020 (91.0˚F).  

Source: http://xmacis.rcc-acis.org/

Although there were a few thunderstorms around on Saturday, the airport received only a trace, so they haven't had measurable rain yet this month either.  With warmth continuing and wind on the rise, the National Weather Service has issued a red flag warning through late Wednesday for the Salt Lake Valley as well as much of the state of Utah.

Source: NWS, 2:40 PM MDT 7 June 2021

The good news is that we should see significant cooling on Thursday.  The GFS forecast valid 2100 UTC (1500 MDT) Thursday shows a surface cold-front over central Utah with northwest Utah in the...dare I say it...cooler post-frontal westerly to northwesterly flow.  


The 700-mb temperature forecast is around 0˚C over the Salt Lake Valley, which would equate to surface temperatures in the...wait for it...60s Thursday afternoon.  

Looking forward to it.