Western Showers, Eastern Deluge?

Changes are afoot that will result in a shift in the weather for Utah and a significant rainfall event in the eastern United States.

The pattern currently developing over North America will give weather forecasters headaches from coast to coast.  It features multiple interactions between upper-level closed lows and high-amplitude ridges, with a tropical cyclone thrown in just for good measure.  The interactions between these features are notoriously difficult to nail down and this leads to considerable forecast uncertainty.

The low hanging fruit is in Utah.  Our run of well-above-average temperatures will come to an end on Friday as an upper-level trough from the Pacific swings into the Intermountain West, bringing cooler air and showery weather.

After that, it's tough to say.  The models have been all over the place dealing with the interaction of Friday's trough with another upper-level trough dropping down from British Columbia over the weekend (such an interaction between two troughs is called the Fujiwara effect).  I'm giving up on details for the weekend except to say that temperatures will thankfully be more seasonable.

The real forecast challenge in the east.  A significant rain system is sweeping through the northeast currently, then it looks like a prolonged rain event will develop along the mid Atlantic and southern New England coast through Friday night in advance of tropical cyclone Joaquin.  Such rain events are sometimes called predecessor rain events or PREs.

After that, we have diverging solutions from the various members of the GEFS and Euro ensembles regarding the track and intensity of Joaquin ranging from a direct track into the mid atlantic states (see GFS above) to a track that keeps it well offshore.  The Euro ensemble has more members keeping Joaquin or its remnants offshore, whereas the GFS has more members calling for something moving into the mid atlantic or at least along the coast (see below).

Source: Penn State e-Wall

Put them together and you have a huge range of possibilities.  A good summary is provided by the National Weather Service Sterling, VA area forecast discussion:

"FORECAST CONFIDENCE SIGNIFICANTLY DECREASES OVER THE WEEKEND AS MODELS CONTINUE TO STRUGGLE TO RESOLVE THE BLOCKING PATTERN (CLOSED LOW TO OUR SW...HIGH OVER NORTH ATLANTIC) AND HOW TC JOAQUIN INTERACTS WITH IT. SOLUTIONS RANGE FROM A COASTAL IMPACT TO THE TC REMAINING WELL OFFSHORE. PLEASE REFER TO NHC BULLETINS FOR THE LATEST DETAILS AND BE AWARE THERE IS AT LEAST POTENTIAL FOR HEAVY RAIN AND FLOODING (THE LARGEST THREAT GIVEN THE TWO PREDECESSOR RAIN EVENTS)...WINDY CONDITIONS...AND COASTAL FLOODING OVER THE WEEKEND."

Overall, this is a great example of a low predictability pattern, but one with the possibility of high impact weather.  Rainfall associated with the PREs is likely, but precisely where and how much.  Then, will that be followed by a further deluge?  From a scientific perspective, the challenge is developing ensembles that provide reliable estimates of event probability.  From a communications perspective, the challenge is how to effectively inform the public and decision makers when the range of possibilities is very large.

Record Setting Late September Temperatures and Their Potential Hydrologic Implications

We've had a remarkable period of sustained warmth over the past week in Salt Lake City.  Not only have we set two maximum temperature records (93ºF on Sep 25 and 90ºF on Sep 26), the average temperature for the past week (Sep 21–27) of 74.1ºF is the highest on record, easily eclipsing the 72.9ºF observed in 2001.

A look at the time series above suggests that this past week is indeed quite an outlier and one of only 5 such September periods going back to 1874 with a mean temperature above 70ºF (note that the records above are a composite of observations collected in the Salt Lake Area as the airport didn't exist back then!).

An unfortunate aspect of this hot dry weather is a loss of moisture from the big rains we had from September 14–16.  As shown in the chart below for the Mill D North SNOTEL in Big Cottonwood Canyon, those big rains greatly increased the soil moisture content of the soils at both 2 and 8 inch depths.

Data Source: NRCS

 Similarly, soils elsewhere at all elevations, including in the Salt Lake Valley, received quite a boost.  Unfortunately, as can be seen in the plot above, we've now lost soil moisture to evaporation and transpiration, the process by which moisture is carried through plants for photosynthesis.  Sun exposed lawns that haven't been irrigated since mid September are starting to feel crunchy and look thirsty.

In the mountains, if that moisture is not replaced before the first snows, the soils will be the first place that the snowmelt goes in the spring (rather than to the rivers and streams).  That might be a good thing if we end up having a huge snow year, but if our run of meager winters continues, it would exacerbate the crappy runoff situation even further.  As we have discussed previously (see Wasatch Weather Weenies Survival Guide for El Nino), the current Super El Nino doesn't really load the dice one way or the other for us, so at this point, we have to have a wait-and-see approach to what happens between now and the first snows, as well as during the winter.

Aspens on Fire

The Aspens were on fire today in Big Cottonwood Canyon.

Some groves have dropped their leaves, others haven't turned yet.  Upper elevations are probably going to lose a lot of leaves this week, but mid elevations will probably still be good next weekend.  We hiked up Gobblers Knob and Mill A Basin is probably at peak, but the Butler Trees were still pretty green and I suspect next weekend might be quite nice (I haven't bothered to see if the weather might cooperate!).

Congratulations to Dave Hanscom

Long-time friend to the nordic and backcountry skiing communities of Utah, Dave Hanscom, was inducted into the Intermountain Ski Hall of Fame on Thursday.  It couldn't have happened to a nicer guy.

Along with Alexis Kelner, Dave is the co-author of Wasatch Tours, Volumes 1, 2, and 3, the first definitive guides to backcountry skiing in the Wasatch Range.  Volume 2, covering the northern Wasatch, including the tri-canyons, contains wonderful prose.  One of my favorites is the description for the approach to Thomas Fork.

"No ski area developers have cleared the willows and oak, so considerable ingenuity and determination are required to get through the brush.  True cross country touring is, after all, a character developing and strengthening form of recreation." 

I don't know if Dave or Alexis wrote that section, but the entire book series is filled with great commentary of this type. 

Dave has also contributed greatly to the nordic community of Utah through The Utah Nordic Alliance (TUNA) and his efforts for the Wasatch Citizens Series.  A more complete summary of his skiing contributions is available in this recent article in the Park Record.

I first met Dave in the Hakuba Valley of Japan where we were sent to learn as much as we could about the logistics of putting on the 1998 Nagano Olympics.  His area was cross-country skiing, mine was weather, and I was fortunate to learn a good deal from him about the impacts of weather on cross country racing.  Watching the mens 4x10 km relay, the so-called Super Bowl of nordic skiing, with Dave was one of the highlights of my "Olympic" career.  

Dave Hanscom and I at the Snow Harp cross-country skiing venue, Hakuba Valley, Japan

Dave also played a vital role in my book Secrets of the Greatest Snow on Earth.  I had hoped to start the book with a history of the phrase Greatest Snow on Earth, and assumed that someone would have hunted this down as part of the trademark infringement suit brought forth by the Ringling Bros. & Barnum and Bailey Circus.  Nope.  So one day I called Dave and he suggested that a guy named Mike Korologos might know the story.  I eventually crossed paths with Mike and he sure did know the story.  His brother Tom came up with the phrase in 1960 and I was able to eventually find the original article that appeared in the Salt Lake Tribune that coined the phrase.  

Finally, I must mention Dave's 20+ year service to the University of Utah computer science and engineering program.  Go Utes!

Congrats to Dave on this well deserved recognition of his many contributions to Utah skiing.  

Webinar on Lake Effect

The American Meteorological Society Committee on Mountain Meteorology hosts a webinar series exploring various topics in mountain weather research and forecasting.  Yesterday I had the opportunity to give a webinar on the influence of mountains on lake effect, which was followed by a discussion of operational issues by Paul Sisson of the National Weather Service Forecast office in Burlington Vermont.

I considered embedding the video here, but it's much better viewed in full format, which you can access by clicking here.

Access to the complete seminar series, which includes a number of topics that may be of interest to readers of this blog, is also available by clicking here.

Yogi Berra Quotes

Yogi Berra leaping into Don Larsen's arms after his perfect game in
the 1956 World Series encapsulates the joy of sport. 

Yogi Berra passed away yesterday at the age of 90.  He was one of the greatest catchers in baseball history and participated in 21 World Series as a player or coach.  Nevertheless, for many of us who never saw him play, we know him more for his quotes.  Here are five that are relevant for the weather weenies, scientists, and academic types out there.

"In theory there is no difference between theory and practice.  In practice there is." 

I'm sure that quote was baseball motivated, but substitute application for practice and you are on to something for scientists and academics.  

"I wish I had an answer to that because I'm tired of answering that question."

I'll be using that one at my next lecture on global warming.

"You can observe a lot just by watching." 

Damn straight, and a good line for modelers, theoretical meteorologists, and model-centric forecasters to remember.  Take a glance out the window and at the weather map from time to time!

"It ain't the heat, it's the humidity." 

Exactly.  That's why I live in Utah and not Washington D.C.

"It's like deja-vu, all over again."

I took a quick look via Google and found that I've used that line many times for Wasatch Weather Weenies posts.  Once a pattern is locked in, it's not unusual to have a couple of similar, even anomalous weather events back-to-back, like a couple good homers.  

2015 Easily on Pace for Warmest on Record

Last week, the August climate numbers were released by the National Centers for Environmental Information (NCEI) and not surprisingly 2015 continues to be a hot one.

For the January–August period, 2015 is well ahead of any previous year on record for global average temperature and a full 0.1ºC ahead of second place 2010.

Source: NCEI

The numbers for August the past two years are really out there.  August 2014 was 0.09ºC warmer than second place August 2009, and then August 2015 doubled down and added another  0.09ºC.

Source: NCEI

These big numbers reflect the long-term global warming combined with the strong El Nino that has developed in recent months.  Similarly, 1998 was a remarkably strong El Nino and it was a real outlier in terms of temperature (see the top bar chart).  Those wishing to argue that global warming "stopped" have frequently used 1998 as the start point of their time series as it results in a relatively flat trend over the last several years.  As we have discussed (see Global Warming Hasn't Stopped), global warming never stopped, even if the short-term trend in global atmospheric temperatures was small, and it was only a matter of time until the shorter-term trend produced by climate variability (such as associated with the development of a strong El Nino) phased with the long-term trend in a way to give us a big warm up.  That time is now.

Wasatch Ski Report

Still a couple of storms away (ha ha)

But with weather like today

That's okay

Two Potential Weather-Related Disasters in Utah

Monday's flash floods contributed to the deaths of 19 individuals, with one still missing.  It's Utah's worst day for weather-related loss of life in history.  Moving forward from here, the good news is that weather forecasts, watches, and warnings have never been better and will continue to improve in the future.  The bad news is that with increasing population, development, tourism, and recreation, Utah's vulnerability to severe weather has never been higher and is only likely to increase in the future.

Here are two potential disasters that have yet to occur, but concern me as a meteorologist.  We probably can't eliminate the potential risks, but there are steps that can be taken to reduce the likelihood or severity of catastrophe.

Avalanches in Little Cottonwood Canyon

As I discuss in chapter 6 of Secrets of the Greatest Snow on Earth, 50 avalanche paths intersect SR-210 and other roads and parking lots in Little Cottonwood Canyon.

Source: Secrets of the Greatest Snow on Earth

This along with heavy traffic, yields the highest avalanche hazard index of any major road in the United States.  On average, the highway is hit by 33 slides per year, most when the road is closed, but not always.

Individuals contributing to the reduction of avalanche threat along the highway, including those at UDOT, Alta Ski Area, and Snowbird, do an exceptional job, but it is impossible to completely eliminate risk along the highway as it exists today.  As noted by retired UDOT Avalanche Program Safety Supervisor Liam Fitzgerald, “Because of the density of traffic, because of the number of avalanche paths that affect the road, and how close the starting zones are to the road, if you open the road to the tune of 5 or 6 thousands vehicles, a small avalanche can come down, block the road, and now you have hundreds of vehicles sitting stationary under these other avalanche paths, and it does turn into a catastrophic situation very quickly.”

As suggested by Liam, perhaps the worst-case scenario is to have traffic snarled in the canyon during a period of rapidly escalating avalanche hazard.  It doesn't take an avalanche for this to happen.  Chances are you've experienced the infamous red-snake, produced by the break lights of a seemingly endless line of cars crawling down the canyon at the end of a big ski day, especially when road conditions are poor.  Such situations, when combined with heavy snowfall and increasing avalanche hazard, could go south quickly if the road is hit by an avalanche, burying cars and sweeping them off the highway.

Catastrophe has been adverted in the past.  In 2006, an avalanche swept an SUV containing nine people off the highway.  Fortunately, all were wearing seat belts and incredibly everyone was shaken up but not seriously harmed.

Improvements in infrastructure, monitoring, and forecasting in recent years have reduced but not eliminated the threat in the canyon (Note: avalanche concerns exist along other Utah highways, but the hazard threat is greatest in Little Cottonwood).  Some additional incremental improvement is likely possible, but reducing this threat significantly likely involves highway realignment, tunneling, and shedding of the highway, or a similar approach for mass transit alternatives (e.g., rail) in the canyon.

Lightning or Severe Weather at an Outdoor Event

Amongst states, Utah ranks in the top 20 for total lightning fatalities and #2 for lightning deaths per million people.  I'm unaware of any lightning catastrophes that have killed more than 2 individuals, but there have been some that have apparently killed hundreds of sheep!

Perhaps the biggest potential for a major catastrophe is at outdoor events such as concerts or football games.  An example of the potential occurred at the NASCAR Sprint Cup Race at Pocono Raceway in 2012 when one fan was killed an nine injured by lightning.

In 2006, Joel Gratz, now CEO of opensnow.com, and Erik Noble, wrote a great article for the Bulletin of the American Meteorological Society evaluating lightning safety at large stadiums in the United States, exposing the need for managers to both anticipate and prepare for lightning threat.

The good news is that some outdoor venues now have developed lightning safety action plans and monitor for lightning during events.  You may recall the lightning delay during the Utah–Michigan game last year.  The bad news is that all of them don't do it, it's difficult to evacuate an outdoor stadium in the event of a rapidly developing storm, and often spectators are reluctant to move to their cars or a safe indoor location.

Encourage your favorite outdoor venue to be doing all they can with regards to lightning safety and promptly move to a safe location in the event of lightning or severe weather.

How Unusual Was the Storm That Produced the Hildale Flood?

A critical question pertaining to the meteorology of the Hildale flood is how unusual was the storm that triggered it.

I'm going to provide some preliminary analysis here based on radar precipitation estimates.  I want to emphasize preliminary because there are a host of issues regarding radar precipitation estimates that will ultimately need to be explored in the coming weeks.

The image below shows the estimated storm-total precipitation in the Hildale area for the period ending at 2301 UTC (5:01 PM MDT).  All but about 0.1" of this total was produced during the flood period from 2000–2300 UTC (2–5 PM MDT).  The black square is located in the upper reaches of Maxwell Canyon along the axis of maximum precipitation and just north of Hildale.  The greatest estimated precipitation accumulation is actually southwest of Hildale.  Amounts in the area generating the flood are around 1.5 inches.

The bar chart below shows the storm-total estimated precipitation on a scan-by-scan basis.  There are two periods of heavy precipitation.  The first from 2007–2029 UTC (2:07–2:29 PM), which produced 0.88 inches of estimated precipitation, the second from 2218–2237 UTC (4:18–4:37 PM), which produced 0.52 inches of estimated precipitation.  In the case of the latter, most of that precipitation fell in a 10 minute period from 2227–2237 UTC (4:27–4:37 PM).

From this we can extract the maximum precipitation rates, with some adjustments when necessary to account for the mismatch with the time between radar scans:

5 min: 0.4 inches (2227–2232 UTC/4:27–4:32 PM)
10 min: 0.53 inches (2007–2016 UTC/2:07–2:16 PM), adjusted from 9 min accumulation of 0.477 inches
15 min: 0.72 inches (2011-2025 UTC/2:11–2:25 PM), adjusted from 14 min accumulation of .67 inches
30 min: 1.21 inches (2007–2029 UTC/2:07–2:29 PM), adjusted from 22 min accumulation of .885 inches

More difficult is adjusting the total precipitation.  Collectively, the total precipitation is 1.4 inch over a period of 3 h and 30 min.  Thus, I'll use 1.2 inches and 1.4 inches as a range for the 3-hour accumulation.

We can then compare these amounts to return intervals for the Hildale area that I obtained from the NOAA Precipitation Data Frequency Server.  WIthin the ranges of statistical confidence, these amounts have return intervals of 10-50 years depending on duration period.  Keep in mind that return interval is a misleading term.  For example, a 1 in 25 year accumulation doesn't happen every 25 years, but instead has an estimated likelihood of occurring in any given year of 1 in 25.

These numbers are a bit lower than you may have heard in the news where the rainfall was described a 100 year event by the National Weather Service.  They may have good reason for a rarer event estimate. First, there are a number of algorithms to estimate precipitation using radar data and they may be using a different approach than the one I am using above that they feel is more appropriate.    Second, the data I'm using above is somewhat lower resolution than what they use in real-time.  It could be that a more intense maximum would be evident in higher resolution data.  Finally, they could be using a different approach for calculating return intervals as this is another source of uncertainty.  These are issues to address in the coming weeks.

Some additional food for thought.

First, while we can calculate return intervals for precipitation rates, the real question is how anomalous was the flooding that occurred in Hildale.  That's a more difficult question to answer given the paucity of streamflow data at that location and the rare nature of these events.  This might be a topic for a future post, but I'll probably move on to other things.

Second, I've focussed on the peak precipitation rates above, but the event featured two periods of high intensity separated by a short period.  One can use a 3-hour total accumulation as I've done above to account for this, but how unusual is it to have to short periods of intense precipitation occurring within 3 hours and how does that ultimately affect the runoff?

Third, it is important to remember that the return intervals (or better put the odds of an event in any given year) are for a point.  Monsoon convection is highly localized.  Precipitation rates like those above might be rare at any given location, but they are quite likely to happen somewhere in southern Utah in any given monsoon season.  For this reason, I don't consider the Hildale precipitation intensities to be all that unusual, even if they led to an unusual flood by recent human experience in the Hildale area.

Triggering of Convection over the Central Wasatch Today

Pretty nifty loop below showing the very persistent triggering of convection over the central Wasatch as the main precipitation band approached from the west.  Note how radar echoes extend downstream all the way to the UT-WY border.

Monday Was the Worst Weather Day in Utah History

In terms of loss of life, the Hildale Flash Flood was the worst weather-related disaster in recent decades, but was it the worst in Utah history?

It depends.

Tragically, 12 are confirmed dead in the Hildale Flash Flood, with one missing.  Records of weather disasters are better in recent decades but than in the distant past, but there is evidence of at least one weather-related disaster in Utah history that was worse.  On February 13, 1885, avalanches killed 15 in what was then the mining community of Alta, Utah.  This is documented in an article by Mark Kalitowski entitled The Avalanche History of Alta, which appeared in the December 1, 1988 issue of The Avalanche Review.

C. R. Savage photo of Alta, UT on July 3, 1885 following a winter in which avalanches nearly destroyed the town

However, late yesterday we learned of another tragic flash flood catastrophe that occurred on Monday in Zion National Park's Keyhole Canyon.  Four are confirmed dead, with three missing.  That increases the count of confirmed fatalities in the two events to 16, which likely makes Monday the worst weather day in terms of loss of life in Utah history.

Whether or not the Hildale and Keyhole Flash Floods are the same disaster depends a bit on one's perspective.  Keyhole canyon is only about 15 miles north of Hildale.  Without better time lines of when each incident occurred, it's difficult to ascertain if the same convective cell produced the floods that washed away the victims in both areas (I suspect not, but more careful analysis is needed).  On the other hand, even if the generating cells were distinct, they were both associated with the same large-scale system, so some people might combine them into a single event.

If you are wondering what the most expensive weather-related disaster is, it is probably the 1983 Thistle landslide, which dammed the Spanish Fork River, inundating Thistle and cutting off a major rail line and nearby state highways.

Source: http://geochange.er.usgs.gov/sw/changes/natural/elnino/

The USGS suggests that the total direct and indirect costs of the slide were $688 million in 2000 dollars.  At the time, it was the most expensive landslide in US history, but I wonder if has subsequently been topped by the 2014 Oso slide in Washington.

You'll notice that I use the term "weather-related".  Most Utah "weather" disasters aren't produced exclusively by meteorology, but a combination of meteorological, geological, hydrological, and/or human factors.  An unfortunate aspect of Monday's fatalities is that they occurred despite apparently good forecasts and warnings.  Similarly, the challenges in avalanche safety involve avoiding heuristic traps, ensuring your perception of risk matches the reality, and then making good decisions (e.g., McCammon 2002).  

Striving to produce more timely and more reliable forecasts is what we do as meteorologists, but ultimately, as we look back on these events, there may be more to learn about how to minimize human loss through better understanding of the human factors.  Following the 1997 Antelope Canyon flood disaster, which killed 11, significant improvements in flash flood forecasting and communication were made that I'm sure have saved lives.  At issue as we look back on Monday's events is whether or not further improvements can be made.  An optimist might say yes, a cynic no, but the only way to find out is to study and learn.  

Convective Line Blasts Across Mt. Timpanagos

A quick post on today's storm, which moved slowly through the Salt Lake and Utah Valleys and produced some urban flooding.  Being a mountain meteorologist, however, my thoughts are always on the high terrain and one thing that impressed me is how the convective line moved across the Wasatch Range, especially the imposing bulk of Mt. Timpanogos, like nothing was there.  We're talking a barrier that is over 2000 m high.

It would not have been pleasant to be on Mt. Timpanogos when that went through.  Lightning, heavy precipitation, and probably some snow, hail, and graupel thrown in for good measure.

Tragedy Strikes Hildale Utah

A terrible tragedy struck Hildale, UT yesterday afternoon.  Reports on ksl.com this morning suggest that at least 16 people were caught in a flash flood just north of the city, with eight confirmed dead and five still missing.

The topo map below provides some perspective on the local terrain.  According to KSL, the vehicles had stopped in Maxwell Canyon, which extends northwest from the thumbnail and were swept into Short Creek, the main drainage that runs past Hildale and ultimately southwest to Arizona highway 389 south of the map.  KUTV reports that the cars were swept away near the crossing of Canyon Street and Williams Avenue.  I can't find the latter on Google Maps, but the former is near the thumbnail.

The time of the flood is a bit uncertain.  The KSL report says a bit before 5 PM MDT (2300 UTC).  Media reports last night suggested a bit after 4 PM (2200 UTC).

The radar loop below shows two periods of heavy rainfall that may have contributed to the flash flooding (the Hildale area is identified with a brown box).  The first sweeps over the area from about 2000–2030 UTC (2:00-2:30 PM MDT), the second from about 2215–2300 UTC (4:15–5:00 PM MDT).   There is a possibility that the two storms provided a one-two blow that resulted in a more substantial flash flood event than if either had occurred in isolation.

Radar estimated precipitation shows a swath of rainfall ≥ 1.25" Maxwell Canyon and Short Creek areas through 5 PM.  Greater values, exceeding 2 inches are found to the southwest.  Note that there are uncertainties that can affect both the amount and location of the radar precipitation estimates, so further analysis will be needed to gain a better estimate of how much precipitation fell in the drainages that generated the flash flooding.  Analysis is also needed to ascertain the importance of precipitation intensity on the flooding of this event.  The totals below occurred primarily in two bursts rather than steadily over a multihour period.

An unfortunate characteristic of the geology of southern Utah is that the precipitation produced by monsoon convection can be concentrated into severe flash flooding that strikes quickly.  Flood waters can overtop or destroy banks along flood channels rapidly.  This serves as a tragic reminder of the importance of staying well clear of washes, slot canyons, and flood waters when heavy precipitation is in the area.

Addendum @11:10 AM:

The NWS storm report issued this morning (below) suggests that flooding produced by the first cell produced the fatalities.  Note the 3:18 PM event time.

Thus the timeline of events is still uncertain.  It could be the fatalities occurred with flooding from the first cell, with the flooding exacerbated by the 2nd cell (which would have further complicated rescue and recovery efforts).  Careful analysis of the timeline will be needed to nail the details down.  

The Holy Grail of Nowcasting

Shortly after 4 PM today, a thunderstorm moved over the University of Utah, providing a nice downpour of rain with some embedded small hail just to add insult to injury for anyone walking around campus.

Could someone have issued a nowcast with 30 minute lead time that this storm was going to hit campus?

No.

The loop below shows that the storm blew up rapidly in the central Salt Lake Valley and moved northeast over the University of Utah in only 15 min.  The first echoes produced by the developing cell were observed at 2149 UTC (3:49 PM MDT), with rain beginning on campus at about 2205 UTC (4:05 PM MDT).

There is no human or computer-based forecast tool available today that can reliably forecast the development of a storm cell from nothing on such short time scales.  Very-short-range forecasting, known as nowcasting, is based primarily on the linear extrapolation of the motion of existing radar echoes (there are some exceptions, but for the most part, nowcasting is based on linear thinking).  It's extremely difficult to anticipate the intensification or decay of storm cells in such short time periods.

What about computer models?  Not at the present time.  First you need a really big computer, bigger than anything used for operational forecasting today, because you need a lot of resolution.  Then, you need to ability to rapidly assimilate radar and other observations into your model.  This is also extremely difficult and we are in the early stages of figuring out how to do this effectively.

Essentially, developing computer models that can provide detailed and reliable forecasts of convective storms at short lead times represents the holy grail of nowcasting.  This is an area of active research in the atmospheric sciences and perhaps we will make some inroads in the coming years and decades, if not for storms like the one above, perhaps for  severe convective phenomena like derechos and supercells.  For a look, click here.

Smoke from California Fires

The past few days have been beautiful in northern Utah, but a shift in the flow late yesterday and overnight has brought a return of smoke to the Salt Lake Valley.

Below is a comparison of yesterday morning (top) and this morning (bottom).  Things aren't too bad yet, but there's been a noticeable decline in visibility between the two days.

The primary source of the smoke appears to be California, although we may have some from Oregon or Idaho mixed in just for good measure.  The MODIS image below shows the leading edge pushing into northern Utah late yesterday.

Dealing with a little smoke is a minor inconvenience for us.  One California fire, the Butte Fire, has grown rapidly from 100 acres on Wednesday to 65,000 acres this morning with 132 structures destroyed.

Ah, September!

September is one of my favorite months in Utah and today was simply a beautiful day.  My plans were blown out of the water this morning when I was driving down I-215 and found out that Big Cottonwood was closed.  Then I thought I'd do a hike in Mill Creek, but it was blocked by a fire!  The intermediate option was Neffs Canyon, which requires considerable pain and agony to get to the good stuff, but once you are in the upper canyon, it's simply beautiful.

A rough, steep ascent of a bit over 2000 vertical feet puts you in the meadow and the start of the upper canyon.  Plenty of color today.  It seems a bit early.  Perhaps a good sign?  Let's hope so.



There are many bird's-eye views to be had of Salt Lake City in upper Neffs.  This one is from near the divide with Thaynes Canyon, which drops into Mill Creek Canyon.

More beautiful colors in the upper canyon along the divide between Neffs and Big Cottonwood.

I ended up bagging peak 9642, which was one of two minor peaks along the Neffs-Big Cottonwood Divide that I hadn't previously summited (Hobbs is the other).  The views into Big Cottonwood are spectacular and even after spending last week in the Alps, looking into the lower canyon was pretty damn impressive.

A couple photos to stimulate thoughts of backcountry skiing.  Gobblers and Raymond.

Mineral, Mill-B, Broads, Stairs Gulch.

Starting to get excited....

What Was in the 9/11 Smoke Plume?

Photo: Stan Honda, AP

It has now been 14 years since 9/11.  We all have deeply personal feelings and views of the confusion, fear, and tragedy of that day and the days and weeks that followed.

Amongst my most vivid memories are the efforts of the first responders in the days following the attack to find survivors or just bring closure for those who had lost loved ones.  It was a heroic effort in an extremely difficult environment, with exposure to smoke and dust that was emitted from the smoldering pile long after the collapse of the towers.  

A team of scientists led by noted aerosol research Tom Cahill and including University of Utah Professor Kevin Perry collected and analyzed samples of particulate matter from very near the collapse site, with their results summarized in article entitled "Analysis of Aerosols from the World Trade Center Collapse Site, New York, October 2 to October 30, 2001", which appeared in the journal Aerosol Science and Technology in 2004 (click here for free access to the article).  

During the period investigated, plumes were typically elevated away from the collapse site, so exposure was greatest to workers at the collapse site.  As noted by the authors, "while the impacts of the plumes at sites away from the WTC collapse pile were episodic, that is not true for workers at the site itself." At the collapse site, concentrations of very fine particles (less than 1 micron in diameter), which can penetrate deep into the lungs, were extraordinarily high, described by the authors as "the highest we have recorded in a variety of studies, including on the ground in the oil fields of Kuwait, June 1991."  In addition, the composition of the dust and smoke produced by the smoldering collapse site was substantially different than that commonly associated with air pollution episodes, such as those we experience along the Wasatch Front.  Very fine particles consisted of sulfuric acid, polycyclic aromatic hydrocarbons (PAHs) and their derivatives (produced by incomplete fossil fuel and organic matter combustion), and glasslike silicon containing aerosols.  Larger particles included powdered concrete, gypsum from dry wall, glass shards, and man-made metals.  

It is clear that the heroic first responders at 9/11 were exposed to an unusual acrid mix of smoke and dust.  This is a major reason for elevated rates of respiratory problems amongst first responders and justifies careful monitoring for certain forms of cancer and other diseases.  Although linkages between dust and smoke exposure and cancer and other diseases are often difficult to establish, there is strong justification for ensuring that the 9/11 first responders receive more-than-adequate health support and treatment for their health challenges.

This Summer Was Surprisingly Comfortable, but Unusually Hot

Do you feel like this has been a remarkably pleasant summer?  It didn't seem as hot as years past. 

I feel the same way, but the data doesn't support that view, at least if you look at the average temperature.  For the entire summer (June, July, and August), the average temperature was 77.5ºF, making it the 8th warmest on record at the Salt Lake City International Airport.  

Source: NOAA Regional Climate Centers

What gives?  Well, timing is everything.  If you want to have an enjoyable summer with an overall temperature that is unusually warm, it's best to stick the warmth in June, which is a climatologically cooler month than July or August.  That's exactly what happened.  June was easily the hottest on record.  

Source: NOAA Regional Climate Centers

However, July, which is climatologically hotter, was instead cool relative to the recent past (i.e., since about 1998).  

Source: NOAA Regional Climate Centers

Similarly, compared to the past decade or so, August was perhaps a shade below the recent average.  

Source: NOAA Regional Climate Centers

So, June really skewed the summer statistics, but heat in that month is not as uncomfortable as July and August.  In fact, if you look at the average for each month this year, they were all right around 77.5ºF, and that is manageably comfortable in Salt Lake City.  

If we had instead put the anomalous warmth in July, our perspectives would be different.  Timing is everything.  

Weird Stuff on Radar

Perhaps I'm just suffering from jet lag, but I could use an assist from a radar guru out there to help decipher this morning's radar loop.

As shown in the loop below, things this morning start innocently enough with wide spread clear-air returns.  As the morning progresses, however, some blobs of high returns persist, in some cases generate over the Great Salt Lake, and move downstream with the large-scale flow.

What are these blobs?  I doubt they are meteorological as there is nothing to be seen on satellite.  Dust or birds?  I've looked at the some of the additional fields provided by the polarimetric radar, including correlation coefficient, and nothing obvious jumped out at me, although I confess my experience examining bugs and insects with radars is limited.

Any thoughts?

European Tidbits

After a weekend of sightseeing, I'm back in the US, but not quite back to Salt Lake City.  For my students who are reading this, yes, I should be back in time to teach class.  For the rest of you, here are a few photos.

Bicycles are everywhere.  The photo below was taken at the train station in Salzburg.

Surprisingly, few people wear helmets.  I think that's one custom I won't adopt.  

Speaking of alternate forms of transport, I'm sure this horse is grateful for the waterproof and breathable hard shell.  

Austria: Where the meat is meat and the vegetables are wrapped in bacon.

Schnee!  Yup, winter is coming. 

Our travel to Munich followed the main corridor of refugee migration to Germany.  Mrs. Powder Professor was able to lend a hand to one extremely polite Syrian family.

On the train to Munich, I saw one refugee in tears.  Heartbreaking.

Our train in Munich was met by the Polizei, who segregated the refugees into a different area.  All was peaceful and this process occurred without incident.  Their future, however, remains uncertain.