Friday, September 30, 2016

Weather Observations on the Salt Flats

The Bonneville Salt Flats, a remarkable geological wonder, in July 2008
The Bonneville Salt Flats are a remarkable geological wonder and well worth a visit and a hike of a nearby mountain.  Most people drive through them at a high rate of speed trying to get to Nevada or California as quickly as possible, but even a quick stop reveals a world completely different than any other you have experienced.

The Bonneville Salt Flats are perhaps best known for land-speed events that take place on the hard salt crust to the northeast of Wendover.  In recent years, however, that salt crust has thinned and degraded, forcing cancellations or restrictions in speed events and sparking controversy concerning management of the salt flats.

Brenda Bowen, a professor of Geology and Geophysics and director of the Global Change and Sustainability Center at the University of Utah, is leading a 3-year study to improve understanding of the Salt Flats and their recent change (see this Scientific American article for more information).  Yesterday, some intrepid members of our MesoWest team installed a weather station on the Salt Flats to help with the effort, and returned with some great photos.

These photos illustrate the highly dynamic nature of the Salt Flats.  It's not uncommon for portions of the salt flats to be covered with water, but thanks to recent storms, the coverage and depth is quite high.

Click here to access weather observations from the station.

Thursday, September 29, 2016

Are Recent Bad Snow Years at Alta Due to Climate Change?

Since the 2010/11 ski season, the Wasatch Range has experienced below average snowfall years.  Data from the Utah Avalanche Center shows an average seasonal (October-April) snowfall at Alta of 497 inches since 1945/45, but over the last five seasons we've received only 330, 383, 358, 268, and 393 inches.  

I am often asked if these poor snowfall years are due to climate change.  

The answer is no.  

Many people are surprised to hear this, but here's why I do not think the recent poor snowfall years at Alta are due to climate change.  

First, the base of Alta is at 8500 feet, well above the freezing levels of most storms during the winter.  While it is possible that you can experience a brief rain-on-snow or drizzle-on-snow event at Alta, nearly all of the precipitation that falls there during the cool season falls as snow.  The low numbers over the past five years are not due to more wintertime precipitation falling as rain, but instead less precipitation.

Second, at that elevation, the fraction of precipitation that falls as snow during the cool season is relatively insensitive to another 1ºC (about 1.8ºF) of warming.  The image below from my book Secrets of the Greatest Snow on Earth and based on work by Leigh Sturges and John Horel here at the University of Utah shows the percentage of snow that currently falls as snow that would instead fall as rain if the climate were 1, 2, 3, or 4ºC or warming.  Alta is blessed with high altitude and thus snowfall at that elevation is less sensitive to the first couple of degrees of warming.  

Percentage of snow that would instead fall as rain with 1, 2, 3, and 4ºC of warming
Third, we're not really sure if the cool-season precipitation in northern Utah will increase or decrease with global warming.  Some model projections suggest we'll be drier, others wetter.  For all future emissions scenarios most climate models lean to a wetter future (the blue color bars below indicate the average winter precipitation change amongst models, the whiskers the middle 50% of the projections, and the dots the middle 80%).  Bottom line is that at present there isn't a strong reason to expect global warming to cause a decrease in wintertime precipitation, although it can't be ruled out.  

Projected seasonal and annual precipitation change over the central Wasatch and surrounding region for the 30-year periods centered on 2040 (2026–2055), 2060 (2046–2075), and 2085 (2070–2099) relative to 1976-2005.  See Fig. 6 for emissions scenarios.  Winter is December through February, Spring is March through May, Summer is June through August, and Fall is September through October.  Bars show the average change across the model runs, whiskers the range between the 25th and 75th percentile of the model runs, and dots the range between the 10th and 90th percentile of the model runs. Source:
Instead, I see the recent poor snow years at Alta as largely a reflection of climate variability instead of climate change.  Shifts between wet and dry periods are evident in both the instrumented and paleoclimate (e.g., tree ring) records.  The causes for these shifts are not well understood and I hesitate to speculate as to the causes of recent poor snow years, but my view is that the climate-variability dice simply have not rolled in our favor the past five seasons.

That being said...

This analysis is for Alta, a high elevation site in the Wasatch Range.  It does not mean that climate change is not influencing snowfall and snowpack at lower elevations (e.g., base of PCMR, Mountain Dell, etc.) or that Alta and the upper elevations of the Wasatch will not suffer pain and agony in the future.  It also doesn't mean that it isn't getting warmer in Utah (it is).  Different snow and climate measures (e.g., temperature, snowfall, snowpack, etc.) respond differently to climate change depending on elevation, aspect, and regional and local climate (for example, see Western Snow Trends and Global Warming: Part I and Part II).   When it comes to snow, we simply need to be careful about generalizing across all climates, elevations, and aspects, and cautious about conflating climate variability with climate change.  


Shortly after posting this article, I remember I've written about this topic previously.  See Is This a Long-Term Trend.

Tuesday, September 27, 2016

Degraded Air Quality in Late September

Dude, I can barely see the Oquirrhs!
I hope this isn't a harbinger of things to come, but there is actually an elevated air quality event underway over Salt Lake with some characteristics similar to what we see during the winter.

As everyone is aware, late last week and last weekend and deep upper-level trough and associated cold-air intrusion rumbled through Utah.  The maximum temperature on Friday was only 51ºF.

As the trough moved downstream, a high-amplitude upper-level ridge built rapidly over the western United States.  This led to significant warming in the mid- and upper-levels of the atmosphere at a rate faster than solar heating could warm the colder air near the surface.

As a result, yesterday afternoon, the atmosphere over the Salt Lake Valley was capped by a series of stable layers.  The lowest of these stable layers was only a few hundred meters above the valley floor.

Source: Storm Prediction Center
Weather camera images yesterday showed a clear layer of gunk over the Salt Lake Valley with a pronounced top.  Look toward Lone Peak in the image below.

Source: MesoWest
And the buildup of pollution is evident in the time series below, which shows that we are now in the moderate air quality category for PM2.5.

Such conditions are a bit unusual for September, but there are probably three issues at play.  The first is the depth of the weekend trough and strength of the cold air, followed by the building of a strong ridge and associated rapid warming aloft.  Second, we received a great deal of rain Friday and Saturday, leading to high soil moistures.  As a result, a portion of the sun's energy that often would be partitioned into heating the ground and atmosphere is being used for evaporation and transpiration.  Finally, we simply have to realize that we have more people living here and driving farther than every before.  I suppose there might also be some smoke sources out there, although I'm unaware of any major incidents in the immediate area.


Monday, September 26, 2016

Looking Back at Summer

White capped mountains signal that fall is finally here
Meteorological summer ended earlier this month.  Astronomical summer ended on Friday.  Although temperatures will rebound some this week, summer is finally over.  Good riddance.  Don't let the door hit you in the butt on the way out.

The climate numbers for summer (June–August) were released last week by the National Centers for Environmental Information.  You already know that this summer was the 2nd hottest on record at the Salt Lake City airport, but how did things go statewide?

Well, it was a hot summer by old-timers standards, but not for the young.  With a statewide average temperature of 71.6ºF, this summer was tied for only the 5th warmest on record.  However, the four ahead of this year, as well as the other years tied with it, have all occurred since 1994.  

Source: NCEI
So, compared to the climate of the latter 19th century and most of the 20th century, this was a very hot summer statewide.  Compared to the climate since 1990, it was hot, but not exceptionally so.

Globally, Boreal summer (June–August, summer in the northern hemisphere) was the hottest on record, although from a statistical perspective, it's probably in a dead heat with last summer.

Source: NCEI
For the year to date, however, 2016 is easily the front runner.  It's a near virtual lock for hottest year on record unless something truly surprising or catastrophic happens in the last 4 months of the year.  

Source: NCEI
Public Service Announcement:

With the Presidential debate on tap for tonight, a reminder to everyone that there is still time to register to vote in the upcoming election.  If you live in Utah, you can register to vote at this web site

Friday, September 23, 2016

Severe Convective Storms Yesterday, Mountain Snow Today and Tonight

Wow, what insanity.  After a meteorologically boring summer, fall comes in with a bang.  I'll go into rapid-fire mode for this one:

1. Ogden Supercell?: Yesterday afternoon, a long-lived thunderstorm with supercell-like characteristics developed near Dugway Proving Ground and tracked to the Ogden Area over about a 2.5-hour period.  It was a right-moving storm, in that it was moving somewhat to the right of the steering-layer flow and the tracks of other convective cells.  This is common characteristic of supercell thunderstorms, which are long-lived thunderstorms with rotating updrafts (note: there are also left-moving storms, but they are less common).  The Doppler velocity signature of the storm, however, wasn't especially pronounced, so I'll leave it to the severe convective storms experts to ascertain whether or not the storm qualifies for Supercell status.

2. Severe straight-line winds.  The storm brought strong straight-line winds to the Ogden area and the northern Wasatch Front.  Here's a remarkable video of the straight-line winds from Antelope Island:

Colleagues here in our mountain meteorology group installed a sensor on the playa just east of Antelope Island earlier this summer that collects data every minute.  The passage of the storm's gust front was accompanied by a nearly instantaneous drop in temperature of more than 20ºF, wind shift from SSE to W, and a wind gust of 75 mph.  

3. Ogden tornado. The storm also spawned a tornado south of Ogden, which was captured in a video posted by Neil Essig on YouTube.

3. Tornado Damage Scale.  I have been asked by a few people how strong the tornado was.  Tornadoes today are classified using the Enhanced Fujita (EF) Scale, which is an updated version of the Fujita Scale originally developed by Ted Fujita, a meteorological pioneer in many areas, including forensic investigations of tornadoes and severe storms.

Source: NWS
Other than to say it was probably an EF-2 or lower tornado, I hesitate to speculate on the tornadoes EF rating based on videos and photos, especially given the wide-spread straight-line winds observed in the area.  Careful site surveys are needed to ascertain the characteristics of the damage path, the degree of damage, and to separate damage from the tornado and the straight-line winds.

5. Try to avoid saying it was "only" and EF-0, EF-1, or EF-2 tornado.  I used to tell people that I really wanted to see a tornado, and then I saw the August 11, 1999 tornado move through the Avenues.  I was completely naive about the damage that a "small" tornado could do.  Like a surgical knife, it cut through the neighborhood, doing considerable damage along a path one or two houses wide, with nearby homes mostly unscathed.  For those impacted, "only" and EF-0, EF-1, or EF-2 makes little sense.  Their homes and lives have been upended.

6. Overnight snow.   Yup, the white stuff has arrived in the upper elevations of the Wasatch Range.

Source: Alta
The Alta-Collins automated sensor shows a total snow depth of 7", but don't get too excited about that as it was at 4" when there was no snow on the ground prior to the storm.   You can see this in the 5-day time series below.  Accumulations so far at that elevation (9700 feet) probably are around 3 inches.  Not quite enough to break out the new skis...

7. Future snow.  The circulation center for the system is currently moving over us and precipitation is occurring mainly to the north and west of the Salt Lake Valley.

If you feel disappointed, don't despair, we will see more snow today and tonight.  I'm going to go for another 5-10 inches through 6 am tomorrow morning at Alta-Collins.  There's a chance for more, and indeed there were 2 members of last night's NCAR ensemble that pumped out more than 1.5" of water today and tonight for that area (which would probably give us something like 12-18" given the high densities we are dealing with), but 5-10" is the most likely range.  

Thursday, September 22, 2016

Today's Thunderstorm Potential

Editors Note: Post has been updated to include correct SPC categorization of thunderstorm risk, which was erroneously called "severe" in the original.

Yesterday evening, the northern portion of the state won the thunderstorm lottery with strong storms developing over the West Desert and Great Salt Lake and moving across the Northern Wasatch Front, Box Elder County, and Cache County.

Strong wind gusts were reported at a remote observing site east of Snowville (78 mph) and the Logan airport (61 mph).  Lightning data shows numerous cloud-to-ground strikes across that area, but none south of Ogden or over the Salt Lake Valley.  

The National Weather Service watches, warnings, and advisories map is lit up statewide today.

Source: NWS
Issues of concern for today include flooding and flash flooding, high winds, and severe thunderstorms.  The Storm Prediction Center has upped our severe thunderstorm risk from severe marginal to slight.

Source: SPC
The weather situation this morning shows that we are currently sandwiched between two precipitation bands, one to our west that is near a surface trough (not shown) and the other to our east.

During the course of the day today, the surface trough is expected to progress slowly into northwest Utah, while the precipitation band to our east remains roughly between Salt Lake and Vernal.  The big question mark for our weather is whether or not something will bubble up in the intermediate dry slot.  The HRRR shows this as a possibility.  Note the strong simulated reflectivity cells between the two precipitation bands early this afternoon.  

However, these types of storms are very chaotic and we're just going to have to see how this plays out.  

This evening the surface trough will approach Salt Lake, and should be accompanied by showers and thunderstorms.  It's not the usual rapidly moving cold front.  It sort of stalls over northern Utah as the upper-level trough moves through and eventually the so-called "wrap around precipitation" moves across the state.  Tonight through tomorrow night looks quite unsettled and the mountains will get snow.  I need to run to class, however, so discussion of that will need to wait until tomorrow. 

Wednesday, September 21, 2016

Severe Convective Storms Possible

Forecasts haven't changed much overnight, except that moisture is streaming into northern Utah a bit earlier than expected today, increasing the potential for scattered thunderstorms this afternoon.

Over the years, I've learned to pay careful attention to weather situations that involve the interaction of upper-level troughs in the midlatitude westerlies with monsoon moisture as this often leads to the development of severe convective storms.  The pattern through Thursday night fits this description and demands this careful attention. 

Patterns of this type have the three key ingredients for convective storms: Instability, Moisture, and Lift.  With regards to instability and moisture, I've cherry-picked a couple of soundings from the 0600 UTC NAM forecast for Salt Lake City (below).  In these soundings, plotted on a thermodynamic diagram known as a Skew-T, the forecast environmental temperature and dewpoint are displayed as red lines (with temperature > dewpoint and the right-most line).  The grey line is the temperature of a hypothetical surface parcel if lifted "dry" to the point of saturation or cloud base (grey circle) and then "moist" above that with water vapor condensing and releasing heat.  The hatched area shows how much warmer this parcel would be than the environment and equates to the Convective Available Potential Energy (CAPE) of the parcel, a measure of the amount of energy the parcel would acquire if it were lifted in this fashion.  Although there are problems with this theoretical approach, the magnitude of the CAPE provides a rough guess at the strength of the instability if convective clouds can form.  
The plots above show CAPE values of 709 and 957 Joules.  For our part of the world, those are pretty high forecast values.  In addition, the precipitable water, a measure of how deep the water would be if you condensed all the water vapor out of the atmosphere, is 27.5 and 24.1 mm (roughly an inch).  Again, those are fairly high values for our part of the world, especially in the latter half of September.  

So, we have instability and moisture, but we also have lift.  First, we will be downstream of the upper-level trough axis, an area typically associated with large-scale lifting.  We also have a nearby cold front and in all likelihood a variety of smaller-scale surface boundaries as the upper-level trough moves in to initiate convective storms.

So, three boxes checked.  However, we also have some wind shear, which helps storm organization. 

Based on these ingredients, the Storm Prediction Center has placed much of central and eastern Utah in a Marginal Thunderstorm Risk category from tomorrow morning through Friday morning.   Salt Lake and Provo are on the edge of the Marginal Threat Area.  

A marginal risk means isolated severe thunderstorms (Note: showers and non-severe thunderstorms will be greater in coverage) that are limited in duration and/or coverage and/or intensity.  The main threats from these storms are strong winds and small hail.  

With regards to rainfall, through tomorrow afternoon, the NCAR ensemble is generating the greatest average precipitation, maximum precipitation, and highest probabilities of precipitation greater than 1" or 2" between Salt Lake and Vernal.  
That doesn't mean, however, that other areas won't see some showers or thunderstorms.  Let's see how this comes together and keep an eye on official forecasts, watches, and warnings from the National Weather Service

Tuesday, September 20, 2016

Summary of the Action over the Next Few Days

Some weather excitement is on the schedule for later this week as the first significant mid-latitude trough of the fall taps into monsoon moisture to give us a wild ride.  

Phase 1 covers today and tonight, although northern Utah isn't really in on the action.  An upper-level trough dropping into the western U.S. helps to coax a monsoon surge and the remnants of Hurricane Paine (doesn't that just roll of the tongue) into the southeast US, with showers and thunderstorms affecting a broad area from SoCal and BaCal through southeast Utah and California.  

Although for us its "No Paine No Gain" today and tonight, the monsoon surge establishes a reservoir of moisture over the southwest that is pulled into northern Utah as the upper-level trough subsequently develops along the west coast and the surface cold front impinges on northern Utah.

Thus, tomorrow (Wednesday) will be at transition day as moisture streams northward.  After that, I'll describe the weather as "highly unsettled" as showers, thunderstorms, and a slow moving front impact northern Utah Wednesday night, and Thursday.  I hesitate to attempt to forecast gory details as there is a complex stew of ingredients coming together.  I do know that the weather often gets interesting around here (heavy rain, strong thunderstorms, etc.) when midlatitude troughs toy with monsoon moisture in the fall, so I look forward to seeing how things play out.

Amongst the new tools for us to examine on this winter are downscaled forecasts from the Short-Range Ensemble Forecast System (SREF).  Forecasts from the 26-member SREF for Salt Lake City show the activity picking up Wednesday evening and night and continuing into Friday.  Variations in the slopes of the accumulated precipitation lines show uncertainties in the timing of precipitation and the wide range through the period (from about 0.3 inches to 1.7 inches) shows uncertainty in the total accumulated precipitation for this portion of the storm.
Nevertheless, if my quick math is correct, we've had only 0.43" of rain in the past 3 months and it looks like we have a good shot of exceeding that, perhaps by a lot, by Friday afternoon.  For what it is worth, I moved my automated sprinkler system to the "off" position this morning.

The most recent model forecasts call for snow levels to drop Thursday night.  Right now it's looking like snow at times in the upper Cottonwoods through Friday and possibly Saturday.

Yesterday's GFS was calling for something like 28" of snow for Alta.  Although it's easy to be seduced by a forecast like that, remember it's a long-range forecast and the GFS has been prone to overforecast since it was upgraded to an effective grid spacing of 13 km.  In fact, I find the precipitation produced by the GFS to be of limited value (in the summer, it is nearly unusable!).  The NAEFS ensemble from last night shows most members in the 5-10" range for Alta, with a few larger-accumulation outliers.

Further fueling anticipation is that this is the first possible accumulating storm of the year.  Let's keep those emotions in check and see how things look in a couple of days.  

Monday, September 19, 2016

Most Exciting Week in Months on Tap

Yesterday evening served up the quintessential "Spectacular September Sunset."  Golden hues everywhere.  My old cell phone doesn't do it justice, but if you were out, you know what I'm talking about.  

The computer models are suggesting that this coming week will be the most exciting meteorologically in months.  The main culprit is a midlatitude upper-level trough that will develop along the west coast over the next couple of days.  First it will toy with the remnants of Hurricane Paine and bring a pronounced monsoon surge into the southwest (missing us though). 

Then, as the trough amplifies and migrates eastward, a major precipitation event will develop over much of the interior west with showers, thunderstorms, frontal precipitation, and the like.  Very interesting!

The pattern above suggests a very active period later in the week with the bottom falling out temperature wise.  We haven't seen anything like this in months and will take a closer look as the system approaches.  

Friday, September 16, 2016

Personal Reflections on Advocacy

I am often asked why I am not more actively involved in advocacy regarding climate change.  This is a complicated issue and I'd like to share some personal perspectives.

I think it is important for scientists to share their knowledge, understanding, and perspectives with the public.  In doing so, striving to describe what we know as accurately as possible is paramount.  As Nobel Prize winning physicist Richard Feynman once said:
"The only way to have real success in science is to describe the evidence very carefully without regard to the way you feel it should be (my emphasis)."
This doesn't mean that scientists need to be dispassionate or lack political views and perspectives.  I write and give talks on climate change and sometimes express strong viewpoints.

It also doesn't mean that scientists are infallible.  Science is a human endeavor and errors and mistakes occur.   Commitment to the truth means that results are checked and triple-checked and that retractions and corrections are made when errors and mistakes are discovered.   It means doing your best when writing and speaking to be accurate.

Finally it doesn't mean that scientific communication is unbiased.  Even Mr. Spock was biased.  Watch a few Star Trek episodes and this will become clear, although you can hardly fault him.  He was half human.   Human interpretation is affected by personal experience and knowledge.  I strive to be impartial, but anything I write or say will reflect my experience and understanding.  One reason why panels and committees are are often used to summarize of scientific knowledge is to limit the influence of personal biases.

So, my goal in science communication is to be an entertaining version of Mr. Spock, describe what we know as accurately as possible, and limit the influence of personal bias.

That being said, what I write and say on this blog, in my book, or during talks is a form of advocacy.  The Wikipedia definition of advocacy is "an activity by an individual or group which aims to influence decisions within political, economic, and social systems and institutions" and yes, I do hope to influence your decision making.  Knowledge is power and after learning about weather and climate, I hope that you use it.

I am, however, reluctant to advocate for a specific climate policy or in areas outside my scientific expertise.  Actually, I think I do advocate for reducing greenhouse gas emissions as quickly as possible.  What I try to avoid is public endorsement of a specific policy option (e.g., carbon tax or cap-and-trade), attendance at political rallies, or alignment with specific political groups.

There are a number of reasons for this.  The first is that my background is weather and climate, not public policy, economics, or business.  My views on topics like carbon taxes, cap-and-trade, free-market economics, regulatory policy, and the like are not based on critical analysis.  When I discuss options such as these, I usually try to make it clear that my views are personal and not based on expert knowledge.

The second is that I wish to be a resource for individuals and groups regardless of political persuasion, even those who might strongly dispute my scientific reasoning and conclusions.

The third is, as Groucho Marx said, that "I refuse to join any club that would have me as a member."  When it comes to climate, the last thing I want to be is a member of a club.  I value my independence.  I like to question everything and I doubt there is a political group that I could strongly endorse.  Finally, I like to attack problems, not people.

My views on these subjects are, however, constantly evolving.  In addition, I'm no saint and I'm sure I'm sometimes hypocritical of the views shared above.  Sometimes it's hard to be human.

Thursday, September 15, 2016

The Coldest 24 Hours Since May

OK, I'm stretching the climate data a bit here, and admittedly scanned the table of maximum and minimum temperatures over the past few months awfully fast, but it appears this afternoon and tomorrow morning will offer up the lowest maximum and minimum temperatures at the airport since May.

Today the maximum temperature looks to be in the high 60s, which will make it the first day with a maximum below 70 since May 25th.  The minimum tonight looks to dip into the high 40s, making it the first day below 50 since May 26.

It feels good to be nestled in a fleece jacket!

Wednesday, September 14, 2016

Thunderstorms Bring Some White Stuff

Well, I have to admit that I was caught off guard by the coverage and intensity of thunderstorms late yesterday and overnight.  Months of drought has dulled my senses and lowered my expectations.  It was great to see rain, lightning, and thunder again, although I could have lived without the rapid, heart-pegged ascent to my house at the end of my ride as I raced an approaching storm.   Nevertheless, it was worth the price of admission.

And, we even have the first snow of the season in the high Wasatch, as caught by one of the Snowbird cams this morning.

Source: Snowbird
Looks like a dusting down to perhaps 10,500 feet or so.  A reminder that winter is coming and none too soon.

Tuesday, September 13, 2016

Last Night's Brief But Intense Dust Storm

Late in the day yesterday, a cold front pushed into northern Utah, ushering in a period of strong northerly winds and blowing dust.  The plot below shows the situation at 9 PM MDT (0300 UTC), with sustained winds on top of Fremont Island of 46 mph and strong flow across much of the Great Salt Lake and adjoining salt playa.  Strong flow also penetrated into the western Salt Lake Valley.  At this time, the area around the University of Utah was relatively protected, with lighter winds.

Source: Mesowest
Colleagues at the University of Utah are operating an observing site on the playa just east of Antelope Island.  The flow at this site was northerly to north-northeasterly for most of the afternoon, but increased dramatically at about 1900 MDT (7 PM) to about 25 mph with higher gusts.  The temperature at this time also dropped dramatically.  

Source: MesoWest
The Great Salt Lake is currently remarkably low with a great deal of exposed playa.   MODIS imagery from Sunday shows that nearly the entire northeast arm, with the exception of Willard Bay (a reservoir) and perhaps some of the wildlife refuges, as well as most of Farmington Bay, to be water free.  Vast areas around the western and northern side of the lake are also exposed.  

Source: NASA
While remote dust sources are often important during wind events in Utah, last night appears to be a case we were dealing with dust primarily from the exposed playa surrounding the Great Salt Lake.  PM2.5 levels were especially high just behind the front.  The image below shows values along the TRAX line from 8:20-9:20 PM, with a peak of over 80 ug/m3.  

Source: MesoWest
Sorry east benchers, but there was no escape for you.  Peak concentrations at Olympus Cove reached almost 110 ug/m3, much higher than observed during most wintertime inversions, although fortunately the event was short lived.  

Source: Mesowest
On the plus side, I did hear rain drops pitter-pattering last night, with the airport recording .02" of rain.  Will miracles never cease!

Monday, September 12, 2016

Maybe a Flake?

I don't want to get everyone too excited, but the latest GFS forecast has below zero 700-mb (10,000 ft) temperatures at 1800 UTC (1200 MDT) Wednesday.

I'm so desperate for material that I'll just mention this and, given the cold trough, the potential for perhaps seeing a flake or two in the highest elevation.

It's not much to go on, but it's something.

Plus, if my quick skim of the temperatures over the past few months is correct, Wednesday's high @KSLC, which right now looks to be around 70-72ºF, will be the lowest maximum temperature since May 25th, when we hit only 68ºF.  Wunderbar!

Friday, September 9, 2016

La Nina Watch Cancelled, But You Shouldn't Care

Ah, how I enjoy watching some prognosticators make seasonal climate predictions.  Like sports pundits predicting the winners of college football games each Saturday, they confidently predict what will happen during the coming winter.  If only Mother Nature was persuaded by bravado instead of the laws of physics and the behavior of chaotic systems.

A great beat-down of the seasonal outlooks from last winter was written last week by Joel Gratz of  My disdain for the "deterministic" nature of these outlooks is well documented, and something described in depth in my post from March 20th, 2016 reflecting on last winter and more recent post Silly Season Returns.

The usual approach taken in producing these outlooks is to decide whether or not the coming winter will feature El Nino, La Nina, or ENSO neutral conditions (i.e., neither El Nino or La Nina) and then make predictions based on past events.  In both of these steps, the outcomes need to be assessed probalistically, meaning that one needs to consider the probability of say La Nina developing and in turn what the likelihood of outcomes is given that development.  Even when this is done, there are challenges.  For example, we have a relatively small number of historical events for calibrating our model and assessing outcomes statistics.

The latest news in the seasonal climate prediction area is that the Climate Prediction Center took down their La Niña watch yesterday.  Disaster!

To be sure, outlooks issued by the Climate Prediction Center (CPC) have never guaranteed La Nina.  A La Nina Watch is issued when conditions are favorable for the development of La Nina in the next six months.  CPC outlooks issued over the past few months had La Nina probabilities for this coming winter that varied from about 55% to 75%.  Their latest outlook revises these probabilities downward. Even now, a range of possibilities exists, including the development of La Nina, although the odds of La Nina are lower and the odds of either neutral (i.e., not El Nino or La Nina) or borderline La Nina conditions are higher.

CPC precipitation probabilities are issued based on probabilities and identify areas with a greater than or less than climatological chance of above or below average precipitation.  Given the weighted odds of La Nina that existed last month, the outlooks issued in August identify the Pacific Northwest as an area with greater than climatological odds of above average precipitation.  Note the use of the term "precipitation probability" in the descriptor.

Source: CPC
What often happens in the media or in outlooks issued by some meteorologists is that these weighted odds are converted into overconfident outcomes.  An example is an article published by UnofficialNetworks on July 7th, a piece of which I've sampled below.  There is no mention of probabilities anywhere, despite the fact that farther down in the article they actually include the CPC probabalistic outlooks.

Source: UnofficialNetworks
I expect with the downgrading of La Nina odds, the forthcoming precipitation outlooks from CPC will see a similar shift in probabilities toward climatological odds.  In other words, we simply can't say with any confidence how this winter will evolve over western North America, except perhaps to say that the dice are loaded a bit for above-average temperatures because of Global Warming.

So, the bottom line for this winter is the La Nina watch is cancelled, but really you shouldn't care.  None of this changes anything.  Hope for snow and ski it if it's white.