Wednesday, November 30, 2016

This Will Be the Hottest Fall on Record

Given the fact that we are experiencing our coldest temperatures since February, much of the Salt Lake Valley is snow covered, and we have a 40" base in upper Little Cottonwood Canyon, it may be hard to believe this is going to be the hottest fall on record, but it is going to be the hottest fall on record. 

With one day left to go into the record books (today), the average temperature for this fall at the Salt Lake City International Airport sits at 57.7ºF, 0.7ºF warmer than 2015.  

Source: NOAA Regional Climate Centers
Although we are going to lose a little ground today, my hazy, jet-lagged, early morning math suggests we will come out ahead of 2015 when today is in the books.  Regardless, both years add to our string of five consecutive years with exceptionally warm falls.  How much the recent fall warmth is due to long-term global warming or climate variability is an interesting question.  Thanks to global warming, the dice are loaded for above average temperatures, but my view is that the last few years the large-scale flow has also been favorable for us to have warmer falls.  

Monday, November 28, 2016

Good Early Season Skiing Begins

I've been traveling for work and unfortunately missed out on most of the excitement today.  Further evidence that the best way to ensure a big storm in the Wasatch is to send me out of town.

As of 9 PM, it looks like a total at Alta since 0000 MST 27 November (Sunday) of about 40" based on accumulations on the interval board.  Total snow depth broke the 40" barrier this evening, qualifying for the start of "good early season conditions" on the Steenburgh scale.

Thanks to Mother Nature for making Utah snow again!

Sunday, November 27, 2016

Things Are Looking Good and I'm Not Going to Jinx the Next Storm

Is there anything better than storm skiing on a day that you can just make out the sun through the clouds?  

From last night through 3 PM this afternoon, the Alta-Collins stake has picked up 13" of snow with 0.78" of water.  If you picked your routes carefully to avoid rocks and stumps, the ski touring today was quite nice.

Forecasts are optimistic with another trough coming in tomorrow morning with deep moisture and instability.

After a lull in the storm tonight, the NAM puts out about 14 inches of snow from 6 am tomorrow morning through 11 AM Tuesday at Alta.  Most of this falls by 11 PM Monday.

That's a hefty amount of snow for that model, which doesn't fully capture the influence of the Wasatch Range.

Since part of the storm extends beyond the forecast range of the NCAR ensemble, here's the NCEP Short Range Ensemble Forecast (SREF) system plumes for Alta.  Most call for things to pick up tomorrow morning with heavy snow through the day tomorrow.
I've been goofing off this weekend and won't be issuing a forecast.  Yup, that's a cop out, but this looks like a good storm so why jinx it?  

Friday, November 25, 2016

Opening Day 2016/17

The winds were blustery, but the sky sunny for our first day of the season today.  

Although there were many tracks, some good powder could be found in shady, wind-sheltered areas.  Even on my old-school touring skis, the kid showed decent form.

More snow is in the forecast, which will hopefully help the resorts and the backcountry.

Thursday, November 24, 2016

There's Much To Be Thankful For

Happy Thanksgiving to all Wasatch Weather Weenies.  We have much to be thankful for.

First we have yesterday afternoon's frontal passage, which pushed into the Salt Lake Valley with one hell of a shelf cloud and frontal nose.

Second we have the overnight storm, which was fueled by the front, the orographic lift of the central Wasatch, and the lake.  The latter two can be seen below in the form of a narrow, but intense lake band over the southern Great Salt Lake and a region of enhanced radar reflectivity over and upstream of the central Wasatch.  Note also the narrow precipitation shadow downstream of the central Wasatch.  Sorry Wasatch Mountain State Park, no soup for you.  

Third we have a spectacular snow coated Thanksgiving Day with clear skies and unlimited visibility.  I love sunrises like this morning's.

Finally, we have 12 inches of new snow at Alta, making it two storms in a row that have produced near the top of forecast expectations.  At last measurement, total snow depth at Alta-Collins sits at 20 inches.

Alta Ski Area reports that they are closed to uphill skiing, although the Albion access road and Catherines area are open.  Additionally, the Utah Avalanche Center rates the avalanche hazard at Considerable.  Don't let irrational exuberance get the best of you if you are heading out today.

Wednesday, November 23, 2016

Lake and Orographic Effects in Wake of Frontal Passage

There's much to love in the radar loop below taken in the wake of this evening's frontal passage.  The box over the Great Salt Lake shows an area of persistent triggering of lake-effect convection, which trains southeastward into the Salt Lake Valley where it transitions to a broader, more stratiform band.  Meanwhile, the orographic effects in the central Wasatch (larger box) are also persistent and pronounced.  Note the persistent echoes over the high terrain with the abrupt rain shadow further to the southeast.  The Salt Lake County/Utah County line strongly marks the transition.

Alta picked up a fast 6" of snow through 8 PM and there's good reason to expect more moderate to heavy snow for the next hour.  After that, everything will depend on the post-frontal and lake-effect crap shoot.

White Thanksgiving for Wasatch Front?

If you are dreaming of a white Thanksgiving you may be in luck.

Regional satellite, radar, and 700-mb temperatures over the past 18 hours show the landfall of a Pacific frontal system along the northern California coast followed by its redevelopment over north-central Nevada.

That frontal system has its sights set on the Wasatch Front for later today.  The latest HRRR shows the surface cold front pushing through the Salt Lake Valley around 2300 UTC (4 PM MST) this afternoon, with a band of frontal precipitation in its wake for much of the Wasatch Front.

Snow levels will drop quickly after frontal passage to bench and eventually valley levels.  This looks to be a quick hitting event, but 1-3 inches on cold surfaces along the east bench of the Salt Lake Valley seems like a good possibility.  Valley accumulations will be less, but perhaps enough to whiten cold surfaces.

The HRRR (above) generates lake-effect in the wake of the front, but one needs to be cautious interpreting that forecast.  First, lake geometry uses by the HRRR is based on 2001 data, leading to a Great Salt Lake that is much larger than it is at present.  U graduate student Brian Blaylock send me the image below showing the HRRR surface temperatures (degrees Kelvin) and you can clearly see the massive area of the HRRR Great Salt Lake compared to a more recent lake-shoreline outline (black line).  This means that the reliability of HRRR lake-effect forecasts will likely be low.  Of course, this doesn't mean we won't get lake effect tonight.  It is a modest possibility, although the odds of an intense, long-lived band are low (but not zero).  If you get some, consider yourself fortunate.

Temperatures during the frontal passage are favorable for relatively low density snow up in the mountains.  The 1200 UTC NAM generates 0.44" of water for Alta-Collins.  Overnight NCAR ensemble forecasts have 9 members between about 0.3 and .75 inches of water, and one less optimistic member going for just 0.1".

Based on that range of water equivalents, I would normally lean for 5-10" of snow, but the environment tonight looks favorable for lower density snow, perhaps with 5-6% water content.  That would mean something like 6-15" of snow if we ignore the less optimistic NCAR ensemble member (and I really want to do that).   Fifteen seems like a lot, however, unless the post-frontal and lake-effect precipitation really gets going.  I think something in the range of 6-12" is more likely and will stick with that and hope for more.

Tuesday, November 22, 2016

Two Ensemble Pitfalls to Avoid

If you are a user of some of our ensemble products on, I thought I would share a two pitfalls to avoid.

The first pitfall is assuming that ensemble members in the middle of the distribution are more likely to verify than those on the tails.  Although that could be the case, there are times when that's a bad assumption. 

Here's an example based on the NCAR ensemble forecast for Alta Collins for the 2-day period ending this afternoon and encompassing our most recent storm (focus on the top graph).  In the NCAR ensemble, every member is an equally likely outcome.  And, in this particular forecast, the outcomes are relatively evenly distributed.  The odds of 0.6 inches are about the same as 1.4 inches (the latter verified).  

Hedging your forecast to a subset of the plumes makes little sense when the distribution of forecasts is so even.  It might make sense when there is a strong clustering of forecasts, but one also needs to keep in mind that this is only a 10-member ensemble, so in some instances, that clustering might not be significant and you might want to be cautious about biting on it.  

The second is assuming that the full spread of the ensemble (from the low to high members) captures the full range of possible outcomes.  All of the ensemble forecast systems in operations today are underdispersive.  That means they don't fully capture the full range of possibilities in a given forecast period.  For example, at mountain sites in the western U.S., the spread of downscaled 5-day forecasts derived from the Global Ensemble Forecast System, which represent a portion of the forecasts used for the NAEFS-downscaled products on, encompasses the observed amount produced during major precipitation events only 56% of the time.  During the other 44%, the observed amount lies outside the downscaled GEFS spread.  

Monday, November 21, 2016

This Year, Ski Season Will Come with a Whimper, Not a Bang

Over the past few days I've been looking at the medium range ensembles and, although I don't see a storm in the next week to get excited about, there is a series of modest events that should slowly but surely add to our non-existent to meager snowpack.  We start with last night's precipitation (upper-elevation snow only), see a bit more today and tonight (with lower snow levels), and continue with a couple more storms over the next week.
Water and snowfall totals presently being advertised by the models for the next week are not game changers, except perhaps for the wettest, snowiest ensemble members.  Looking beyond the 1-week period presented above, there's hope of continued activity, but I don't like to talk about details in such long-range forecasts.  

Thus, it looks like this ski season will come in with a whimper, not a bang.  We'll get a little here and there.  Resorts may open a trail or two with snowmaking during the Thanksgiving weekend (no promises as we don't have snowguns in our models).  Backcountry skiers will be teased, not satiated.  It is what it is.

Saturday, November 19, 2016

Beautiful Weather for Everything but Snowmaking

Everyone along the Wasatch Front and Back awakes this morning to a beautiful day with a think veil of high clouds blanketed over snowy mountains.

Everyone that is except for the snowmakers.

Toying with the idea of skinning and skiing the white ribbon of death down Collins Gulch tomorrow, I took a look at the web cams from Alta and saw nothing in the way of operating snow guns.

How can this be?  A building ridge and southwesterly flow conspired to raise our temperatures dramatically last night.  Check out the temperatures at Alta Base over the past 24 hours.  We peaked at 33ºF yesterday and cooled into the mid 20s shortly after sunset.  Then, after midnight, temperatures rose dramatically and currently hover near 40ºF.

There are, however, a few places where shallow pools of cold air did not scour out of valleys or basins.  For example, temperatures in the Snyderville Basin and near the base of Park City Mountain Resort remain below freezing this morning.  Yup, they can make snow at the base, but nowhere else.

It won't take long for temperatures there to rise above freezing, so if they are running a few guns down there, they won't be able to do it for long.

Thursday, November 17, 2016

Kiss and Make Up with Mother Nature NOW!

Our first all elevation "winter storm" of the season is winding down.  Radar imagery from 1221–1512 UTC (0521–0812 MST) shows the last gasp of lake- and mountain enhanced showers decaying and moving downstream.

We had just enough to coat the grass around campus.  Up at Alta-Collins, there is a 5" snow total with 0.27" of water equivalent, clearly on the low end of the most likely range we discussed yesterday.  Maybe they will pick up a bit more, but these are pretty paltry numbers and nothing to get excited about.

I don't know what you people have done to irritate Mother Nature, but kiss and make up now.  This has been going on for 5 years now.  FIVE LONG YEARS.  I'm not getting any younger and I don't want this year to be a sixth.

Wednesday, November 16, 2016

Known Knowns, Known Unknowns, and Unknown Unknowns

In this post, I will be channeling Donald Rumsfeld, who once famously said.
"There are known knowns. There are things we know that we know. There are known unknowns. That is to say, there are things that we now know we don't know. But there are also unknown unknowns. There are things we do not know we don't know."
Rumsfeld was lampooned for that quote, which many considered to be nonsense, but I understand exactly what he meant.

Known Knowns

Our computer models have gotten pretty good at predicting large-scale airmass changes.  That's why the massive drop in temperature from yesterday (record high of 73ºF and the latest 73ºF on record at the Salt Lake City airport) to tomorrow morning (low 30s) is a known known.  Think of this period as a time machine in which you are transported from early Fall to late Fall in two days.  We are in transit today as cooler air is already moving in aloft and the surface front, marking the leading edge of even cooler air, is scheduled to arrive this afternoon.

Known Unknowns

Difficulty predicting the timing and amount of precipitation, especially snowfall, are known unknowns.   Adding insult to injury is the fact that we are dealing with a front that does not have a well developed precipitation band this morning, as illustrated by the 1400 UTC (7 AM MST) analysis below.

Some models are, however, bullish on precipitation developing along the front.  Others are bullish on precipitation behind the front.  This leads to significant differences in the timing and amount of precipitation tonight and tomorrow morning.

From the operational models, we see water equivalent totals for the Salt Lake City airport ranging from only 0.1" (0000 UTC GFS) to .26" (0600 UTC NAM).  All models produce some frontal precip (step part of the curves, lags the actual surface front by a few hours), but of differing amounts.  Only couple produce a burst of post-frontal precipitation (increases around 1200 UTC give or take).  The National Weather Service forecast (green line) is the wettest of all (.32"), primarily because they call for post-frontal (and presumbaly lake-effect) precipitation to continue late tonight and tomorrow morning.  Most of the models below do not realistically simulate such precipitation.

For experimental models, we can look at the NCAR ensemble, which has the advantage of being much higher in resolution (3 km).  We'll also shift our attention to Alta as I know just a few of you have an interest in that.  Again, we see dramatic differences in precipitation amount produced during the frontal passage (from about 00-06 UTC) and then during the post-frontal period (after 0600 UTC).  Totals range from .3 to 1 inch of water equivalent.

The final known unknown is uncertainty in the snow-to-liquid ratio for the storm.  Drier snow yields larger accumulations per unit of water.  I expect the snow in the mountains from this event to be at or below average water content.  In the valley, accumulations will be limited by snow densification as it melts on the warm ground (accumulations will be greatest on cold surfaces).  However, there is uncertainty in predictions of snow-to-liquid ratio, and this is an additional source of error in forecasts.

Unknown Unknowns

I have spent much of my career studying lake effect so it pains me to say this, but we really can't predict the location and amount of lake effect worth a damn.  We have gotten better predicting the likelihood of lake effect (will it happen or not) and we can look at why lake-effect is likely tonight using the graphs below.  We have, for example, a forecast for a remarkably cold airmass moving over a remarkably warm lake (illustrated by top two left hand panels), a moist low-level airmass (lower left panel), and NW-N flow (top right).  Based on training to past events, this gives us a probability that lake-effect develops (note: this just means that we get some, not that we get a lot) that peaks at about 90% tomorrow morning.

That's all fine and dandy, but we still struggle with these forecasts for a number of reasons.  One is that the models aren't perfect.  They have errors in wind direction and humidity.  Another is that lake effect comes in many flavors.  It can be banded (intense and localized) or non-banded (weaker, but broader in coverage).  What causes those differences in flavor are basically unknown unknowns.  We don't know why some events feature banding and others don't.  Finally, despite the fact that all of the large-scale factors appear to add up to lake effect, we still have events where it doesn't happen (it's not as simple as cold northerly or northwesterly flow moving over the lake as that happens all the time with no lake effect).  Again, this is an additional unknown unknown.

Putting it all together

I think this remains a forecast with a broad range of possibilities.  I'm sticking with my forecast of 1-2 inches of snow for the benches (cold surface accumulation) and 5-10 inches of snow for Alta as I those ranges represent the most likely outcomes.  Could we get skunked and come in below those numbers.  Yes, if the front is less productive than advertised and the post-frontal doesn't come through.  Could we do better?  Yes, if the post-frontal showers late tonight and early tomorrow, possibly with lake effect, get going.

One thing to note about the lake effect is that the forecast flow for tomorrow morning is somewhat sheared, with the wind veering (turning clockwise) with height from northwesterly to near northerly.   As a result, in the NCAR ensemble, the probability of more than 1" of water equivalent is highest in the Oquirrh Mountains, maxing at 60%.  In the central Wasatch odds are generally around 20%.  

Clearly the best option is to keep expectations low and hope for the low probability, heavy precipitation outcome to verify in the central Wasatch.

Tuesday, November 15, 2016

Last Day of Summer Today, Winter Tomorrow Night

I guess we can call today the unofficial last day of summer.  I was going to put summer in quotes, but it is not as ridiculous as it sounds.

This morning's sounding had a 700-mb temperature of 6.8ºC, which represents the average for mid September, technically not meteorological summer, but within astronomical summer.

Source: SPC
It should be noted, however, that there have been higher 700-mb temperatures observed at the airport in November, including 8.7ºC on Nov 19 (LST).  Model forecasts for later this afternoon top out at 7.6ºC (NAM) and 6.9ºC, so we're not in completely rarified air yet.

Nevertheless, the day is going to be splendid, with the maximum temperature constrained only by how much we mix out the strong valley inversion that was present this morning (see above).  At 11 am, we were at 63ºF at the airport and 65ºF at the University of Utah.  Bench locations will likely eclipse 70ºF today.  The maximum at the airport is, however, quite tricky to forecast as much depend on whether or not the southerlies can scour out the cold air along the valley floor and keep the lake breeze at bay.  

At 11:28, the strong influence of the Great Salt Lake was apparent.  Over the northern Tooele Valley, where the lake breeze was in f ull force, temperatures were only in the 50s, compared to the 60s near Tooele and 64 at Stockton.  Over the Salt Lake Valley, the lake influence on temperature is weaker, but light northerly flow was evident near the Kennecott Tailings pile.  

Given that we got to 70 yesterday, and the southerly flow is stronger today, I'm going to live dangerously and say we will break the daily record today with a high of 71ºF.  If the southerlies really get going, it could get quite a bit warmer than that, but I think it will be difficult for the cold air to completely mix out.  Note that the lake breeze could usher in some cooler air, especially near the airport, later today.  

Getting to the important stuff, the models have converged on a solution similar to that advertised by the ECMWF and NAM yesterday.  As such, it is likely that the cold front will push into the Salt Lake Valley tomorrow afternoon, probably after 2 PM.  Right now, the models call for a dry frontal passage, with precipitation moving in during the evening when snow levels will drop rapidly, falling to near the valley floor by 9 PM or so.  By Thursday morning, expect temperatures in the low 30s.

Snow?  Yes, I think everybody will see some and I expect snow on cold surfaces when I awake Thursday morning.  Amount forecasts remain dicey.  The models typically are best for precipitation generated by cold fronts and it looks like an inch or two is possible on the benches from that.  Where things get dicey is following the frontal passage and whether or not the post-frontal environment will be sufficiently unstable to get going with or without assistance from the lake.  We'll take a look at that tomorrow, although you should expect continued hand waving.  

For the mountains, I've consistently said that there are a wide range of possibilities and I remain uncertain about the size of this storm except to note that the odds of a major dump in excess of 18" are lower today than yesterday (but not zero).  Water equivalents being produced by the models today are fairly paltry, but low snow density may help generate larger snowfall accumulations.  My take is that 5-10" is probably the most likely range for Alta, but I would not be surprised if we came in below or above that range.  

Monday, November 14, 2016

Thursday Will Bring a Shock to the System

It has been a remarkable fall across the entire Northern Hemisphere.  The large-scale upper-level pattern has been totally locked in.  As shown by the mean (left hand side) and departure from average (a.k.a. anomaly, right hand side) 500-mb analyses below, the pattern has featured anomalous troughing over the northeast Pacific, ridging over North America, and ridging over the North Atlantic and Arctic.

That large-scale pattern remains in force today, leading to well above average temperatures in the Arctic, where sea-ice coverage is at a record low and above average temperatures across much of North America.  In contrast, ,below average temperatures exist across much of Eurasia, especially Siberia. 


This weekend, I watched some of the World Cup skiing races from Levi, Finland and it was like viewing another planet as it sure looked like winter there, whereas here in Utah I threw on shorts and a t-shirt to mountain bike.  

In fact, the past month (13 October - 13 November) rates as the 2nd warmest on record at the Salt Lake City International Airport, with an average temperature of 55.6ºF.  Just 0.1ºF ahead of it is the comparable period from 1927.  

Source: NOAA Regional Climate Centers
However, dramatic and abrupt change is coming.  The GFS 500-mb and 6-h accumulated precipitation forecast below shows a deep upper-level trough centered over Utah at 1800 UTC (1100 MST) Thursday.  WHOOPIE!!!

The transition from Tuesday through Thursday is going to be enormous.  The GFS calls for a 35ºF temperature swing at 11,000 feet.  

Basically, we are looking at a transition from temperatures that may reach 70ºF at the airport tomorrow (Tuesday) to snow on the valley floor possibly as early as Wednesday night and Thursday.  

There is a great deal of spread amongst the models in terms of the how everything will go down Wednesday and Thursday.  The 0600 UTC GFS favors an amplified trough, which leads to a later frontal passage and later precipitation, as well as a longer period of precipitation following frontal passage.  In contrast, the 0000 UTC ECMWF and 1200 UTC NAM (which just came in) favor a weaker trough, which leads to an earlier frontal passage on Wednesday and precipitation moving in as early as late Wednesday afternoon or Wednesday evening.  

In either event, Thursday is going to bring a shock to the system.  Given the spread in forecasts, it's too soon to discuss with any confidence the details of how this storm will evolve, but prudence dictates that you take care of your car and commute winterization needs by Wednesday afternoon. 

Should you get the skis waxed?  Well, I still see a wide range of outcomes given the diversity of model forecasts in the various ensembles, with perhaps a storm total of 6 inches being on the low end of possibilities and something like 30" at the high end if everything were to come together wonderfully.  

Below are our downscaled snow estimates from the North American Ensemble Forecast System and these show the mean of all ensemble members being around 18" for upper Little Cottonwood with about a 90% chance of 6 inches or more, 70% chance of 12 inches or more, and 20% chance of 24 inches or more.  
We've made some changes to this algorithm over the summer and it's not as "jacked up" as it has been in the past.  My take, however, is that if one were to add the European ensemble to the mix, these numbers would shift downward a bit.  Keep expectations low and hope for the bigger solutions to verify.

Saturday, November 12, 2016

Rocky Mountain Power Is Scared

During the past week, Rocky Mountain Power announced that they are recommending a three-part monthly rate increase for future residential net-metered solar customers, including a $15 fixed charge, a $9.02 per kilowatt for peak period demand, and 3.81 cents per killowatt-hour for the amount of energy used.  While not applying to existing home solar produces, this would greatly disincentivize future installations.

The argument for doing this is based on a study conducted by Rocky Mountain Power claiming that rooftop solar customers are underpaying their actual cost of service by $400 per year.  Subsequently, Rocky Mountain Power's external communications director Paul Murphy argued in an op-ed piece in today's Salt Lake Tribune that Rocky Mountain Power is committed to solar and customer fairness, but that the cost noted above represents a substantial subsidy.

If Rocky Mountain Power is committed to solar (and I doubt that they are), this action clearly shows that they want large-scale solar farms rather than residential solar.  As a regulated monopoly, that makes perfect sense.  They want to deliver all the power that we use, rather than a fraction.  Residential solar production is a major threat to their revenue stream and that would really suck for them.

It is also rich that Rocky Mountain Power is so concerned about this particular subsidy.  The International Energy Agency estimates that annual fossil-fuel subsidies amount to approximately a half-trillion dollars globally.  Such subsidies do not include the externalized costs arising from air pollution, climate change, and other effects from fossil fuel combustion.  Rocky Mountain Power gets a free ride on all those externalized costs.  In a way, we as electrical consumers get a free ride too on our electrical bills, although we pay the price in other ways.

They also don't seem concerned about federal subsidies for rural electricity production or federal loan and loan guarantees.  They aren't worried about the uneven costs of producing and providing electricity to rural and urban areas.  Clearly some are subsidized and some are paying more than their share (NOTE: I am a firm supporter of ensuring that all American residence have reasonable access to electricity at reasonable costs and that we each bear the costs of ensuring that).

So, let's get real.  If residential solar is as costly as they claim (and that should be confirmed by an independent audit rather than letting the fox guard the henhouse), Rocky Mountain Power is basically choosing to go after it simply because the last thing that they would want to see is a stampede to a paradigm where we the people are producing an increasing fraction of our own power. This happened in Nevada, affecting Nevada Energy's bottom line, ultimately leading to voters deciding to end their regulated monopoly.

My view is that Rocky Mountain Power is scared.  Solar is getting cheaper.  Residential electrical storage options are improving.  Disruptive change is coming and people will be generating more and more of their own power and disappearing from the grid.  These are attractive options not only for environmentalists, but anyone who believes in choice over monopolies.

Note: I purchased solar through the U's community solar program after moving this summer.  We are scheduled for installation this month, but are already under contract and not affected by Rocky Mountain Powers proposed changes.

Addendum @ 3:45 PM 12 Nov: Details on RMPs filing for net metering rate changes available here.  Comments can be sent to the public service commission at

Friday, November 11, 2016

Maybe a Storm, But Be Realistic

When in a snow drought at the beginning of the season, one tends to look into the deep future for any trough that might lay down some snow.  Indeed, we have one in the forecast, which the GFS pushes through the state next Thursday.

This storm is already being hyped, despite the fact that its nearly a week away.  There are some things we can be confident in.  For example, we are going to get colder later next week.  However, you really can't count on precipitation amount forecasts that far in advance.  The storm track could change some and, when it comes to Wasatch snowfall, the Devil is in the details, and those details can't be reliably anticipated at such long lead times.

To further sober you up, rather than show one exciting solution from the GFS, let's look at the NAEFS downscaled ensemble forecast for Alta.  There are a few members calling for 10-20 inches on Thursday, but others going for quite a bit less.

Bottom Line: There remain a wide of possibilities.  Hope for the best.  Low expectations are the key to a happy life.

Thursday, November 10, 2016

Post-Election Smog Settles in over the Salt Lake Valley

Salt Lake Valley from the Bonneville Shoreline Trail, 4 PM 9 November
A seriously nasty post-election smog episode has settled in over the Salt Lake Valley today.  Visually, it basically looks like crap.  Here are a couple of more photos of Downtown and the Wasatch Range from the Bonneville Shoreline Trail. 

The setup for this event is important for two reasons.  First, we did not have a previous surge of low-level cold air prior to the development of the high-amplitude ridge over the past few days.  Second, there is no snow cover.  As a result, the cold pool that is present over the Great Salt Lake Basin is relatively weak.  In fact, yesterday's high at the Salt Lake City airport was a remarkable 69ºF and some sites in the valley peaked above 70ºF.

OK, so perhaps the air quality won't be that bad, right?  Wrong!  There are two flies in the ointment making our lives miserable.  The first is that we continue to burn fossil fuels and pollute the valley atmosphere.  That has changed little.  If we took that out of the equation, I wouldn't be writing this blog post.

The second is the Great Salt Lake.  The Great Salt Lake is quite cold at the moment compared to the overlying airmass.  There is a buoy operating on the lake about 6 miles west of Antelope Island and you can see how the lake has steadily cooled over the past month.  Temperatures near the surface spike each day, currently reaching about 58ºF, but below the surface hover around 55ºF.

Therefore, temperatures over and around the lake are lower, the cold pool stronger, and the mixing more limited.

The stable layer of air over the lake is having a major impact on temperatures and pollution.  This impact was especially pronounced yesterday afternoon.  For example, at the Neil Armstrong Academy in the West Valley temperatures briefly spiked to just over 70ºF at about 1 PM.  What a wonderful moment that was as the pollution mixed out and briefly dropped to only 3 ug/mg (compare top and bottom graphs near the center.  Shortly thereafter, the temperature dropped abruptly 10ºF and the PM2.5 rose rapidly again.  The temperature drop and pollution spike were both associated with the passage of the lake-breeze front.

Today, the situation is a bit different.  Temperature have topped out at 60ºF (right hand side of top graph above).  It has stayed cool because the low-level flow has been out of the northwest and from the lake for most of the day.  In fact, the wind became consistently out of the west or northwest beginning at about 9 am (top graph below) and shortly thereafter the PM2.5 rose rapidly to 18 ug/m3 (PM2.5 presented above and below).  It subsequently rose further, spiking at 32 ug/m3.

Meanwhile at the University of Utah the evolution of PM2.5 has been quite extreme.  Overnight last night, the air was very clean, but with the onset of upslope northwesterly flow today and the eventual penetration of more stable, polluted air from the Great Salt Lake and downtown, PM2.5 levels rose to more than 25 ug/m3 this afternoon.

Finally, I'll note that this is an event in which the top of the pollution is not especially sharp, but poorly defined.  In the photos above, for example, its difficult to tell if one is in or above the pollution.  There is a top to it somewhere, but it's less sharp than we sometimes see since the capping stable layer is relatively weak.  

Decreasing Carbon Emissions Is Not Impossible Under Trump

In the wake of the national election, I've seen several articles, blogs and quotes suggesting that the election of Donald Trump is a disaster for efforts to reduce carbon emissions and address global warming.

It is certainly not good news in those areas, but the situation is not necessarily hopeless.

Carbon emissions in the United States come from several sectors including electricity generation, transportation, industry, agriculture, and commercial/residential.  The electric power sector represents one of the brighter areas in which the US has "bent" the carbon emissions curve, with a general decline over the past several years.

Source: US Energy Information Administration
The causes for the decline are multifaceted, but include increased use of renewables (especially solar and wind) and a transition from coal to natural gas, which is less carbon intensive (but still carbon emitting).  
Source: US Energy Information Administration
As a candidate, Mr. Trump called climate change to be a hoax perpetuated by the Chinese and advocated policies to increase fossil fuel and coal combustion.  We can probably expect his administration to work hard to bend the curve again, this time back to upward.

However, declines in carbon emissions can still occur.  Much is happening at the local and state levels, as well as in the marketplace.  For example, California is the 2nd largest carbon-dioxide emitter (by state) in the United States and I would expect them to continue to aggressively pursue decarbonization over the next four years.  Innovation and economics can also affect how and how efficiently we generate power in coming years and could yield advances that help in the effort.  

I've long been skeptical that humans will be able to get their arms around this problem fast enough to avoid a major shift in climate.  Efforts to reduce carbon emissions today have the potential to put the brakes on global warming, allowing us to avoid crashing into a brick wall, but won't prevent us from bouncing off a few barriers along the way.  Mr. Trump will probably not help apply the brakes and he could cause some harm, but it is worth remembering that there are other ways to slow this thing down.