Wasatch Weather Weenies

Weather is weird, and it frequently does not conform to our climatological expectations.  Meteorologists often say that climate is what you expect and weather is what you get , but this winter seems even wackier than usual.  From the "Mother of All Inversions" to storms that produce more snow in the valley than the mountains, this winter has given us a full range of insanity, which continued yesterday. In the higher elevations, very low density snow fell during the day on Tuesday.  We're talking 4% water content.  Then higher density snow fell yesterday which, when combined with rime, contributed to the development of upside down snow.  Today's Utah Avalanche Center report pretty much tells the tale. There was a major change in snow conditions that happened on Wednesday.  Higher density snow fell coupled with strong winds creating an 'upside down' layering situation.  This was capped off with a nice rime event which produced a crust varying in t...

Automated weather observations indicate that we are starting to see higher density snow fall in the mountains.  For example, at Alta-Collins, we've seen three inches of snow with 0.38 inches of water over the past five hours. There are also reports of riming, which will further densify the snow surface.  Note the ice on the southwest facing camera on top of Snowbird. The rime and high density snow are a recipe for upside down snow in which high density snow is sitting on top of lower density snow.  The UAC reported snow water contents as low as 3-4% from yesterday's storm.  Alta-Collins measured 16 inches with .68 inches of water for 4.25%.  Now we're putting something like 10-13% on top of it.  The resorts were probably tracked out today, but this will probably create punchy, inverted turning conditions in the backcountry and further exacerbate the avalanche hazard.  Let's be careful out there.

Snow Miser and Heat Miser from the Rankin Bass classic, A Year without a Santa Claus Heat Miser has officially announced that he has temporarily ceded the Wasatch Front to his brother Snow Miser.  "It was a deal brokered by my mom, Mother Nature, as compensation for global warming.  Snowy gets to sock it to some midlatitude region every now and then just to keep his spirits up." Meanwhile, a reliable source tells me that the government weather control experts have brokered a deal with Snow Miser to bring this storm cycle to an end.  Some periods of snow through tomorrow morning, then we get a break.  

The image below shows the radar reflectivity (purple = high) this morning at 1300 UTC (0600 MST) and the dramatic effects of the mountains on the precipitation during this event.  Note the higher returns over the Stansbury, Oquirrh, and most of the Wasatch Mountains (see also previous post).  I have also annotated the outlines of the ski areas on this map in red.  There are issues with radar sampling over and downstream of the Wasatch range (for example, the lack of returns over Snowbasin is due solely to beam blockage by the terrain - it was snowing hard there during this period).  Nevertheless, this image illustrates that in the central Wasatch, the heavier precipitation was found over/near the western slopes, with a dramatic dropoff in radar reflectivity as one moved eastward to the Park City ridge line and the Wasatch Back.     In addition, the storm was quite shallow in the Cottonwood Canyons.  I just got an informal report from Snowb...

Lots of interesting stuff going on in todays storm.  Check out in the loop below the very persistent echoes over the Northern Wasatch, the Stansbury Mountains, the Oquirrh Mountains, and the area around the Cottonwoods (crudely identified by red boxes). The Northern Wasatch has really gotten a pounding.  Ben Lomond Peak near Ogden has seen its snow depth increase 20 inches in the past 24 hours.  They will be moving into "too much of a good thing" territory if this keeps up. Similarly, the Middle Bowl site at Snowbasin has a storm total of 18 inches. Check out what is happening across the Cottonwoods.  The flow at crest level is westerly.  There is strong enhancement evident along the Wasatch Front, but the strong echoes barely penetrate to the Park City ridgeline.  There are very few echoes by the time one gets downstream of the Cottonwoods. Here's what automated snow depth sensors show since the beginning of the storm last night through 10 am...

There have been a few events this year during which the enhancement of snowfall over the mountains has been limited.  Some have started to call these "upside down" storms, although being a powder skier I prefer to use the term upside down to describe storms in which the snow density increases with time. Meteorologists typically refer to the ratio of mountain to lowland precipitation as the orographic ratio .  In a storm in which the mountain and lowland precipitation is the same, the orographic ratio is one.  If the mountain precipitation is four times the lowland precipitation, the orographic ratio is four.  In an upside down storm, the orographic ratio is less than one. On average, the orographic ratio between Alta and Salt Lake City during January is nearly 5.5.  This is the highest average orographic ratio of any month during the year and illustrates that on average January features the greatest enhancement of precipitation by the Wasatch Range.   ...

It appears that the inversion smog over the Great Salt Lake was dragged back into the Salt Lake Valley with the cold front this afternoon.  Check out this marvelous video of it from George Wilkerson's web cam (www.ocwx.com, video compilation by Prof. Steve Kreuger, University of Utah Atmospheric Sciences). Note the shallow nature of the cold air, the formation of low level "scud" clouds where the southwesterly prefrontal air is lifted over the frontal nose, and the smog, haze, and fog behind the front.  Don't worry, this is a short-term setback.

Ding Done the Inversion Is (almost) Dead! The inversion has finally cracked!  At least for most of the Salt Lake Valley, south winds ahead of an approaching cold front scoured out the fog and smog last night.  Weather cameras show fog and smog are lingering in some areas, as you can just make out in the weather cam image below. Looking NW from Holiday.  Note smog/haze just beyond downtown SLC. Source: Meteorological Solutions Inc.  With the inversion nearly behind us, it's time to move onto better things, snow!  The snowpack in the Cottwonwoods has really suffered over the past month.  We now sit at only 79% of average and, in fact, we're almost even with where we were last year at this time. Water year 2013 snowpack SWE at Snowbird (green line) compared to the 1981–2010 average (blue) and 2012 (red).  Source: NRCS & NWS. We have a cold front coming in for later today and tonight that should bring a much needed dump to the entire...

A friend described yesterday's freezing rain as the 7th plague.  I'm not sure what the other six are, but I suppose we could include split flow, inversion, and pollution.  Today we can add fog.  We might have to add drought if this pattern continues.  Feel free to comment with your additions. By Utah standards, there is a remarkable rain crust on the snow here in the Salt Lake Valley.  It leaves a  shimmer on the snow and is several millimeters thick. Crusts of this type, sometimes far stouter, are not uncommon where I grew up in upstate NY. I swear I still have bruised shins from trying to walk, snowshoe, and ski on days like this.  I had a far lower tolerance for bad snow then than I do now. It may be foggy and not look too polluted, but an inversion remains in place and a quick look at the real-time charts from the Utah Division of Air Quality shows that Salt Lake, Utah, Weber, Uinta, Tooele, Cache, and Box Elder counties remain abo...

Don't be fooled by the light drizzle and fog.  The air is still filthy and nasty out there.  The 24-h average PM2.5 levels in Salt Lake City have climbed to near their highest point of this inversion event.  I remain perplexed as to why they were lower for the last couple of days and whether or not that was truly representative of the valley as a whole, but I think we can probably conclude that we are still above National Ambient Air Quality Standards (NAAQS). Source: Utah Division of Air Quality There has been some drop in PM2.5 levels at North Provo (thankfully!).  However, they remain well above the NAAQS. My cup runneth over this week.  I need a vacation, preferably involving either a warm beach or deep powder.  Anyone willing to sponsor such a trip should give me a call.

Trevor Alcott provided me with an analysis of hourly surface observations from the Salt Lake City International Airport that help illustrate the unusual nature of our ice storm: Since 1940, there have been only 9 measurable freezing rain events (0.01 inches or greater) at the Salt Lake City International Airport None of those events occurred with temperatures lower than 26ºF.  Today's began at 20ºF.   The latest accumulation (0.08 inches as of 11 am) is the largest freezing rain accumulation since 31 Dec 1983.  There are only three events that top this one in terms of freezing rain accumulation: 0.13 inches that fell at 32ºF on 9 Feb 1976 0.16 inches that fell at 29–32ºF from 26–27 Dec 1983 0.21 inches that fell at 30–32ºF from 30–31 Dec 1983 (.11" of this fell as heavy sleet) So, it appears this is the coldest measurable freezing rain event in the period of record and it is the fourth largest (so far) in terms of accumulation.  

" The ice storm is an event, and it is not an event which one is careless about " - Mark Twain The winter of our discontent continues.  We have not only failed to mix out the cold pool and pollution, but temperatures last night remained warm enough aloft that we have light freezing rain falling across the Wasatch Front.  Freezing rain is very rare in Utah, and this event is shaping up to be a doozy.   The culprit in all this is the cold pool/inversion combined with a wedge of warm air aloft.  Temperatures in the shallow cold pool at the surface are below freezing (18ºF at the airport when the sounding was taken at about 4:30 am).  Aloft, temperatures are well above freezing within the warm wedge (in this graph, known as a Skew-T, the 0º line is slightly skewed and indicated by a solid black line – everything to the right of this line is above freezing).  Snow falling from the cloud deck aloft melts in the warm wedge, turns to rain, and then fr...

One of our professors here at the U, John Horel, and several students are participating in a wintertime ozone study over the Uintah Basin this winter.  Amongst the tools that they are using is a laser ceilometer, which sends a pulse of radiation upwards and measures how much is scattered back. The concept is similar to a radar, except the wavelength is shorter, so it is sensitive to small particles (e.g., particulate matter) and it takes a series of vertical profiles rather than horizontal scans. The data being collected is quite remarkable.  One can see not only layering of the pollutants, but also waves.  Most of these are probably  internal gravity waves , which are the atmospheric equivalent of the waves that you might see on the ocean.  They are the very short waves apparent in the top image below. Source: John Horel (click to enlarge) However, if you look carefully, you can see longer waves.  These are also gravity waves, but they may be more r...

There's much to talk about today.  We'll do this rapid-fire style. • As discussed in the previous post from last night, the inversion is now at its maximum strength.  In this morning's upper-air sounding from the Salt Lake City airport, the temperature increased from -15.5ºC (4.1ºF) at the surface to 7.6ºC (45.7ºF) at 2130 m (6988 ft).  Within the large-scale inversion, which is elevated just a bit above the valley floor, the temperature increases from -12.7ºC (9.1ºF) at 1623 m (5325 ft) to 7.6ºC (45.7ºF) at 2130 m (6988 ft).  The loop below shows the lowering and strengthening inversion over the past 8 mornings, concluding with today.   • With the inversion lowering, higher elevations on the east bench are getting tantalizingly close to clean air.   • Overnight low at the Salt Lake City airport 4ºF. Overnight low on Mt. Baldy (11,000 ft) 34ºF.   • The 24-hour average PM2.5 peaked overnight at 127.8 ug/m3 in North Provo.  That is ...

I can't help but share this crazy stuff tonight.  The inversion has strengthened further as temperatures have climbed aloft with the ridge moving eastward.  Check out the sounding from 0000 UTC (5 PM MST) this afternoon.  There's a 17ºC temperature inversion. Source: NCAR/RAL The depth of the cold pool seems to be getting shallower.  Perhaps this explains the modest increase of visibility on the east bench this afternoon. Notice that the temperatures in the sounding are pushing 5ºC at 700 mb.  It's running near 40ºF on Mt. Baldy (11,000 ft) and we hit 52ºF at our Alta-Atwater observing site on the south facing aspects across from Alta this afternoon. The Alta-Atwater site might be overcooking, but it is safe to say that it is very warm in the mountains, as it will be tomorrow too.

The big question on everyone's mind is when will we get rid of this inversion and the pollution (especially in Utah county where PM2.5 levels this morning are at 120 ug/m3, nearly 3.5 times the National Ambient Air Quality Standard).  There is a much advertised trough coming in on Thursday and it may help, but I'm not sure if it will give us complete relief. The problem is that the trough, at least as forecast, is not very strong and brushes by to the north.  We get the tail end of the system, which brings our 700-mb (near-crest-level) temperatures down to about -6ºC and gives us some precipitation, but that's about it. To fully mix out the cold pools that are present over most of the valleys and basins of northern Utah likely requires colder temperatures aloft and/or stronger winds.  Thus, this may be a case where the inversion is stirred, but not shaken.  We will probably see a drop in PM2.5 levels (precipitation will help with this too), but not a comple...

Just to be an equal opportunity offender, here are a couple of photos shared by our readers of the mank and murk in Salt Lake County.   Looking north from Suncrest area Sunday 20 Jan.  Courtesy David Yorty. Similar view, Monday 21 Jan. Courtesy Jim Edman And a great one here showing Mt. Timpanogos and the Utah Valley smog. Looking south from Suncrest area Monday 21 Jan.  Courtesy Jim Edman. As fascinating as all this is meteorologically, I'm looking forward to this episode being over.

Looking north over the smog of Utah County. Courtesy Jeff Massey. The most remarkable (and depressing) PM2.5 readings so far during this "Mother of All Inversions" event come from Utah County. Online data from the North Provo site operated by the Division of Air Quality show that 24-hour average PM2.5 concentrations reached 104.3 ug/m3 this morning.  That is almost 3 times the National Ambient Air Quality Standard. Source: Utah Division of Air Quality I thought I would try and take a look at how this compares to recent events.  To do this, I went to the Utah Division of Air Quality Air Monitoring Center Data Archive for PM2.5 .  There you can find a Byzantinian array of data.  I ended up grabbing the highest maximum 24-hour PM2.5 observation from any Utah county station during each year in the Yearly Percentile Frequency Report. Plotted below is a comparison with our current event (the data for 2012 was not available).  Assuming I'm usin...

We remain mired in the inversion, but there are some curious oddities with the PM2.5 concentrations that warrant analysis by people who know more about emissions and air chemistry than me. From a stability perspective, there's been little change over the past couple of days.  The inversion remains very strong, with a temperature increase of about 13ºC sitting on top of the valley cold pool. During this period, the 24-h average PM2.5 concentrations at the DAQ sites in Logan and North Provo  climbed fairly steadily.  Utah County is now approaching a putrid 100 ug/m3. Source: Utah DAQ In contrast, the 24-h average PM2.5 concentrations in Ogden and Salt Lake have declined somewhat.  Source: Utah DAQ Perhaps someone can chime in and explain these declines.  Yes, there are differences in the magnitude and timing of weekday and weekend emissions, but why would Logan and North Provo keep climbing steadily while Salt Lake and Ogden decline?  ...

The changes are subtle, but over the past three days, the inversion has gradually lowered and strengthened, reducing the depth of the valley cold pool through in which pollution is trapped. A quick look at the air quality data shows we have exceeded the National Ambient Air Quality Standard for 24-hour average PM2.5 in several counties including Utah, Salt Lake, Davis, Weber, Cache, and Tooele.  This is a regional scale event with a large fraction of Utah's population impacted. In Salt Lake, our 24-hour average PM2.5 presently sits at about 60 ug/m3.  Despite a drop in hourly PM2.5 overnight, there seems to be little reason not to expect the longer term upward trend to continue. Source: Utah DAQ Our first opportunity for a bit of stirring will be mid week.  The models still lack consensus, however, concerning how much of a mixout we may get.  Keep your fingers crossed.

That quote, uttered by Bill Murray character John Wingo in the Oscar-snubbed film Stripes , pretty much sums up the situation this morning. The upper-air sounding from this morning shows little change compared to yesterday.  We are capped under a very strong inversion in which temperatures increase from -13.1ºC at 5933 ft to 0.0ºC at 7534 ft. In the Salt Lake Valley, particulate matter concentrations continue to climb.  The eclipsed the National Ambient Air Quality Standard for PM2.5 yesterday and now sit at 47.5 ug/m3. Source: Utah Division of Air Quality The one silver lining in this event (if there is one) is that the base of the inversion is still elevated.  As a result, emissions are mixing through a layer that is about 1700 ft deep, which probably helps keep concentrations a bit lower than they would be if the inversion where based at the valley floor, as sometimes occurs during inversion events. We're stuck with this until at least Tuesday.  For...