Saturday, March 31, 2012

Dust Sources

Based on visible satellite imagery, the West Desert was the big producer today.  As is often the case, just a few wispy clouds can complicate dust detection and that was the case today.  Nevertheless, I've highlighted below a few areas where on can see evidence of plume initiation in the late-day satellite imagery.

There's also a very nice image MODIS that shows the plumes over the West Desert this afternoon.  Click to enlarge and you can also see a plume extending from the Skull Valley over the Great Salt Lake.  If you look really carefully, there seems to be some dust over the Tooele Valley that may be related to strong winds over and downstream of South Mountain.

2020 UTC 31 Mar 2012 Aqua/MODIS image
The origin of the dust over the Salt Lake Valley is a bit more of a mystery.  There's not an easily identifiable plume that we can trace upstream.  There may be a number of smaller point sources, as suggested in the top satellite image above.  There are techniques to better identify dust using all the channels received by the satellite that we can perhaps try in the coming days, but it could be that the dust over the Salt Lake Valley is not concentrated enough to be clearly identified.

A Historic Day

It appears we've at least tied if not broken the all-time record high for March at the Salt Lake City International Airport.  It was 78ºF until today.  It appears we've reached 79ºF so far.

I'd say wow, but after seeing what happened in the east a couple of weeks ago, this seems pretty tame.  Further, over the next few decades, we'll leave this in the dust.

Speaking of dust, things are just starting to get interesting.  I can't see the Oquirrhs anymore and the Wasatch are starting to look a titch fainter.

I suspect the entire valley will be enveloped eventually as the large-scale flow should gradually shift to southwesterly and put us in the dust-plume cross hairs.

On a weekend like this, the Wasatch Weather Weenies are like pigs in slop.


Amazing Imagery

Click on the above for a higher res version, but what a beautiful loop of the frontal cloud shield penetrating across the Sierra-Cascade ranges and dust in the southerly and southwesterly flow ahead of the front. I've indicated with boxes a few areas where plumes are visible, the most impressive being the Carson Sink of western Nevada which is absolutely lit up right now.

The Dust Is Here

Thusfar, the central Wasatch have escaped the wrath of the dust, but that's not the case in the western Salt Lake Valley and southern Oquirrh Mountains, as evident in the image above, which was taken facing south from the Avenues.  Note the obscuration in the right half of the image.

One of the most prominent plumes thusfar today is to our west, appears to originate in the Skull Valley (near the diamond I've annotated), and blows off downstream over the Great Salt Lake.

There's a chance this is smoke and not dust, but I can't imagine anyone would be burning anything today with so much lead time for the high winds.  The UDOT cameras also suggest it is dust.

Thusfar, we've had a wind gusts over 50 miles per hour at several stations in the lowlands of northern Utah, with a maximum of 62 miles per hour out in Dugway Proving Grounds.  I think we'll see higher gusts over the next few hours as the storm intensifies.

Hot and Dusty

Looks like a hot and dusty day is in store for today.  The day has dawned with a mostly clear, remarkably dry airmass in place over the Intermountain West.

Source: NCAR/RAL
The NAM time-height section for Salt Lake City (time increases to the left) shows dry air (relative humidity < 30%) aloft and in the lower troposphere (<70%, including near 30% at the surface).  

NAM relative humidity (color fill), wind, and equivalent potential
temperature analysis (contours)
Actual surface relative humidities will likely be even lower than indicated by the NAM.  And, the NAM forecast for this afternoon shows strong southwesterly flow over Utah.

All of this adds up to a hot dusty day.  Hot in this instance is relative to climatology.  The all-time record high for March is 78ºF and we'll make a run at that today.  I think something close to that is likely.  Some have called for a high in the 80s.  While that's not impossible, I think it's not likely as the airmass is not that warm.  

Dust?  Yup, it's pretty likely.  The flow is coming from the primary source regions for dust in Utah (West Desert, Sevier Desert, Escalante Desert, and Milford Valley in western and southwestern Utah) and is certainly strong enough to support emissions and transport if the surface conditions are favorable.  

Hopefully clear skies will persist through this afternoon so we can get a good look at any plumes that form.  

Friday, March 30, 2012

The One and Done Storm

Source: ESPN
Given that it is Final Four weekend, I'm naming our pending storm "One and Done," as in one monsterous airmass change.

The latest GFS calls for tomorrow to be warm and windy.  Crest level (700-mb) temperatures tomorrow are forecast to be near +6C at Salt Lake City, which would be the warmest airmass we've seen thusfar this Spring.

We'll probably see a high temperature at the Salt Lake City airport near 78ºF, which is the all-time record high temperature for the month of March.  Time will tell if we go into uncharted territory.  Blowing dust is likely, although we'll have to see if the trajectory is right for Salt Lake and the central Wasatch to get hit.

The GFS brings the surface front between midnight and 6 am on Sunday.  Should that verify the temperature change will likely still be impressive, but not as large as it would be if it came through in the afternoon.  You can't have everything!

By noon Saturday, the forecast crest-level temperatures have dropped to -10ºC, cold enough for snow down to the valley floor.

So, shorts Saturday, flakes Sunday.  I suspect we won't see much precipitation ahead of the front, but I like 6-12 inches at Alta by the end of the day Sunday and perhaps 1–3 inches on colder surfaces on the east bench as well.  I emphasize colder surfaces because the ground is so warm and likely to be warmer after Saturday's heat.

How quickly it gets cold behind the front is a critical factor in the snow forecast for the valley. The heaviest precipitation will likely come following frontal passage.  If the colder air lags the surface front, that precipitation may fall as rain or slushy snow and accumulations will be limited.  If temperatures fall quickly to near or below freezing, and precipitation rates are high so that ground temperatures can drop, accumulations will be greater.  Even in this case, we'll see major differences in accumulations depending on the surface.

Thursday, March 29, 2012

IPCC Speaks on Weather and Climate Extremes

The Intergovernmental Panel on Climate Change (IPCC) has just released a Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (a.k.a. SREX).  The Summary for Policy Makers and Full Report are available here.  Ignore the press coverage and go straight to the source.  

I haven't had a chance to fully peruse the report, which is more than 500 pages long (surely you will all consume and digest this by tonight).  However, since we have been talking the past week about heat waves and snow records, I thought I would summarize some of the key findings with regards to trends in extreme events:
  •  "There is evidence in observations gathered 1950 of change in some extremes. Confidence in observed changes in extremes depends on the quality and quantity of data and the availability of studies analyzing these data, which vary across regions and for different extremes."
  • "It is very likely that there has been an overall decrease in the number of cold days and nights, and an overall increase in the number of warm days and nights, at the global scale, that is, for most land areas with sufficient data."
  • "In many (but not all) regions over the globe with sufficient data, there is medium confidence that the length or number of warm spells or heat waves has increased."
  • "There have been statistically significant trends in the number of heavy precipitation events in some regions. It is likely that more of these regions have experienced increases than decreases, although there are strong regional and subregional variations in these trends."
  • "There is low confidence in any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity (i.e., intensity, frequency, duration), after accounting for past changes in observing capabilities. 
  • "It is likely that there has been a poleward shift in the main Northern and Southern Hemisphere extratropical storm tracks."
  • "There is low confidence in observed trends in small spatial-scale phenomena such as tornadoes and hail because of data inhomogeneities and inadequacies in monitoring systems."
My take is that is a pretty good summary of current understanding given limitations in observational datasets.  Note how the confidence is higher for those phenomenon for which we have good understanding and observations (e.g., temperature) and lower where there is insufficient data or understanding to adequately assess or evaluate trends (e.g., hurricanes and tornadoes).   They also note that there are regional variations in the quality of data and depth of analysis.  We see this even within the western United States where our understanding of climate is stronger on the Pacific coast, in part because of the strength and number of climate groups in California, Oregon and Washington, compared  to the Intermountain West.  

Wednesday, March 28, 2012

Snow Depth 451

Following up on the previous post and comments, I'm now a full-blown skeptic when it comes to the Tamarack, CA seasonal snow depth record of 451 inches, as recognized by the National Climate Extremes Committee.   When I say I'm a skeptic, I'm not dismissing it, I'm just saying that I'd like to see stronger evidence as the data available online from the National Climatic Data Center (NCDC) simply does not support such an extreme number, especially if it is supposed to represent the settled snow depth on level ground in a wind-sheltered area.  Ditto for other records from Tamarack.

What we need is an ambitious weather historian to follow the paper trail and possibly do some additional analysis of all the available data from the Sierra Nevada, including the historical archives from that era (e.g., newspaper, etc.).  Sorry kids, but you can't do all this on the Internet, which is precisely why I'm going back to running my computer models and hoping that one of you gets a spark of ambition to seek climatological fame and glory.   The truth?   Without a time machine, we'll never know, but it would be nice to assess the likelihood that this record is legit.  Perhaps Danny Kaffee has already won the trial and a report is buried somewhere in the NCDC archives that provides the evidence.

Tuesday, March 27, 2012

What Are the US Snowfall Records?

Sounds like an easy question, but the answer isn't so simple.  

I figured I'd go to the National Climatic Data Center, and sure enough, I found a web page for "National Snowfall and Snow Depth Extremes."  Ah, an answer.

Source: NCDC
But, years of wasting time reading about snow caused me to scratch my head about the numbers above.  I seemed to recall that California had some prodigious snowfalls.  Indeed, it's easy to find web sites with conflicting numbers from California.  In particular, many claim that the monthly snowfall record is actually 390 inches at Tamarack, CA in March January 1911 and the single storm snowfall record is 189" at Mount Shasta Ski Bowl from Feb 13–19 1959.  

I'm not sure why the difference in the monthly snowfall record, especially since it appears the NCDC data above includes an analysis of March 1911.  Perhaps the March 1911 data was deemed suspect?  I also wonder if the Mount Shasta record might extend over slightly longer than 7 calendar days and thus doesn't meet the bar for a 7-day records.  

Got any clues?  Let me know.  

Snow for Fools?

The medium range forecast models suggest we could see an April Fools' Day dump.  The GFS forecast looks especially nice.

I'm tempering my excitement given that this is a 5-day forecast, but I'm also thinking I'm going to be keeping the skis waxed and ready.  When it comes to powder, I'm no fool...

Monday, March 26, 2012

Orographic Convection

Gorgeous stuff being generated over Lone Peak and environs in the large-scale southwesterly flow. 

The Rainy Season Begins

On average, April is the wettest month of the year at the Salt Lake City International Airport and, although it is only March 26, it sure feels like the beginning of the "rainy season" today.  It's dark out, windy, and the rain is pelting the windows of my office, which face south.   I also think I saw a flash of lightning produced by the cells that were located in the eastern Salt Lake Valley earlier this morning.

Temperatures dropped like a rock at the University of Utah this morning.  After holding near 56ºF for much of the night, we're now at 37ºF.

There was a 51 mph wind gust at 8:15 too.

Yup, the rainy season is officially here.  Enjoy.

More Heat Wave Discussion

To followup on our discussions of the heat wave in the eastern US, Stefan Rahmstorf and Dim Coumou have just posted a discussion of linkages between global warming at heat waves at RealClimate.  They have a recent paper on this topic, although it's cost-for-access.  Those on the University of Utah campus should be able to access it for free due to our campus license.

Sunday, March 25, 2012

Like George Costanza, Do The Opposite

One of my favorite Seinfeld episodes is The Opposite, in which George Costanza realizes that every instinct he has ever had is wrong, and vows to do the opposite, with grand results. 

I often tell students, especially those who are used to the meteorology of the eastern United States, to take such advice to heart.  Often, the weather here works in ways that counter your every instinct.  

Tonight and tomorrow offer a straightforward example.  The NAM forecast for midnight tonight shows that the flow over Utah is from the south at the surface and 700-mb.  Instinct says it must be bringing in warm air right?

Wrong Costanza, do the opposite!  This is a situation where cold air pushed southward off the California coast the past couple of days and will swing into Utah from the southwest tonight and tomorrow.  As a result, that southerly flow is bringing in cold air.   

And, it will give us a changeable day tomorrow with the fast moving system giving us a few inches of snow in the mountains tomorrow.  

So, sometimes in meteorology you need to do the opposite, or at least avoid generalizations that are bound to break down when Mother Nature throws a curveball.  

Saturday, March 24, 2012

Weather Underground Extremes Web Page

My head is still spinning from the heat wave in the eastern United States (not to mention Canada).  The Weather Underground has a nice web page for examining weather extremes, including high temperatures, low temperatures, rainfall, and snowfall here, with an example of all-time monthly temperature records set on March 22nd shown below.

Source: Weather Underground
Enjoy a look at this extraordinary event.

Friday, March 23, 2012

Finding Powder

Incredibly, even though the high temperature at the Salt Lake City International Airport was 71ºF yesterday and the weather station at the top of the Collins Chair at Alta (10,400 ft) reached 43ºF, there was still some settled powder to be found in the Wasatch Mountains this morning.

Where?  Up very high on an aspect that faces due north.  I mean right on the north compass point.  Going even just a smidge off that compass point and you'll be dealing with a sun crust or manky snow depending on the time of day.

How is it that powder can survive when the free air temperature is above freezing?  First, the air is very dry.  The dewpoint temperature at the top of the Collins Chair at Alta, which we'll use as roughly representative of the highest elevations in the Wasatch, has lingered in the mid teens for the past couple of days.

As a result, while there is some heat flux from the atmosphere to the snow, there is also a net loss of energy because the snow is sublimating.  That means that ice is converting to vapor.  Sublimation leads to cooling, just like evaporation does.  If the dewpoint were higher, the sublimation would be weaker and it is more likely that the snow would become wetter on the north aspects.

Second, these aspects are in the shade.  Most of the energy to melt snow comes from the sun, so cutting direct solar heating out of the surface energy balance makes a big difference.  This only works on northerly aspects that are clearly shaded all day.  Lower-angle northerly slopes can still see the sun and that's all it takes to trash the powder.

I don't know if the powder we found today will survive the winds that are coming, but there is another storm coming in on Monday.  It looks to be a warm one and potentially a quick hitter, but perhaps it will give us another quick flirtation with freshies.

Thursday, March 22, 2012

Northeast Heat

I've been looking at the heat in the northeast and it is truly mind boggling.  The Snowmiser has clearly seceded ground to Heatmiser.

Yesterday's high temperatures are ridiculous.

Burlington, Vermont hit 81.  Their old record for the date was 68.  Bangor, Maine reached 83!  83 in Maine in March, are you kidding me?   Their old record was 64.  Caribou, Maine made it to 73 compared to an old record of 57.  How about these ridiculous numbers from Michigan.  The high in Marquette was 81.  Their previous record high was 49 (although their climate period only goes back to 1961).  In fact, the minimum temperature in Marquette yesterday was higher than their record high temperature.

Source: NWS
Then there's some web cam photos from northeast ski areas.  First, Hunter Mountain, Snowmaking Capital of the World.

Source: Hunter Mountain
Killington, Vermont, where I once skied in June.

Source: Killington
Stowe in northern Vermont.

Source: Stowe
Welcome to the new climate in which heat waves are pushing farther outside the envelope of what has been observed previously during the historical record.  To quote Hansen et al. (2011), "Today's extreme anomalies occur because of simultaneous contributions of specific weather patterns and global warming."  I'm usually very cautious about linking weather events to global warming as there is considerable natural variability in the system, but these are jaw-dropping records and such events are more likely today than 60 years ago.  Note how the distribution of local temperature anomalies has shifted into warmer values and become broader over the past 6 decades.

Source: Hansen et al. (2011)

The bottom line is that extreme outlier events like this one are becoming more common and more jaw dropping.  

Wednesday, March 21, 2012

Vermont: Crazy Warm

Some wild stuff is happening back east.  Unbelievable temperatures in the northeast.  Burlington in northern Vermont hit 80ºF yesterday, the earliest occurrence of 80 degrees in the historical record, which dates back to 1883.  In fact, it breaks the old record by 9 days and is only the 6th 80 degree day ever observed in March.   Today will be the fourth consecutive day of "crazy warm" temperatures.

In fact, as of 10:30 AM, the current temperature of 69F was already a record for the day.

Win Smith, President and owner of Sugarbush ski area describes the situation well in his blog post from yesterday.  Actually, I found this post to be quite forthcoming and lacking the sort of candy coating that one often sees on ski area web sites.  Of course, New England skiers have always enjoyed whatever skiing they can get.  Kudos to them.

Tuesday, March 20, 2012

Here at the Wasatch Weather Weenies, our posts typically concentrate on the science of mountain weather and forecasting.  Although we often discuss the forecast, education and outreach is our primary mission and objective.  

Looking for resort-specific forecasts for the Wasatch Mountains?  You might consider checking out, a web site run by Atmospheric Sciences students at the University of Utah that provides forecasts for every resort in Utah as well as the Wasatch backcountry.  Have a look, but be sure to come back to the Wasatch Weather Weenies for the geeky stuff.  

And, for you University of Utah snow geeks out there, Ned Bair of UC-Santa Barbara will be giving a seminar tomorrow (Wednesday) at 3 PM in 110 INSCC entitled "A Field Study on Failure of Storm Snow Slab Avalanches."  The seminar specifically examines the mechanisms of avalanches in new snow that has net yet undergone metamorphosis into faceted or rounded grains.  

Monday, March 19, 2012

Perishable Powder

If you aren't skiing today, my advice is that you call in sick tomorrow.  Whatever humans haven't tracked and trashed today, Mother Nature is going to take care of the next couple of days.

The GFS is calling for a rapid rebound in 700-mb (crest level) temperatures to -4ºC by late tomorrow afternoon and 0ºC by Wednesday afternoon.

For the powder on all but shady upper-elevation northerly aspects, this means easy come, easy go.  Our brief flirtation with winter is almost over.  I'm heartbroken already, but it is better to have loved and lost than never to have loved at all.

Embellishment Not Needed

Sunday, March 18, 2012

Good Things Come to Those Who Wait

Kevin Hammonds
Finally!  A decent day of backcountry skiing.  In fact, it was probably my best day of the year as I missed the last decent run of powder thanks to a balky back.  Conditions were quite good above 9000 feet and not bad below that, although it got a tad stiff at elevations that were in the melting band during the snowfall late yesterday and overnight.  Even south aspects skied well thanks to the persistent cloud cover.   Most of our turns were at elevations above 8500 feet.

Looks like about 23" now at Alta-Collins since yesterday afternoon.  I'd say more like 10-12" where we were today, but that was enough given the right-side-up density profile.

Big Totals for Some

Sometimes I love when a forecast busts.  Sometimes I don't.  I'm not sure what to think of this one.  It's been a crazy night.

The Utah Avalanche Center reports 13–16" in the Cottonwoods, 8–10" in the Park City mountains, and a trace–2" in the Ogden and Provo area mountains.  That distribution reflects the fact that beginning in the late afternoon yesterday, a persistent, localized band of precipitation setup and really hit the central Wasatch, as discussed in posts from yesterday.

Temperatures and snow levels have been high, but are falling this morning.  Nevertheless, given how high they were for much of the night, there's a huge contrast in the snowfall as you move from about 7500 to 9500 feet.  Location and altitude dictated accumulations overnight.

We stopped getting data from Alta-Collins at 5 am, but at that time, there was 14" of snow produced by 1.51" of water since things got going yesterday afternoon.  That is a lot of water weight and Little Cottonwood is presently closed for avalanche control work.

In the last few hours, we've transitioned to a situation where the precipitation is more wide spread and driven by larger-scale factors.

Temperatures should be dropping during the day as colder air moves in, which will hopefully lead to lower density snow.  Enjoy it if it's white.

Saturday, March 17, 2012

Luck of the Irish?

As suggested in a comment from one of our readers, perhaps the luck of the Irish is shining on us tonight. There is still an area of precipitation sitting over the central Wasatch, Mount Timpanogos, and environs.

Source: NCAR/RAL
It's really quite remarkable.  The northern Wasatch, which sometimes does well in southwesterly flow, has been largely skunked.  Keep in mind that snow levels are still quite high, so accumulations are minimal below 8000 feet, but it's piling up in the higher elevations, with 8" since 2 PM at Alta-Collins with .94" of water.  Yeah, it's Cascade Concrete, but who are we to be choosers this year?

Dust and Snow

The dust is finally here, at least in the western Salt Lake Valley as the Oquirrhs are becoming obscured.

And, good fortune continues to shine on the upper Cottonwoods and environs as that precip band is just locked in.

It's pretty warm up there, 29F at Alta-Collins and 35F at the base.  The snow level must be near 8000 feet.  Nevertheless, we'll take it, and it never hurts to start a storm with some high-density stuff.

It's Good To Be Lucky

For the past couple of hours, there has been a persistent train of echos extending along the southwesterly flow from southern Utah County across Mount Timpanogos, the upper Cottonwoods, and the Park City ridge line.

At times, things looked quite sinister from the Salt Lake Valley, with some mammatus for a brief period of time (photo below a bit fuzzy, sorry...).

Alta is getting quite a thumping, with .29" of water equivalent recorded from 1-4 PM, including .21" in the past hour, with 2" of snow (ignore the snow depth in the data table below).

You never know where bands like this are going to setup.  You can see another one to the west side of the radar loop that's also been fairly persistent (but not as broad).  It's good to be lucky!  Hopefully good luck will shine further on us tonight.

Addendum @ 455 PM

Altitude is everything.  During the period above, Alta gets the goods, downtown Park City the drips.