Saturday, April 21, 2018

Peak Snowpack, Emerging Snirt

Based on the forecasts I'm seeing right now, there's a pretty good chance we're at at the apex of the seasonal upper-elevation snowpack right now.

The latest from the Snowbird SNOTEL shows a snowpack water equivalent of 30.1 inches (green line), which is 71% of median for the date and 70% of the peak median.  Those are close because the average time of peak median snowpack is about right now. 


Forecasts for the next 10 days show loaded dice for warm, dry conditions.  You know, the stuff we can't seem to shake.  There's always hope that a weak system or two can generate something, or that the forecasts are simply wrong, but the 6-10 day outlook is pretty telling. 


Thanks to the dust storm earlier this week, snirt is emerging pretty quickly and was visible in many areas this morning.  The photo below is of Lake Peak in upper White Pine. 


The dust is co-mingled with the melt-freeze crust that developed prior to the Tax Day snowfall. 


Sadly, wind and warmth are quickly laying waste to that snowfall and dust is emerging on the top of the snowpack.  This is the basic problem with dust.  The storms are most prevalent in spring, they put dust near the surface of the snow, and it quickly emerges once the snow starts to melt.  In this instance, most of the dust is from a local source in the Cedar Valley west of Utah Lake, although there may have been some more remote sources, such as the Sevier lake bed, contributing later in the day on Monday. 

Turns?  I'm not sure what to call the conditions above 10,000 feet.  Settled powder if generous.  It didn't ski too bad above that level. 


Our future is quite clear in the photo below.  Look how dark that dust is!  It's going to be really really ugly in a few days. 


My advice: Ski this weekend if you can.  After that, it's going to be Snirty Dancing. 

Friday, April 20, 2018

How I Became a Meteorologist

How (or why) did you become a meteorologist?  It's a question I ask my students on the first day of class each semester.  Many people who are meteorologists have wanted to be one for most of their lives.  Often they can point to a specific weather event, perhaps a tornado, hurricane, or winter storm, as the moment that they decided to go into meteorology.  In some cases, I know multiple people who were motivated to become a meteorologist by the same storm

I was infected early by the weather bug.  My path to meteorology was paved by youthful experiences in the Adirondack Mountains.  The weather in the Adirondacks is usually somewhere between partly and mostly crappy,  and in the late 1970s and 1980s the forecasts were truly terrible.  Whether hiking, backpacking, canoeing, nordic skiing, or alpine skiing, we had to be prepared for anything. 

There are, however, two backpack trips that were essential for sparking my interest in weather.  My father and I used camp or backpack in the Adirondacks every Columbus Day weekend, which is a long weekend in New York State.  In 1981, the trip was especially memorable because it had snowed at upper elevations.  We spent three days in the High Peaks Wilderness and hiked much of the Great Range, one of the most spectacular areas in the Adirondacks.  Our experiences greatly stoked my love of snow and my interest in mountain weather.

Dad and I on the trail.  Heavily clothed in cotton.  We had plastic ponchos too.  It was a different time!
The Great Range from Big Slide Mountain.  Gothics is just left of center, named by Adirondack Guide Orson Phelps for the slides that resemble Gothic architecture.   
Filling water bottles from a local stream.  I don't remember ever filtering or treating water.  It was a different time!


The Great Range and other high peaks from Armstrong Mountain

On the summit of Gothics.  This was my 9th "high" peak, one of 46 Adirondack Peaks thought to be at or above 4,000 feet in early 20th century surveys.

On "belay".  Well not really, but some Adirondack trails have cables and other contraptions to aid in the ascent and descent.
A second trip, which I usually cite as the moment I decided to become a meteorologist, occurred a couple of  years later.  We were on an overnight backpack in the High Peaks when we were caught in a torrential thunderstorm.  We hastily descended to a low pass and pitched our tent, eventually waking the next morning in a pond of water.  It was at that time that I decided that was never going to happen to me again and that I would become a meteorologist. 

A strong desire to understand and predict the weather I encounter in the mountains has been a great source of ideas and motivation for me through my career.  When in the mountains, I still feel like a kid in a candy shop.  So much to observe and understand!  The paths of others in my field may be somewhat different, but passion for weather and the natural world seems to flow through nearly all of our veins. 

Thursday, April 19, 2018

Passage of a Bowling Ball

Interesting forecast situation through Friday night as a closed upper-level low, which rumbles like a bowling ball across the American southwest, moves along the Utah–Arizona border.


If you look at the 3-h NAM precipitation forecasts above (color fill) you can see that northern Utah misses out on the action initially, but does get some after the low enters Colorado thanks to so-called wrap-around precipitation.  In the NAM forecast above, that precipitation primarily affects northeast Utah, especially the Uinta Mountains.  The Wasatch are at the edge of the action and in fact Alta gets no precipitation from the forecast above (but it is right on the edge of it). 

The strong contrast in precipitation probability from west to east across northern Utah is better illustrated by the probability of more than 0.10 inches of precipitation during the 12-hour period ending at 0600 UTC 21 April (0000 MDT Saturday) based on forecasts by the Short Range Ensemble Forecast System (SREF).  Note the sharp gradient from about Antelope Island to the western Uintas.


Indeed, if we downscale those SREF runs to account for local terrain effects, we see large spread at Alta, with members producing anywhere from 0 to 0.7 inches of water.  This would fall mostly as wet snow above 8000 feet, with snow levels possibly flirting with 8500-9000 feet Friday night should precipitation linger.
My take is that thisI is that we may see a few snow showers Friday and Friday night, but accumulations will likely be 1-4 inches.  A skunking is perhaps more likely than a surprise dump.  The latter would require the wrap around to extend further westward than indicated by most of the models I'm looking at this morning. 

After Friday night, the forecast for the weekend looks warm and pleasant.  If we do get a decent dump Friday or Friday night, it will turn to mank quickly on Saturday if it isn't already mank at sunrise. 

Tuesday, April 17, 2018

Tax Day Lake Effect Graupelfest

The tax man cometh and hath taken away your spring.

Following a high of 75˚F yesterday, it makes perfect sense to wake up to a coating of snow this morning.  After all, this is spring in the Intermountain West.


Most of that snow was produced by the passage of the frontal band overnight.  However, early this morning, lake effect got going and trained off into the Salt Lake Valley eventually shifting eastward into my neighborhood, namely the Avenues and University of Utah at around 1340 UTC/0740 MDT.


Most of the precipitation falling from then through 0800 MDT was in the form of graupel, which is basically a small ice pellet formed as supercooled liquid water droplets freeze on contact with ice crystals.  The graupel was relatively warm and cohesive and clung together just enough for demonstrations of the viscoelastic nature of snow.



The ski cognoscenti know that graupel is wonderful to ski on.  I would take a good, prolonged graupel storm over the cold smoke any day of the week.   The first thing that came to mind when the graupel started falling as I walked to the bus was, "I wish I was skiing!"

A couple of additional factoids about graupel.  Because of it's higher density and fall speed, and in some cases large size, it can often penetrate farther below the freezing level than regular snowflakes before melting.  Second, it is one of the ingredients for getting charge separation and thunderstorm development.  I haven't seen any lightning detections so far in this storm, but it happened in our lake-effect event last Friday.

Looking for Ski Crampons

I'm looking for some Dynafit ski crampons.  110 mm or 100 mm width.  If you have a used pair to sell, drop me a note at jim.steenburgh at gmail.com.

Monday, April 16, 2018

Where Today's Dust Is Really Coming From (Not Sevier Lake)

The Wasatch Front has long had episodes of poor air quality related to elevated PM2.5 concentrations during our dreaded wintertime inversions.  We have also seen episodes of elevated and sometimes unhealthy PM2.5 concentrations due to blowing dust.  There are multiple dust sources in southern and western Utah, but this winter, the Cedar Valley west of Utah Lake has been especially productive.

One of our post-docs, Derik Malia, first brought this source region to my attention in December.  In my blog post on December 21, we discuss two major dust plume events that clearly originated from the Cedar Valley on 3 December and 19-20 December.  Below are MODIS imagers of those two events clearly showing the plume extending from the Cedar Valley to the Salt Lake Valley.



Today?  Same story.  The latest MODIS shows the Cedar Valley is the primary source for the dust impacting the Salt Lake valley.  Look at the clear plume that begins just to the west of Utah Lake.


Sadly, media reports, such as the one below in the Deseret News (available in full here), are stating that the dust is coming from the Sevier Lake Bed.

This is also being suggested in the tweet below from the Utah DEQ.

The Sevier Lake Bed can be an important source for dust, but in the MODIS image for this afternoon, that dust is going northward into the West Desert (look closely).  Our dust today, and in the December events, is coming primarily from the Cedar Valley.

These plumes are repeatedly impacting over 1 million people in the Salt Lake County and portions of Utah County.   Dust from these plumes, once deposited on the Wasatch snowpack, result in an accelerated snowmelt due to greater absorption of solar radiation.  

Reducing emissions from the Cedar Valley won't eliminate wind-blown dust events, but it would certainly reduce the frequency, duration, and severity of these episodes in the Salt Lake Valley.

Nearly Another Tax Day Storm

Strong cold fronts and associated mayhem are pretty common in northern Utah around Tax Day.  The all-time classic is the 15 April 2002 Tax Day Storm, which produced the 2nd lowest sea level pressure observed in Utah since record keeping began in 1892, temperature falls of 7˚C in 10 seconds and 19˚C in 2 hours, and wind gusts of more than 60 knots.  Others include the 2015 Tax Day Storm, described by Judy Fahys in this KUER article

We would have another today, if not for an oddity in the calendar.  Chances are you've noticed the nuking southerly flow, and the NWS has wind advisories or warning's up for much of weatern and southern Utah.


The view from my office is starting to look dusty.  What a shame it will be if we put down a layer of brown goo on the wonderful white snow we have right now. 

The culprit in this case is a strong front and surface trough to our west.  These features are forecast by the HRRR to extend across far NW Utah at 2000 UTC (1400 MDT) this afternoon. 


Frontal passage is expected late this afternoon (the HRRR pegs it at around 5 PM MDT for the northern Salt Lake Valley).  Sadly, the surface frontal passage will be a dry one, although precipitation will develop in it's wake tonight.  It's a quick hitter event, but don't be surprised if you wake up to some white stuff on cold surfaces tomorrow depending on the elevation of your home.  As usual, monitor official forecasts. 

Now, getting back to Tax Day, what is so special about it?  Basically, its a noteworthy day in the heart of the peak season for strong cold-frontal passages in the Intermountain West. 

Source: Shafer and Steenburgh (2008)
Today's frontal passage almost qualifies as a Tax Day Storm.  Normally, April 15 is Tax Day, but April 15 fell on a Sunday.  While that should shift Tax Day to today, Washington D.C. observes Emancipation Day on April 16, which pushes Tax Day to April 17, tomorrow.

However, if you want to call this a Tax Day Storm, I'm good with it.