Saturday, April 30, 2011

Lake Effect Powder Sampling

Hard to believe that tomorrow is May 1st.  This is two years in a row with great skiing on April 30th.

The cover in the Wasatch is incredible.  If we can get a corn cycle going, we could have some great chute skiing in the BC for the next few weeks.

Tim Garrett send me some photos today from his new snowflake cam that Howie and the folks at Alta have been running the past several days.  I'm really looking forward to having these at full res and in real time next winter.  Here's a teaser.

Source: University of Utah/
Center for Snow Science at Alta

Lake Effect Powder

Source: NCAR/RAL
An active night of lake-effect last night, such as the band above, gives the Alta-Collins site 15" since yesterday afternoon.  The powder just keeps coming!

I suspect some sites in the Salt Lake Valley are waking up to a pretty good coating as well, but the NWS has yet to post up their observer totals.

Little Cottonwood is presently closed as they are shooting the highway this morning.  Anticipated opening is 8:30 am.  I think we all owe a debt of gratitude this year to the snow-safety pros who have had an incredibly long season.

Friday, April 29, 2011

240 Miles, 24 Degrees

After my last class on Wednesday, we bugged out to Moab for a much needed thawing out.  The drive back today was incredibly dramatic from a meteorological perspective, beginning in mild pre-frontal conditions in Moab where it was about 62F, and ending in scattered snowshowers and temperatures in the 30s.  We'll call it 240 miles and 24 degrees for alliterative purposes.

11 am on the Moab Rim
Looking NW into the orographic cloud from just south of Price.
It was post-frontal here, but as is often the case in Price during NW
flow, we were solidly in the orographic rain and cloud shadow.
Spanish Fork Canyon.
About 5 PM in Salt Lake.
Currently, convective snowshowers abound around northern Utah, with some indication of a bit increased intensity and duration downstream of both the Great Salt Lake and Utah Lake (a loop shows this better, but the best I can do on short notice is the still show below).

There was a really nice banded, ragged cloud base over Utah Lake as we drove through Provo, but I couldn't risk a quick snapshot given the traffic and driving conditions.  Yes, I know I should be able to simultaneously talk on a cell phone, text, and take photos, but keep in mind that my first computer was a Commodore 64.

Lake-effect prospects for tonight look quite good with deep instability and moisture.  We'll have to see if Mother Nature brings the goods and if she directs the action to the Cottonwoods before the flow veers to northerly.  

No matter what happens, anything we get is icing on the cake of a great ski season.

Wednesday, April 27, 2011

Start Building an Ark?

Beaucoup snowpack out there.  Let's have a look thanks to the National Weather Service Colorado Basin River Forecast Center web site.

Tony Grove Lake (8400 ft) is at 64.7" of snow water equivalent (SWE), ahead of their highest previous water year, 1982.

How about a lowland site in the northern Wasatch?  Ben Lomond Trail (6000 ft) is at 23.1" of SWE.  There has been some decline in snowpack the past couple of weeks at this elevation, but the total SWE remains near all-time marks (1984).

Lookout Peak (8200 ft) near the top of City Creek Canyon, 54.1" of SWE, which puts it at a whopping 246% of average, the highest since site installation in 1989.

Snowbird is at 72" of SWE, which incredibly is still a smidge behind the peak in 2005.

You get the point.  The Snotel records for these sites go back 2 or 3 decades, so they are short-term climatologies, but it is safe to say that we have an incredible snowpack not only at upper elevations, but also at lower elevations, a point well made by National Weather Service hydrologist Brian McInerney in his latest spring flood potential briefing.

In addition, there's another storm coming.  We'll have a brief warmup tomorrow and then another deep trough moves across Utah on Friday and Saturday.  The NAM model brings in 700-mb temperatures that are below -14C by Saturday morning.  

In a word, unfreakingbelievable.  So, it is in the bag that we are going to go into May with an incredible snowpack in the upper and lower elevations.  In other words, we're "locked and loaded."  A big runoff is coming.  At issue is will the weather release all this water in a way that is gradual so the flooding is localized or rapid so it is widespread.   Let's hope we don't need an Ark.

Source: Evan Almighty

Tuesday, April 26, 2011

Alta 200!

The Alta-Collins snow stake just hit the coveted 200" snow depth mark!

It's now official.  The ski season has attained EPIC STATUS.  Time to celebrate with a cold one from my favorite brewery.

In fact, I think they need to come up with a winter ale for next year to celebrate this momentus occasion.

Alta 700?

I suppose I shouldn't rely on such non-scientific estimates, but Alta does a good job collecting snow data and speculating on a seasonal total of 700" being reached is fun.

Alta was reporting a seasonal snowfall of 680" yesterday morning.  Since then, Alta-Collins has recorded 5" yesterday, 12" overnight, and 3" this morning.

Fortunately, I can do this math with all my fingers and toes: 680+5+12+3=700!!!!!!!!!!!!!!!!!!!!

Whether or not that will be the official party line from Alta, I don't know, but it's hard to imagine their PR department does math any differently than I.  Besides, there's another storm coming, so 700 is in the bag and the only questions now are will be get to a 200" base and will this ever end?  What is the Alta seasonal snowfall record?  Another storm is coming...

Ongoing Lake Effect

Lake-effect snow showers continue over much of the Salt Lake Valley this morning.  It looks like winter out my window.  Wish I was skiing.

As we have seen in some lake-effect events, there appears to be weakly confluent flow over the Great Salt Lake and northern Salt Lake Valley.

An ongoing debate around here concerns the mechanisms for this confluence.  Is it a result of the superposition of the large-scalel southwesterly flow with the thermally forced circulations of the Great Salt Lake, or a reflection of topographic blocking?  Concavities in terrain have been shown to drive confluent flow and increase precipitation rates in idealized modeling studies (e.g., Jiang 2006).  We don't have a clean concavity given the basin-and-range terrain south of the Great Salt Lake, but there likely are concavity effects.  On the other hand, the confluence could be thermally driven.  Perhaps both play a role?

Alta-Collins update: 14" new since 7 PM yesterday.  Snow depth 196".

My Radar Secret Weapon

With the KMTX radar dead thanks to a lightning strike, one needs to resort to desperate measures to peer into our ongoing storm.  Fortunately, I have a secret weapon.

The FAA operates a Terminal Doppler Weather Radar (TDWR) near the southeast shore of the Great Salt Lake.  The TDWRs were developed to help with the detection of wind shear, an important aircraft hazard.  They are also quite useful as precipitation radars, although the Bountiful siting, while advantageous for detecting low-level wind shear near the Salt Lake Airport, suffers from considerable beam blockage to the east (by the Wasatch) and south (by the Avenues foothills).

A loop of TDWR radar imagery this morning shows lake-effect snow squalls moving off the Great Salt Lake into the Salt Lake Valley.

Unfortunately, the east bench and the area around Alta is shielded by beam blockage, but the Alta-Collins stake shows 10" from 5 PM yesterday through 7 am this morning.  They are oh so close to a seasonal total of 700" and a base of 200".  Come on Mother Nature!

Monday, April 25, 2011

KMTX Radar Out

The KMTX radar is presently down.

It was struck by lightning and will not be up any earlier than tomorrow.  I'm really glad we don't have a team deployed doing soundings of lake-effect now as without the radar, the case would have been a total loss.

Spring Rumblers

Pea sized hail (or perhaps better put, "grail" since it's almost more like graupel than hail) fell in the Avenues  with a thunderstorm just before 7 PM.  Ah, spring!

Apparently, the ongoing cold weather can be attributed to a software bug on the National Weather Service computers.
Courtesy Bill DeMong via Karl Weatherly

Prospects for Deep Powder Skiing

Feeling the itch for one last deep powder day before the season comes to and end?  Tomorrow could be the day, but it could pay to wake up and check the Alta-Collins snow stake or Snowbird Snowcam before calling in sick.

Although there are times when one can bank on a powder day, there are other times when there are synoptic possibilities, but whether or not we get the goods for a great powder day depends on mesoscale processes that cannot be confidently forecast 24 hours in advance with current technology.  A good analogy is storm chasing in the midwest where the potential for tornadic thunderstorms can be forecast a day or two in advance (sometimes longer), but success on a storm chase depends on factors that are not predictable at such long lead times.

This cartoon cracks me up, but have no idea who created it!
Thanks to the anonymous comedic meteorologist. 
So, tomorrow we have the possibility of a deep powder day, but whether or not Mother Nature brings the goods depends on mesoscale processes that are not well handled by our computer forecast models and are difficult to predict a full day in advance.

What we do know is that a cold front will move across northern Utah this evening.  The NAM model puts this front on our doorstep at 9PM this evening.

The NAM time-height section for Salt Lake City shows the frontal passage quite clearly at about 0300 UTC (9 PM), with moist, potentially unstable flow with and following the frontal passage.

The post-frontal flow is northwesterly, and the NAM produces heavy orographic and lake-effect precipitation overnight.

If this were to verify, it would be epic late April skiing in the Cottonwoods tomorrow, provided the convection doesn't produce too much graupel (and even if it does, sometimes that skis good too).

On the other hand, we have to remember that this is a model simulation.  Of concern:
  • The NAM model has a grid spacing of 12 km.  The processes that generate orographic and lake-effect convection are NOT resolved well (if at all) at that resolution.  
  • The duration, intensity, and location of orographic and lake-effect convection are very sensitive to small changes in upstream temperature, moisture, and wind, which limits predictability. 
  • The NAM uses (we think) climatological Great Salt Lake temperatures, that are probably higher than the actual lake temperature.  
  • What is the actual lake temperature?  We don't know because there are no publicly accessible real-time lake-temperature sensors over the interior of the lake.  Ridiculous!!!
So, we have synoptic possibilities, but ultimately the quantity and quality of the we get depends on mesoscale processes that are poorly resolved by the NAM and are sensitive to upstream flow characteristics.  I think things look pretty good for a powder day tomorrow, but what ultimately happens depends on fickle mesoscale processes.

Update: 9:45 AM

Here's the latest AVHRR 7-day mean Great Salt Lake temperature courtesy of Erik Crosman

which yields a 7-day mean lake temperature of about 11.3C.  Climatology if 15.1C.  Thus, the NAM is likely "Jacked," although that doesn't mean lake-effect won't occur as even with the lower observed lake temperatures, we have the possibility of lake effect tomorrow morning.  Unfortunately, for the reasons noted above, that's about all we can say.

Saturday, April 23, 2011

Winter 2010-11: Approaching Epic Status

The skiing isn't great right now, but it ain't bad and more like winter skiing than spring skiing.  Where is the sun?  Who cares.  We've had nearly 6 consecutive months of quality skiing with barely a hint of spring.  Today offered up another day of light snow, no crowds, friendly locals, and good skiing for 23 April.

Winter 2010-11: The gift that just keeps giving.
Erik on Gunsight.
You can't complain about turns like this on 23 April.
April hasn't been as good as last year, but it's been pretty good.  We've had a hell of a year.  I wasn't ready to stamp this year as epic a couple of weeks ago, but continued good skiing is getting us close.  Further, there's more snow coming.

Last Push for the Alta 200?

We're sitting at about 180" at the Alta-Collins snowstake, with a peak thusfar this spring of 195".  The pattern has been unsettled the past few days, but we need a big dump to get us to the magic 200".

Perhaps our last chance to take a run to 200" will be over the next 3-4 days.  The pattern remains unsettled, and the NAM model produces a fairly healthy trough passage with a prolonged period of cold, unstable northwesterly flow Monday night into Tuesday.

The GFS model is also looking optimistic for snow during the period.  It's far enough out that we can't get too excited about the model forecasts yet, but they are showing the potential to get Alta-Collins to 200".  Further, they could bring some pretty good powder skiing back to the Wasatch.  Last year my best day of backcountry powder skiing was on April 30th.  Perhaps another late April repeat?  Stay tuned.

Friday, April 22, 2011

Sobering Thoughts on Earth Day

Source: NASA Goddard Space Flight Center
On December 2, 2004, Richard Smalley, the 1996 Nobel Laureate in Chemistry, gave the Frontiers of Materials Research presentation at the Materials Research Society Fall Meeting in Boston.  An edited transcript of the talk entitled Future Global Energy Prosperity: The Terrawatt Challenge was then published in the Bulletin of the Materials Research Society.  I don't recall how I came across it, but since I can't seem to find it online (even in the BMRS online web site), I'm making it available here for your Earth day reading pleasure (or perhaps displeasure).

Although the intro is somewhat dated and contains some political banter that you may or may not like depending on your political persuasion, it contains a very sobering assessment of the energy challenges we are facing.  In particular:

  • In 2004, average global energy consumption was about 14.5 terawatts, or the equivalent of 220 million barrels of oil per day.
  • Most (~80%, ) of this energy is generated from oil, gas, and coal, although nuclear fission, hydropower, and biomass contribute.
  • Solar, wind, and geothermal account for only ~0.5%.

That's where we were just recently.  Global energy demands are expected, however, to double by the mid-21st century and it is estimated that it will take 60 terawatts of energy production to bring 10 billion people to the level of energy prosperity of the developed world.  Current projections put the world population between 7.5 and 10.5 billion by the year 2050.

Now, if you are like me, you probably don't have any idea how big a terawatt is, but Smalley does a nice job of putting it into perspective.  A large nuclear reactor produces about 1,000 megawatts of power.  To produce 10 terawatts of power requires adding 1,000 megawatts of power generating capacity, or the equivalent of one large nuclear reactor, every day for the next 27 years.   This power production doesn't have to come from nuclear, but the analogy helps put the scale of the energy challenge into perspective.

So, let's get real.  If we wish to dramatically reduce global carbon emissions and make a significant dent in future global warming, we're not going to accomplish much with incremental improvements in efficiency or lifestyle changes such as riding bikes and driving hybrid cars.  There are good reasons for doing those things, such as improved personal health and urban air quality, but, as Smalley argues, we should not be distracted from the overarching need to produce "cheap, clean energy in vast amounts." In other words, innovation is needed to make a quantum leap in how we produce, distribute, and store energy.  That is the challenge facing us this Earth day.

Thursday, April 21, 2011

Wet Soil Is Weak Soil

Strong winds associated with thunderstorms ripped through northern Utah this afternoon.  Several sites reported wind gusts of more than 65 mph, including the Salt Lake City Airport.

MesoWest observing sites reporting wind gusts greater than 65 mph this afternoon.
Several large trees were blown down.  Although some snapped, others fell over with the entire root ball (see Salt Lake Tribune story).  

Source: SL Tribune, courtesy Greg Farley.
A contributing factor to these tree blowdowns is the rainy April we've had and the anomalously wet soils.  Wet soil is weak soil, and trees are more likely to pull up in the fashion above when the ground is saturated or near saturated.   

Powerful Storms

A line of powerful thunderstorms is moving through northern Utah.  The National Weather Service has issued a severe thunderstorm warning for several counties in northern Utah.

Several sites have reported gusts in excess of 60 miles per hour.  The big one thus far is Ogden Peak with a gust of 104 mph.  

An impressive 67 mph was recorded at KSLC airport.

Nighttime Thunderstorms

Scattered thunderstorms moved across northern Utah not only yesterday afternoon, but also overnight.  The Salt Lake City Airport, for instance, reported lightning to the east at 0653 UTC (12:53 AM MST).

A radar loop covering that time shows several strong cells moving across the Great Salt Lake and a line of strong convection late in the loop near the Utah-Idaho border.

Many people are mystified by the development of nighttime thunderstorms, especially in Utah.   Are nighttime thunderstorms unusual?

In a seminal paper on the diurnal variation of summer thunderstorm frequency, Wallace (1975) showed that in midwest of the United States, summer thunderstorms are more common at night than during the day.  

The diurnal cycle of thunderstorm frequency in the summer.   The barbs
indicate the normalized amplitude of the diurnal cycle (half barb=5%; full barb=10%;
flag=50%).  Phase indicated by orientation.  From the north indicates midnight
(0000 LST) maximum, east 0600 LST, south 1200 LST, and west 1800 LST.
Source: Wallace (1975).

On the other hand, in the Intermountain West, the maximum is in the late afternoon and early evening.  So, it is not unusual for thunderstorms to develop at night, but in Utah, it is somewhat less common.

Last night, however, differential temperature (and moisture) advection with respect to height helped to generate instability.  Note how the wind in yesterday afternoon's KSLC sounding veers (turns clockwise) with height in the low levels (from the surface to about 700 mb) and then backs (turns counterclockwise) with height from 700 mb to 500 mb.  This implies (based on our dynamical understanding of atmospheric flows) low-level warm advection and mid-level cold advection, which helps to generate thermodynamic instability.

Overnight, moisture was also on the increase at low levels.  In fact, by 6 AM MDT this morning (1200 UTC), we have a positively juicy sounding to play with.  There's a stable layer at low levels, but a parcel lifted from the top of this stable layer (831 mb, dashed line) has a deep layer positive area and 877 J/kg of CAPE to play with.  

So, last night we destabilized the atmosphere through differential temperature and moisture advection.  No solar heating needed!  It is pretty quiet at the moment, but instability and moisture are present and things should get interesting later today as a trough approaches from the west and provides the lift needed to trigger convection and thunderstorms once again.

Wednesday, April 20, 2011

I Can't Take It Anymore!

As a meteorologist who skis, I live for cool stormy weather, but like many of you, I can't take it anymore!  It's time to join the Homer Simpson Angry Mob Fun Run and declare open season on Mother Nature.  These spring storms don't provide great powder skiing and do nothing but muck up the corn.

We're in a bit of a break now, but I just looked at the short- and medium-range forecast guidance and unsettled weather continues for the next several days.  I wish we could send this weather to Texas where they could use a dousing for the wildfires have now charred a million acres.

Is there a bright side?  Well, perhaps we can finally get the Alta-Collins snowdepth over 200" and the seasonal snowfall over 700" (we sit at 181" and 664" right now).

Tuesday, April 19, 2011

Salt Lake Lightning and Thunder

A line of thunderstorms rumbled through the Salt Lake Valley last night, with ice pellets pounding my north-facing bedroom window and waking me from deep slumber.  

Students in my class that went high for the probability of thunder will be pleased as it did verify at KSLC airport.

Monday, April 18, 2011

Wasatch Snow Climate

Alta and Park City are about 10 miles and 1500 vertical feet apart as the crow flies, but the difference in weather and climate is mind boggling.  These web-cam photos are both from today, albeit at different times.

Park City
Maybe they should start selling an Interconnect Tour that combines mountain biking and skiing?

Spring Storm Update

It's feeling quite maritime out there this morning as temperatures and dewpoints are in the mid 40s, there are low clouds hanging all over the mountains, showers are widespread, and the snow level is quite high.

I find it quite depressing to check out the weather cameras from the mountains. Nothing "eats" a snowpack like the combination of high dewpoint temperatures, low clouds or fog, and rain.  Here's a quick visual tour from below to above the melting layer.

Wolf Creek Ski Area.  Looks like a Vermont ski day.
Parleys Summit.  Looks like a Cascade ski day.
Top of Snowbird.  Looks like a Sierra ski day.
The morning sounding from the Salt Lake airport shows the freezing level to be at 6179 ft above ground level, or almost 10,500 ft above sea level.  The snow level is typically about 1000 feet below the freezing level.  Right now, the Alta-Collins observing site at 9662 ft is 32F.  They've received 2" of snow with .46" of water since midnight.  Yes, that's more than 20% water content.  It's 38F at the base of Alta, so if you are skiing today, you'll get a good lesson in how to ski in the melting layer and should bring your best Hefty bag to wear.

Stream gauge data suggests several rivers and creeks in northern Utah are near bankfull, above bankfull, or above flood stage.

A National Weather Service flood watch continues through Tuesday morning for the Cache Valley, Wasatch Mountains from I-80 north, Wasatch Mountain Valleys, and northern Wasatch Front.  They have also issued a flood warning for the Blacksmith Fork River in Cache County.  The hydrograph shows that river reached flood stage this morning.

Periods of rain will continue today as the trough moves through.  For the latest on flood conditions, see the National Weather Service web site.