Wasatch Weather Weenies

There's a little frost on the pumpkin this Halloween morning and, if you want something scary, talk of a dirty ridge .  There is no official definition of a dirty ridge, but it is typically used by meteorologists to describe situations in which clouds and precipitation are found on the downstream (typically eastern) side of long-wave upper-level ridges.  This might be viewed as a surprising place to find clouds and precipitation since the area downstream of an upper-level ridge is typically associated with fair weather.  Such a view, however, neglects to look at the entire weather picture.  Let us take the forecast dirty ridge as an example.  The situation this morning features an upper-level ridge centered west of California with an upper-level trough further upstream just east of the dateline (dashed line). Waves in the upper levels have a mixture of wavelengths and meteorologists typically distinguish between long waves, which span perhaps a few thou...

The phrase pattern change is pretty vague and it really doesn't tell you much.  For instance, it's a pretty crisp out there this morning, and one might describe this as a pattern change, but should you get excited for snow? The weather over the past couple of weeks has been dominated by persistent ridging over western North America.  For example, the average 500-mb height pattern for 22-28 October shows this ridge, which was strongest over Canada and weaker to non-existent over northern Mexico.  Except for the occasional trough that was able to slip through the net to give us a few showers, the pattern has been mainly dry.  Over the past couple of days, that ridge moved downstream and the Pacific trough progressed into the western U.S. leading to the cooling we feel today.  However, the phasing of that trough with moisture was insufficient to give us any precipitation, and we've been left high and dry while precipitation develops ahead of the trough ...

Although I tread into political commentary from time to time on this blog, in general, I try to keep it relatively politics free, especially on topics that are outside my area of expertise.  So today, I merely want to give a pep talk to everyone to get out and vote this year.  If you are registered in and live in Utah, you can do this by mail, at an early polling location, or on election day.  Complete information, including early and election day polling locations, is available at vote.utah.gov .  Voter turnout in the 2016 election was around 56% for males and 60% for females.  It was lowest amongst the young (people 24 or younger) and increased with age.  It would be great to see numbers that are even higher, especially from younger voters who are the future of our country.  I've always considered voting to be more than a right and privilege, but a responsibility.  Especially informed voting.  National races, especially those in ...

The print version of today's Salt Lake Tribune included a preview for the upcoming ski season.  It got me to thinking about a similar preview that was published a long time ago and introduced the world (or at least the region) to the phrase Greatest Snow on Earth .  When I was writing my book Secrets of the Greatest Snow on Earth , I really wanted to include a section describing where the phrase Greatest Snow on Earth came from.  I figured there had to be a good story behind it.  I was aware that the Ringling Brothers and Barnum and Bailey Circus had sued the State of Utah over the use of the phrase (they argued it was too similar to Greatest Show on Earth), but the court ruled that Greatest Snow on Earth did not dilute their slogan.  I thought that the origins of the phrase would have been hunted down for that trial, but it wasn't.  Instead I had to do some digging. I began by calling a friend, Dave Hanscom, who I met through our work for the 2002 Olym...

It is a question that I am asked frequently, how much lake effect did Lake Bonneville produce? Lake Bonnevile was an ancient lake that existed during the last ice age and covered much of the Bonneville Basin of Utah, Nevada, and Idaho.  About 14,500 years ago  the lake reached its highest level, burst through Red Rock Pass, and flooded southern Idaho and eastern Washington via the Snake River, resulting in a drop in lake elevation to 300 feet.  The Great Salt Lake is a remnant of Lake Bonneville. At high stand near the end of the ice age, Lake Bonneville was over 1000 feet deep and glaciers existed in 15 mountain ranges within its drainage basin.  The bulk of this glacier ice was in the Wasatch and Uinta Mountains. Lake Bonneville at maximum extent (blue) with mountain glacier systems in transparent light blue. Source: Laabs and Munroe (2016) We don't really have much knowledge about the effects of Lake Bonneville on local climate.  Geological studie...

There is no obvious end of the monsoon, although in the southwest U.S., it is sometimes defined to be 30 September.  The monsoon, however, is sometimes slow to die, or rises from the dead in October, which seems fitting for a month that ends with Halloween. Contrary to conventional wisdom, which views monsoon as a heavy downpour, the word monsoon is typically defined based on a seasonal reversal of the wind and is now used broadly to describe large-scale circulation and precipitation changes that occur due to differential heating of land and ocean/sea surfaces.  In North America, the cool-season over the southwest U.S. and Mexico is characterized by predominantly westerly flow, but during the warm season, the development of upper-level ridging over North America leads to mean easterly flow that spreads northward from Mexico into the southwest U.S. from June to July.  This easterly flow is typically associated with increased moisture and precipitation, although both are ...

With us sitting ski purgatory with an 11" of snow at Alta Collins enough to screw up high country mountain biking and hiking but not enough to enable early season skiing, we're fortunate that the weather over the past few days as simply been spectacular for hiking and mountain biking in the foothills.  Some scenes from the BST yesterday are below. There is something rotten, however, in the state of Denmark (er, Utah), and that is increasing smog as we slowly approach what is known colloquially as inversion season.  Here's a view looking west yesterday.  The smog is most apparent when the sun is in front of (rather than behind) you.  This is a consequence of what is known as forward scattering of the visible radiation.  In addition, I suspect the particular matter concentrations are greater in the afternoon over the Great Salt Lake, western Salt Lake Valley, and Tooele Valley because the airmass over the Great Salt Lake this time is often cooler, res...

How much does a shrinking Great Salt Lake affect Wasatch snowfall?  It is a question that I am frequently asked and one that of course has a complex answer. To begin, we should instead ask the question, how much of the snowfall in the Wasatch Range is produced by lake-effect precipitation?  Conventional wisdom might suggest a lot, but the actual numbers are probably lower than most people think. Kristen Schepel (née Yeager), Trevor Alcott, and I set out to answer this question several years ago as it hadn't been adequately answered previously.  The effort involved combing through a gazillion radar images over 12 cool seasons (mid September to mid May), identifying lake-effect periods, and figuring out how much precipitation at observing sites in northern Utah is produced during those periods.  The results are below and indicate that in an average cool season, lake-effect periods (LEPs) produce about 60 mm (2.4 inches) of water equivalent at the Dry Fork SNOTEL ...

Last night we received the first snow of the season in the upper Avenues, with a coating of white on colder surfaces. Radar imagery showed a band of precipitation passing through the area early this morning, which led to the snow.  That band was drifting southward and brought a little snow to the central Wasatch, although accumulations were likely less than in inch (the Alta-Collins data feed to Mesowest is currently down, so this is guesswork based on cameras).  Today will probably be the coldest day of the season so far and the coldest day we have seen around here in months.  If my quick look at the records is correct, the last day we had here with a high below 50ºF was April 17 when it reached 49˚F.  If you continue to go back in time, the next day below 50ºF was March 26 (48˚F), which was preceded on March 25 by a high of 44˚F.  The forecast high for today from the National Weather Service is 47˚F.  It might be a good day to switch from flip f...

Editors note : This post has been edited to correct the category of Hurricane Micheal at landfall.  Due to a typo, it was incorrectly described as at the top end of category 5, when it was at the top end of category 4. I never paid much attention to tropical meteorology until I moved to Utah and had to deal with the monsoon and occasional hurricane remnants.  Then my parents bought a house in Florida.  Hence, I take a peek south of 30ºN from time to time. Hurricane Michael was easily the most impressive landfalling U.S. hurricane that I've ever observed.  My students and I followed it closely on Wednesday morning as it made landfall.  Meteorologists everywhere were watching it, and I highlight the women and men in the National Weather Service, including local forecast offices and the National Hurricane Center, who worked tirelessly to provide forecasts and updates for the public.   A National Hurricane Center Public Advisory as Michael made l...

A recent article in the Salt Lake Tribune ( Utah just experienced its driest year since scientists have kept records ) strongly suggests that our recent drought is due to climate change.  While global warming is a contributor, drought has many drivers and it is essential that we recognize that fact as we plan for the future. Drought is nothing new to the American southwest.  Historical records and proxies based on tree ring records show long-term fluctuations from drought (dry periods) to pluvial (wet periods) are characteristic to the region even before human influence on climate. Tree-ring reconstructed streamflow for the Bear River. Drought and pluvial (wet) periods illustrated by black and grey fill, respectively.  Note that this graph is smoothed to illustrate slower climate variability. Source: DeRose et al. (2015). That human influence on climate is, however, growing and expected to play an increasing role in drought over the American southwest.  It i...

" I'm going to go up and take a lap today, interested? " - Text received 7:45 AM Ski conditions in the upper Cottonwoods have improved dramatically since the lunatics below braved skiing Gunsight a couple of days ago. The overnight storm came through in spades and as of 0800 MDT has delivered 0.59" of water equivalent and 14" of fresh at Alta Collins, bringing the total snow depth to 21 inches.   Source: MesoWest That should release the hounds today.  These are still very marginal snow depth, especially given the modest water equivalents (perhaps the gauge is underreporting some).  Painful as it is to say, I'm electing to sit today out, but might try a lap or two up Collins gulch once it is skied and perhaps packed out some by the cats.   The latest radar imagery (ending 1440UTC/0840 MDT) shows ongoing post-frontal valley rain and mountain snow showers, with some likely lake enhancement.   Water equivalent rates the ...

Compared to yesterday, this morning's (0900 UTC initialized) SREF is much wetter for Alta, with  a mean water equivalent of nearly an inch through 1800 UTC (1200 MDT) tomorrow (Wednesday), with a range of about 0.35 to 1.25 inches.  My impression surveying the various deterministic models (NAM, GFS, FV3) is that the pattern is looking healthier as well.  The time-height section from the NAM shows high relative humidies through a deep layer from later today through mid day tomorrow.  About all that is missing in that forecast is a full shift of the winds to northwesterly.  For the most part, they stay WNW.  Numbers from that model run for Alta show 1.03 inches of water and about 11 inches of snow through 1200 MDT tomorrow.  Bottom line is that this is now looking like a healthy early-season storm.  Something in the 8-16 inch range for Alta-Collins is looking likely through tomorrow afternoon.  It will be interesting to see how th...

Snow accumulations in the Wasatch Mountains are probably starting to give snow-safety professionals heartburn, especially considering the forecast. Automated snow depth measurements at Alta Collins show 8 inches on the ground as of 6 AM MDT this morning.  At the Daybreak measurement site at 9250 feet above Canyons Village at PCMR, its up to 10 inches.  It's tough to say how much to trust these early automated snow depth sensors, and they may or not be representative, but given the persistent easterlies over the past couple of days, I would not be surprised if the upper-elevations of the Park City Ridgeline had a snow depth similar to that at comparable elevations in upper Little Cottonwood.  Certainly the camera at Crescent Ridge is looking snowy this morning. Source: Park City Mountain Resort, downloaded 8:07 AM MDT Higher up, at the top of Collins, Alta is looking wintery. Will we get more? Sure.  Perhaps a few more snow showers today in the central...

If you were in the Salt Lake Valley and looked toward the Wasatch this morning around 8:30 you may have noticed that there was a cloud sitting several kilometers west of the Wasatch Range (note darker band of clouds below).  The cloud sat several km west of the Wasatch Range and didn't extend into the mountains.  Over the mountains, it was snowing, but not very hard.   What you are seeing is a consequence of easterly flow.  There is a band of precipitation that currently extends from from SW to NE across the region, but this is embedded in easterly flow.  If you look carefully at the image below, the radar reflectivities at 8:18 AM were actually higher east of the Park City Ridgline (look along the border between Salt Lake and Summit Counties) than on the Cottonwood side of the Wasatch.   So, in the photo above, the snow in the mountains is spillover.  Then, a harder, darker cloud base exists where a lee wave is producing risin...

With winter approaching (conditions currently and over the next few days are really just a teaser), it seems a good line to discuss some of the forecast products that we have available on weather.utah.edu . All products available on weather.utah.edu are based on computer models run by the National Centers for Environmental Prediction (NCEP), a part of the National Weather Service.  We download and process this data, producing a variety of plots, graphs, and tables that can assist in the preparation of a weather forecast.  Really, what we provide on weather.utah.edu are not forecasts but guidance , which is defined by the National Weather Service Glossary as computer generated materials used to assist the preparation of a forecast.  Output is available from the Global Forecast System (GFS), North American Mesoscale Forecast System (NAM), High Resolution Rapid Refresh (HRRR), North American Ensemble Forecast System (NAEFS), and the Short Range Ensemble Forecast Syste...