Wasatch Weather Weenies

Readers of this blog know that I frequently discuss issues with lightning safety at outdoor stadiums.  Prior to yesterday's game, I discussed the difficulties of the game-day forecast and the potential for thunderstorms during the game (see prior post Difficult Game Day Forecast ).  I did not catch the start of the game as we were out with friends, but when I turned on the game at some point into the first half, I heard some discussion about their camera people leaving for safety.  Nevertheless, the game was going on.  I thought this was quite odd.  They returned to the field at some point and the game went on, with the Utes achieving a convincing victory. This morning I decided to look into things.  Information on lightning strikes is available at lightningmaps.org.  According to their site, there was a lightning strike 4.3 km (2.7 miles) from Rice-Eccles stadium at 2:49 UTC/8:49 PM MDT during the game.  The NCAA Sports Medicine Handbook...

Tonight's game against Washington State is scheduled for 8 PM and I'm glad I don't have to give Kyle Whittingham the forecast as it is extremely challenging. Below is the HRRR forecast valid 0300 UTC (9 PM MDT).  If this forecast validates, we'll be post-frontal at Rice-Eccles Stadium, with precipitation, in the form of showers and thunderstorms, just to the north.  We are, however, unable to forecast the development and position of showers and thunderstorms with precision at such long lead times.  In a best case scenario, those showers and thunderstorms stay north of Rice Eccles and game conditions are fine.  In a worst case scenario, we see thunderstorms at the stadium, leading to delays and the like.  It is worth noting that the Storm Prediction Center has us in marginal risk for organized severe storm episodes today and tonight.  Here's their summary...see Northern UT to central WY below.  Bottom Line : There are a range of poss...

Source: NWS.  Downloaded 5:42 MDT Friday 27 September A potentially historic early season snowstorm is expected to affect Montana over the next few days as an unusually deep early season trough develops over the western United States combines with easterly upslope flow and moisture of Pacific and Gulf of Mexico origins.  Call it a perfect storm if you must.  The latest National Weather Service forecast calls for 24-30 inches at Marias Pass in Glacier National Park, but higher totals, exceeding 36 inches, in some mountain locations. Downscaled SREF forecasts show mean snowfall totals for the period exceeding 36 inches in higher elevations of Glacier National Park where every SREF member is generating more than 24 inches of snow.   The event will feature strong surface winds, which will make driving conditions even in the plains very difficult.  Meanwhile, in the Wasatch, we're looking at a warm, south wind period Saturday with a cold front...

Meteorologist and MIT Professor Ed Lorenz is considered the father of chaos theory.  His "discovery" of chaos was accidental.  He was running a computer model on an early digital computer and decided do a rerun from the middle of a simulation.  The computer worked with 6-digit precision (e.g., numbers like .207689), but he had a printout based on 3-digit precision (e.g., .208).  When he input the 3-digit variables and did the rerun, he got dramatically different results, despite the fact that the difference between 6-digit and 3-digit precision is very small.  This is the essence of chaos.  Small differences (sometimes very small) can evolve into differing outcomes.  It is one of the reasons why the atmosphere cannot be predicted precisely and why ensembles of computer model forecasts, which attempt to account for uncertainty that arises from chaos (and other sources) are so important for weather forecasting.  Unfortunately, ensembles require ...

You may have heard some rumors of potential mountain snow in the extended-range forecast. From a forecast perspective, it's a tricky case of downstream development in which a high-amplitude ridge develops over the North Pacific, which leads a deep trough digging into the western United States.  Below is the dynamic tropopause (jet-stream) level forecast from the GFS valid at 0600 UTC (0000 MDT) Sunday.  Note the high amplitude ridge over the Gulf of Alaska and the deep trough along the Pacific coast of the continental U.S. Such a trough will bring some cold air to the western U.S., but the details of the downstream development, such as the strength and position of the trough, embedded disturbances within it, and interactions with Pacific moisture, are difficult to anticipate with precision at this time.  For example, we could look at the 42 forecasts produced by the North American Ensemble Forecast System (NAEFS), which we downscale and apply some algorithms to...

Today is the #climatestrike.  While I won't be participating, I am supportive of efforts to transform our energy economy to one that is cleaner and ultimately carbon free. Along these lines, I did notice that KSL ran a piece yesterday about University of Utah students who have started an online petition calling for more student parking on campus. A University of Utah student started an online petition calling for more student parking and more spaces closer to campus. The petition is gaining steam as other students have voiced concerns over parking problems. #KSLTV https://t.co/OirDNkCaRS pic.twitter.com/m7AWqgkTR0 — KSL 5 TV (@KSL5TV) September 20, 2019 In the 24 years that I have been a professor at the U, I have seen the remarkable growth of the Wasatch Front and campus and how this has resulted in increased gridlock around campus. When I arrived here in 1995, there was no Huntsman Cancer Institute or Hospital.  There was no Primary Children's Outpatient Services ...

Frontogenesis is meteorological jargon for the birth or strengthening of a front.  Intermountain frontogenesis thus refers to the birth or strengthening of a front over the Intermountain West, as will happen today. Forecasts from the NAM for the 700-mb level (crest level or about 10,000 ft above sea level) for 1200 UTC (0600 MDT) this morning show a deep trough with cooler air over the Pacific coast.  Ahead of this trough, the flow is southwesterly and temperatures warmer.  Over Nevada, the focus of this talk, the 700-mb temperatures are around 6ºC in southern and central Nevada and 0˚C in extreme northwest Nevada.  There is a slight wind shift across Nevada with the flow weakly confluent, or merging.   By 1800 UTC (1200 MDT), we see the first signs of frontal strengthening.  Note how the isotherms , or lines of constant temperature, have come closer together over northwest Nevada, indicating a strengthening gradient in temperature.  T...

Changeable weather is on tap for the work week. For today, increasing south winds as a strong cold front approaches from the west.  The situation at 1800 MDT this afternoon shows the strong pre-frontal southwesterly flow, which reaches 50 knots at 700 mb (crest level). The NWS has issued wind advisories, high wind warnings, and/or red flag warnings for much of the state.  Salt Lake City has both a wind advisory and wind flag warning.  Today is a good day to batten down the lawn furniture and avoid playing with matches.  Winds will likely be strong this evening as well. There's a little monsoon moisture to play with, so there's also a slight chance of thunderstorms. Tonight the front comes through.  It will likely bring a few showers and possibly some thunderstorms.  By 0600 MDT (1200 UTC) tomorrow morning, we're post frontal and 700-mb temperatures are down to 0˚C, which is about 10˚C cooler than where they are this morning. They eventuall...

With the cool season approaching, we now turn our attention to a critical question for the prediction of deep powder days in the western continguous United States (CONUS): How good is the new GFS? The GFS was upgraded in June and the changes were substantial.  The so-called "dynamical core" of the model, the guts of a numerical modeling system that are responsible for solving the equations that govern atmospheric motions, is all new and based on the NOAA Geophysical Fluid Dynamics Laboratory (GFDL) Finite-Volume Cubed-Sphere dynamical core known as the FV3. The equations that govern atmospheric motions are well known and based on physical principles such as the conservation of mass, conservation of momentum, ideal gas law, etc.  Solving these equations efficiently for a sphere (i.e., Earth) on a massively parallel computer, however, isn't straightforward.  The old dynamical core of the GFS was dated, not optimal for modern computer infrastructure, and problematic a...

University of Utah students may be wondering if they should run over to the Merrill Engineering Building and learn how to build an ark as it's been a wet one with some intermittent heavy downpours this morning. Radar imagery shows a number of srong cells developing over or near the Great Salt Lake and moving downstream.  Northern Salt Lake County and Davis County have seen the most intense cells. Seven-day mean lake temperatures show that the lake was quite warm prior to the passage of last night's trough with a mean temperature of 23.3˚C. That's no surprise given the remarkable warmth observed earlier this month.  Why the convection isn't organizing a bit more downstream of the lake is a bit less clear, but it could reflect the general instability and moisture of the airmass and the relatively weak flow.  Given that we really don't understand what controls the mode of lake effect, I won't speculate further. Although the heaviest stuff is falling i...

Seasonal outlooks have little useful skill for skiing.  By popular demand, here's mine for the 2019/2020 season.  Basically the same as last years, with a couple of minor changes.   I am completely comfortable telling people that we have no idea how the season is going to turn out.  Oh sure, you can find some people selling you what you want to hear, and they might get it right.  I could tell you, for example, that there's a 2/3 chance that this winter will give us near-average or above average snowfall at Alta.  Alternatively I could say there's a 2/3 chance that this winter will give us near-average or below-average snowfall at Alta.  Pick whichever one makes you feel happy.  Don't obsess over the outlook. 

The times they are a changin', with the transition from summer to winter now clearly underway. We're finally starting to get a tease from the mid-latitude storm track here in Utah.  The loop below shows yesterday's trough passage, as well as a deeper trough expected to affect our weather this week. Yesterday's trough, and associated showers and thunderstorms, yielded a high for the day of only 79˚F.  We haven't had a day with a high that low since June 22nd, so it was well deserved. The trough anticipated this week will be eventful in a few ways.  First, in advance of the trough, we will see increasing temperatures and southerly flow on Tuesday, which will likely complicate efforts to contain wildfires in central Utah. The trough itself and associated surface cold front and precipitation band is currently forecast to push into northern Utah Tuesday night. Although it is coming in at night, with some monsoon moisture and instability to play with, it cou...

By any measure, Hurricane Dorian has already had a long and impactful life, beginning as a tropical wave of western Africa, developing into a tropical depression at 1500 UTC 24 August (the easternmost triangle below), and then strengthening into a tropical storm and hurricane as it continued its march toward the Bahamas. Source: FleurDeOdile via Wikipedia Commons Dorian reached category 5 status in the Bahamas, where it stalled over Grand Bahama and caused incredible damage.  It then curved along the southeast coast of the United States, remaining just offshore of Florida, Georgia, South Carolina and most of North Carolina.  At 0900 EDT, the National Hurricane Center reported that Dorian made landfall at 0835 AM over Cape Hatteras.  As illustrated by the radar image below, Cape Hatteras (HAT) was within the eye.   Although this will be the only landfall in the U.S., Dorian has a long life ahead and is likely to make at least one more landfa...