Wasatch Weather Weenies

The GPS-measured precipitable water at KSLC has been climbing steadily the past two days and is now approaching nearly 4 cm/1.5 inches. The analysis of precipitable water over the western United States at 0600 UTC from the Global Ensemble Forecast System (sorry this is a bit old, but it's all I've got from home) shows PW > 1 inch across most of the southern Great Basin and > 2 inches in southern Arizona (contours).  The color fill shows the departure of analyzed values from climatology in terms of standard deviations (each color fil level represents one standard deviation).  Across much of the Intermountain West, the precipitable water was 2 standard deviations above the mean, with a peak of about 3 standard deviations around Area 51.  Hmmm... The National Weather Service has issued flash flood watches for portions of southern Utah and Nevada, with a flood advisory presently in place for Death Valley.  Looks like they are getting some rare rains down ther...

The Alta-Collins snow-depth sensor finally hit 0 today, July 31. It took an incredible 100+ inches of snowmelt over the past month to finally bring an end to "winter."  There are still a few patches and lines to ski, but for this meteorologist, it's time to start thinking about 2011–12.

We've posted a few times about discrepancies between precipitable water measured by GPS and National Weather Service Soundings (e.g., How Moist Is It? ).  Bob Maddox, former director of the National Severe Storms Lab, discusses how these two measurements compared during summer 2010 in today's post on his Madweather blog . Given that the differences are sometimes quite large, I wonder how much of an impact the sounding precipitable water, which frequently looks to be too low in the afternoon, impacts numerical forecasts and reanalyses. And, in case you are wondering, the precipitable water in soundings from KSLC has ben substantially lower than that measured by GPS for the last two days. Source: NOAA/ESRL   

Tropical Storm Don presently moves toward the south Texas coast at about 22 km/hr.  Landfall is expected this evening. Image: NOAA/National Hurricane Center Although tropical cyclones are commonly thought not to impact the southwest United States, they frequently modulate and contribute to monsoon precipitation.  This may be the case with Don, which has been tracking to the west-northwest in the easterly flow on the equatorward side of the monster ridge that has been parked over the central and eastern US for the past few weeks. 48-h loop of 925-mb winds, precipitable water, and IR satelite imagery ending 1500 UTC 29 July 2011.  In particular, note the slug of high precipitable water accompanying Don across the Gulf of Mexico and how Don's present track is taking it toward northern Mexico, west Texas, and southern New Mexico and Arizona. We can track the remnants of Don in the GFS forecast initialized 0600 UTC 29 July.  To do this, I've plotted 925-mb ab...

The summer doldrums have settled in meteorologically and we're stuck in this persistent pattern of weak flow with some afternoon convection.  Being a snow guy, I've never had a great deal of interest in the nuances of convection, so my attention has turned back to issues related to the white stuff. I was curious about skier and snowboarder avalanche fatalities, especially incidents in which lifts are used to access the backcountry.  The American Avalanche Association provides a summary of US avalanche accidents on their avalanche.org web site, which allows one to get at least a cursory look at the circumstances contributing to these accidents. Skiers and snowboarders today often use terms like backcountry, frontcountry, slackcountry, and sidecountry.   Steve Romeo  has some rational definitions of these terms, but for my interests, I simply broke things down based on whether or not the skier or snowboarder accessed the terrain with or without lift assist.  ...

With the snow at Alta-Collins nearly gone , I'm looking for a new station to keep an eye on and am zeroing on the SNOTEL station near Paradise Ranger Station on Mount Rainier. As discussed previously , there was an incredible snowpack on Mount Rainier this year.  Although it didn't peak out at record levels, thanks to cool weather, the snowpack SWE is now running the same as it did during its biggest snow year (presumably 1971-72). Source: Pacific Northwest River Forecast Center I suspect that puts the current snow depth at record levels, although some sleuthing is needed to confirm that a year other than the record max SWE year didn't sneak in. Any bets on the last day of measurable snowpack SWE at the Paradise SNOTEL? Update @ 2:13 PM: Mark Albright pulled data and reports that snow was on the ground 6 times out of the past 28 summers (since 1984) on July 26.  This year's 50.9 inches is eclipsed only by 53.1" in 1999.  So, we're not at a record, ...

Reanalyses are retrospective analyses of past conditions that typically concentrate on the atmosphere, ocean, and/or land surface.  They are widely used in atmospheric sciences for everything from climate research to weather forecasting to commercial applications.  Unfortunately, it is surprisingly difficult to find information about reanalyses, including ways to obtain and analyze the data.  Sure, "power users" know how to do this already, but we need reanalysis democracy where everyone has equal access.  Being and educator, I like anything that knocks down the barriers to my students performing science at the speed of thought. Enter reanalyses.org , a wiki to "facilitate comparison between ranalysis and observational datasets." It contains a nice summary of atmospheric and oceanic reanalyses, as well as plotting and data manipulation tools.  This looks like a great start to at least lower the barriers to access.

The snowdepth at the Collins snow stake has fallen to 15".  Over the past month, the snowdepth has decreased over 100 inches, or a bit more than 3 inches a day. I have been hoping that we would make it to August with measurable snow at the gauge.  That would be a great psych point and a nice end to a huge season, but with 5 days to go, we might not make it.  Of course, the gauge could get flaky, or an adventurous student could hike up there and make some "adjustments" to make it happen... Just kidding.

We've already discussed some of the differences in precipitable water measured by soundings and ground-based GPS , but today provides a particularly aggravating example. A two day loop of IR satellite imagery, Dynamic Tropopause pressure, and precipitable water shows quite nicely the monsoon surge that brought us showers last night, but also the advection of drier air from the west early this morning. Two day loop (1400 UTC 24 Jul – 1400 UTC 26 Jul 2011) of dynamic tropopause pressure (shaded), precipitable water (contours), 925-mb wind, and IR imagery. These changes in moisture are important for assessing the potential for convection today.  Knowing the importance of looking at real data, I decided to see what the ground-based GPS shows.  Consistent with the loop above, it shows a pronounced peak in precipitable water at over 3 cm just after 0000 UTC yesterday afternoon, followed by a gradual decrease to about 2.6 cm today. Source: NOAA/ESRL The NWS sounding...

We have another surge of monsoon moisture into Utah today.  Altostratus has overspread northern Utah and the PW has risen sharply to about 2.25 cm at KSLC. Source: NOAA/ESRL Similar to the event from last monday , the approach of a mid-lattitude trough in the mid-latitude westerlies may be playing a role in the surge. Two day loop of PV (color fill), 925 mb wind, and precipitable water (contours) ending 1600 UTC 25 July 2011. At issue in these events is to what degree the cyclonic circulation associated with the upper-level trough and associated PV anomaly induces southerly flow at low levels and the advection of monsoon moisture into the Intermountain West.  Is this an important player, or are changes in the large-scale circulation associated with the ridge over the central United States and perhaps embedded disturbances in the easterly flow over Mexico and the Southwest US important? This issue has been explored to some degree by Stensrud et al. (1997) , Fuller an...

Yesterday's 108F high in Newark, New Jersey was even higher than Salt Lake's all time record high set on 13 July 2002 of 107F.  Remarkable. Truly oppressive, however, is the combination of heat and humidity.  Let's do a quick comparison.  When Salt Lake hit 107, the dewpoint was about 40F and the relative humidity 10%. That's a heat index of "only" 101F. In contrast, when it hit 108F yesterday in Newark, the dewpoint was 69F and the relative humidity 29%.  That works out to a heat index of 117F.  Unbearably uncomfortable, although I suspect there were locations with a higher heat index in the region.

We take a brief break from the weather to talk about how incredible this years Tour de France is.  Three riders sit within 57 seconds of each other heading into tomorrow's 42 km time trial (a.k.a. the Race of Truth ).  Several riders today gave it all and finished the race fully depleted.  Alberto Contador with his aggressive attack early in the ride, Andy Schleck who was still feeling his stage 18 victory in his leg, Cadel Evans who had to fight back from mechanical problems, Thomas Voeckler who tried desperately to keep the yellow jersey, and Pierre Rolland who rode an inspired race and in a real upset won the stage on top of the famous Alpe d'Huez.  Kudos to them all. Twenty-one switchbacks faced by the riders on the climb up the Alpe d'Huez.  Source: Wikipedia Commons Tomorrow every rider will be by themselves, riding against the clock.  No hiding behind team members.  What a race it is going to be.  Will Evans make up the time, or will ...

Source: NASA The Atlantis touched down this morning at 5:57 EDT, bringing to an end the shuttle-era at NASA. Born in 1967, I was a bit to young to remember the moon landing and have no recollection of the later Apollo moon missions, which concluded with mission 17 in 1972.  I did, however, grow up in the shuttle era.  I recall the promises of regular space flight (at 2 week intervals), the testing of Enterprise, the launch of Columbia in 1981, and the catastrophic explosion of Challenger in January 1986. Source: Wikipedia Commons The Challenger disaster is one of a handful of moments in my life that I remember vividly where and when I was when I heard the news.  I was in a barber shop, and, upon the completion of my haircut, spent the rest of the day in my dorm following the news. The shuttle program never lived up to early promise, and proved to cost about $1 billion per launch...far costlier than advertised early in the program.  Nevertheless, I think w...

The latest (20 Jul 2011) updated from the National Snow and Ice Data Center (NSIDC) shows that the Arctic sea ice extent is currently running lower than it did in 2007, when the September minimum set a record. The difference is fairly small, so time will tell if this year's minimum will be a new record.  See NSIDC's Arctic Sea Ice News & Analysis web site for more information and updates. And, further to the south... Congrats to Andy Schleck for winning todays Tour de France stage in an incredibly daring 60-km breakaway, and to Thomas Voeckler and Cadel Evans for champion-like performances in pursuit.  The three of them, along with Andy's brother Frank, sit within 1 min 12 sec of each other in what is shaping up to be one of the most unbelievable tour finishes.  

Tomorrow, during a grueling stage 18 of the Tour de France, riders will be making a 2409 m (7902 ft) climb from Revello to the Col Agnel.  This is the first of three major climbs on the day (classified as Haute Category, or Beyond Category), culminating in the highest finish in tour history at Galibier Serre-Chevalier (2645 m/8676 ft). Image: letour.fr Tour de France riders are amongst the fittest humans on the planet.  They are the elite of the elite.  Five time winner Miguel Indurain had a resting heart rate of 28 beats per minute and a cardiac output of 50 liters/minute .  In the case of the latter, a fit amateur cyclist has a cardiac output of about 25 liters. Nevertheless, even at at this elite level, athletic performance is affected by altitude.  Oxygen comprises 21% of the atmosphere.  At sea level, where the mean pressure is about 1000 mb, the partial pressure of oxygen is about 210 mb.  At Revello, it is about 203 mb, and at the Co...

As we anticipated yesterday , it was a wet stage today in the Tour de France, with the weather contributing to some important shuffling in the race for Le Maillot Jaune. On wet roads, Alberto Contador laid down a surprise attack on the final climb of the day, with Cadel Evans and Samuel Sanchez following in pursuit while the Schleck brothers and Thomas Voeckler fell behind.  On the subsequent descent to the finish, superb bike handling by Evans, a former professional mountain biker, enabled him to open up a small gap on Contador and Sanchez.  The gap was probably 10 seconds at one point, but closed to 3 seconds as the road flattened and Contador and Sanchez were able to team together to make up ground before the finish. Frank and Andy Schleck lost more substantial ground, with Andy criticizing the descent as dangerous .  Such is bike racing and those who made up ground today took advantage of an opportunity, got out in front to avoid crashes, and utilized their bike h...

If you want to be meteorologically humbled, try forecasting deep convection in the Intermountain West.  I thought yesterday we would see some scattered deep convection in the Salt Lake area.  Although it came close, most of the action remained to our south and east and we were left with a few sprinkles from "cumulus pancakus." Source: NCAR/RAL As discussed by Doswell (1987) and Johns and Doswell (1992) , there are three necessary ingredients for deep convection: a moist layer of sufficient depth in the low-mid troposphere steep enough lapse rates to allow for "positive area" (i.e., CAPE) sufficient lifting for a parcel from the moist layer to reach it's level of free convection (LFC) In short, this comes down to instability, moisture, and lift .  Instability and moisture are commonly called "thermodynamic factors" and are typically assessed using observed and model soundings, whereas lift can be assessed using model vertical velocities, quasi...

Today is a rest day in the Tour de France, but tomorrows Stage 16 takes the riders from Saint-Paul-Trois (red pin) to Gap (purple pin) in the western Alps. The stage could be wet.  A strong cyclonic potential vorticity anomaly will be swinging across France tomorrow, with rain sweeping into the western Alps during the race. GFS dynamic tropopause pressure (red contours), surface wind (grey vectors) and 6-h accumulated precipitation (color filled every 5 mm after initial .25 mm contour) at 1200 UTC 19 July 2011. Source: Don Murray/ESRL. Velonews reports that up to an inch of rain is expected for the finish in Gap, with temperatures in the 50s or low 60s .  The riders are fortunate that this is a relatively low Alpine stage with a maximum altitude of 1268 m in the Col de Manse. Source: Velonews The forecast available on the official Tour de France web site calls for "Persistent and heavy rain, locally thundery, in the morning....mostly cloudy during the stage with o...

The IR, precipitable water (contours) and wind vector loop below shows quite nicely the "surge" of moisture from the south and east into Utah over the last couple of days. As seen in the 0100 UTC (0700 PM MST) regional radar composite below, precipitating convection was confined primarily to eastern Utah yesterday evening, but should be statewide (but scattered) today. Source: NCAR/RAL The GFS dynamic tropopause loop (top image below) shows nicely the large-scale evolution responsible for the surge.  We have the persistent long-wave troughing along the west coast and monster ridge over the midwest, but note also the cyclonic potential vorticity (PV) anomaly digging down the back side of the upper-level trough and another cyclonic PV anomaly (a.k.a., easterly wave) moving across northern Mexico in the easterly flow on the subtropical side of the ridge. The net impact of this large-scale pattern is strong confluence between relatively dry air from over the eastern Pac...

There's nothing I like better at the end of a summer weekend than sitting on the porch as the sun sets and reflects of the Wasatch and some high based "cumulus patheticus." Those of you searching for your pot of gold should climb Lone Peak tomorrow.

I've seen some e-mails from friends at the University of Oklahoma describing the "nuclear summer" they have been having there. The time series below, which covers the last 2 weeks, makes me sweat just looking at it.   As I write this, the temperature in Norman is 104F, but at least the dewpoint is only 63!

Weather has always played a role in the Tour de France , and this year is no exception.  This year's tour has featured a large number of crashes, of which there are probably multiple causes , including weather. Stage 10 pileup.  Photo: Graham Watson/VeloNews For crashes, rain can be an issue, especially a light rain, which isn't sufficient to wash all the oil off the asphalt.  Further, the traffic lines in France are often made of plastic rather than paint, and can be quite slick when wet.  This contributed to a crash by Levi Leipheimer during stage 6 .  Rain even influences the choice and tuning of equipment used by the riders . Weather also affects strategy during the race.  Wind, for example, plays an important role in peloton dynamics.  Cross winds make drafting more difficult and can blow the peloton apart.   Special strategies are needed for dealing with strong cross winds , and astute riders can take advantage of the chaos they impo...

Photo: John R. Southern/Wikipedia Commons As reported in today's Salt Lake Tribune , there have been two tragic lightning deaths in Utah this week .  On Monday, a man was struck and killed near the Wedge Overlook in the San Rafael Swell, and yesterday a Boy Scout was killed while camping at Scofield Reservoir.  Apparently, the Boy Scout was moving to shelter when he was struck.  What a tragedy. Perhaps today is a good day to discuss lightning safety and what you can do to minimize lightning hazard.  The NWS has a brochure on lightning safety available here .  The bottom line is that there is no outdoor place that is safe during a thunderstorm.  Head indoors or get in your car.  When car camping, move from your tent into your car. Many readers of this blog spend considerable time in the backcountry where one can take steps to minimize (but not eliminate) lightning hazard.  Plan ahead.  Know the forecast.  The rule of thumb to be of...

After 2 weeks in the Pac NW, I returned to a remarkably humid, green, and lush Utah late yesterday.  The drive through Sweetzer Summit at sunset was incredible as it looked more like mid-May than mid-July. Indeed, in trying to recalibrate myself to Utah, I started checking out recent observations for KSLC.  Dewpoints primarily above 50 for the past week with a few peaks in the low 60s! Remarkable stuff.  No wonder the grass is so green.  Average dewpoints this time of year at KSLC are in the 40s.  Not only do I need to recalibrate for Utah, I need to recalibrate for an early monsoon surge. We had a brief burst of heavy rain this morning, so I thought I'd look at the radar.  Not an echo in sight!  WTH? Source: NCAR/RAL Surprised, I took a look at the visible satellite imagery, which did show that most of the Great Salt Lake basin is presently quiet, but there are some decent cells to our southeast. Source: NCAR/RAL Turns out the radar i...