Wasatch Weather Weenies

The last week has been a godsend for Wasatch snow.  Precipitation totals (water equivalent) since Thanksgiving (11/22) are now at about 3.5 inches at Alta Collins and 4.5 inches at Snowbasin Middle Bowl.  Source: MesoWest With 8 inches overnight, the total snow-depth sensor at Alta Collins cracked 40 inches, which officially marks the beginning of "early season skiing" based on the Steenburgh snow-depth scale.  Source: MesoWest If you are wondering, I consider anything before we get to 40 inches to be "pre season."  Some might grumble about that number being too high, but remember that this blog is about mountain meteorology and snow snobbery.   Here's something we haven't seen around here in a while, SNOTEL stations with above median snowpack water equivalent.  Paraphrasing Gordon Gecko, "green is good" (blue is even better) and there's quite a bit of it on the map below.  Relative to median, here are a few specific numbers: Sno...

Looking south from the upper Aves at around 7 AM this morning Yesterday's precipitation fell with little wind, allowing for to develop overnight along the Salt Lake Valley floor.  This has led to a difficult commute in some areas and some spectacular views from bench areas above the fog, such as the upper Avenues pictured above.  I am hoping that the Bay Area feel of the view might be a good omen for the Utes as they prepare to face the Huskies in Santa Clara on Friday for the Pac-12 Championship. The fog was also evident from the top of the tram at Snowbird.  Time lapse video from campus, compiled by Brian Blaylock, was really fascinating to watch and illustrates the complexity of local flows and wind shear that exists within the Salt Lake Valley and how rapidly they can change, even in a relative quiescent flow pattern.  Wait for it at 10 seconds.

Although it is not unusual for the GFS to be wetter than the NAM, the difference between the two models over the next couple of days is exceptionally large.  For Alta from 5 AM this morning through 11 AM Saturday, the 0600 UTC initialized NAM generates 0.84 inches of water and 12 inches of snow.  In contrast, the 0600 UTC initialized GFS generates 2.84" of water and 39 inches of snow.  There are several reasons why this is the case, but a major one is the track and characteristics of the storm that will move across the region Thursday night and Friday.  The NAM produces a trough that is displaced further south with precipitation occurring mainly near and south of the Salt Lake-Utah County line. In contrast, the GFS trough is further north and precipitation occurs all the way up into southern Idaho.  There are also some details about the upper-level trough orientation that are different, but which I won't get into here.  Although I do not have co...

The post is a bit redundant with the previous, but it's been so long since I've seen a model forecast like the GFS 10-day loop below that I feel the need to share it.  Check out the action across the southwest.  The European model is generally similar for the first 6 days or so, but deviates quite a bit on the last few days of the loop.  In addition, the GEFS shows a wide of solutions at 10 days. Source: Penn State E-Wall Thus, perhaps the GFS run might overdo the persistence of the southerly storm track, but we can still enjoy seeing it as it sprinkles some variety into our lives. The downscaled 7-day NAEFS quantitative precipitation (water equivalent) and snowfall probabilities also show nearly the all the mountains of the western U.S. getting some action over the next week.  For northern Utah, much will depend on how productive the bits and pieces are and how far south the storms track.  For once, we probably need to be hoping the storms shif...

The next 7-10 days we will see something that we've seen little of over the last few years (with one notable seasonal exception) and that is a series of storms affecting the southwest U.S. The loop below covers the period from 1200 UTC 24 November through 1200 UTC 1 December with jet-level wind speeds in excess of 40 meters per second (80 knots) color filled.  Note how the jet stream over the eastern Pacific and most of the US is south of 40ºN for much of the period, especially after 1200 UTC 27 November (5 AM MDT Tuesday). With the storm track to the south, the southwest will be seeing a series of storms and getting some much needed precipitation.  Over the next 10 days, the GFS is putting out over 4 inches of water equivalent the Sierra Nevada (peaks over 6 inches) and more than 2 inches in higher altitude areas of Utah and western Colorado. This is not a pattern with a huge tap of persistent, tropical moisture.  Thus, water totals are not ginormous, but tha...

I thought it would be worth taking a quick look at how our downscaled NAEFS ensemble forecasts did for the storm-total precipitation over Thanksgiving weekend.  Below are forecasts plumes from the 0000 UTC 20 November downscaled NAEFS forecasts for Alta-Collins, Brighton, and the Canyons Lookout observing site.  I've added red bars to each of these showing the Utah Avalanche Center reported water equivalent and snowfall amount in upper-little Cottonwood, Big Cottonwood, and the Park City area mountains.  The result is a bit of an apples and oranges comparison since the forecast is for a point and the observed amounts are from several sites, but there's no data available for snowfall and precip at the Canyons Lookout site and for snowfall at the Brighton site. For the most part, the observed water equivalent and precipitation fell within the ensemble range at all three sites, although the lower water and snowfall totals in Little Cottonwood were just outside of it....

I write this around 8:15 AM Sunday morning.  I've been up for a while already as I was awoken by the remarkable frontal passage early this morning.  The meteogram from the Salt Lake City International Airport shows as clear a frontal passages as you'll ever see between 445 and 450 MST (1145 and 1150 UTC) with an abrupt shift in the wind from southerly to north-northwesterly and temperature falls of about 5F in 7 minutes and 8F in 9 minutes.  Source: MesoWest The front was accompanied by a narrow band of strong radar reflectivity, evident in the yellow color fill below.  Twitter user @UtahWxMan took this great photo of the shelf cloud accompanying the front as it moved through Bountiful.   Shelf cloud associated with the cold front moving through Bountiful right now. @ChaseThomason @AllisonCroghan @NWSSaltLakeCity @JimCantore @StormHour @WasatchSnow @ProfessorPowder @ABC4Devon @kvandykewx @Ginger_Zee @ReedTimmerAccu @weathercaster...

It's been a long time since we had a major storm cycle around here and I confess that I am really excited for the weather we will see this holiday weekend.  The Thanksgiving trough passage is really just an appetizer.  The mashed potatoes and gravy, stuffing, and 25-pound butterball follow on Friday when a strong upper-level trough approaches the Pacific Northwest coast and moisture and precipitation spread inland into Utah.  It's been a long time since we've seen a time-height section like the one below.  DEEP moisture for an extended period of time.  There is the Thanksgiving storm, then a bit of a break, followed by strong, moist, westerly crest-level flow for about an extended period before a frontal passage early Saturday morning.  For the period ending 11 AM MST Saturday, the 12-km NAM is putting out just over 3 inches of water for upper Little Cottonwood.  Through Saturday afternoon (5 PM) the SREF ensemble mean for Alta Collins ...

In writing this post, I am assuming that you are more interested in seeing some snow for skiing than dry weather for going over the river and through the woods to Grandma's house. We begin with a quick look back at the past so we can put the forecast into proper perspective.  You might recall that the season started out with  12 inches on the 9th and 30.5" of snow for October at Alta, which is probably fairly close to average.  Since then, things have quieted down, with only 12.5 inches of snow falling so far in November.  Variable snow conditions exist, with no snow on sun exposed slopes, even at upper elevations, and rotten, faceted snow on upper-elevation north aspects.  The photo below, from Trent Meisenheimer's most recent Utah Avalanche Center report, shows a snowpack in Martha Bowl that "was completely faceted and rotten to the ground." That should cause a shiver to go up the spines of backcountry skiers.  On the plus side, the cold weather ha...

Yesterday's frontal passage did little to put a dent into the November snowfall drought, generating an inch on the Alta Collins snowfall stake.  Sadly closed for uphill skiing and a close personal inspection, I suspect that there will be decent top-to-bottom skiing at Alta when they open, even if the terrain is limited, thanks to assistance from artificial snow. Hopefully, we will also get some help from Mother Nature over Thanksgiving weekend.  For the past few days, the models have been suggesting some storm systems will move through the area during that period, but amounts have been variable.  The latest NAEFS ensemble is looking up a bit, however, with all ensemble members producing precipitation at Alta-Collins on Thanksgiving (22 November) and then periods of precipitation through the 24th (Saturday).  For most ensemble members, the totals being produced by our downscaled NAEFS product plotted above vary from about 1.2 to 2.7 inches of water equivalent an...

Looking toward the central Wasatch Mountains from the Avenues Foothills 3:30 PM Friday 16 November 2018 A lot of people have asked me if the haze in the valley is smoke from the fires in California.  There is probably a small amount of smoke that is in our area, but for the most part, what you are seeing in the valley is pollution of our own doing. The vast majority of the smoke from the California fires remains over the central Valley, Bay Area, and offshore Pacific ocean, although there is some that extends eastward across the Great Basin.  This is illustrated by the HRRR-SMOKE analysis below for near-surface smoke concentrations.  Note that the HRRR estimates near-surface smoke concentrations to be 4 ug/m3 or less over northern Utah.    Source: ESRL I'm not sure how much to trust that estimate, but let's go with it.  PM2.5 concentrations on the University of Utah campus today have been running around 14 to 20 ug/m3, much higher than the HR...

As far as I'm concerned, November can suck it.  I'm tired of mountain biking in the cold, wishing I was skiing.  Yeah, it's cold enough for snowmaking, but I don't live in Utah to ski fake snow.  I'd rather have some warm weather that's more enjoyable in the valley.  It's worth taking a look at historical November snowfall at Alta Guard, where the US Forest Service and now the Utah Department of Transportation have kept records back to 1945.  The average November snowfall is 69 inches, although there is great variability (note that 1972/73 is missing in the graph below). It is also apparent that the 1980s and early 1990s were exceptional for November snowfall, with the 10-year running average (thin line below) peaking at over 100 inches in the early 1990s.  November 1994 was the ultimate with 206 inches.  At issue is this.  Is our recent string of bad Novembers really all that unusual, or were the snowy 1980s and early 1990s the true outlie...

The Camp and Woolsey Fires in California, which have been fanned by Diablo and Santa Ana wins, have produced a true wildfire catastrophe.  The 7 PM 12 November incident update for the Camp Fire near Chico reports 42 civilian categories and over 7,000 structures destroyed, including 6,453 single residences.  It is now the deadliest wildfire in California history.  The incident report for the Woolsey fire near Thousand Oaks and Malibu, also updated 7 PM 12 November, reports 2 civilian fires and 435 structures destroyed, although this is an estimate. I happened to be in the Los Angeles area this weekend.  One of the oddities of Santa Ana conditions is that in the absence of fire and smoke, they produce good air quality and visibility.  Below are a series of MODIS images for 9, 10, 11, and 12 November.  In the top image (9 November), the Woolsey fire was raging with strong Santa Ana winds blowing the smoke plume offshore.  The LA basin was smoke free....