Wasatch Weather Weenies

I'm swamped rewriting our paper on how the Sierra Nevada influence cold fronts over the Intermountain West, so today I'm simply going to say that the next few days will feature fire and ice . The fire is just beginning to smolder today, but will reach full inferno tomorrow as the GFS forecasts 700 mb (crest level) temperatures of +3C in the afternoon. Yup, bring your wax if you are going skiing.  Without much of a regular frost freeze cycle, the "snow suck" should be nasty.  Further, those 700-mb temperatures are high enough that we should make a run at 70F for a high in Salt Lake City. But don't put the puffy jacket away tomorrow because Mother Nature is quite fickle in the spring.  The models have not quite agreed yet on the details, but a major airmass change will likely occur on Saturday evening and the GFS forecast 700 mb temperatures plummet to -11C by Sunday afternoon. Yup, looks like a period of fire and ice.

In the previous post , I suggested that we might be in for a period of riming in the mountains, which we often see in moist, northwesterly flow downstream of a low-amplitude upper-level ridge (a.k.a., the dirty ridge). That riming appears to have come to fruition.  The Utah Avalanche Center reports "overcast skies and light snow, rime, and graupel" in the mountains this morning and there are multiple pilot reports along the Wasatch Front of light or light-to-moderate icing. Maximum icing severity analysis with pilot reports of icing annotated. Source: NOAA/NWS Aviation Weather Center Frequent blog reader David clued me into the the product above, which is is produced by the NOAA/National Weather Service Aviation Weather Center and available here .  For you science geeks, the techniques used to produce the analysis are described by Bernstein et al. (2005) .    I suspect lead author Ben Bernstein, who was my next door neighbor as an undergraduate at Penn S...

The Wasatch are facing a couple of days with warm advection in northwesterly flow downstream of a low amplitude upper-level ridge.  The pattern, sometimes referred to as a dirty ridge sets up tomorrow and is progged by the NAM model to persist through early Thursday. In this type of pattern, which we've had on a few occasions this year, we often have a shallow altostratus deck that can produce a little snow, but also rime .  Rime is produced when supercooled liquid water (i.e., cloud droplets or drizzle that is below freezing but remains liquid) freezes on contact with the snow surface, trees, the ski lift, your googles, etc. Riming in the Wasatch is tame compared to that in coastal ranges, but can still be a pain.  We'll have to see how things pan out over the next 48 hours, but it will be interesting to see what happens on the higher peaks and ridges of the Wasatch if things come together as forecast by the NAM model.

Last week I suggested that we were about to make a run at the big 200 (i.e., a 200" base depth) at the Alta-Collins site .  An active pattern was setting up with several major trough passages.  I thought we would get close. Indeed, it was an active week, but none of those troughs brought the major one day total.  Instead, we got a few to several inches of snow nearly every day, with 59" falling at Alta-Collins since March 20th. Source: NWS/Alta This made for a great week of Spring Break skiing, but daily settlement made a push to 200 impossible.  Instead, base depths increased from about 155 inches on the 20th to 174 inches at present (see light green fill).  Note the retreats after each storm as the new snow settled. Source: MesoWest/Alta So we sit at a fairly solid 170+ inches, but climatologically the peak snowpack at Alta-Collins occurs in mid-to-late April, so the "Alta 200" isn't over yet.  Think Snow.

JH, 26 March 2011 Being a certified Utah terrain and powder snob, I don't leave the Wasatch very often to ski elsewhere, but crossed the border for a fantastic day of late season skiing at Jackson Hole (JH) on Saturday.  In addition to my son Erik, my partners for the day included two of the best mountain weather meteorologists out there, Jim Woodmency, a Jackson icon who provides forecasts for several of the local radio stations and runs mountainweather.com , and Jamie Yount, a Utah Meteorology alum who does avy control on Teton Pass.  Jim and Jamie also offer a winter weather forecasting class through the American Avalanche Institute that I hear is top notch.  Keep an eye out for future offerings. With a good day of skiing to stimulate the senses, I thought I'd take this opportunity to talk a bit about the weather and climate of JH.  Let's begin by putting the resort into its proper topographic context. Geographic setting and topography JH is located on t...

This morning's radar loop provides a great opportunity for instruction in radar interpretation.  In particular, there are three major precipitation features evident in the loop: Persistent, quasistationary orographic precipitation. A cold-frontal precipitation band. Radar echos generated in the southwesterly flow aloft. Have a look for yourself. The area inside the red box provides a nice example of persistent, quasistationary orographic precipitation .  This is an area of pre-frontal orographic precipitation enhancement over Mount Timpanogos and the Little Cottonwood-American Fork divide.  This is a common feature in southwesterly flow.  By quasistationary we mean "almost stationary" meaning it moves around a little, but generally stays fixed to the topography.  Orographic is just a fancy word for mountain-induced.  If you watch the loop, you can clearly see the cold-frontal precipitation band , which is moving from west to east during the loop. ...

The front is coming in a touch sooner than anticipated last night and at 1348 UTC (7:48 MST) is already moving across the West Desert and impinging on the Cedar Mountains along the I-80 corridor. The frontal temperature change was quite apparent at I-80 Milepost 29.  You gotta love MesoWest , which puts data like this at your fingertips.

Friday is shaping up to be a very interesting weather day.  A cold front is presently moving into western Nevada and bringing heavy snow to the northern Sierra and southern Cascades. Source: NCAR/RAL and NCEP/HPC The 0000 UTC 25 Mar initialized NAM brings the front through the Wasatch Front at around 1800 UTC (noon MDT).  Right now, this looks like a bench snow valley "wintery mix" event.  The 700-mb temperature during and following frontal passage is -8C to -10C, which is right on the cusp for valley snow this time of year, especially during the day.   With a strongly forced cold front coming through, the forecast challenge for this event is related to precipitation type in the Salt Lake Valley.  A degree or two warmer or cooler can make the difference between valley rain and snow, respectively. A useful product for these types of situations is the Short Range Ensemble Forecast system (SREF), which is an ensemble of 21 simulations by numerical forecast m...

The Ruby Mountains are a spectacular Wasatch-like range located southeast of Elko, NV that contain some great skiing ( heli and backcountry ) and frequently produce dramatic orographic precipitation effects.  As shown in the image below, the Ruby Mountains (center of image) are isolated, narrow, and elongated.  There are at least 10 peaks in the Ruby Mountains and the adjoining East Humbolt Range (the high topography immediately southeast of Wells) that reach over 11,000 feet. The Ruby Mountains stand out like a sore thumb in the Nevada precipitation climatology.  Incredible gradients in precipitation are found on both the windward and leeward side of the range, with estimated average annual precipitation approaching 45" in the highest terrain (for comparison, Alta averages 54"). Source: OSU Prism Group and Wester Region Climate Center This morning provides a remarkable example of the influence of the Ruby Mountains on precipitation.  With flow out of the we...

It has been a fantastic snow season in Utah this year, but also in the Sierra, which are going to get the goods yet again today. The snow depth at the Sesame Snow Study Plot at Mammoth Mountain presently sits at about 180" and has increased over 40 inches in the past 3-4 days.  This site is located at about 9000 feet, not far from the main lodge at Mammoth.  Snow depths on the upper mountain are certainly higher. As far as Sierra ski areas go, Mammoth is a very interesting meteorologically for a number of reasons.  First, it has altitude on its side, with a summit elevation of over 11,000 feet.  Second, although it is thought of as an eastern Sierra resort, it actually sits on the Sierra Crest in an area where the height of the High Sierra is relatively low and there is a dearth of high topography upstream, especially to the southwest where the San Joaquin River lies. Mammoth Mountain is located very near Mammoth Lakes in this image. What this means is tha...

With 6 inches yesterday and another 5 inches falling overnight, the snow depth at the Alta-Collins observing site now stands at 165".  Looking at the GFS forecast for the next week, it certainly appears that we are going to make a run at the big 200.  The pattern looks quite active through the weekend, with three more major trough passages coming in the next seven days. Further, for the date, the current snowpack SWE for Snowbird is higher than observed in any water year since 1990 when the online record begins. We still have a ways to go to match the 75" maximum SWE observed in 2005, when the snow just kept flying until mid May, but the next week is going to help.

I don't know what took so long given how persistent the wind has been, but the dust has finally arrived in Utah County Photo and Caption: BYU and in the Salt Lake Valley. Photo: MSI Click here for a nice loop showing the penetration into the Salt Lake Valley, courtesy George Wilkerson and MSI.

Today is one of those days where the lack of decent radar coverage in central Utah is a real impediment to nowcasting , the prediction of what is going to happen in the immediate future. There are only two radars in Utah, one on Promontory Point (KMTX) and the other on Blowhard Mountain just east of Cedar City (KICX).  This makes for a huge gap in radar coverage and, on a day like today with flow from the south, difficulties tracking precipitation features from central Utah into northern Utah.   Today's composite radar image never shows any echos over central Utah. As a result, when we look at the KMTX radar, precipitation features seem to come out of nowhere before moving into northern Utah. The useful range of a radar is influenced by a number of factors, but most important during a situation like this is the curvature of the Earth and the tilt of the radar beam that is sent out relative to the horizon.  The lowest-elevation tilt of the National Weather Servi...

The good news is that it snowed last night and some today.  Alta-Collins picked up 8 inches overnight and another inch today. The bad news is that it remains windy, although today was not as windy as yesterday.  The Mount Baldy site shows gusts today to about 50 mph, compared with 60+ mph yesterday. Despite the wind, there is good skiing to be had.  We had a surprisingly good day of touring in the backcountry today where the overnight snow fell on the settled powder from Wednesday night's storm and wasn't damaged by the wind.  In fact, it was good enough that we had no problem finding the motivation for 6,000 vertical feet of climbing today.  Sometimes it pays to ski with meteorologists. It is spring break this week at the U and, although I'll be working most of the week, I'm sure many blog readers are thinking about the prospects for deep-powder skiing. It will be windy through tomorrow night, but there is a trough moving through that should bring peri...

A "breezy" day today in the Wasatch.  This wasn't an outlier wind event, but there were pretty decent gusts at times throughout the range including 77 mph at Park City-Jupiter Bowl, 76 at Snowbasin-Strawbery, 75 at Deer Valley-Empire Peak, and 66 at Mount Baldy.  It appears most of the ski areas had gusts near their summits of 60 mph or better.  This made for some interesting ground blizzard skiing .   Sugarloaf Pass@Alta at 11:30 AM Conditions were generally crappy (that's a scientific term), but with some poking around, you could find some smooth creamy turns in steep wind-loaded terrain.  Some nice snow streamers were observed over the higher peaks, including the Broads Fork Twin below.  In this photo, there is also a banner cloud forming downstream. Broads Fork Twin Peaks at ~1:30 PM Thanks to the winds, crowds were light at Alta, especially on the Sugarloaf Chair.  You don't see this many empty chairs very often at mid morning on a weeke...

I've been a bit surprised already at the wide spread dust that appears to be present across much of the region despite flow that is not especially strong. You can just make out the Oquirrh Mountains looking west from Olympus Cove. Although one might be tempted to call this haze, the relative humidity is far to low to produce haze particles.  The relative humidity is presently 30% at the Salt Lake City Airport and typically needs to be above 70% for haze droplets to form. In the previous post, I noted that the Sevier Lake bed and Milford Flat fire scar are often dust emission sources for Utah, but they don't seem active today, and unfortunately most of the area to our southwest  is covered by clouds, which makes dust source identification nearly impossible.  Thus, I'm working on a mystery without any clues! Sometimes even with modern technology it's tough to figure out what's going on.  Today is such a day.

Over the past few years, there have been a number of insidious dust storms that have swept up southern Utah and inundated the Salt Lake Valley with poor air quality and made a mess of our spring skiing. Tax Day Dust Storm, April 15, 2002 Snow with dust layering, Alta, UT, Spring 2009 (Photo: T. Painter) Not only does the dust make for ugly snow with poor glide, it increases the absorption of radiation from the sun, leading to "mushier" snow on spring days, an earlier loss of snow cover, and a shorter ski season for diehards who just don't know to quit when the powder stops flying. Thusfar this year we have escaped the wrath of major dust storms, but that could change this weekend.  The NAM model is cranking up the southerly and southwesterly flow on Saturday afternoon. 1800 UTC 17 Mar initialized NAM forecast valid 2100 UTC (3 PM MDT) 19 Mar 2011. These winds are strong enough for dust emission and transport from areas where the land surface has dried and...

Our front delivered last night, but somewhat less snow than I expected.  The Alta-Collins site peaked out at 9" when the snow petered out at about midnight, with a whopping 1.09" of snow water equivalent.  Assuming all that snow water equivalent fell as snow, that's an density of 12%, close to the average found in the Cascades. The overnight snowfall, as suggested by the computer models, simply didn't materialize.  The NAM model forecast from yesterday morning, for example, kept the precipitation going through early this morning. Instead, the storm ended at Alta-Collins at about midnight.  As a result, the snowfall was less than expected, and the coating of lower density fluff for faceshots failed to materialize. Although the computer forecast models have improved dramatically, predicting what happens following the passage of the frontal snowband remains a bit of a crap shoot, as shown last night.  At issue is the best approach to take to improve compute...