Wasatch Weather Weenies

Just a quick post today following up on some themes from posts the past few days. The graphic below lops through GFS 228, 204, 180, 156, 132, 108, and 84 hour forecasts valid at 0000 UTC 4 December (5 PM MST Sunday).  Imagine trying to forecast for Sunday afternoon based on just this single forecast system.  Good luck. The loop also illustrates the folly of forecasting based on model trends, or what forecasters call "DModel/Dt" (i.e., the rate of change of the model forecast with respect to time).  Clearly, there is no evidence of a consistent trend in those forecasts.  The pattern is too chaotic, leading to a lack of run-to-run consistency, even in the more recent forecasts. It's fun to talk about DModel/Dt, but studies have found that it has little forecast value for medium-range forecasts.  Hamill (2003)  examined the value of DModel/Dt and here's what they found: "Extrapolation of forecast trends was shown to have little forecast value. Also,...

The medium range models have been calling for the ridge from hell, which I'll officially name "Heartbreak Ridge", to develop over the western U.S. next week. Just check out these GEFS forecasts from this morning. Penn State E-wall Blocking patterns don't come much uglier than that, and the ECMWF ensemble forecast (mean and standard deviation below) is no prettier. I've been in denial about these forecasts for a few days, hoping that we might get something Sunday/Monday for storm chasing and to help the skiing some, but it hit me today that we could be hosed big time. Let's put the situation into historical perspective. Records for the Snowbird SNOTEL cover 29 years.  Time series of snowpack water equivalent from 1 October to 1 February are provided below.  We currently sit at 3.1 inches, which I've circled below.  There are only 2 water years with less snow, 2000 and 2010.      Source: NWS That wouldn't be cause for panic, b...

Having cut my teeth in an era before ensembles, I confess some tendency to pull up the medium range forecasts produced by the Global Forecast System (GFS) when I arrive at the office during times of drought to scan for the next hope for flakes. This is a colossal mistake, especially in the current pattern.   The predictability at 4-7 days seems to have been remarkably low the past few weeks, leading to individual GFS forecasts that might be described as "all over the place," although one might argue that in general they have trended to drier as the forecast lead-time decreases. Here's an example of the types of changes that one sees.  The 162 hour forecast from the GFS initialized at 0600 UTC 27 January  November shows a major storm for all of the mountains of Utah on Sunday afternoon.  Great hope right? Two days later, the 114 hour forecast from the run initialized at 0600 UTC last night says NO SNOW FOR YOU ! Let's consult an ensemble forecast....

Yesterday's frontal passage was a bummer for skiers, providing little in the way of the white stuff in the Cottonwood Canyons, but provided us with plenty of excitement thanks to the Doppler on Wheels. We deployed that morning to a rattlesnake speedway in the Utah desert where a dark cloud rose from the desert floor and we headed straight into the storm.  If you have no idea what that means, watch the video below.  More accurately, we set up along the side of the causeway to Stansbury Island, just north of the Tooele Valley.  When I drove out to meet the team, the surface front had already pushed into the northern Tooele Valley, with low level "fractus clouds" seen in the photo below at levels just abouve the ground, near its leading nose.  At this time, the front was quite shallow.   The rattlesnake speedway in the Utah desert was actually the Stansbury Island Causeway, ideal for surveying the frontal structure over the Tooele Valley and...

Looking west from the University of Utah Campus at about 7:15 AM this morning It was a Mordor-like sunrise over the Salt Lake Valley this morning (e.g., above), simultaneously spectacular and apocalyptic.  With the overnight southerly flow, there is a decent plume of dust over the western valley (evident below the fire-lit clouds above), but clear skies to the east.  The weather over the past 24 hours has been quite remarkable if you know where to look.  While it was quite mild across much of northern Utah during the holiday weekend, a thin lens of cold air remained over the relatively cold waters of the Great Salt Lake.  Our Hat Island observing site, for example, hasn't eclipsed 55ºF over the past five days.  Source: MesoWest Yesterday, that airmass made its presence known by penetrating into the northern Salt Lake Valley.  At 4 PM (2300 UTC), a sharp lake-breeze front extended across the central part of the valley with southerly flow to the s...

Tree skiing anyone?  Source: Park City Mountain Resort It's not too often that I hop on my bike at 10 AM on November 25th, but that's what I did today and I even wore fingerless gloves.  Whatever. The plot below shows the range of temperatures each day this month (dark blue bars) compared to the normal range (green region) and the maximum (top of red) and minimum (bottom of blue) temperatures. Source: NWS Little wonder why the past month has pretty much been a downer for skiing.  The past four days have had minimum temperatures close to the average maximum for this time of year. I am asked two things in patterns like this.  The first is will the next storm deliver.  The second is when will the pattern change. If forced to pick between a yes and a no, I'll have to go with the latter for the first question, at least for the central Wasatch.  If you bought into the medium range forecasts from the GFS a few days ago, your hopes may have been rai...

The weather this Thanksgiving weekend has been and will be completely outrageous based on climatological standards. The mean temperature at the Salt Lake City Airport on Wednesday and Thursday was 55.8ºF.  If that number holds for through Sunday, it would be more than 5ºF warmer than any Nov 22–26 period on record.   Source: NOAA Regional Climate Centers With three days to go, you could say I'm cherry picking, but the low last night was about 44 (won't know officially until 11 AM), the National Weather Service forecast high for today is 60, and the numbers for Saturday and Sunday are 40/63 and 44/67.  Those would give an average temperature for the period of 54.1, still blowing away any comparable period on record and likely representing the warmest Thanksgiving in Salt Lake history (I haven't bothered doing calculations for the variable thanksgiving dates, so that's really only a guess).  With this recent string of warm weather, I thought we migh...

For nearly three years, the National Center for Atmospheric Research (NCAR) has produced a daily, 10-member, cloud permitting ensemble at 3-km grid spacing known as the "NCAR Ensemble".  For those of us in the western U.S., the NCAR Ensemble forecasts, available from web sites hosted  by NCAR and the University of Utah , attempted to do something that no current operational forecast system could three years ago — capture the extreme spatial contrasts and quantify the inherent uncertainty of precipitation over the western United States.  Last night's forecast, for example, shows the major deluge expected to affect the Pacific Northwest through Thanksgiving.  At 3-km grid spacing, the NCAR ensemble accounts for many regional and local topographic influences and, with 10-members, one can derive statistics related to the range of possible forecast outcomes and the likelihood of precipitation above certain thresholds (our standard 1" and 2" thresholds work well ...

It's not quite like an east-coast snow-eater event when temperature are near 50, fog, and rain, but for Utah, this is as close as it gets. Current (7-8 AM) temperatures in the central Wasatch are 37 at Spruces, 39 at the base of Park City, 38 at the base of Alta, and 33 at Alta-Collins, and 31 at Germania Pass.  That puts the freezing level at about 10,000 feet.  In addition, dense, mid-level overcast is draped over the mountains, with some west snow at upper elevations, rain at mid elevations, and the transition zone in between.  The Alta webcam below summarizes the dreary conditions quite well.  For the most part, snow on north facing aspects will survive just fine this time of year under clear, dry conditions, even when temperatures are above 32ºF.  Without direct sunlight, you simply don't have enough energy to melt snow. However, if you can add humidity and cloud cover to the mix, things change.  You lose the cooling effect of snow sublimati...

High resolution forecast models are not necessarily better forecast models and precipitation forecasts produced by the NAM Conus Nest (hereafter the NAM-3km) are a prime example of this.  The NAM-3km covers the continental US at a grid spacing of 3 km, four times the resolution of the 12-km NAM in which it is nested.  With such high resolution, you would think the NAM-3km would be especially useful for precipitation forecasting over the complex terrain of the western US, but it isn't, because it has a major overprediction problem. Tom Gowan, a graduate student in my research group, recently led a study examining the performance of several forecast models at mountain locations across the western U.S. during last winter.  I have been holding off on publicly sharing these results broadly since the paper describing this work is still in review, but the results are too pertinent to forecast needs right now not to share at this juncture.  In the case of the NAM-3km, we...

1. Yes Virginia, there is skiing I debated for a while whether or not to ski this weekend.  I'm not a fan of low snowpack, bony conditions and often stick to skiing the main run along Alta's Collins lift under such conditions.  With Alta closed to uphill, we opted to take a couple of laps at Brighton in the Great Western area since rumors were that they were asking tourers to avoid other parts of the mountain.  I pulled out my oldest sticks for the day, a pair of Karhu Jak BCs that are probably 10-12 years old. However, I was pleasantly surprised to survive both runs without harming a single rock.  I was also glad to rediscover that the Jak BC really was a great ski, even if you didn't see them much in Utah.  We stuck to grassy runs that were heavily traveled.  The touring and skimo crowd cut up the area pretty good.  Some sections of untracked could be found in some areas and we went home satisfied, without injury, which is the main go...

Antelope Island has been very good to me the past two days.  On Friday, we had a great IOP basing near the Fielding Garr Ranch.  U grad student Trey Alvey took the shot below at the end of the IOP.  Talk about a great vantage point for orographic precipitation research. Driving around the island in the rain yesterday morning reminded me that I needed to return, so we took a quick trip there this morning to survey the views and the bison.  The photo below is from Buffalo Point.  Hard to believe this is a short drive from metropolitan Utah.  There was an interesting cumulus streamer reminiscent of a banner cloud forming on the lee side of Farnsworth Peak (Oquirrh Mountains).  One has to wonder what it was like for the pioneers to gaze upon this body of water after traveling for weeks across the plains and mountains.  A highlight of the day was watching this beast lumbering through the grass. Medium range forecasts suggest a bel...

I like to joke that "storm chasing" Utah style involves sitting in one place and scanning storms repeatedly, which is exactly what we've been doing today for OREO IOP2. After our overnight team returned to Salt Lake late last night, today's day team deployed to Antelope Island near the Fielding Garr Ranch. Antelope Island is a great place to operate the DOW as there are unblocked vistas of much of the northern Wasatch and even the Salt Lake Valley.  It's a bit farther from the Cottonwoods than we like, but we can do a great deal looking at other parts of the Wasatch. Much of the day we scanned a relatively broad frontal band.  Pretty boring by our standards, but it might still yield some interesting data.  However, during the afternoon, the flow shifted to WNW and the atmosphere destabilized, yielding some shallow convective showers.  These showers produced a bit of graupel in downtown Salt Lake City and the Avenues (and perhapse elsewhere). One...