Wasatch Weather Weenies

  It's been a while since we did a list on this blog, so let's create a list of 10 scary things for Halloween: Not only is this season a crappy one for snow, but we have several more in the rest of the 2020s, resulting in further decline of the Great Salt Lake. I wake up one day and all of the code used to create products for weather.utah.edu is gone.  Or worse yet, I just accidentally delete it.  Even with backups, it would take a huge amount of time to get everything running again. I abandon the Wasatch Weather Weenies due to the demands of new "workload policies" being implemented at the University of Utah   The 10% budget cuts being floated by legislative leaders for the University of Utah come to fruition and instead of cutting administration, most of the pain is passed down to instructional units that are already stressed by recent enrollment increases.  The legislature passes a revised version of last year's Senate Bill 226 , the so-called School of...

Change is on the way as a deep upper-level trough is expected to move into the western United States early this week.  The GFS forecast for 0000 UTC 29 October (6 PM MDT Monday) puts the surface front over northern Utah and the Salt Lake Valley in cooler, northwesterly, post-frontal flow.   This storm reminds me a good deal of the last with the trough digging into California and the bulk of the "dynamics", or large-scale lift ahead of the trough, moving across southern Utah and Colorado.  However, there is potentially one important difference.  Instead of closing off over central Utah, the trough remains what we call an "open wave" which means the GFS ultimately puts us into a colder, moister, northwesterly flow on Tuesday, as illustrated below.   Our GFS-derived forecast for Little Cottonwood Canyon ultimately generates just over an inch of water and 16 inches of snow through 6 AM MDT Wednesday.  This is a colder storm than the previous one two, ...

Fall this year has been pretty quiet and warm.  September at the Salt Lake City Airport brought only 0.42" of precipitation compared to a normal of 1.06".  October only 0.61" so far, compared to a normal of 0.96" for the month to date.   Average temperatures for September 1 - October 22 have also been remarkably high.  In fact, they are the highest on record, with a mean of 70.2°F, just ahead of the same period in 2022 (70.1°F).  We had a mainly dry frontal passage in the Salt Lake Valley last night, so it will be cooler today before ridging returns, but the models are now advertising some major changes next week including a deep trough forecast by the GFS to be over the western US at 1200 UTC 29 October (6 AM Tuesday).   Snowfall produced by this system will depend a lot on track as this one has some potential to "go south" literally and figuratively.  In the GFS forecast above, much of the flow and dynamics is going into southwest Colorado,...

Our first storm of the year is in the books.  Alta-Collins came in with about 1.46" of water and, per resort reports this morning, 8" of snow. Snow depth on the ground at Alta-Collins sits at 6", although that is a point measurement and I suspect there is a good deal of variability.  Due to the warm nature of the first part of the storm, snow cover at the base is lower and perhaps an inch or two based on web cams.   I like to look back at our model-derived forecasts so we can identify capabilities and limitations for future improvements.  Let's first look at the forecast I used for my post these used from my two posts covering the storm.  From Wednesday ( A Storm System with Lots of Moving Parts ), the 06 UTC GFS forecast was going for a storm total of about 1.3" of water and just over 12" of snow.  I've reproduced that forecast below.   And below is the 00 UTC Utah Snow Ensemble forecast showing a range for water equivalent of about 0.75" to...

The surface cold front passed the airport last night at a bit before 1 AM MDT as denoted by a 5F or so drop in temperature and a veering of the winds from southerly to WNW.  Look carefully in the top plot below for the abrupt drop in temperature and rise in dewpoint and humidity.   Source: mesowest.utah.edu And so the endless summer of 2024 came to an end.  Although we could be flirting with the upper 70s again next week, we'll call that fall or autumn, whichever you prefer.   Showers and then widespread precipitation then moved into northern Utah with the precipitation in the early morning hours being more widespread than I anticipated yesterday.  That's a good thing as we have had little to no precipitation for over 3 weeks and this is beneficial precipitation to saturate soils and settle down the Yellow Lake Fire.  As of 7 am, the snow line is sitting somewhere around 9600 feet.  Alta web cams show the white stuff covering the ground abov...

Enjoy the last day of summer today.  Big changes are coming in the form of a storm system with a lot of moving parts.   Let's have a look at some of the details as predicted by the GFS and HRRR.  For this 2100 UTC 16 Oct (3 PM MDT this afternoon), the GFS calls for dry southwesterly flow at 700-mb (lower left) and by extension, the surface.  I don't expect strong winds today, so let's just call it breezy.   For the same time, the more detailed HRRR is producing some scattered showers over central Utah and the western Uintas.  This could produce some strong gusty winds for the Yellow Lake Fire. I am hoping for the best there during this windier pre-frontal period.  Summer ends sometime tonight with the arrival of the surface cold front.  The latest HRRR has the cold front entering the northern Salt Lake Valley around 0500 UTC 17 Oct (11 PM MDT this evening).  Unlike some cold fronts which have an intense line of precipitation, this o...

Believe it or not it is looking increasingly likely that we will see an end to endless summer later this week.  The models are advertising the movement of an upper-level trough over the western later this week.  We may first begin to feel it's effects Wednesday with an increase in southerly flow and a last warm day as the trough approaches and then cooler air moves in later in the week.  The GFS forecast for 1200 UTC 18 October has a bonafide cold front over northern Utah.    It's a bit soon to lock in on that solution, so let's have a look at the Utah Snow Ensemble for Alta-Collins.  All of the ensemble members are dry through 0000 UTC 17 Oct (6 PM MDT Wednesday).  Then nearly all produce precipitation at some point during the 2.5 day period through 1200 UTC 19 Oct (6 AM MDT Saturday.   Timing and amounts vary with the ECMWF ENS members generally being drier than the GEFS.  Through 1200 UTC 19 Oct (6 AM MDT) the former produces an avera...

I've been watching the new Utah Snow Ensemble looking for both bugs in the code and a pattern change.  I did find one bug (you probably didn't notice its effects) that has been corrected and now I'm seeing the possibility of a pattern change.   As illustrated by the plume diagram for Alta-Collins below, the central Wasatch are locked into dry weather through 00000 UTC 14 October (6 PM MDT Sunday).   Then, a weak trough drifts across northern Utah.  A few ensemble members bring some showers in either on the 14th, 15th, or 16th, but most keep us dry and it remains mild.  Not much to get excited about there.   However, after 0000 UTC 17 October (6 PM MDT next Wednesday), we start to see the possibility of a shift.  The median wet-bulb temperatures drop to below 7000 feet and the many of the ensemble members produce precipitation and snow.  The forecasts though produce a wide range of precipitation and snow totals.  Additionally, w...

Anchoring bias causes us to rely heavily on the first piece of information that we encounter.  I think of it a lot when I am interpreting model guidance, especially ensembles.    Here's an example, which I draw from the new 82-member Utah Snow Ensemble.  One of the first products I often pull up is the plume for Alta-Collins.  I find it impossible not to immediately look at the snowiest ensemble member, which for last night's run is producing about 28.5" of snow from 3" of water.   Like a drug, my heart rate doubles and I feel the adrenalin rush. Then I pull up the four-panel total snowfall forecasts through 240 hours.  Again, my eye moves immediately to the lower right, which is the maximum snowfall.  Beautiful!  28.5"! The problem is that such amounts are extreme outliers and highly improbable. What you don't see in a first glance at the plume is that more than 90% of the ensemble members aren't producing any snowfall.  That would...

The wheels have come off in Phoenix or maybe better put burned off.  They have now set or tied daily records on what appears to be 8 consecutive days, set an all-time record of 117 for September and set an all-time record of 113 for October.  The murderer's row of daily records is: Sep 24: 108 Sep 25: 113 Sep 26: 110 Sep 27: 113 Sep 28: 117 Sep 29: 113 Sep 30: 108 Oct 1: 113 The eight-day mean average high temperature of 111.8F obliterates the previous eight-day mean average high temperature record after September 1 of 108.6, which was set in the seven day period ending on 11 Sep 1979.   The graph below shows the 8-day average mean temperature for 24 Sep - 10 Oct each year since records began in the Phoenix area, and illustrates just how anomalous the 8-day period has been.   Min temperatures during this period have also set a record for the 8-day period. Forecast highs for the airport are in the high 100s to 110 for the next several days.  What a stre...