Wasatch Weather Weenies

Although dry weather will continue through Friday, the ensembles are showing more and more signs of a pattern change that should usher in some precipitation beginning Saturday or Saturday night with more storms to follow.   Members of the European ensemble (ENS) generally bring in the precipitation the earliest, so I'll show the ECMWF HRES forecast (a member of the ENS) valid 1500 UTC 14 November (0800 MST Saturday) to illustrate the change.  Although we are currently under the influence of an upper-level ridge, that ridge progresses slowly eastward over the next few days with a digging trough moving into the western United States and bringing precipitation into Utah on Saturday.   The overall pattern is one that we might expect to see a lot of this year with strong flow across the US southwest and overall flow splitting along the west coast.  In the forecast above, the trough tracks far enough north to give us some precipitation.  That said, the split...

 I got out for my first turns of the season today.  Some youngsters dragged me up the mountain. Coverage on the "Collins Glacier" above the angle station is good.  Below the angle you'll find some rocks.  Reports are it's thin and getting thinner down there with skier traffic and lack of snowmaking.  The Alta-Base station doesn't have an RH sensor, but across the street at the Atwater site, the wet-bulb temperature hasn't been below the magic -2°C threshold for snowmaking since 0900 MST yesterday (Saturday 7 November).   There's a bit of cooling coming for Monday night, which maybe will allow for a bit of snowmaking, but temperatures rebound on Wednesday.  By and large, through next Friday above average temperatures and mainly dry conditions look to prevail.   The waiting game continues.

In dry times, it's easy to be seduced by long-range forecasts.  This is especially true if one is looking at plume diagrams, such as those produced by the Utah Snow Ensemble because the eye is drawn to those members that tick up and suggest maybe there will be some snow.   An example is the forecast for Alta Cillins from a few days ago (0000 UTC 2 November).  This forecast includes the Sunday storm, the weak trough passage last night, and then a relatively dry period for a few days.  At the end of the run though, just before 0000 UTC 12 November, there are some members ticking up, which might get you excited.   From that same period, one could find other forecast systems, such as the ECMWF AIFS (AI Forecast System) suggesting regime change.  Below is the 240-hour forecast showing an extension of the Pacific Jet into the western United States with precipitation over the Wasatch and Western Colorado.   The reality though was that most of t...

If you are a skier and you are interested in snow level or snowmaking, you should get to know something called the wet-bulb temperature .   Most of the time when we refer to temperature we are talking about the ambient air temperature or what is known to meteorologists at the dry-bulb temperature .  This is the temperature measured by a thermometer that is exposed to the air but protected from radiation and moisture.  Bulb refers to the rounded end of an old school liquid thermometer and dry bulb indicates that the air temperature recorded is not affected by moisture.   The wet-bulb temperature is the lowest temperature that can be achieved through evaporation under current ambient conditions.  In the past, it was measured by wrapping the bulb of a thermometer in a wet muslin (hence "wet bulb").   Old school dry and wet-bulb thermometer setup.  Source:  https://collection.sciencemuseumgroup.org.uk/objects/co518421/wet-and-dry-bulb-...

Extensive flooding continues along the San Juan River in Colorado, New Mexico, and Utah.   Shiprock, NM.  Source: Navajo Police Department/Handout, via Via Reuters, New York Times Rainfall in the upper San Juan Basin has been remarkable since the start of the water year on October 1st. SNOTEL records in the basin only run back to 1987, but liquid precipitation averaged at sites in the basin is up to 15.9 inches, which is well above the prior record.     Source: NRCS Additionally, the snowpack water equivalent at those sites is only 4.4", so only about a quarter of that precipitation has been retained in the snowpack.   Other headwater basins of the San Juan also received record precipitation, much in the form of rainfall to relatively high elevations.   Meanwhile, the statewide numbers for Utah are also quite remarkable.  At SNOTEL stations, the statewide average precipitation since the start of the water year is  6.5 inch...

A pretty good upper-elevation storm cycle is coming to an end at the upper elevations.  Total water equivalent at Alta-Collins since October 30th is as of 7 AM this morning (Monday, November 2nd) is 2.6 inches.  Total snowfall during the period based on interval measurements is now up to 17 inches with the total snow depth now at 19".   At 9662 ft, Collins received mostly snow in this event.  It's possible that there was rain at that elevation or rain mixed with snow for brief periods as the wet-bulb temperature reached as high as 34°F during a few periods.  The wet-bulb temperature, which is the lowest temperature that can be achieved through the evaporation of water, is a better (but still imperfect) discriminator of precipitation type than normal temperature.  It's a about a 50/50 chance of snow at a wet-bulb temperature of 33°F, so when you go beyond that, it's getting closer to a rain situation.   At the base (8530 feet), yesterday was a...