A Very Juicy Storm

I woke up this morning refreshed from an extra hour of sleep and excited to check out the storm.  First thing I did was pull up the radar and saw something that one doesn't see all that often.

As full and complete coverage of precipitation as you can observe with the KMTX radar.  

It's rare to see situations where there is complete coverage of radar echoes here, but there you have it.  Such a situation also allows you to see all of the places where the radar beam is blocked or partially blocked by the topography.  These produce bands of lower reflectivities or no reflectivity "down radial" or beyond the terrain feature as one moves away from the radar. Below is a schematic of this effect.

Source: Secrets of the Greatest Snow on Earth

One can also see a ring around the radar that looks a bit like a donut.  This area of higher radar reflectivities is produced where the beam cuts through the melting layer where falling snow is warming, melting, and becoming rain.  Water coated snow is highly reflective of radar energy, leading to this band.  

A look at observations from Little Cottonwood Canyon shows that precipitation and upper-elevation snowfall really picked up at around 0300 MST.  Since then, Alta-Collins has recorded a 4" increase in interval snow depth.  

Source: MesoWest

I'm writing this almost an hour after the last observation above was taken.  The latest snowcam image shows about 6" on the interval board now.  Not surprisingly given the mild temperatures (32°F at Collins), it looks like the sort of high density base builder that we need.  

The unfortunate news so far is that accumulations at the base have been limited given the high snow levels to start.  A look at the Mt. Superior Cam suggests snow level has just gotten down to near base level. 

Forecasts from the RRFS ensemble (and other modeling systems) suggest snow levels will be hanging near the base today.  The wet-bulb 0.5°C level, a rough guess for where snow is transitioning to rain, is predicted by all six members of the ensemble to be near or just below the elevation of Collins (9662 feet) through this afternoon (within the oval in the lower left-hand panel).  I suspect snow levels will flirt with near the base for much of the day.  

The RRFS is also predicting precipitation and snowfall rates to lower today compared to the past few hours.  We will see if that happens. I suspect, including the overnight precipitation and snow, that we will be looking at a storm total of 12-24" at Alta-Collins, with snowfall amounts decreasing fairly rapidly near or below its 9662 ft elevation due to warmth overnight and today.  Hopefully I'm wrong and snow levels will drop enough for base accumulations to be better down to the base of Alta if not Snowbird.