Thursday, February 27, 2014

Spring Storm Sampler

I love satellite images like the one above for 1700 UTC (1000 MST) this morning with an overlay of the 500-mb heights (black) and absolute vorticity (colors).  These are two fields commonly used by meteorologists to track upper-level troughs, which I've identified with some pretty ugly red lines.  I also highlighted my best guess for the position of the developing low center with a red "L."

You can see quite nicely the two systems that will impact Utah through the weekend.  The first is currently centered over Nevada and precipitation associated with that system is moving into northern Utah this morning.  At 10 am it was 35ºF at Snowbasin Middlebowl and 33ºF at the base of Snowbird.  Yup, another day for a good shell.  Freezing and snow levels will drop as the system moves in and precipitation picks up, but will be near 7000 feet this afternoon.

The models currently call for a decent break between systems late tonight and tomorrow, with the second moving in late Friday and giving us precipitation through Saturday morning.  NAM forecasts are not quite as wet and snowy as yesterday and generate about 1.7 inches of water and 17 inches of snow in the upper Cottonwoods through 5 PM Saturday (see lower two panels below).
An interesting aspect of the model forecasts for these two storms is that the GFS is actually a bit wetter than the NAM, producing 1.8 inches of water by 5PM Saturday, which is pretty unusual.  Most of that difference is produced by the 2nd storm.  The GFS is a lower resolution model, which means it doesn't resolve the terrain of the western U.S. as well.  I think what may be happening in this case is that the GFS brings too much moisture across the high Sierra with that 2nd storm and this helps compensate for the model not resolving the Wasatch all that well.  Thus, this may be a case of two wrongs make a right.

I'm guessing the several inches we get today might ski decent tomorrow up high in the backcountry as it should be right side up even if it is a bit dense to start.  Through Saturday afternoon, I'll go for 15-24 inches total in the upper Cottonwoods with about 2 inches of water.  No shoveling in the valleys.

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