Monday, May 15, 2017

How about a Second Season?

May 16, 2015.  A reminder that late-spring storms are part of the Wasatch climatology.
We've said it many times this spring, it ain't over until its over.  It was only a few days ago that I was bemoaning the return of colder weather to California as I was thinking of a Sierra corn harvest trip.  Well, if I'm lucky, things might just work out just fine, but in an unanticipated way.  Forecasts from the day of that post showed a deep, closed, upper-level flow digging through northern California on its way to the southern Sierra.  Not a great scenario for either Sierra corn or, for that matter, Wasatch powder.

However, forecasts change and that trough is now expected to amplify later and moves into the western U.S. as an open wave accompanied by a strong cold front that is expected to push through northern Utah late Tuesday night and early Wednesday morning.

Ooooh, the lower right hand panel of that GFS forecast is a beauty!

The forecast, however, is no slam dunk because this is a case where the trough is amplifying and closing off over the western US, as evident a bit later in the forecast cycle.  

That closing off process tends to be somewhat chaotic, and that in turn leads to uncertainty regarding the position of low, accompanying precipitation bands, and the characteristics of the flow impinging on the Wasatch Range.

Thus, we'll take a look at the downscaled forecasts from the short-range ensemble forecast system.  Some members produce some precipitation this evening, tonight, and tomorrow in advance of the trough.  Others are dry for that period.   Perhaps we'll see some scattered mountain rain and snow showers with a clap or two of thunder.  That would be nice, but the potential for real snow is really Tuesday night and early Wednesday with the frontal passage.  Temperatures during that period will also be dropping like a rock.  Most members are enthused about the frontal passage and produce anywhere from about 0.6 to a bit more than an inch of water.
Much will depend on how much falls with and following the frontal passage.  We need a pretty good dump to bury the coral reef that will exist underneath the new snow as the spring snowpack refreezes, although falling temperatures and a right-side up snowfall certainly helps.  No guarantees, but I'm keeping an eye on this.

1 comment:

  1. This incoming trough is a little intriguing to me. It began as one of those intense storms over the Bering Sea that frequently hit Alaska (which it did), and as forecast it has been maintaining a compact and tightly wrapped core structure for several days all the way along its track. It is hard not to notice the bull's eye in both the height and temperature fields as it approaches. Even though I am completely done with valley snow, I am curious to see what happens with it.