The Early Bird Won't Get the Worm

After many days (seemingly weeks) of little storm action, we are going to get some tomorrow and tomorrow evening.  Details are difficult to project, but it's more action than we've seen in some time, so that has me excited, even if I'm uncertain how it will all play out.

The NAM forecast for 2100 UTC (2 PM MST) tomorrow shows some of the key features of the event.  The first is precipitation associated with moist, southwesterly flow ahead of the approaching cold front and occuring in the forecast below over the Wasatch and Uinta Ranges.  The second is precipitation associated with the cold front, which at 2 PM tomorrow, is forecast to be pushing into western Utah.

The NAM precipitation forecast graph below shows the two part system with a burst of precipitation in th southwesterly flow from about 5 AM tomorrow to 1 PM in the afternoon in the moist southwesterly flow, then a lull in the precipitation, and then a burst with the front late tomorrow and tomorrow evening.  Total water equivalent produced by the forecast is about 1.25 inches, which would be a godsend.

The moist southwesterly flow is always a bit more of a crapshoot, especially at Alta, than the frontal precipitation.  I'm not betting on precipitation starting at 5 am, or a lull at 1 pm, but I do think we will see some periods of precipitation tomorrow ahead of the front.  Further, the pattern is one in which the Park City side should do nearly as well as Alta-Collins (possibly better) for water equivalent given the strong southwesterly flow tomorrow and the strong large-scale forcing accompanying the front.

In addition to the southwesterly flow crapshoot, another wildcard tomorrow is the snow level.  The NAM wet-bulb zero graph below provides some guidance on snow level.  The wet-bulb temperature is a thermodynamic variable used by meteorologists and the snow level is typically about 1000 feet below the elevation of the wet bulb zero level (i.e., the level at which the wet bulb temperature is near 0ºC.  For much of the day tomorrow, the wet-bulb zero is near or above 8000 feet, before it finally falls near and around the time of frontal passage later in the day.  This means what precipitation we get tomorrow ahead of the front will probably fall as rain below 7000 feet (possibly lower in the afternoon as temperatures begin to fall) and as wet snow above 8000 feet.  I wouldn't be surprised to see a bit of mixed precipitation between those two levels depending on the time of day (especially in the morning) and precipitation intensity (heavier precipitation typically lowers the snow level).

Overall, this is a forecast in which the early bird probably won't get the worm.  Most aspects are now crusted up pretty well (I *tried* to ski tour this morning and it was heinous) and it's going to take some snow to bury it.  My plan is to go out tonight to drown my sorrows for today's lousy skiing, sleep in, and decide late tomorrow morning if I should bother heading up for some storm skiing tomorrow afternoon.  If the southwesterly flow is productive, I'll ski in the afternoon (possibly late afternoon).  Otherwise I'll probably work.  Waiting until Monday will probably yield the best conditions, especially in the backcountry, although duty will preclude me from taking advantage.

For upper Little Cottonwood, the National Weather Service forecast issued this afternoon called for  .7 to 1.3" of water and 6-12" of snow for a storm total.  I think I might go for a bit more than that.  Say .9 to 1.5" of water and 8-14" of snow.  I suspect that the upper mountain of Park City will do just as well, but the lower mountain will see far less.