Thursday, March 20, 2014

Flies in the Ointment This Weekend

Last Friday we discussed how short-wave troughs can sometimes cause forecast problems in long-range forecasts (see Short-Wave Mischief in the Medium Range Forecast).  Today we'll discuss how they can serve as flies in the ointment of short-range forecasts (3 days or less).

The forecasts from yesterday (Wednesday) morning called for a short-wave trough to skirt us just to the north, with cooler, drier air moving into northern utah on Saturday morning.  Precipitation in northern Utah was very limited, with only a very small are of light precipitation on the north slope of the Uinta Mountains in the NAM.

Overnight, however, we see a subtle change in the characteristics of the large-scale forecast with a weak, but still significant extension of the trough extending west-southwestward into northern Nevada.  This leads to more humidity over the state (compare lower left panels) and a band of precipitation over the Uinta Basin.

The net impact of such a shift is an increase in the forecast cloud cover over northern Utah and an increase in the possibility of precipitation over the northern part of the state, perhaps mainly in that area near the band.

As forecasts shifts go, this is a minor one for most day-to-day activities, but I'm desperate for material, so give me props for the effort!  In addition, when we start thinking about the management of power generated by alternative energy sources, such as solar, subtle changes in the forecasts can be very significant.  Those thin cirrus clouds that most of us hardly notice for our day-to-day activities can dramatically reduce solar energy production and are damn tough to forecast.  


  1. The ECMWF (at least from what I could see at wunderground) picked up on this yesterday before the NAM, and even calls for some precip into central Utah, albeit light.

    1. And now so does the NAM, better late than never, I always say!

    2. I'm not surprised the EC had it earlier.

      I would have been looking at the 0Z EC yesterday morning. My time to look at the weather is often before the availability of the 12z runs. Pity!