Wednesday, November 20, 2013

Forecast Concerns the Rest of the Week

An extremely difficult forecast period is on tap for northern Utah meteorologists.  The large-scale pattern is forecast to undergo rapid amplification with a major ridge developing over the northeast Pacific and northwest North America while a closed low forms off the coast of California.  This can be seen in the forecast dynamic tropopause (jet-stream level analysis) in the top image of the loop below, which covers the period from 11 PM last night through 11 PM Friday.

These patterns are often difficult to forecast since the models really need to nail both the amplitude and the position of the developing systems in order to allow for a skillful assessment of local weather.

Potentially in play the next three days are two major forecast concerns.  The first is the mountain snowfall expected later today and tonight.  The challenge here is determining where the fragments of precipitation making it into the Great Basin will end up and the productivity of the front that sags into northern Utah Wednesday night and Thursday morning.  My guess is 4–8 inches in the upper Cottonwoods, but there is a wide range of possibilities.

The second is the potential for downslope winds along the northern Wasatch Front Thursday night and Friday morning when the models are calling for the development of strong easterly flow across the northern Wasatch Mountains.

The forecast lead time is long enough that it is difficult to assess with confidence the strength of this event.  Thus, it is best to keep an eye on the forecast from the National Weather Service Salt Lake City Forecast Office and perhaps take some cautionary steps to secure outdoor items that are prone to wind transport (trampoline owners you know who you are!) just in case.

1 comment:

  1. It looks like the strong cold front coming down across the high plains pushes a fairly strong surge of cold air westward along the I-80 corridor early tomorrow, spilling over the Continental Divide's low point between the Uintas and Wind River Range. You can really see this in the NAM time series (central US 850-mb 4-panel) on the U of U page. It looks like this may reach us around midday tomorrow just as the mid-level winds are turning northeasterly around the same time. Will be interesting to watch and see what happens.