Joe's Weather Blog

Why I think Casper will see its first measureable snowfall of 2012 this week!

This Wednesday morning, we’ll see a cold front put an end to the 40’s and even low 50’s early this week. This is a stronger front that will have enough strength behind it to push south across the entire state and much of the region. This front should not only drop temperatures Wednesday and Wednesday night; but it will also drop a chance of accumulating snow.

A trough of low pressure will be digging south over the intermountain west Tuesday into Wednesday morning. You can see the position of the trough at 2 A.M. Jan., 11 below in fig. 1.

Figure 1. Map of NAM model 500 hPa heights and geo. abs. vorticity at 2 A.M. Jan., 11 - Image Courtesy Golden State Weather Service

Ahead of the trough, there should be substantial upward motion, even as the energy becomes spit between the trough and the cut-off low over California. That upward motion should promote cloud and snow growth over Wyoming.

We can also look at the jet stream at the same time using the same model run (12Z – 5 A.M. January 9^th).

Figure 2. Map of NAM model 300 hPa heights, isotachs and Jet Stream at 2 A.M. Jan., 11 - Image Courtesy Golden State Weather Service

I want to show you the jet stream position at this same time as well. A dip in the jet stream will position the jet streak (generally the strongest winds within the jet stream) right over Wyoming. The Right-Entrance Quadrant of the encircled jet streak (shown above in fig. 2) is found to promote the best growth of snowfall. A source on that is below in figure 3. The entrance regions of jet streaks are found to be excellent sources of enhanced winter weather.

Figure 3. Basic dynamics of a jet streak - Photo courtesy of MetEd.

The jet streak position matters to where you could potentially see the heaviest snowfall. I will compare the right-entrance region of the jet streak in figure 2 with the NAM forecasted snowfall below in figure 4.

Figure 4. NAM forecasted 3-hour precipitation at 2 A.M. January 11 - Image courtesy IPS Meteostar

Okay, here is the nitty-gritty…the snowfall forecast. The below images show the NAM forecasted snowfall for the Wyoming area. Generally, 1-3” is possible for areas north and east of a mountain range (Casper, Lander, Sheridan, Buffalo, Glenrock, Douglas, Lusk, Wheatland and Torrington). This model run is also going strong for snow on Casper Mountain (up to 8 inches). The timing looks to be through Wednesday morning. The snow will quickly pass and should be done by the afternoon.