Ah, Spring

The ongoing spring battle between the Snow Miser and the Heat Miser continues this week.

Snow Miser and Heat Miser from the Rankin and Bass classic,
A Year Without a Santa Claus

As discussed in a previous post, a deep upper-level trough is forming off the west coast and will bring a very active weather pattern to Utah and the western United States the next few days.  This morning's NAM model forecasts the trough to be centered over northeast California by 6 PM MDT tomorrow afternoon with a sharp cold front and concomitant precipitation band extending from central Nevada across northern Utah.

Temperatures are high enough that the valley precipitation through that time should be rain through tomorrow afternoon, but the mountains will be seeing more of the white stuff, so my friend the Snow Miser will be happy.  At issue is precisely where the frontal band will be.  We'll have to see how that plays out over the next day and a half.  

This is a very deep trough and quite anomalous climatologically.  In fact, forecast 500-mb heights near southern California for 1800 UTC (1200 MDT) 8 April are 3-4 standard deviations below average. 

Source: National Weather Service Salt Lake City Forecast Office

Thus, this will be a system with significant impacts across the southwest, but one ingredient that is missing for it to be a regionally historic event is anomalous moisture.  There isn't presently a strong connection to the subtropics or a significant atmospheric river evident in satellite imagery.

Source: SSEC

Further, the forecast precipitable water values over the southwest are not especially anomalous and are within a standard deviation of climatology.  

Source: National Weather Service Salt Lake City Forecast Office

So this is an event with anomalous dynamics, but average precipitable water on the large scale.  It will have impacts on Utah and the southwest, especially in any areas where precipitation is concentrated for an extended period, but will probably fall short of being historic regionally, like the pre-Christmas 2010 event that had wide spread impacts from SoCal to northern Utah.