An Active Holiday Week Ahead

The upper-level pattern is setting up to make the holiday week a stormy one in northern Utah.  

Below are the average 500-mb height anomaly forecasts from the GEFS ensemble valid at 0000 UTC 25 December (5 PM MST 24 December) and 0000 UTC 29 December (5 PM MST 28 December).  The 500-mb level is a good proxy for the upper-level flow.  Anomalies are departures from the long-time average 500-mb heights.  Positive anomalies indicate anomalous ridging, negative anomalies anomalous troughing.  The images below show persistent ridging over the central Pacific and troughing along the Pacific Coast, a pattern that can be very good for northern Utah snowfall provided it doesn't become too amplified (i.e., the trough along the west coast becomes too deep).  

Source: NOAA/ESRL/PSD

Consistent with the upper-level pattern, our downscaled NAEFS ensemble product for Alta-Collins shows a major shift in the pattern beginning around Thursday December 23rd.  Until then, high pressure will predominate, but after that, the pattern becomes quite active.  

The NAEFS mean water-equivalent and snowfall through 0000 UTC 27 December (5 PM MST 26 December are about 3.65" and 60" respectively.  There is a wide range, but over 80% of the members are producing over 2" and 30".  The downscaled NAEFS seems to have a high bias at Alta this year, but even adjusting for that, this looks like the start of a pretty healthy storm cycle that may continue deep into the holiday week.

Ho ho ho.