Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
307 AM EDT Sat Apr 20 2019

Valid 12Z Sat Apr 20 2019 - 12Z Tue Apr 23 2019

...The Mountains of south central to southwest MT south across Wy
and central CO/northern NM...
Days 1-3...

A shortwave dropping slowly along the WA/OR coast today will drift
onshore California and into the Great Basin on Sunday. Associated
with this feature, an upper jet slowly retreating to the east will
leave the favorable diffluent right entrance region across the
ranges of southwest to south central MT, then extending across the
border into WY. The low level convergence and moisture convergence
ahead of the 700 mb front leads to accumulating snow in these
mountains, with several inches in favored upslope areas possible.

On day 2 Sunday,  the 700 mb front drops south towards CO while
the upper low closes off near the Four Corners. The combination of
lift due to frontal convergence and increasing mid-level
divergence in an area of enhanced moisture focuses a period of 
snow extending out of the ranges in western WY across the front
range in central CO, as well as the Uintas of UT. Despite high
snow levels, several inches are likely. WPC probabilities feature
a moderate risk for 8 inches as the along the front range of CO. 

On day 3 Monday, The mid-upper low drifts east across AZ into NM. 
The pool of moisture sinks south from CO into NM as does the lift
along the frontal boundary, which is supported by 300 mb
divergence maxima shown in the 00z ECMWF in southeast CO to
northern NM.  Several inches of snow is expected from the
mountains of southern CO, focused in the Sangre DeCristos, and
then into northeastern NM.  The stronger lift and heavier precip
is over the high Plains where current progs indicate it is likely
too warm for snow. Agreement among models with the evolution of
the southwest closed low is better than normal, with slight timing
differences.

The probability of significant freezing rain is less than 10
percent Days 1-3.

Petersen