Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 404 AM EDT Wed Oct 10 2018 Valid 12Z Wed Oct 10 2018 - 12Z Sat Oct 13 2018 Day 1... ...Eastern Dakotas/Minnesota... An area of enhanced lift in the 700-500 mb layer ahead of a negatively tilted trough moving across the Upper MS Valley should combine with an area of mid level frontogenetic forcing to produce precipitation across eastern ND and northern MN. Model soundings along this axis showed moisture and lift in the dendritic growth zone, which could result in banded precipitation on this axis. Temperatures in the 925-850 mb layer suggest rain changing to snow as colder air becomes ingested in the lower level circulation. An axis of 4 to 8 inches was indicated across eastern North Dakota and northwest MN. These amounts are supported by the 00z HREF snowfall mean, 21z SREF Mean, and 00z GEFS Mean. The 12z ECMWF Ensemble mean shows less coverage due to precipitation type issues. Also, the intial snow will be heavy and wet (low snow to liquid ratios), with some melting likely due to warm ground temperatures. The snow winds down as low pressure departs across the border into Canada. ...Rockies/Great Basin... An upper low near the ID/UT/WY border early today is forecast to deamplify and move quickly across WY and CO today and on to the Plains tonight in tandem with an upper level jet maxima. The primary mid level lift occurs early in the period across northern UT and western WY, which wanes with the departure of the upper trough. The lift is induced by upper divergence maxima and moisture is deep enough in the column for snowfall at higher elevations. Several inches of snowfall is expected over the ranges of western to central CO and western to southern WY, with lesser amounts across the northern Wasatch in UT, as well as the WY Bighorns. The probability of significant icing (quarter inch or more) is less than 10 percent. Day 2... ...The Ranges of CO... Confluent 700 mb flow across CO results in bands of persistent convergence that act in tandem with upper divergence maxima downstream from a Great Basin trough to produce several inches of snow in the ranges of western CO. The event should be focused during Thu and gradually taper Thu nigh t as the upper trough moves east onto the central Plains. QPF amounts from the GFS/NAM/ECMWF are higher than 24 hours ago, so locally heavy snow is possible. 24 hour QPF of half to three fourths of an inch supports 6 to 10 inch snowfall amounts over favored mountains in western CO. A minority of ECMWF and SREF ensmeble members forecast sas much, so a spread of solutions remains in place. The probability of significant icing (quarter inch or more) is less than 10 percent. Day 3... ...The Ranges of Northwest MT... The ECMWF/GFS show an upper level trough crossing southeast from British Columbia and Alberta across the MT Rockies. The trough passage is accompanied by a surge of moisture advection and lift, supported by 300 mb divergence maxima in advance of the upper trough. Lift is not sustained,waning with the upper trough passage, and most models forecast light snow amounts on the order of 1 to 3 inch snowfall amounts, mainly across the MT Front Range/Glacier National Park. Just a couple of the ECMWF ensemble members indicate potential for 4 inches of snow, with the tepid NAM and SREF Mean liquid equivalents supporting lighter amounts. The probability of significant icing (quarter inch or more) is less than 10 percent. Petersen