Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 523 AM EDT Tue Apr 12 2022 Valid 12Z Tue Apr 12 2022 - 12Z Fri Apr 15 2022 ...Pacific Northwest... Days 1-3... A blocking pattern over the eastern Pacific is expected to persist, with models showing a closed low developing near Vancouver Island/western Washington today and remaining in place through early Thursday. A series of shortwaves moving through the broader circulation will cause the flow to back and support periods of organized, heavier precipitation across western Oregon and northwestern California. Heavy accumulations are likely for the Oregon Cascades. With snow levels remaining low, some minor accumulations are possible across the lowlands, with locally heavy amounts possible across the higher elevations of the coastal ranges. ...Northern Rockies through the Northern Plains... Days 1-3... ...Significant and potentially historic blizzard likely for portions of the Northern Plains... A historically significant, high-impact blizzard is expected to unfold across the northern Plains today, producing record-breaking snowfall amounts for portions of eastern Montana to central North Dakota today. A compact low moving across the northern Rockies this morning will continue to track east, assuming a negative tilt as it moves over the High Plains later today. As the upper low moves east, a powerful surface cyclone will track east from the High Plains toward the upper midwest. Strong low-to-mid level frontogenesis overlapped by coupled upper jet forcing northwest of the low will support the development of heavy snow from eastern Montana to North Dakota. HREF guidance is showing banded snowfall evolving, with rates of 1-2 inches/hr developing from eastern Montana into western North Dakota and then slowly drifting northeast across western to central North Dakota into the evening. The potential for locally heavy snow will persist into Wednesday as the upper low continues to deepen and slowly drift east across the northern Plains. While confidence in the potential for very heavy snow remains high, its placement remains limited by continued model spread regarding the timing and amplitude of the upper system. Even with some uncertainty in the finer details, WPC probabilities indicate that by early Wednesday, accumulations of a foot or more are likely, with accumulations over two feet possible from the southern Montana-North Dakota border northeastward into north-central North Dakota. In addition to the heavy snow, strong and gusty winds supported by a tight pressure gradient on the northwest side of the low is expected to produce blizzard conditions with significant blowing and drifting snow. By late Wednesday the potential for heavy snow is expected to diminish, however gusty winds and some additional light to moderate snows are likely to continue into Thursday as the system begins to lift north into Canada. Across western into north-central North Dakota, storm total amounts in excess of two feet, with locally heavier amounts approaching three feet are possible with this system. For Days 1-3, the probability of 0.10 inch or more of ice is less than 10 percent. Pereira ~~~Key Messages for April 12-14 Blizzard~~~ --A long duration, significant winter storm will continue to impact portions of the northern Rockies today and the northern Plains through Thursday. --A combination of heavy snow and strong wind gusts will produce blizzard conditions with significant blowing and drifting of snow from the eastern slopes of the northern Rockies across the northern Plains. --Travel will be very difficult to impossible, and widespread power outages and tree damage are expected. Significant impacts to young livestock are also possible. --Snowfall may reach record levels in parts of eastern Montana and western and central North Dakota, with maximum storm total snowfall in excess of two feet possible.