Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 424 PM EDT Sat Oct 22 2022 Valid 00Z Sun Oct 23 2022 - 00Z Wed Oct 26 2022 ...Northern/Central Rockies and Northern High Plains... Days 1-2... Deep trough moving through the Pac NW and northern Rockies late Saturday will deepen into Sunday as 500mb heights dip to around -2.5 sigma. Oblong (E-W) shape to the trough allows for the eastern part to split into its own upper low over WY and move through the Dakotas on Monday with the help of a vort max rounding the base. Additional trailing vorticity moving through the southwestern side of the upper trough will dig into the Four Corners at the same time before turning east as the two entities detach from one another. This southern upper low will provide some light snow to the higher terrain of New Mexico and far eastern AZ. Northern upper low will drive the bulk of the wintry weather the next two days, aided by an increasing southern stream jet over the Plains and a deepening surface low out of Wyoming into the Dakotas Sunday into Monday. Attendant cold front wavering through the Rockies and Great Basin will continue to sink southeastward tonight into Sunday, with lowering snow levels to below 4000ft west of the Plains and down to around 1000ft over the High Plains as the system wraps up. Modest moisture plume into the Interior West from the Pacific (PW anomalies +1 to +2 sigma) will wane over the next 24 hours as the fronts clears through the region, but strong dynamics and ample moisture will promote heavy snow rates >1-2"/hr over the higher terrain from UT through CO where WPC probabilities of at least 8 inches are moderate to high (>40% or >70%, respectively), especially above 7000ft. SLRs will be on the lower side to start with the mild Pacific influx, but cooling column will drive SLRs higher post-FROPA as the precip starts to wind down. As the surface low occludes and wraps up over the Dakotas, potential exists for deformation band to the NW of the low to yield some heavier rates as the column cools enough to support snow. Moisture plume will tap the western Gulf tomorrow and stream northward, wrapping around the upper low into a TROWAL as the low continues to lift northeastward. There remains some spread in low and mid-level thermal profiles among the guidance (and a higher DGZ relative to the best vertical motion), resulting in a varied amount of snow solutions. However, a dynamically vigorous system can be more aggressive than forecast (i.e., a little colder and more QPF) that could allow for some >6" totals in eastern MT. WPC probabilities of at least 4 inches there are mostly >60%. ...Pacific Northwest into the Northern Rockies... Days 2-3... Second and third shortwave in quick succession will slip through Washington and British Columbia as broad troughing slowly sinks southeastward out of the Gulf of Alaska. Each will bring a brief cooling aloft and modest QPF to promote light to moderate snow to the Cascades, Blue Mountains, and northern Idaho/northwestern Montana. Though snow levels will fluctuate a bit, most of the appreciable snow will fall above pass level. The probability of significant icing is less than 10 percent. Fracasso