Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 318 PM EST Fri Nov 8 2024 Valid 00Z Sat Nov 09 2024 - 00Z Tue Nov 12 2024 ...Colorado Rockies and Adjacent High Plains... Day 1... ...Heavy snow and major impacts continue for portions of the Colorado Rockies and Interstate 25 corridor into Saturday morning... Strong low pressure system causing this major winter storm will track north along the CO/KS border tonight, producing final rounds of heavy snow east from the Front Range over eastern CO into the overnight before diminishing into Saturday morning. Downstream height falls and divergence will combine with a modestly coupled jet structure to produce impressive large-scale ascent across the Southern/Central Rockies and High Plains as well as a surface low center tracking north over western KS tonight. This low is accompanied by enhanced forcing through persistent moist isentropic lift which will continue to bring TROWAL through eastern CO into the overnight. An axis of elevated instability beneath the TROWAL, collocated with an axis of deformation, will continue to allow 1-2"/hr snowfall rates in the heaviest TROWAL bands. This activity will lift from southeast CO through at least the Palmer Divide through this evening with bands weakening a bit as they track north from the Denver metro to southern WY. WPC snow probs are mainly terrain based with 30-70% values for >6" additional after 00Z across the greater Palmer Divide, the Front Range, and right around the Raton Mesa. Near 10% probs are along the Cheyenne Ridge in southeast WY. However, the intensity of the banding should allow heavy snow to overcome more marginal thermals and accumulate in the valleys, so areas around CO Springs and at least portions of the Denver metro should see some additional impactful snow tonight. As the low occludes and shifts over Neb on Saturday, the moisture moisture fetch is shunted east and thermals farther east do not support snow, so the heavy snow threat generally ends with the Cheyenne Ridge. The Black Hills mainly stay below the snow level, so impactful snow is not expected there, but some flakes should be seen on Saturday. ...Northwest... Day 3... A potent upper trough ejecting from a deep Gulf of Alaska low approaches the Pacific Northwest coast Sunday night and digs down to the northern Great Basin on Monday. Snow levels in the moisture surge ahead of the trough rise to around 6000ft in western WA and 7000ft in OR/northern CA before dropping to 4000-5000ft under the trough on Monday. Day 3 PWPF for >6" are 30-70% over the length of the Cascades. More impactful snow is likely Monday night into Tuesday with at least the higher passes in WA seeing accumulating snow then. The probability of significant ice across the CONUS is less than 10 percent. Jackson ...Winter Storm Key Messages are in effect... Southern/Central Rockies and High Plains: https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png