Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 453 AM EDT Mon Nov 01 2021 Valid 12Z Mon Nov 01 2021 - 12Z Thu Nov 04 2021 ...Northern Colorado... Days 1/2... Ongoing snow bands along the WY/CO border east across the Neb Panhandle into central Neb continue for a few more hours this morning before shifting east into warmer lower portions of the Plains where rain is expected. The next shortwave trough will eject the CA/OR coast today, undercut a ridge across western Canada tonight, and cross the central Rockies Tuesday. Height falls and modest PVA with this trough will drive ascent within a plume of Pacific moisture reaching +1 to +1.5 standard deviations above the climo mean for PW. Day 2 WPC snow probabilities for 6 or more inches reach 30% above 8000ft in the Flat Tops and the northern Front Range/Rocky Mtn NP. ...Great Lakes... Days 1-3... Lake effect snow in the higher elevations in the U.P. continues today, lowering closer to lake level by this evening. Water temperatures near +10C will drive steepening lapse rates and a deepening inversion to above 9000 ft. This should allow for lake enhanced precipitation to expand across the U.P. of Michigan, but marginal low-level thermals should lead to a rain/snow mix outside of the higher terrain such as the Huron and Porcupine Mountains. WPC probabilities for 4 or more inches peak on Day 1 in the Huron Mtns just south of the Keweenaw Peninsula at around 50%. The cold northwesterly flow spreads across the rest of the Great Lakes Tuesday with LES for all typical Great Lake snow-belts by Tuesday night. However, modest duration of forcing and marginal low-level thermals within the column suggest a rain/snow mix with accumulations occurring only in the higher terrain. Day 2 WPC probabilities for 4 or more inches are 50 percent over the eastern U.P. and probabilities for 2 or more inches outside of the U.P. are generally limited to the higher terrain of the interior northern L.P., the Tug Hill area off Lake Ontario and far western NY off Lake Erie. For Days 1-3, the probability of significant icing is less than 10 percent. Jackson