Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 311 AM EST Tue Dec 04 2018 Valid 12Z Tue Dec 04 2018 - 12Z Fri Dec 07 2018 ...CA Sierra Nevada Mountains... The models continue to show an upper low dropping south along the California coast Tuesday-Wednesday. Moisture transport and 700 mb convergence moving inland into the CA Sierra Nevada supports several inches of snow on Tue and Wed, with the Wed snow maxima shifting a bit south in tandem with both the offshore circulation and also the bands of 700 mb convergence. WPC probabilities showing a Slight Risk for accumulations of 8-inches or more for elevations mainly above 7000 ft on Day 2 (Wed-Wed night). By Day 3 (Thu), with the low moving southeast, any heavy snow threat will become more confined to the southern Sierra Nevada, with the 700 mb convergence moving east into the ranges of southern NV and AZ into the four corners region and southwest CO, where light snows should develop. WPC probabilities showing a Slight Risk for 8-inches across the higher elevations Thu-Thu night, with none of the models showing heavy snow area. ...Great Lakes Days 2-3... After a lull on day 1, light lake effect snows pick up in the lee of Lake Superior into the Keweenaw Peninsula of the western UP of MI as a cold front progresses across the region. Low-mid level convergence produces lift with the lake enhancing available moisture. On day 3 (Thu-Thu night), the front moves downstream into the lower Great Lakes, with low level convergence favoring snow picking up for a multi-hour period off both Lake Erie and Lake Ontario. Several inches of snow are possible centered on the Tug Hill east of Lake Ontario and the GFS shows high layer relative humidity and a local maxima of lift in favored upslope areas. The GEFS Mean shows snow extending further inland into the western Adirondacks, where several inches of snow are possible Thu-Thu night. The probability of significant icing (0.25 inches or more) is less than 10 percent days 1-3. Petersen