Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 342 PM EST Sun Mar 01 2020 Valid 00Z Mon Mar 02 2020 - 00Z Thu Mar 05 2020 ...Southern California...Southern Great Basin...Central and Southern Rockies...Four Corners... Days 1-3... Low pressure closing off central CA later today and the end of a very positively tilted trough over the Great Basin will shift south-southeast along the southern CA coast tonight and across the northern Baja peninsula Monday before shifting east across northern Mexico to central TX through Wednesday. Pacific moisture influx south/ahead of this trough/developing low has moistened much of the Southwest CONUS which is converging along a low level boundary oriented from the central High Plains to the southern Sierra Nevada where heavy mountain snow is occurring at around 5000 to 6000ft. Upsloping cold air at the surface is allowing snow for the High Plains east of the WY Rockies. As the south-shifting low develops tonight it takes forcing focus from the entire trough resulting in lower snow rates as the features shift south across CO and UT tonight. Southwesterly low level flow lifts over the southern CA ranges and southern Sierra Nevada tonight allowing locally heavy snow to continue there above about 4000ft. Day 1 snow probabilities are moderate to high for high terrain of the southern Sierra Nevada, southern NV/UT, most of the CO Rockies with low probabilities east of the Front Range in CO, particularly for the Palmer Divide. As the low shifts across the Sea of Cortez Monday, renewed Pacific moisture into AZ and forcing from the low allows locally moderate snow to spread south across AZ and NM. Day 1.5 snow probabilities are low for 6 or more inches and limited only to the highest White Mtns in eastern AZ. Most of the precip is limited to Mexico as the low tracks east with some Pacific and Gulf of Mexico sourced moisture wrapping around into southern NM Tuesday/Tuesday night. Day 2.5 snow probabilities are high for 6 or more inches for the Sacramento Mtns of southern NM. ...Pacific Northwest and Northern Rockies... Days 1-3... A series of mid-level impulses in confluent mid-level flow and a northwesterly jet streak that drifts south from BC will direct an atmospheric river into WA tonight into Tuesday and provide lift for nearly continuous precip for WA Cascades and west for the next three days starting tonight and the northern Rockies starting Monday. Snow levels will quickly rise to 4000 to 5000ft for the Olympics and Cascades tonight as the warm-sourced moist air arrives and only dip 1000ft or so through each impulse/trough passage. WPC probabilities for 6 or more inches on Day 1 are moderate for the highest WA Cascades only, expanding to lower WA Cascades and the highest northern ID/northwestern MT ranges on Day 2, and increasing to high for those ranges on Day 3. Moderately high 48hr probabilities for 18 or more inches are across the higher WA Cascades and Lewis Range in northwest MT. ...Northeast... Day 3... A mid-level trough swinging through the Great Lakes Tuesday becomes positively tilted allowing rapid surface cyclogenesis of a low shifting northeast from the eastern Ohio Valley. This low tracks across interior New England and near the Maine Coast into Wednesday. Existing cold air from the mean trough over the area allows for snow along and left of the low track, with a narrow stripe of enhanced snow looking more likely as a TROWAL develops north/northwest of the low center as it moves across New England Tuesday night. As of now the Day 3 snow probabilities for 4 or more inches are low for the higher White and northern Green Mtns, increasing to moderate for far northern Maine. For Days 1-3, the probability of significant icing (0.25-inch or greater) is less than 10 percent. Jackson