Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 354 PM EST Thu Mar 07 2024 Valid 00Z Fri Mar 08 2024 - 00Z Mon Mar 11 2024 ...Central/Southern Rockies and High Plains... Days 1-2... A broad, positively-tilted upper trough across the western U.S. will have to shortwave troughs round its base through Friday. Both will track over far northern Mexico and reinforce a surface wedge building in behind a cold front that is currently pushing south through the TX Panhandle and surface low will advect gradually eastward over the Central Plains Friday. Downstream of this wave, moisture advection will increase on isentropic ascent surging out of the Gulf of Mexico and lifting northward into the system and wrap cyclonically northwestward which will result in an expanding precipitation in response to the synoptic lift with additional upslope lift into the Front Range on NE flow behind the southward advancing front this evening and overnight. Heavy snow bands over western Neb into northeast CO will continue to drift southeast with cold air advection bringing heavy snows through this evening to southwest Neb and northwest KS. Day 1 PWPF for >6" is 10-30% from west-central Neb to northeast CO. Terrain based snows in southeast WY/down the Front Range and in particular for the Sangre de Christos and out onto the Raton Mesa, then also on the other side of the San Luis Valley in the San Juans occurs tonight, lingering over the San Juans into Friday night. Day 1 PWPF >8" are 20-70% from the south side of the Palmer Divide to the Raton Mesa and the Sangre de Christos. Snow levels start this evening around 6500ft, then drop to around 5000ft by Friday morning. ...Great Lakes and Northeast... Days 2-3... A northern stream shortwave trough rounds a ridge extending from the Pacific NW through British Columbia, tracking over the northern Canadian Prairies Friday, then closing into a low as it dives southeast over the Great Lakes Saturday. A southern stream wave rounding the aforementioned positively-tilted trough over the West continues to promote an inverted trough over the Midwest Friday with a surface low crossing Michigan Friday night. When the northern stream trough approaches on Saturday, the focus at the surface turns to a developing coastal low on the Northeastern Seaboard that lifts north through coastal Maine Sunday. Most of this complex system will be rain with ample Gulf moisture streaming north up the Midwest and then up the Eastern Seaboard. Wrap around snow Friday night/Saturday is limited to the U.P. and northern L.P. of MI where Day 2 PWPF for >4" is 20% or less in favorable Nly/NNEly snow belts. On Saturday night the precip shield reaches the Northeast with snow levels generally 3000-5000ft which limits accumulating snow to the highest elevations of the Adirondacks and Green and White Mtns. However, with the coastal low the primary surface low on Sunday, sufficient cold air with Great Lakes-sourced moisture triggers LES and further snow for the higher terrain northeast from the Adirondacks where Day 3 PWPF for >6" is 40-80%. LES snow bands are probably underdone in PWPF at this point with Day 3 values for >4" generally 10-40% over portions of northern MI and east of Lake Erie. ..Northwest... Days 2/3... A sharp trough moves over the PacNW coast Saturday morning with a second, more intense wave/low crossing Sunday. Moisture surges ahead of these waves will bring moderate to locally heavy precip with snow levels early Saturday generally 4000-4500ft along the length of the Cascades, dropping to around 3000ft that afternoon and staying around there through the second wave. Day 2 PWPF for >6" is generally 10-40% for the Cascades through the Shasta/Siskiyou, then increasing to 40-90% for Day 3 with the stronger wave. Moisture from the first wave reaches the northern Rockies Saturday night with the second wave arriving later Sunday. Day 3 PWPF for >6" are 20-60% over far northeast WA/northern ID into the northwest corner of MT with lower values over the Wallowa Mtns in northeast OR. Jackson