919 FOUS11 KWBC 252035 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 435 PM EDT Thu Apr 25 2024 Valid 00Z Fri Apr 26 2024 - 00Z Mon Apr 29 2024 ...The West... Days 1-3... A series of impulses approaching the PacNW dig southeast tonight to Friday, which builds a substantial longwave trough over the Great Basin. This trough then shifts east, closing into a low over the Four Corners early Saturday before swinging northeast through CO through Saturday night and into the Dakotas Sunday. Pacific moisture streaming in ahead of this trough makes for a broad areas of higher elevation snow to develop across much of the Intermountain West on Friday. Day 1 PWPF for >6" are 50-90% over the OR Cascades which sees the most direct lift of Pacific moisture as this trough crosses tonight (with snow levels dropping from 6000ft to 5000ft), and generally 40-80% above snow levels of 6000-8000ft over the higher Great Basin ranges in NV and UT as well as the Absarokas and Wind Rivers. As the developing low shifts east over the Four Corners Friday night, the heavy snow focus shifts to the Rockies from CO through southwest MT. Lee- side cyclogenesis downstream of the low develops over southeast CO late Friday which focuses flow of Gulf moisture into the north- central Rockies which provides additional ascent through upslope flow and periods of enhanced fgen, potentially overlapping a deformation axis in the Central Rockies, to produce heavier snowfall rates exceeding 1"/hr at times. Snow levels in the Rockies will remain generally elevated, primarily 8000 ft, but with steepened lapse rates beneath the cold trough and some areas of enhanced ascent, snow is possible into the 6000ft elevation range. Day 2 PWPF for >8" is 50-90% over the Wind Rivers, Front Range, and portions of the San Juans and more like 30-70% for the rest of the higher terrain between southwest MT, UT, and central CO. The pivot to a northeast direction over CO late Saturday makes a potential for persistent banding and substantial snowfall at elevation with 2-3ft likely in the higher terrain of the Wind Rivers and Front Range. The low shifts onto the Plains Sunday with a deformation axis possibly bringing accumulating snow to the High Plains and a notable reduction in rates and coverage to the Rockies. PWPF for >4" is generally 40-70% over the CO Rockies into southern WY. The next low tracks from the southern Gulf of Alaska Saturday night bringing moderate precip to the PacNW with snow levels around 4000ft. Day 3 PWPF for >4" is 30-80% in the North Cascades of WA. The probability of significant icing is less than 10 percent. Jackson $$