Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 314 PM EST Wed Feb 07 2024 Valid 00Z Thu Feb 08 2024 - 00Z Sun Feb 11 2024 ...The West... Days 1-3... One trough will be exiting the Rockies tonight with lingering moisture over the Interior West as another trough (with origins in the northeastern Pacific) or closed low dives into NoCal and the southern Sierra into southern NV by tomorrow. This will give another round of snow to the mountains (Sierra down to the SoCal ranges eastward to AZ) with snow levels generally 4000-5000ft falling to 3000ft or so as the colder air moves in behind the main precipitation surge. Despite only average amounts of moisture in the column, modestly sharp height falls and favorable upslope will help squeeze out more than 6-12" at higher elevations. WPC probabilities for at least 8 inches of snow are at least 50% above about 4500-5000ft in CA/AZ/NV and about 6000-7000ft in UT and western CO. Into D2, the small/compact upper low will move eastward out of CO to the central Plains, continuing the snow over UT into the CO Rockies, especially the San Juan Mountains, where WPC probabilities for another 8 inches of snow are >50% above about 7000ft. Farther north, combination of incoming northern streak jet and mid-level height falls will promote snowfall over northern ID into western MT, especially above 5000ft. By D3, last in the long series of shortwaves will dive southeastward from the PacNW/northern Great Basin and through northern AZ by Sat afternoon/evening. Digging northern stream jet in response to building ridging into western Canada will promote a broad area of lift over the Four Corners with light to modest snow over eastern NV into UT and northern AZ. Focus will be driven again by the best upslope coinciding with sufficient moisture which should lie on the southern side of the system. WPC probabilities for at least 6 inches are highest over the Mogollon Rim into the White Mountains as snow levels hover around then fall below 4000ft. ...Northern High Plains and Northern Rockies... Days 1-2... Low pressure organizing over portions of the Northern High Plains will continue to track north/northeast into northwest Minnesota by Thursday evening as the mid-level shortwave energy quickly lifts into the Northern Plains. Precipitation breaking out across today/this afternoon across eastern Montana and the Dakotas will continue through the next day or so, aided by plentiful moisture in the mid-levels being directed northwestward while the falling heights and left exit region diffluence brings about a broad area of forcing. As the low deepens into the Dakotas tonight, moisture wrapping around it will place a TROWAL on its western flank over eastern Montana. Combined with favorable upslope, this is where guidance has trended wetter and stronger with the forcing. A notable jump in the QPF has now pushed higher snow totals for the Day 1 period (00Z Thu-00Z Fri) with broad 4-6", supported by the latest WPC PWPF (even slight 20-30% chances of 8" totals). Across far eastern MT into ND, a period of wintry mix will be possible with a surging warm nose in the lower levels helping to push ptypes over to a mix of freezing rain. While significant icing isn't expected, there are near 20% probabilities of at least 0.01" across portions of ND through tonight. By late tonight, as the low deepens over the eastern Dakotas, the turn in winds to easterly/northeasterly will draw colder air through the column, helping to transition any ptype issues over to all snow and lead to a fairly lengthy period of light/moderate snowfall across eastern MT and ND through Thursday into Thursday night. Some locally higher snowfall rates approaching 1"/hr will be possible. The bigger story will be the increasing winds which may contribute to reduced visibilities and blowing/drifting snow as depicted by the high probabilities for Minor level impacts due to falling snow and blowing snow which will likely result in travel disruptions. ...Central Rockies & Central High Plains... Day 3... Shortwave energy currently moving through the Gulf of Alaska today will dive southeast through the West and eventually carve out a deeper trough and closed low over the Four Corners region by late FridayÂthrough this weekend bringing a broad area of strong forcing for ascent across the region while at the surface, lee cyclogenesis takes place before advancing eastward. There remains considerable uncertainty in the placement and strength of the major synoptic features including the low track/strength and how much easterly flow upslope takes place across the Front Range. But the general trend from the previous forecast cycle is for a wetter, stronger system that brings greater probabilities for accumulating snow to the region, from far southeast Wyoming southward through northeast New Mexico. Within that, there remains some spatial differences, with the CMC being a stronger/wetter northern outlier though the latest GFS is also a wet solution with upwards of 0.75-1" QPF across the CO Front Range. For now, the WWD forecast lies near the NBM 50th-75th percentile with peak QPF around 0.7" for the 24-hr period ending 00Z Sunday. The latest WPC snow probabilities show moderate chances for at least 6" (40 to near 60 percent) from near Cheyenne through Denver and across the Palmer Divide into Colorado Springs. The synoptic setup and ingredients do support locally higher amounts (though location remains more uncertain) but amounts in the 8-12" appear possible, supported by the near 20% probabilities for 12" across portions of the Front Range (south of Denver metro) where favorable upslope flow may enhance totals. Finally, the latest WSSI-P shows fairly high probabilities for at least minor impacts (above 60%) and now advertises 20-30% chances of Moderate impacts including the Denver metro. Fracasso/Taylor