Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 222 PM EST Wed Nov 6 2024 Valid 00Z Thu Nov 07 2024 - 00Z Sun Nov 10 2024 ...Central/Southern Rockies and Adjacent High Plains... Days 1-3... Upper low at the base of a larger western CONUS trough lies over the Four Corners this afternoon and will continue sinking southward tonight into eastern AZ. It will slowly detach from the northern stream and cut off as it wobbles southward then eastward into southern NM by early Friday. Then, feeling the push of the subtropical jet, it will lift northeastward across the northern TX Panhandle and far western OK Panhandle to the CO/KS border by early Saturday. The slow movement of the upper low combined with a fairly steady stretch of moisture as well as upslope enhancement will lead to significant snow accumulations in parts of the NM mountains and across the CO line along the Sangre de Cristo range. Impacts may be major to extreme in some locations and exaggerated by the fact that this is the first significant winter storm of the season for this region. For early D1, frontal boundary slowly sinking southward from western KS to northeast NM on the edge of the height falls will continue to promote light to modest snow through this evening over northeast CO and border regions of KS and NE in an area of surface convergence and beneath bouts of PVA. Through the evening, as the upper low tucks farther southwest of CO, heights should rise and the snow should lessen. Nevertheless, snowfall rates near 1"/hr should yield an additional few inches near/south of DEN and eastward over the High Plains. Farther south over NM, closer to the stream of moisture and vort maxes rotating around the upper low center, snow will increase in intensity over much of the NM terrain on D1 and last through D2 with similar intensity before the upper low lifts north and weakens by D3. The slow movement of the upper low will allow for continued heavy snowfall to its east via persistent IVT values near/above the 90th percentile. This could result in 1-3ft of snow over the NM terrain (WPC probabilities for at least 12 inches are >90% over much of northeastern NM and southeastern CO) along with areas of blowing/drifting snow eastward into the far western OK Panhandle. Snow will continue over northern NM into southern CO along the Sangre de Cristos and onto the High Plains as the upper low sloshes toward the TX/OK Panhandles. Moisture source will add in then largely switch to the western Gulf, wrapping around the upper low and capitalizing on upslope from the northeast through the column. Snow will finally start to taper off by the end of the period (early Saturday). The greatest uncertainty remains along the eastern gradient of snowfall where low-level warmth creeps into the High Plains and leads to a transition toward rain from the KS/CO border to eastern NM and the TX/OK Panhandles. A brief period of sleet is possible as a warm nose aloft ebbs and flows across the High Plains during the event. Exactly where this rain/snow/mix line occurs is still a question, with today's guidance trending westward and a gradually warming transition as the storm weakens by Saturday. All told, 3-day WPC probabilities for at least 24 inches of snow are >50% above 6000-7000ft over the Sangre de Cristos and Raton Mesa, with a large footprint of at least 6 inches over much of eastern CO southward into central NM. Latest WSSI shows these snowfall values as producing widespread Major to Extreme impacts across much of central and northern NM as well as south-central Colorado. The probability of significant ice across the CONUS is less than 10 percent. Fracasso/Snell ...Winter Storm Key Messages are in effect. Please see current Key Messages below... https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png