Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 425 AM EST Tue Feb 14 2023 Valid 12Z Tue Feb 14 2023 - 12Z Fri Feb 17 2023 ...Pacific Northwest and Northern Rockies... Day 1... Cold upper low will sink through OR into the Great Basin today with a last push of precipitation through the region in an active period. Snow levels continue to fall and will meet the valley floor/near sea level early today as precipitation ends, with possible mesoscale bands increasing amounts more than just a few tenths of an inch in the lowlands. Quick pace of the upper low and rebound of mid-level heights by later this evening means a narrow window for additional snowfall, favored mostly for the central/southern OR Cascades into the Klamath Mountains, where several more inches are likely. At the same time, eastern side of the broader trough will carry its own vort max through Wyoming today as a cold front sinks southward out of Canada. This will result in low-level convergence and frontogenesis, aided by post-frontal upslope enhancement, to produce rounds of heavy snow into the terrain from western Montana and the Idaho ranges but especially eastward across southern Montana into northern Wyoming. WPC Snowband Probability Tool highlights these areas for >1"/hr rates later this morning into the afternoon with a stiff northeasterly upslope wind. WPC probabilities are high (>70%) for more than 6 inches of snow across the Absarokas and into the Bighorns and Black Hills of SD. ...Upper Midwest... Day 1... Closed mid-level low and surface low over southeastern CO this morning will lift northeastward today through the Corn Belt and into the western Great Lakes overnight into Wednesday morning. The strength of the low (700/850 mb height at the lowest in the CFSR climo period this time of year) will help draw in a surge of Gulf moisture as flux anomalies rise to over +5 sigma all the way to Minnesota, where rain will initially fall even up to the Canadian border. Negative tilt to the system will promote a WCB to wrap northward and around the upper low into a TROWAL that will lift north-northeastward through the day. With high pressure moving in behind the cold front in Montana, increased northerly to northeasterly winds will create blowing snow and blizzard conditions for parts of the eastern Dakotas into MN this evening (HREF blizzard probs around 30%). The system will be progressive to limit the residence time, but still expect a stripe of a few inches from northeastern SD into northern MN. WPC probabilities for at least 4 inches are greater than 30% in this area with higher amounts/probabilities near International Falls. ...Four Corners, Central Plains, into the Upper Midwest/Great Lakes... Days 1-3... As the upper low over Oregon sinks southeastward D1, it will reorganize and deepen to near -4 sigma (lowest 700mb heights in the CFSR climo record for this time of year) as the upper jet arcs through AZ. Diffluence aloft coupled with mid-level height falls, lower-level FGEN, and upslope enhancement will yield a significant snowfall for the Mogollon Rim and into the San Juans and Sangre de Cristos as the upper low moves right across the Four Corners into D2. Moisture anomalies will be about normal, but the strong dynamics will make up for that. WPC probabilities for at least 8 inches of snow are high in these areas. On D2, the upper low will shear into an elongated vort max as surface low pressure over NM moves eastward along the front before turning northeastward Wednesday evening/overnight. Gulf moisture will again surge northward the but positive tilt to the upper system will prevent a robust development and limit the very heavy snow potential. 00Z guidance continues to struggle with the evolution and QPF amounts/placement, but a consensus remained the steadiest approach. Northeast flow across the central High Plains will favor heavy snow over southeastern CO and western KS as the 700mb low passes across. Farther northeast, as the system elongates, FGEN to the north of the low across KS and southeastern NE later D2 into D3 will eventually stretch all the way to WI/Lower Michigan as the low moves across southeastern Lower MI late Thu into early Friday. Colder air will chase not too far behind the low, driving SLRs higher as the snow winds down. WPC probabilities for at least 4 inches of snow are high (>70%) over southeastern CO into western KS. By D3, >50% probabilities for at least 4 inches stretch from near the Quad Cities into northern Lower Michigan. Two-day probabilities of at least 8 inches are low, generally <40%, except or northern Lower Michigan. Fracasso ...Key Messages for Feb 14-17 Winter Storm... --A winter storm will develop near the Four Corners today and spread a swath of heavy snow northeastward across the Southern Rockies and across the Plains on Wednesday, continuing into the Upper Midwest and Great Lakes on Thursday. --The combination of heavy snow rates and strong winds gusting above 40 mph could result in near-blizzard conditions, especially for the Southern High Plains. This will produce considerable blowing and drifting of snow, very low visibility at times, dangerous travel, and possible impacts to infrastructure. --Farther to the east across the Central Plains, heavy snow rates and gusty winds will likely result in hazardous travel. This combination of heavy snow and strong winds may extend into the Upper Midwest on Thursday. --There is still uncertainty into the exact track of this system into the Midwest, which will affect where the greatest impacts occur. --Much colder temperatures, falling to well below normal values and perhaps near record lows over the Southwest, will follow in the wake of this system.