Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 424 AM EDT Mon Apr 03 2023 Valid 12Z Mon Apr 03 2023 - 12Z Thu Apr 06 2023 ...Great Basin and Central Rockies to the Upper Midwest... Days 1-3... ...A powerful storm system producing heavy snow and strong winds is likely to impact a large portion of the central Rockies and north-central U.S.... Not much change to the large-scale picture, with models continuing to show a powerful winter storm evolving over the Intermountain West and central Rockies today, before lifting northeast into the north-central U.S. Tuesday into Wednesday. This system is likely to spread widespread heavy snow and produce strong, gusty winds across the region. The deep upper-level trough responsible for the upcoming significant winter storm is already diving into the West this morning and is anticipated to close off while sinking further over the Intermountain West through early Tuesday. The strength of this upper-level feature is undeniable, with standardized 500 mb anomalies of -2.5 to -3, as well as record low 500 mb heights for the date throughout the central Rockies on Tuesday. The closed upper-level low is then forecast to turn negatively-tilted within the large-scale trough Tuesday night and race northeastward to the northern Plains. Additionally, a strong 250 mb southwesterly jet streak over the central Plains on Tuesday will likely exceed 150 kts and place the northern Plains within a very favorable region for upper-level divergence and lift through the mid and upper levels. At the surface, the deepening surface cyclone strengthening over the central High Plains on Tuesday and racing into the northern Plains/Upper Midwest on Wednesday will surge warm air to the east along a sharp warm front. This warm front will allow for a period of substantial vertical motion into the colder airmass located across the region, but will also lead to a transition to sleet and freezing rain ahead of a potent dry slot from southeast South Dakota to central Minnesota and the Upper Great Lakes. As far as impacts go, moderate to heavy snow is expected to initially develop along a strong low-to-mid level baroclinic zone settling southeast behind an impressive surface low organizing over eastern UT on Monday. This is likely to produce heavy accumulations over the UT ranges and even some of the lower elevations, particularly around Salt Lake City. Snow levels are to crash to below 2000 ft for much of the event. Meanwhile, strong low-level easterly flow developing north of a strong front east of the mountains, will support the development of moderate to heavy snows (potentially with rates up to 2"/hr) over the central High Plains back into the south-central Wyoming mountains. Snow also begins to spread further into the Plains across far northwest Nebraska and western South Dakota as precipitation rotates around the strengthening low pressure system to the south. By early Tuesday, WPC probabilities indicate widespread snow amounts of 12 inches from central UT to western South Dakota, with locally higher totals likely approaching 2 feet across eastern Wyoming. On Tuesday and Wednesday, strong upper forcing combined with low-to-mid level frontogenesis will support moderate to heavy snow developing on the northwest side of the surface low, with heavy accumulations likely from southeastern Wyoming to the Dakotas and northwestern Minnesota. WPC probabilities indicate that snow accumulations of a foot or more are likely across this area through Wednesday morning. In addition to the heavy snow threat, strong gusty winds afforded by a tight pressure gradient will contribute to hazardous blizzard conditions. Overall, models have remained in fairly good agreement with the larger scale picture. Differences remain in the finer details, especially along the southeastern edge of the heavy snow axis and within the tight gradient of expected snowfall amounts, where marginal temperature profiles are highly dependent on the exact track of the low pressure system. Overnight guidance has trended ever-so-slightly westward with the surface low and therefore shifted the snowfall gradient further northwest across the eastern Dakotas and northwestern Minnesota. This trend will continue to be monitored, especially for areas where conditions could drastically change within miles depending on the particular solution. Closer to this low center and along the warm front, a wintry mix may limit snow accumulations from the southern Nebraska Panhandle into eastern South Dakota, central Minnesota and the Upper Great Lakes. Up to an inch of sleet is possible in spots, with WPC probabilities for greater than a tenth of an inch of ice between 20-40%. The higher April sun angle will also limit accumulations during the middle of the day on Tuesday for areas on the southern edge of the heavier snowfall rates. Storm total amounts of a foot or more are likely to extend from the Utah mountains to northwestern Minnesota, with accumulations exceeding two feet in some locations. Considerable disruptions to daily life are likely. Please see our key messages below for additional highlights regarding this storm. ...Pacific Northwest... Days 1-3... Energy embedded within northwest flow on the backside of the broader-scale trough is expected to produce periods of snow through Tuesday. Snow levels are forecast to fluctuate, but remain largely below at or below 1000 ft through the period. Light accumulations are expected in the lowlands of eastern Washington, Oregon, and northwestern California, with heavy accumulations of a foot or more likely over the Oregon Cascades. Snow levels are forecast to rebound with the approach of warm front and light precipitation on Wednesday. Snell ...Key Messages for April 3-5 Major Winter Storm... --Widespread Heavy Snow Totaling Over One Foot A major winter storm is expected to produce over a foot of snow from the Central Rockies to the Northern Plains, challenging some April snow records in the Dakotas and northwest Minnesota. The highest totals could locally exceed 24â€. Avalanches and significant impacts from snow load are possible across portions of Utah. --Blizzard Conditions in the Northern Plains Strong winds and heavy snow will create whiteout conditions and significant drifting snow Tuesday and Wednesday, causing dangerous to impossible driving conditions and considerable disruption to daily life. --Life Threatening Cold for Anyone Stranded Wind chills will fall to near or below zero during the blizzard in the Northern Plains, which could be life-threatening to anyone stranded outside. --Damaging Winds From the Southwest to the Midwest Widespread gusts in excess of 50 MPH will spread from the Southwest and Four Corners today, to the Plains Tuesday, and Upper Midwest Wednesday. Power outages, wind damage, and blowing dust, even outside of thunderstorm activity, are likely.