Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Apr 01 2023 20:59:18 FOUS11 KWBC 012059 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 458 PM EDT Sat Apr 01 2023 Valid 00Z Sun Apr 02 2023 - 00Z Wed Apr 05 2023 ....Pacific Northwest to the northern High Plains... Days 1-3... ....A major winter storm will produce heavy snow and strong winds from the Intermountain West to the northern High Plains early next week... A leading shortwave that brought periods of snow from the mountains of the Pacific Northwest to the northern Rockies will continue to move east of the northern Rockies and into the High Plains tonight. In its wake, a well-defined cold front will continue to settle south and east across the region, with snow levels forecast to tumble to its north. Even as the leading wave moves east of the region, periods of snow are forecast to continue through Sunday across the Northwest into the northern Rockies as an upper low settling south along the coast of British Columbia directs a steady stream of energy across the region. This energy will begin to carve out a deeper trough across the region. Additional heavy accumulations are likely, especially for the Cascades, with impactful accumulations expected along the major passes as well. By late Sunday and continuing through Monday, a strong shortwave will dig southeast through the broader scale trough, carving out an anomalously deep trough centered over the Great Basin by late Monday. By late Monday, the model consensus shows -2.5 std dev 500mb height anomalies centered over the Great Basin. Heavy snow and strong winds are likely to develop along a strong baroclinic zone following an impressive low developing over eastern Utah on Monday. This will mark the onset of what are expected to be heavy snow accumulations along the Utah ranges. Meanwhile, increasing ascent and moisture advection will support snows east of the Rockies, with amplifying low level easterly winds supporting heavy snows developing over southeastern to south-central Wyoming. By late Monday, WPC probabilities indicate that snow accumulations of 6 inches or more will be common, with localized heavier totals likely across the region. By late Monday and continuing into Tuesday, models show the upper trough continuing to amplify with a closed low developing over the central Rockies. Strong upper forcing, along with low-to-mid level frontogenesis on the northwest side of a powerful surface low redeveloping over the central Plains will support moderate to heavy snow stretching northeast from the central High Plains toward the Upper Midwest on Tuesday. In addition to the heavy snow, strong pressure gradient will generate strong, gusty winds across the region. WPC probabilities indicate that by late Tuesday snowfall totals are likely to exceed a foot in many locations. These include the northern Utah and south-central Wyoming mountains and the High Plains from southeastern Wyoming northeastward into the Nebraska Panhandle and western South Dakota. Heavy snow amounts are likely to extend farther to the northeast as the storm continues to track toward the Upper Midwest beyond the end of the period. See below for the latest Key Messages for this event. Meanwhile, energy embedded within northwest flow on the backside of the trough will continue to support periods of snow across the Northwest, with additional heavy accumulations possible, especially for the Oregon Cascades late Monday into Tuesday. The probability for ice accumulations greater than 0.10 inch is less than 10 percent. Pereira ....Key Messages for Apr 3-5 Winter Storm... --Heavy Snow in Excess of One Foot Likely Confidence continues to increase in a swath of heavy snow in excess of 12 inches, which could challenge some April snow records in the Dakotas and northwest Minnesota. Avalanches and significant impacts from snow load are possible in the Intermountain West, particularly in portions of Utah. --Blizzard Conditions Likely in the Northern Plains Strong winds and heavy snow will create whiteout conditions at times Tuesday and Wednesday, leading to dangerous to impossible driving conditions and considerable disruption to daily life. --Life Threatening Cold for Anyone Stranded Wind chills should fall to near or below zero during the blizzard in the Northern Plains, which could be life-threatening to anyone stranded. --Damaging Winds on Warm Side of System Widespread gusts in excess of 50 MPH will spread from the Southwest and Four Corners Monday, to the Plains Tuesday, and Upper Midwest Wednesday. 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