Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jan 21 2024 08:27:46 FOUS11 KWBC 210827 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 327 AM EST Sun Jan 21 2024 Valid 12Z Sun Jan 21 2024 - 12Z Wed Jan 24 2024 ....The West... Days 1-2 The active weather pattern will continue across much of the West for another couple of days associated with a persistent onshore flow strengthened by an impressive 150-180+ kt jet positioned over southern California into northwestern Mexico. With many mid level impulses moving through and an increase in moisture, widespread precipitation is expected to persist for another few days. The threat of significant winter precipitation however will begin to wane as warmer air from the Pacific flow will lift snow levels and erode the colder air place by late Monday into Tuesday. Until so, a few areas stand the threat of more notable winter impacts including heavy snow in the Sierra Nevada while some notable snow totals will be found for the highest peaks of the Intermountain West above 6000 ft or so. Upslope flow on westerly to southwesterly flow aloft will favor the north-south ranges, especially the Wasatch in UT, but also into the Mogollon Rim and White Mountains in central AZ day 2 as the troughing axis shifts eastward. WPC probabilities for at least 8 inches of snow through the period are at least 50% above about 7000ft. For the Pacific Northwest, a continuation of steady moisture overrunning a cold air mass will keep the threat of ice accumulation going in the Columbia River Gorge where an additional 0.1" to locally 0.20" will be possible (WPC 0.1"+ ice probabilities are over 30-40 percent). Meanwhile, the higher elevations of the OR/WA Cascades and eastward above about 5000 ft steady snow will continue where the latest WPC probabilities for 6-8 inches through day 2 is above 50 percent. ....Southern Plains into the Ohio Valley... Days 1-2 A deepening trough moving out of the Intermountain West and Four Corners region will pivot eastward today, reaching the Southern Plains by late tonight into Monday morning, taking on a negative tilt as it does so. As a result of the strengthening upper divergence, low to mid level southerly to southwesterly flow will pick up, transporting a moist and relatively warmer airmass through the region. The overlapping area of lift and moisture combined with the very cold air mass in place and cold air entrenched in the region will bring a period of freezing rain, initially late this evening across portions of northern TX into southern OK, but quickly spread north/northeast through much of the Plains, Ozarks, and Mid-MS Valley during the day on Monday. A battle of the residual cold air and the warm air advection will make this a tricky ice accumulation forecast, but overall the latest model trends still point toward some potentially significant ice accumulations from eastern OK through northwest AR and southern MO while a much broader area of lighter ice accumulations (but still impactful) expands across much of KS/MO and central OK. The latest WPC ice probabilities for 0.25" peak at 40 percent in southern OK, northwest AR, and southern MO where the combination of this ice accumulation and stronger winds may result in more significant ice impacts. Farther to the northeast, the duration of heavy freezing rain is expected to be less both due to lower anomalous moisture and stronger ascent during the event to erode the cold surface layer more rapidly. A stripe of freezing rain is still probable however across Iowa, Illinois, central to northern Indiana, western Ohio, and southern Michigan where WPC probabilities for 0.1" of ice or more reaching are above 30 percent. ....Great Lakes and Northeast... Day 3... Shortwave energy coming out of the Southern Plains early this week will lift in the southwesterly flow aloft toward the Great Lakes by late Tuesday into Wednesday. Meanwhile, forecast guidance continues to show a strong surface high of 1040+ mb slipping southeast through Canada, settling near Hudson Bay and Quebec. This will put a marginally cold air mass southward into the Great Lakes and northern New York and New England while precipitation associated with the southern stream energy lifts north. A mixed precipitation type event is likely with an area of heavy snow on the northern end and a corridor of freezing rain to the south. Models still are struggling with the strength of the shortwave energy, how much moisture is transported northward, and thermal profiles but several inches of snow will be possible across portions of the central/northern L.P. of Michigan eastward into northern NY and into New England. The WPC snow probabilities for at least 4 inches are up to 20 percent. Further south across southern Michigan into southern NY and northern PA, ice accumulations will be possible and the latest WPC ice probabilities for 0.1" are up to 20-40 percent. Taylor $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .