Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Mar 29 2024 08:15:12 FOUS11 KWBC 290814 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 414 AM EDT Fri Mar 29 2024 Valid 12Z Fri Mar 29 2024 - 12Z Mon Apr 01 2024 ....The West... Days 1-3... An increasingly active period of winter weather is likely across the West into the weekend as an impressive closed low digs along the CA coast, forcing a broad trough to encompass the West with waves of energy and moisture shifting onshore. A closed upper low positioned off the coast of Washington will weaken later today as a stronger shortwave rotates underneath it, leading to a potent closed low by this evening off the coast of California. As this newly formed closed low slides southward, the troughing over the West will amplify and elongate, encompassing much of the West Coast through this weekend. By Sunday, the low center is expected to be off the coast of southern California. This setup will bring a period of forcing for ascent across a large area this weekend. FOr moisture, IVT values will steadily increase through the period as onshore flow becomes increasingly backed in the southwesterly flow. IVT values per the CW3E should top 250-300 kg/m/s and precipitable water anomalies reach +2, especially by Day 2/3. Snow levels are likely to hold steady in the 5000-6000 ft range and bring widespread heavy snow across a good portion of the West. For Day 1, WPC probabilities are high (>70%) for at least 6 inches across the Sierra as well as portions of the northern CA ranges. Moisture spilling eastward will also bring moderate (>50%) to locally high (>70%) probabilities for 6 inches to the Unitas and northern CO Rockies. By Day 2, broader moisture across the region will bring moderate to high probabilities for 6 inches to the western WY ranges southward through the Uintas and southern Wasatch as well as the Sierra Nevada and Transverse and Peninsular ranges. Finally, for Day 3, an embedded shortwave trough breaking off from the main closed low will likely focus heavy snowfall to Intermountain West through the Rockies as well as southward into Mogollon Rim in AZ. The WPC snow probabilities continue to be high for at least 6 inches. For the 3 day period, snow forecast totals may exceed 2-3 feet in the Sierra Nevada and locally 2 feet for the Uintas and Wind River and Teton ranges in WY. ....New England... Day 1... Phasing shortwave energy and an increasingly negatively tilted trough will lead to a rapidly deepening surface low off the East Coast today that moves toward the Gulf of Maine by this evening/tonight. Guidance this cycle continues a slight shift to the east with the low track, with the main axis of banded precipitation expected to affect eastern/coastal Maine. Colder air surging southward into the amplifying system will allow for a changeover from rain to wet snow from portions of northern NH through northeastern Maine. Thermal profiles are still marginal and the greatest accumulations may still end up being elevation dependent but the latest WPC probabilities did trend upward for at least 4 inches, particularly for far eastern/northeastern Maine where they are now up to 50 to near 70 percent. ....Northern Plains and Upper Midwest... Day 1.... A shortwave trough moving through the Rockies early this morning will lift toward the Northern Plains today and will interact will modest upper diffluence thanks to a jet streak to the south. A weak area of low pressure will accompany this system and bring a broad area of isentropic lift producing precipitation. The column into which this ascent is occurring appears more than cold enough for snow, but the DGZ is elevated and only partially saturated, so expect SLRs will be somewhat compromised as the best moisture and lift is warmer than -12C. This should still result in an axis of accumulating snow, but WPC probabilities for more than 4 inches of snow reach peak near 40 percent along the ND/Canadian border with 20-30 percent probabilities spreading across northern MN and the North Shore. 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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .