Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Nov 28 2023 20:49:14 FOUS11 KWBC 282049 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 348 PM EST Tue Nov 28 2023 Valid 00Z Wed Nov 29 2023 - 00Z Sat Dec 02 2023 ....Great Lakes... Days 1-2... Elongated upper low centered over northern Hudson Bay will lift through New England tonight, allowing heights to rise over the eastern Great Lakes. This will allow winds to back from northwesterly/westerly to southwesterly on Wednesday as another weak shortwave moves through Michigan along with a surface warm front. The heaviest snow will fall this evening and early overnight east of Lake Ontario into the Tug Hill as T850 near -15C this evening only slowly rises overnight. Additional light snow of a couple inches is expected off Lake Erie that lifts northward into Buffalo, and also across the U.P. of Michigan and northwestern Lower Michigan. WPC probabilities for at least an additional 4 inches of snow after 00Z/29 are moderate (40-70%) east of Lake Ontario just south of Watertown along and east of I-81. Lower probabilities (<30%) for at least 4 inches of snow lie closer to Syracuse, over southwestern NY, and northwestern Lower Michigan. Snow will diminish into day 2, mainly limited to the northern portion of I-81 in NY and around Buffalo as the SW-to-NE bands collapse and dissipate by Thursday morning. ....Southwest and Southern and Central Rockies... Days 2-3... An upper low currently centered off of the northern California coast is forecast to dig southeast, carving out a well-defined trough over the Southwest on Thursday. The increase in ascent and modest moisture in place should be sufficient for at least light precipitation with orographically focused heavier amounts developing across the Four Corner states Wednesday night. Models have moved into better agreement with the timing/amplitude of the trough and a front dropping into the region, however the spread with respect to QPF remains significant, limiting forecast confidence. This initial system is forecast to move east into the southern Plains by late Thursday, but be followed quickly a second wave amplifying across the region on Friday. In addition to bringing additional high elevation snow to portions of the Southwest, this system is also expected to spread snow farther north through the western Colorado ranges. WPC probabilities do not currently suggest a widespread heavy snow event. However they do indicate the potential for some locally heavy totals across the region, including Arizona's White Mountains and San Juan and Jemez mountains, where WPC probabilities for totals of 4 inches or more are greater than 50 percent for much of the region, with some low probabilities (10-40 percent) for amounts greater than 8 inches. ....Cascades... Days 2-3... The previously noted shortwave amplifying over the western U.S. on Friday is initially forecast to dig southeast from the Gulf of Alaska and northeastern Pacific and into the Pacific Northwest by late Thursday, marking the onset of what is expected to be a prolonged period of unsettled, wet weather across the region. Guidance continues to show near normal moisture and a progressive system, however snow levels are forecast to be low at the onset and below pass level across the northern Cascades. Snow levels are expected to rise as a shortwave ridge builds in the wake of this leading wave and ahead of another well-defined wave digging southeast toward the region. The GFS and ECMWF are more robust with this wave, which along with ample ascent afforded in part by left-exit region upper jet dynamics is expected to support the development of heavy precipitation across western Washington and Oregon, with snow levels ranging from 2500-3500 ft in the Washington Cascades and 3500-4500 ft in the Oregon Cascades. For the 48-hr period ending 00Z Sat, WPC probabilities show a high chance (greater than 70 percent) for accumulations of 8 inches or more for most of the major Cascade passes. Fracasso/Pereira $$ = = = 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) .