Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jan 28 2024 19:52:19 FOUS11 KWBC 281952 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 251 PM EST Sun Jan 28 2024 Valid 00Z Mon Jan 29 2024 - 00Z Thu Feb 01 2024 ....Northeast... Day 1... Boundary layer temperatures have begun to cool down to near or sub-freezing levels as the 850mb low begins to form over eastern Pennsylvania and strong 850-700mb frontogenesis lifts over southern New England. This is evident on radar since 17Z when higher radar reflectivity returns were developing from the Poconos and Lower Hudson Valley to northern Connecticut. Surface temperatures have been reluctant to dip near freezing in northern Pennsylvania and the Southern Tier of New York, but temperatures have been within a degree or two of freezing in the Catskills, northern Connecticut, and central Massachusetts where moderate snow is falling. Portions of northern Connecticut have already received 1-3" of snow and with the ongoing radar trends, this marks just the beginning of the expected heavy snowfall from the Catskills to interior portions of southern New England. By this evening the coastal low will have fully developed and, with the added help of high pressure over Quebec, lead to a surge in colder northeasterly winds over New England. Around 06Z Monday, most guidance show a ~992mb surface just northeast of the Benchmark (40N/70W), which is a textbook setup for heavy snow in southern New England. A band of heavy snow will setup from the Catskills and Berkshires to the Worcester Hills and Merrimack Valley this evening and persist into early Monday morning with snowfall rates of 1-2"/hr expected. Given the relatively lower SLRs and ample low-mid level moisture, snow will be more heavy/wet in nature, adding to the potential for added snow load of tree limbs and power lines. The storm will quickly move east Monday morning and track south of Nova Scotia, leading to stronger NE-NNE winds over the Gulf of Maine that could lead to locally heavy snow rates just inland from the South Shore of eastern Massachusetts and potentially the western suburbs of the Boston metro area. Snow could linger around through the daytime hours Monday in eastern Massachusetts before final concluding Monday evening. For the remainder of the event starting 00Z tonight, WPC 24-hour PWPF shows low-to-moderate chances (20-50%) for additional snowfall amounts >4" in the Catskills, Berkshires, Greens of southern Vermont, and Monadnock of southern New Hampshire. Similar probabilities are present in west-central New York just west of the Finger Lakes for snowfall totals >4" For the areas mentioned above, the WSSI-P shows high chances (>70%) for Minor Impacts (including the northern most section of Pennsylvania along US Route 6). While this is primarily due to the Snow Amount algorithm, there are some moderate-to-high chances (50-80%) for Minor Impacts due to Snow Load from western New York all the way to the western Boston suburbs. Expect hazardous travel conditions in these affected areas through Monday morning with a low chance of heavy snow load causing very localized tree damage and power outages. Overall, this has the feel of a late season winter storm focusing the heaviest totals and most noteworthy impacts across higher terrain and generally well north and west of the I-95 corridor. ....Southern & Central Appalachians... Day 1 & Day 3... Little change in the expected snowfall in the Smokey Mountains through Monday. Brisk northwest flow behind the exiting Northeast system will foster upslope snowfall across portions of the southern Appalachians/Smoky Mountains this evening and into very early Monday as the wraparound moisture in the lower levels swings through. WPC probabilities for at least 4 inches of snow are highest above about 3,500 ft. Above 5000ft, WPC probabilities for at additional snowfall totals >4 inches of snow are around 40-60%. By Tuesday night, a quick moving clipper system tracking south from the Great Lakes will produce snow in the Appalachians of eastern West Virginia. Elevations >3,000ft have low chances (10-20%) for snowfall totals >4", so overall snowfall amounts should remain minor overall for affected areas. ....Northern California... Day 3... A powerful Pacific storm system will direct a conveyor belt of Pacific moisture at the West Coast. Precipitation will work its way gradually inland through northern California throughout the day on Wednesday with snow levels will fall from 6,500ft to as low as 5,000ft over the Salmon and Trinity/Shasta. WPC WPF currently shows moderate-to-heavy chances (50-80%) for snowfall totals >6" in the Salmon Mountains. While it goes beyond the scope of this discussion, expect the slug of Pacific moisture to work its way farther inland Wednesday night and lead to heavy snow in the Sierra Nevada on Thursday. The probabilities of receiving at least 0.1" of ice are less than 10%. Mullinax $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. 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