Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 245 PM EST Sun Feb 11 2024 Valid 00Z Mon Feb 12 2024 - 00Z Thu Feb 15 2024 ...Texas Panhandle to Oklahoma/Ozarks to Ohio Valley... Days 1-2 The closed 500 mb low currently moving through western Texas will track eastward/northeast over the next 24-36 hours, beginning to take on a negative tilt as it approaches the Ohio Valley late Monday night. A strong/impressive amount of forcing with this system combined with very anomalous moisture wrapping into it along with colder temperatures pouring in the lower levels will support a localized but potentially impactful changeover from rain to wet, heavy snow across portions of the Texas Panhandle, northern Texas and Oklahoma northeast into the Ozarks/Mid-MS Valley and eventually the Ohio Valley. The stronger/deeper frontogenesis depicted by the hi-res CAMs will likely overcome any thermal challenges / marginal boundary layer temperatures and result in wet, heavy snowfall with localized snow rates approaching 1-2"/hr (supported by the WPC snow band tracker page). The intense snow rates will likely overcome the warm ground temperatures eventually as well, leading to a narrow but impactful swath of accumulating snow across the region, with the locally higher elevations (Ozarks) likely to pick up the higher amounts. The latest PWPF shows moderate probabilities of 4 inches (40-60 percent) across central OK to southern MO with localized moderate probabilities for 6 inches over the Ozarks. A few spots exceeding 8" will be possible. Further northeast across the Ohio Valley, 2" probabilities are now moderate (40-60 percent) with a slight (10 percent) chance of 4", particularly from near Louisville to Cincinnati and Columbus, Ohio. ...Northwest... Days 1-3... Mid/upper level shortwave energy moving through the Pacific Northwest will direct an influx of 850-500mb moisture into the region that leads to mountain snow in the Cascades through late tonight and early Monday morning. Snow levels in the Cascades will be as low as 3,000ft, but the heaviest totals will generally be confined to elevations above 5,000ft. Snow will continue along the Cascades into Monday as a trailing 500mb disturbance sustains orthogonally-oriented westerly 850-300mb winds into the region, keeping a prolonged period of upslope flow into the mountain range. WPC PWPF shows high probabilities (>70%) for snowfall totals >6" at elevations above 5,000ft in the northern Washington Cascades. The tallest peaks of the Olympics could also see some measurable snowfall, indicated by WPC PWPF showing moderate-to-high (50-80%) chances for >4" of snowfall at elevations above 5,000ft. Farther inland, the initial shortwave trough will advance inland into the Northern Rockies and delivering the same surge in 850-500mb moisture flux into northern Idaho and western Montana this evening and lingering into the day on Monday. By Tuesday, a frontal boundary will bank up against the eastern slopes of the Northern Rockies in western Montana and keep snow in the forecast through Tuesday night. WPC 48-hr PWPF shows high chances (>70%) for snowfall totals >12-18" through Tuesday along the Lewis Range, including ridges surrounding Glacier NP. Localized totals in excess of 2 feet are likely. Elevations above 5,000ft in northern Idaho and above 6,000ft along the Lewis Range are on the higher end of the probabilistic range for snowfall totals >6". The Probabilistic WSSI (WSSI-P) shows high chances (>70%) for Minor Impacts in the highest elevations of the Washington Cascades, the Bitterroots of northern Idaho, and the Lewis Range of western Montana. ...Northeast... Day 2... By Monday morning, the upper low over Arkansas will have been working in tandem with an upper ridge located over the Caribbean to foster a robust subtropical jet (STJ) over the Deep South. ECMWF ensembles centered on Tuesday 00Z show winds at the 850mb and 700mb levels to be above the 90th climatological percentile and tapping into a deep reservoir of Gulf of Mexico moisture. This will be the same moisture source that the 500mb low tracking into the Tennessee Valley Monday evening will direct northward into the Mid-Atlantic and along the Northeast coast. In fact, PWs over the Mid-Atlantic 06Z Tuesday 90th climatological percentile, so there is no shortage of moisture available. Farther north, confluent flow over southeast Canada and northern New England will support a 150kt 250mb jet streak and place its diffluent right-entrance region off the Mid-Atlantic coast Monday night. As a second 150kt 250mb jet streak over the Southeast approaches Monday night, a "kissing jets" setup will foster excellent upper level divergence along the Mid-Atlantic coast, allowing for a surface low to rapidly organize by early Tuesday morning while the initial low over West Virginia gradually weakens. The latest forecast guidance has started to settle on the bigger picture synoptic setup with the stripe of greatest QPF from eastern Ohio through southern New England, with probabilities high for seeing upwards of 0.75" to near 1" of QPF across portions of PA, southern NY, and southern New England. Recent trends still point toward a sharp gradient in precipitation type across portions of southeast Pennsylvania, Delaware Valley into the NYC metro as well as extreme coastal southern New England. However, just north of this axis, the extreme/deep mid-level frontogenesis will easily overcome the more marginal boundary layer temperatures to produce extreme snowfall rates late Monday night into Tuesday morning across portions of PA, interior southern NY where localized 2-3"/hr snowfall rates will be common. These extreme snowfall rates are likely to continue eastward across southern NY through southern New England as well. Altogether, a stripe of heavy snowfall is expected with very high probabilities for 6-8" (above 80 percent) and now showing solid moderate probabilities (50-60 percent) for 12 inches across portions of the Hudson Valley (elevation dependent) through much of MA, southern VT and southern NH. Some high end totals between 12-18" are likely and the latest WPC PWPF indicates a fairly broad area of 10-20 probabilities at that threshold. The latest Winter Storm Severity Index (WSSI) shows a broad area of Moderate to Major Impacts across northern PA, southern NY and interior areas of southern New England. While these areas sport the highest confidence in expected impacts, there are still forecast details that need ironing out over the next 24 hours. On the northern flank of where the deformation zone sets up, a trailing shortwave over the Great Lakes will race in from the west, attempting to advect drier tongue of 700-300mb moisture into the eastern Great Lakes. In addition, such a robust area of frontogenetical forcing over northern PA, southern NY, and southern New England would inevitably lead to some modest subsidence to the north. This is depicted quite well on the 07Z NBM 50th percentile snowfall totals, where amounts in Rochester could end up between 1-2", but southeast towards Ithaca, totals were around 9". This is a common occurrence from northeast Pennsylvania and western New York across southern VT/NH. Any additional shifts in track can still mean increases (decreases) in snow totals. Meanwhile, to the south, the recent trend of a northerly track would in fact make it tough for accumulating snowfall from Philly on north up I-95 to the NYC metro and the immediate coast of New England. However, ensemble guidance continues to show solutions where the deformation axis pivots over northern NJ, the NYC metro, and Long Island. By 00-18Z Tuesday, the ECMWF ensemble mean shows the low deepening from ~995mb to ~976mb, which would lead to a dramatic increase in winds as the low tracks off the coast Tuesday morning. There is still a scenario where as the low rapidly deepens, a burst of snow beneath the deformation axis and strong wind gusts could cause significantly reduced visibilities. While totals could still be minor, the combination of just moderate snow and wind gusts >40 mph may lead to notable impacts from blowing snow. The latest WSSI-P show 40-50% chances for Minor Impacts due to the Blowing Snow algorithm from the NYC metro to Long Island. Probabilities for Minor Impacts due to Blowing Snow jump to as high as 60-70% along the coast of CT, RI, and southeast MA. Mullinax/Taylor ***Key Messages for Feb. 11-13 Winter Storm*** Heavy Snow Stripe Southern Plains to Ohio. The storm crosses the Mid-South tonight into Monday, producing bands of heavy snow from central Oklahoma through southern Missouri. Localized snowfall totals exceeding 6†are possible under the heaviest bands and in the Ozarks. Localized heavy snow with several inches possible can then be expected to work its way along the Ohio River through Monday evening. Norâ€easter Monday Night and Tuesday. A rapidly deepening low is expected to form along the Mid-Atlantic coast late Monday night. This will produce widespread heavy snowfall with rates locally exceeding 2†per hour across northern PA, southern NY late Monday night, and southern New England Tuesday morning. Significant Travel Impacts in the Northeast Tuesday. This fast-moving storm currently has the highest potential for over 8â€+ in a stripe along the Pennsylvania/ New York border through Massachusetts. Powerful winds and heavy/wet snow could damage trees, power lines, and disrupt travel. Moderate Coastal Flooding. Intensification of the coastal low south of Long Island Tuesday is forecast to cause moderate coastal flooding at high tide Tuesday along the Jersey Shore, and portions of the New York and New England coasts.