Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Feb 13 2025 08:57:41 FOUS11 KWBC 130856 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 356 AM EST Thu Feb 13 2025 Valid 12Z Wed Feb 12 2025 - 12Z Sat Feb 15 2025 ....Great Lakes and Northeast...=20 Day 1... Low pressure moving through the Ohio Valley this morning will=20 continue northeastward into southeastern Ontario, with broad WAA-=20 driven snow over northern New England D1 and an icy mix where=20 boundary layer sub-freezing temperatures persist beneath the=20 warming layer ~750-850mb (e.g., North Country, Green and White=20 Mountains). By this afternoon, a forming area of low pressure near=20 the Gulf of Maine will help maintain a colder column over much of=20 Maine, favoring more snow for the Pine Tree State via northerly=20 flow. After 00Z, the whole system will depart into Atlantic Canada. WPC snowfall probs for >4" are highest (>50%) in the higher=20 elevations of the Adirondacks and Green/White Mountains, as well as over the northern half of Maine. Freezing rain probs for >0.1" ice are low (10-20%) over parts of central New England. In its wake, NW/WNW/W flow across the mostly unfrozen Great Lakes=20 will support lake effect snow as 850mb temps of -15 to -20C move=20 across the region. WPC probabilities for >6" low (10-50%) over the=20 eastern U.P. of MI but are high (>70%) south of Buffalo with some=20 moisture flux through the ice and especially southeast off Lake=20 Ontario just north of SYR up to FZY. Snowfall totals locally over a foot are possible. ....Sierra Nevada, Pacific Northwest through the Rockies...=20 Days 1-3... ....Atmospheric River with heavy Sierra Nevada snow affects=20 California tonight into Friday. Key Messages are linked below...=20 Upper low approaching 130W this morning is directing an=20 atmospheric river (AR) into NorCal then shifts south down the coast to SoCal tonight as the low opens/splits into a slow-moving=20 trough. The atmospheric river has IVT around 500 kg/m/s (near the MAX in=20 the CFSR climo period) making for a wave of moderate to heavy=20 topographically- enhanced precip over the Sierra Nevada. Snow=20 levels around 6000-7000ft across CA this morning will drop back to=20 5000-6000ft under the trough axis tonight (Sierra) and around=20 4500ft (Shasta/Trinity). SLRs will be low to moderate given the=20 strong WAA, resulting in plenty of Sierra cement (>5ft and perhaps=20 >8ft at the highest peaks). Snowfall rates will lessen into early=20 Friday (as SLRs rise a bit) and end completely by Friday night as=20 upper ridging builds in. The lingering cold air brings light lowland snow and icing=20 potential for southern WA through western OR. Freezing rain threat=20 will advance northward on the edge of the precip shield this=20 morning from western OR (Coastal Ranges) northward across the=20 Columbia River into southwestern WA. WPC probs for >0.1" are=20 moderate (40-80%) for mainly the Coast Ranges west of the=20 Willamette Valley.=20 Moisture quickly spreads east throughout the Intermountain West=20 through Friday ahead of the slow-moving trough axis. Moisture=20 transport into the Great Basin and Wasatch/Rockies will be notable=20 per the ECMWF EFI and NAEFS IVT percentiles >99th percentile. WPC=20 probs for >8" are above 80% for the Tetons through the Wasatch and=20 Tushar Mtns (UT) and across the western slopes of the CO Rockies=20 with >60% probs for the Sawtooths of ID, and Kaibab Plateau in AZ=20 and northern NM ranges. Snow rates peak early Fri from west to east as the trough axis drifts over the Rockies, but broad light to=20 locally moderate snow persists over much of the terrain into early=20 Sat (end of D2). By Sat/D3, the last piece of the broad longwave=20 trough will slip through the central Rockies, yield another several inches of snow centered over western CO where WPC probs for at=20 least 6 inches are moderate (40-70%). Finally, a sprawling North Pacific system will enter the PacNW at=20 the end of D3 with generally light snow for the WA Cascades. ....Upper Midwest/Great Lakes/Northeast...=20 Days 2-3... Leading edge of the western trough Friday afternoon will manifest=20 itself at the poleward exit region of a 140kt upper jet across the=20 Plains and near the equatorward entrance region of the northern=20 stream jet across southern Ontario. This will promote broad lift=20 over the Upper Midwest with accompanying WAA atop an inverted=20 surface trough. Quick westward flow aloft will keep the system=20 moving through the region, but potential exists for a quick-hitting few inches of snow with room for some localized bands of heavier=20 snow across WI. WPC probs for >4" snow are >50% over much of=20 central and southern WI to the IL border and into Lower MI.=20 Farther east into D3, snow will expand into the Northeast on=20 continued WAA ahead of a deepening upper trough and strengthening=20 upper jet arced from the Lower MS Valley to the St. Lawrence River=20 Valley. Light to moderate snow is forecast across southern Ontario=20 eastward into NY and New England where WPC probs for >4" snow are=20 moderate (40-70%), especially above 1500ft or so. Across the=20 interior Mid-Atlantic, cold surface temperatures from the departing high pressure will be overrun with WAA precip, resulting in areas=20 of freezing rain from the southern Appalachians northward through=20 the Laurel Highlands into the Catskills. WPC probs for at least=20 0.1" icing are moderate (40-70%) with low-end (10-30%) probs for at least 0.25" icing. This will depend on how strong the southerly=20 flow will be to scour out the cold surface temperatures vs precip=20 timing/onset and intensity.=20 Fracasso/Jackson ....Winter Storm Key Messages are in effect. Please see current=20 Key Messages below... https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!47RfJ0KrfWibvV9EriQLY0K0ysz7t3npsK2kq7S3BR1Al= 8Dt0CWum4y07uzoHXi54d007yUsgZXZcIFST14Vy9IqwC4$=20 $$ =3D =3D =3D 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) .