BBS: TELESC.NET.BR Assunto: HVYSNOW: Probabilistic Heavy Snow And Icing Discussion De: COD Weather Processor Data: Wed, 1 Apr 2026 08:26:16 +0000 ----------------------------------------------------------- FOUS11 KWBC 010826 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 426 AM EDT Wed Apr 1 2026 Valid 12Z Wed Apr 01 2026 - 12Z Sat Apr 04 2026 ...Northern Plains through the Great Lakes... Days 1-2... ...Significant late-season snow and freezing rain likely to create substantial impacts... Late-season winter storm will begin tonight as an exiting=20 shortwave out of the Rockies spurs a lee-side low pressure system=20 this afternoon. This shortwave is expected to then develop a=20 negative tilt as it pushes into the Upper Midwest Thursday before=20 exiting into Canada by Friday morning. The combination of=20 impressive downstream divergence ahead of this sharpening shortwave followed by height falls and the LFQ of a modest but strengthening meridionally arcing jet streak will provide widespread deep-layer=20 ascent to help strengthen the surface low as it tracks from=20 Colorado northeastward into Michigan. Impressive moisture will spread northward to support a large swath of all p-types that move through time during the event. Ample=20 upper-level moisture from the southwest and low-level moisture=20 fueled by increasing WAA out of the Gulf will saturate the low=20 levels. The accompanying theta-e ridge emerging northward will help expand the precipitation shield thanks to PW anomalies that surge=20 above the 99th percentile according to NAEFS. This will result in=20 periods of heavy precipitation, first across the Dakotas this=20 morning and then expanding eastward within the WAA plume, reaching=20 Michigan by Thursday morning. Precipitation will continue through=20 Thursday night and eventually end from southwest to northeast on=20 Friday morning. In the locations that receive mostly snow, which is expected to be mostly in the northern half of Minnesota, modest to locally heavy=20 accumulations appear likely. In this area, snowfall rates of 1"/hr=20 are likely via deformation on the NW side of the low as it deepens, leading to 48-hr WPC probabilities that are moderate/high (50-80%) for at least 4 inches of snow, with locally more than 8 inches=20 possible (10-30%) from the Buffalo Ridge through the Arrowhead of=20 MN (40-60%) and into the Keweenaw Peninsula. Lighter snowfall of=20 2-4" is likely south/east of this axis north of the Twin-Cities and Green Bay. In these regions, heavy snow will develop but rapidly=20 change over to a wintry mix and then rain, leading to lesser=20 snowfall. The most substantial impacts from this event may be due to=20 freezing rain. Although the Canadian high pressure over Ontario=20 will retreat quickly, antecedent wet-bulb temperatures are well=20 below freezing (in the low to mid 20s this morning) due to very dry dew point temperatures. Although these will slowly warm as the=20 impressive warm nose surges northward, there is likely to be an=20 extended period of freezing rain (after a period of snow and sleet) from the eastern SD and along/north of the IA/MN border through=20 much of WI and into the northern L.P./eastern U.P. of MI.=20 Exceptional WAA within the warm nose, anomalous column moisture,=20 and a lack of strong dry advection to offset the latent heat=20 release of freezing should limit the freezing rain accretion=20 efficiency. However, there is still likely to be a long duration of freezing rain leading to significant and impactful icing for which WPC probabilities indicate at least a 70% chance of 0.1", with a=20 40-70% chance for at least 0.25" across WI. Locally, more than 0.5" is possible (10-40% chance) in central WI. Considerable impacts=20 from icing are likely as reflected by the WSSI that shows=20 widespread moderate to locally major impacts.=20 Please see a link to view the Key Messages at the end of this=20 discussion. ...CA/Great Basin to the Central Rockies... Days 1-2... A shortwave trough over the Great Basin this morning will continue eastward today. An impressive plume of Pacific moisture (NAEFS=20 shows IVT values of at least 99.5 climatological percentile over=20 the Southwest) will be directed at the Central Rockies with periods of heavy mountain snow from the Wasatch on east through the CO=20 Rockies. Snow will wane from west to east today over NV/UT but=20 continue over the CO Rockies through the day and diminishing=20 overnight. WPC probabilities for an additional 6 inches of snow are >50% over the Wasatch and Uintas. Over the CO Rockies, WPC=20 probabilities for at least an additional 12 inches of snow are >50% above 10,000ft.=20 There is not much of a break in the snowfall as the next closed=20 low tracking through the Northwest directs yet another anomalous=20 IVT (200-300 kg/m/s, or above the 90th climatological percentile=20 per NAEFS) at CA and the Great Basin starting later today. Snow=20 levels in the northern CA ranges (Trinity, Siskiyou, Salmon) drop=20 to as low as 3,000ft with minor accumulations. Heavier totals=20 (amounts surpassing 6") will generally be found at/above 5,000ft.=20 Farther south, the northern Sierra Nevada above 6,000ft have=20 moderate-to-high chances (50-80%) for snowfall totals >6" through=20 tomorrow morning. This same moisture source works its way across=20 the Wasatch, Uinta, and Bear River Ranges of UT, including the=20 southern WY and northern CO ranges by Thursday and lingering=20 through early Friday. WPC probabilities show moderate-to- high=20 chances (50-80%) for additional snowfall >8" in the listed UT=20 ranges with similar probabilities in the Park and Medicine Bow=20 ranges of WY/CO.=20 In summary, any significant impacts will be confined to the higher elevations of these ranges, with one exception being I-80 and=20 US-50 over the Sierra Nevada where the the WSSI shows Moderate=20 Impact potential. Most of these mountain ranges east of the Sierra=20 Nevada are well below normal for cold season snowfall, so while=20 some travel impacts are possible, the snowfall is also welcomed=20 with the cold season trying to make up for lost time.=20 ...Pacific Northwest to the Northern Rockies... Days 1-2... A powerful closed upper-low diving southward from the Gulf of=20 Alaska will be the catalyst for renewed mountain snow in the=20 Olympics, Cascades, the Salmon/Siskiyou of northern CA, and as far=20 east as the Blue Mountains this afternoon and continuing through=20 Thursday. The approaching 850-500mb layer heights associated with=20 the closed low are below the 2.5 percentile per NAEFS and snow=20 levels will drop as low as 2,000ft Wednesday night in the Olympics, Cascades, and even as far south as the Siskiyou. A steady stream=20 of Pacific moisture embedded within SWrly mean layer flow, suitable for upslope enhancement as well, will also favor locally heavy=20 snowfall rates in these ranges. Drier air on the backside of the=20 closed low arrives Thursday afternoon, although lingering westerly=20 low-level winds should support light-to-moderate snow in the=20 Cascades for the remainder of the day on Thursday. Precipitation=20 tapers off east of the Divide by Thursday night. Farther east, snow will start tonight and continue through Friday=20 over Montana. The closed low will weaken to an extent, but it=20 remains well intact as it moves east with healthy upper-level=20 divergence out ahead of the closed low. In addition, NAEFS shows=20 >90th climatological percentile levels for 500mb and 700mb mean=20 specific humidity (g/kg), indicating unusually high moisture=20 content higher up in the atmospheric column. With a 500mb low track from the WA/OR border ESE across central ID into central WY, snow=20 will be heaviest on the low's northern flank across the Blue=20 Mountains, Bitterroots, Absarokas, Tetons and into the Bighorns.=20 The western MT ranges will also see moderate snow totals closer to=20 the 700mb low and added assist of low-level easterly flow that=20 results in upslope enhancement. WPC 48-hour probabilities for at least 12 inches of snow are high=20 (>70%) in the OR Cascades above 4,000ft with at least moderate=20 chances (>50%) for snowfall totals >8" at elevations >3,000ft. The=20 WA Cascades will see lesser snowfall totals than their OR neighbors given the best Pacific moisture plume will reside farther south,=20 but several inches of snow at pass level (Snoqualmie and Stevens)=20 are expected. To the east, WPC probabilities for at least 12 inches of snow are moderate-to-high (50-70%) above 7000ft or so. The=20 peaks of the Blue, Sawtooth, Absaroka, and Tetons have low-to- moderate chances (30-50%) for snowfall totals in excess of 18"=20 through Friday. ...Northern New England... Day 2... Moisture streaming north out ahead of the Midwest winter storm=20 will be paired with increasing 850-700mb WAA aloft that produces=20 another round of precipitation. High pressure over Quebec will help to lock in sub-freezign wet bulb temps from the White Mountains=20 northward through interior Maine, allowing for yet another mixed=20 wintry precipitation Thursday afternoon and lingering through=20 Thursday night. Snow will be the primary precipitation at the onset in northern Maine, but even there it will flip over to a wintry=20 mix Thursday night with both sleet and freezing rain into Friday=20 morning. Eventually, strong low-level WAA will erode the sub- freezing temperatures at the surface and precipitation will change=20 over to plain rain late Friday before ending overnight. Prior to=20 the changeover to rain, WPC probabilities for at least a tenth of=20 an inch of ice are moderate (40-60%) over the White Mountains and=20 along the northwestern Maine/Quebec border. Snow will really be=20 limited to just the Allagash where WPC probabilities for at least 4 inches are 20-40%.=20 ...Northern Plains to the Upper Midwest... Day 2.5-3... The relatively progressive pattern across the CONUS will introduce another round of potentially impactful snow to the Northern Plains to the Upper Midwest Friday into Saturday. A slower moving 500mb=20 closed low over WY will generate healthy PVA aloft and increased=20 700mb Q-vector convergence over the northern High Plains early=20 Friday. Snow will already be falling over central MT and the Big=20 Horns Thursday night, but as a surface low strengthens along the=20 KS/NE border Friday morning, 850-700mb WAA to the north of the low=20 will support banded precipitation on the northern flank of the=20 500mb low. Guidance is in good agreement on the presence of a very=20 moist 700-300mb column, although exact placement of the heaviest=20 QPF axis is still unclear. The area of low pressure will track=20 northeastward through Iowa and cross into WI by the end of this=20 forecast period (12Z Sat), though there is spread in the speed of=20 the low. Snow will remain on the northwest side of the low over the Dakotas to northern MN but an area of mixed precip (sleet/freezing rain) is again likely over parts of southern MN into WI and the=20 U.P. of Michigan.=20 WPC probabilities show a large swath of at >50% probability for at least 4 inches of snow from northeast WY and southern/southeastern MT through northern SD and southern ND east-northeastward to=20 northern MN. Given the slower progression of the upper low and=20 likely banding associated with this storm, snowfall rates >1"/hr=20 for a prolonged period could result in localized amounts exceeding=20 12" -- WPC probabilities show 20-40% chances in southern ND into=20 northern SD. Farther east, WPC probabilities for at least a tenth=20 of an inch of ice are 10-40% over southeast SD/southwest MN but=20 40-60% over northern WI into the U.P. of Michigan where most of the precipitation will fall overnight Friday into early Saturday.=20 Changes to the forecast are likely but this system will likely have impacts for much of the region, especially those who see a wintry=20 mix from the prior system later today/Thursday.=20 Fracasso/Mullinax/Weiss ...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_1.png__;!!DZ3fjg!7LXNvgEotodsiPtRLncNZZFH7w0ysb5ByUQIYWixIQ6yv= -LQ6D73B2VQP6jitBqGvh-v6DyvnioWBSFVeEppxkkRe5Q$=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 3.28-Linux * Origin: Capitol City Online (1:2320/107) ----------------------------------------------------------- [Voltar]