Subj : Late-season Winter Storm To : All From : Mike Powell Date : Wed Apr 01 2026 07:39:06 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 shortwave out of the Rockies spurs a lee-side low pressure system this afternoon. This shortwave is expected to then develop a negative tilt as it pushes into the Upper Midwest Thursday before exiting into Canada by Friday morning. The combination of 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 ascent to help strengthen the surface low as it tracks from 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 upper-level moisture from the southwest and low-level moisture fueled by increasing WAA out of the Gulf will saturate the low levels. The accompanying theta-e ridge emerging northward will help expand the precipitation shield thanks to PW anomalies that surge above the 99th percentile according to NAEFS. This will result in periods of heavy precipitation, first across the Dakotas this morning and then expanding eastward within the WAA plume, reaching Michigan by Thursday morning. Precipitation will continue through Thursday night and eventually end from southwest to northeast on 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 accumulations appear likely. In this area, snowfall rates of 1"/hr 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 possible (10-30%) from the Buffalo Ridge through the Arrowhead of MN (40-60%) and into the Keweenaw Peninsula. Lighter snowfall of 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 change over to a wintry mix and then rain, leading to lesser snowfall. The most substantial impacts from this event may be due to freezing rain. Although the Canadian high pressure over Ontario will retreat quickly, antecedent wet-bulb temperatures are well below freezing (in the low to mid 20s this morning) due to very dry dew point temperatures. Although these will slowly warm as the impressive warm nose surges northward, there is likely to be an 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 much of WI and into the northern L.P./eastern U.P. of MI. Exceptional WAA within the warm nose, anomalous column moisture, and a lack of strong dry advection to offset the latent heat release of freezing should limit the freezing rain accretion 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 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 from icing are likely as reflected by the WSSI that shows widespread moderate to locally major impacts. Please see a link to view the Key Messages at the end of this 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 shows IVT values of at least 99.5 climatological percentile over the Southwest) will be directed at the Central Rockies with periods of heavy mountain snow from the Wasatch on east through the CO Rockies. Snow will wane from west to east today over NV/UT but continue over the CO Rockies through the day and diminishing overnight. WPC probabilities for an additional 6 inches of snow are >50% over the Wasatch and Uintas. Over the CO Rockies, WPC probabilities for at least an additional 12 inches of snow are >50% above 10,000ft. There is not much of a break in the snowfall as the next closed low tracking through the Northwest directs yet another anomalous IVT (200-300 kg/m/s, or above the 90th climatological percentile per NAEFS) at CA and the Great Basin starting later today. Snow levels in the northern CA ranges (Trinity, Siskiyou, Salmon) drop to as low as 3,000ft with minor accumulations. Heavier totals (amounts surpassing 6") will generally be found at/above 5,000ft. Farther south, the northern Sierra Nevada above 6,000ft have moderate-to-high chances (50-80%) for snowfall totals >6" through tomorrow morning. This same moisture source works its way across the Wasatch, Uinta, and Bear River Ranges of UT, including the southern WY and northern CO ranges by Thursday and lingering through early Friday. WPC probabilities show moderate-to- high chances (50-80%) for additional snowfall >8" in the listed UT ranges with similar probabilities in the Park and Medicine Bow ranges of WY/CO. In summary, any significant impacts will be confined to the higher elevations of these ranges, with one exception being I-80 and US-50 over the Sierra Nevada where the the WSSI shows Moderate Impact potential. Most of these mountain ranges east of the Sierra Nevada are well below normal for cold season snowfall, so while some travel impacts are possible, the snowfall is also welcomed with the cold season trying to make up for lost time. ....Pacific Northwest to the Northern Rockies... Days 1-2... A powerful closed upper-low diving southward from the Gulf of Alaska will be the catalyst for renewed mountain snow in the Olympics, Cascades, the Salmon/Siskiyou of northern CA, and as far east as the Blue Mountains this afternoon and continuing through Thursday. The approaching 850-500mb layer heights associated with the closed low are below the 2.5 percentile per NAEFS and snow 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 of Pacific moisture embedded within SWrly mean layer flow, suitable for upslope enhancement as well, will also favor locally heavy snowfall rates in these ranges. Drier air on the backside of the closed low arrives Thursday afternoon, although lingering westerly low-level winds should support light-to-moderate snow in the Cascades for the remainder of the day on Thursday. Precipitation tapers off east of the Divide by Thursday night. Farther east, snow will start tonight and continue through Friday over Montana. The closed low will weaken to an extent, but it remains well intact as it moves east with healthy upper-level divergence out ahead of the closed low. In addition, NAEFS shows >90th climatological percentile levels for 500mb and 700mb mean specific humidity (g/kg), indicating unusually high moisture 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 will be heaviest on the low's northern flank across the Blue Mountains, Bitterroots, Absarokas, Tetons and into the Bighorns. The western MT ranges will also see moderate snow totals closer to the 700mb low and added assist of low-level easterly flow that results in upslope enhancement. WPC 48-hour probabilities for at least 12 inches of snow are high (>70%) in the OR Cascades above 4,000ft with at least moderate chances (>50%) for snowfall totals >8" at elevations >3,000ft. The WA Cascades will see lesser snowfall totals than their OR neighbors given the best Pacific moisture plume will reside farther south, but several inches of snow at pass level (Snoqualmie and Stevens) 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 peaks of the Blue, Sawtooth, Absaroka, and Tetons have low-to- moderate chances (30-50%) for snowfall totals in excess of 18" through Friday. ....Northern New England... Day 2... Moisture streaming north out ahead of the Midwest winter storm will be paired with increasing 850-700mb WAA aloft that produces another round of precipitation. High pressure over Quebec will help to lock in sub-freezign wet bulb temps from the White Mountains northward through interior Maine, allowing for yet another mixed wintry precipitation Thursday afternoon and lingering through Thursday night. Snow will be the primary precipitation at the onset in northern Maine, but even there it will flip over to a wintry mix Thursday night with both sleet and freezing rain into Friday morning. Eventually, strong low-level WAA will erode the sub- freezing temperatures at the surface and precipitation will change over to plain rain late Friday before ending overnight. Prior to the changeover to rain, WPC probabilities for at least a tenth of an inch of ice are moderate (40-60%) over the White Mountains and along the northwestern Maine/Quebec border. Snow will really be limited to just the Allagash where WPC probabilities for at least 4 inches are 20-40%. ....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 closed low over WY will generate healthy PVA aloft and increased 700mb Q-vector convergence over the northern High Plains early Friday. Snow will already be falling over central MT and the Big Horns Thursday night, but as a surface low strengthens along the KS/NE border Friday morning, 850-700mb WAA to the north of the low will support banded precipitation on the northern flank of the 500mb low. Guidance is in good agreement on the presence of a very moist 700-300mb column, although exact placement of the heaviest QPF axis is still unclear. The area of low pressure will track northeastward through Iowa and cross into WI by the end of this forecast period (12Z Sat), though there is spread in the speed of 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 U.P. of Michigan. 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 northern MN. Given the slower progression of the upper low and likely banding associated with this storm, snowfall rates >1"/hr for a prolonged period could result in localized amounts exceeding 12" -- WPC probabilities show 20-40% chances in southern ND into northern SD. Farther east, WPC probabilities for at least a tenth of an inch of ice are 10-40% over southeast SD/southwest MN but 40-60% over northern WI into the U.P. of Michigan where most of the precipitation will fall overnight Friday into early Saturday. Changes to the forecast are likely but this system will likely have impacts for much of the region, especially those who see a wintry mix from the prior system later today/Thursday. Fracasso/Mullinax/Weiss ....Winter Storm Key Messages are in effect. Please see current Key Messages below... https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png $$ --- SBBSecho 3.28-Linux * Origin: Capitol City Online (618:250/10) .