


Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
631 FOUS11 KWBC 011840 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 240 PM EDT Tue Apr 1 2025 Valid 12Z Tue Apr 01 2025 - 12Z Fri Apr 04 2025 ...Northern Plains & Upper Midwest... Days 1-2... ...Major winter storm to bring heavy snow and gusty winds to portions of the Dakotas and Minnesota. Key Messages have been issued for this system and are linked below... This is no April Fool`s joke - a major winter storm will develop late tonight and then expand and intensify into Minnesota late Wednesday. The trough responsible for this evolution will be elongated across the western CONUS at the start of the forecast period, with an embedded shortwave trough sharpening and digging across the Northern Plains by Wednesday morning. As shortwave amplifies, it will close off over SD Wednesday, and the continue to deepen, with 850-500mb heights dropping to below the 1st percentile within the NAEFS CFSR climatology. This indicates a strong system, and as the strongest height falls and PVA from the mid-level evolution overlap with the increasingly intense diffluence within the LFQ of a pivoting jet streak, a strong and intensifying surface cyclone will develop and track from eastern Nebraska through the Arrowhead of MN before exiting into Canada Thursday aftn. There continues to be some latitudinal spread amongst the various global model systems, leading to a bit lower confidence in the exact track of the low and subsequent placement of the greatest impacts. The GEFS/CMCE systems are more aligned with each other with the surface low track, and are both a bit north of the ECE ensembles. The key difference appears to be with the dominant surface, as the ECMWF wants to keep the southern edge of the elongated low the dominant feature, whereas the GFS and CMC make the northern low the primary feature. The GFS/CMC also are more aligned with the now available high-res guidance, so the northern track seems a bit more supported. Additionally, looking at the D3 clusters (from yesterday), the EC cluster is heavily influenced by its own ensembles (74%) so it may be a bit under-dispersive as well. This indicates that a more northern low track is probable which will allow for warm air to flood farther north, leading to a mixed precipitation axis from both a warm nose and a subsequent dry slot, from far northeast SD to potentially across the Arrowhead. Northwest of this, however, significant snow accumulations with heavy snow rates and gusty winds are likely. Despite the now early-April sun, a potent deformation axis overlapped with an increasingly impressive TROWAL, especially across northern MN, will cause heavy snow rates for which the WPC prototype snowband tool and the HREF probabilities suggest will reach 1-2"/hr. Even these kinds of rates could overwhelm the warmth due to April sun, leading to rapid snow accumulations. The heaviest snow amounts are likely from eastern ND through northern/central MN where the potent deformation axis will pivot and then translate northeast. Here, WPC probabilities are high for 6+ inches of snow, with locally 8-12 inches possible. The Arrowhead of MN will also be a focus for locally heavier snowfall as reflected by a 70-90% chance for 8 inches here, but there remains some uncertainty into how effectively lake enhancement can occur. South of this axis of heavy snow, a swath of mixed precipitation, including freezing rain, is likely. The heaviest icing is expected across the Coteau of SD, and parts of lower MI, where WPC probabilities for 0.1" of ice or more range from 10-50%. ...Northeast... Day 2... The same system that will bring the major winter storm to the Northern Plains/Upper Midwest will bring some wintry weather to the Northeast as well. As the primary surface low over MN occludes to the east into the Great Lakes, an attendant warm front will begin to lift northeast downstream of this secondary low pressure. As this warm front lifts into the Northeast, it will spread increasing moisture across Upstate NY and northern New England, especially after 00Z Thursday. The accompanying lift through WAA will ascend isentropically, especially along the 290K-295K surfaces, which will push PWs to above the 99th climatological percentile according to NAEFS, while at the same time driving a warm nose above 0C northward. The impressive ascent along this warm front will result in axis of heavy precipitation, but with p-type gradually changing from snow to a mix to rain, even into northern Maine. The fast progression of this event, combined with heavy precipitation rates, and the transitioning p-type will limit overall amounts, but impacts will still be notable due to snow, sleet, and freezing rain. WPC probabilities for more than 4 inches of snow are modest at just 30-50% in the higher terrain of NH and ME, but more than 0.5" of sleet is possible across a larger portion of those areas. Additionally, freezing rain has a 50-70% chance of accreting to more than 0.1" of ice across the Adirondacks, southern Greens, the Northeast Kingdom of VT, and northern NH. ...California... Day 1... A shortwave trough embedded within the much larger trough encompassing much of the West will advect onshore central CA at the start of the period and then continue to traverse southeast into the Great Basin Wednesday aftn. Confluent flow south of this feature combined with a slowly departing jet streak will maintain steady moisture advection onshore, characterized by IVT that will continue above 250 kg/m/s the first half of D1. This moisture will be forced efficiently into the Sierra, with upslope flow wringing out moderate to heavy snow above generally 3000 feet. While the heaviest accumulations are likely before this forecast period, additional snowfall will still be significant as snow rates remain above 1"/hr at times, and many of the area passes will experience impacts to travel. WPC probabilities for more than 6 inches of additional snowfall after 00Z tonight are as high as 70% across the higher terrain of the Sierra. ...Rockies... Days 1-3... Widespread light to moderate snow D1-D2 potentially becomes more significant across the Southern/Central Rockies late D3. For D1 and D2 /00Z Wednesday through 00Z Friday/, the entire region will be covered by large but diffuse troughing extending from the Pacific Coast through the High Plains. Beneath this large and slow moving trough, waves of vorticity will rotate through, leading to periods of enhanced ascent within steep low level lapse rates and aided by upslope flow. In general, this forcing will be modest across the region, but an exception is likely across southern Montana into Wyoming on D1, where a stalled cold front and accompanying weak wave of low pressure will drive more pronounced ascent through fgen leading to areas of heavy snow. The heaviest accumulations D1 are likely above 3500 ft in this region, where WPC probabilities indicate a high risk (>70%) for more than 4 inches of snow in the Absarokas, Wind Rivers, and into the Black Hills of SD. Elsewhere on D1, light to moderate snowfall across much of the terrain from the Four Corners and Great Basin Northward has a less than 30% chance of exceeding 4 inches. Then through much of D2 forcing again remains modest but widespread across the Rockies, leading to areas of light to moderate snow in most of the terrain. A local exception will again exist, this time across the Northern Rockies and maybe as far south as Yellowstone NP as a cold front digs out of Canada leading to some increased fgen and enhanced upslope flow in its wake. This will cause heavier snow rates and at lower snow levels (falling to 2000-3000 ft) leading to accumulations that have a high risk (>70% chance) of exceeding 6 inches around Glacier NP, and 10-30% chance around Yellowstone. Some locally heavier snow is also expected D3 in the vicinity of the Four Corners, especially across UT and CO as a shortwave pivots northeast, and WPC probabilities indicate a moderate risk (30-50%) for more than 6 inches in the southern Wasatch and San Juans. Then during D3, more impressive and consolidated ascent begins to manifest across the central and southern Rockies, generally from WY through CO and into NM as the tail shortwave within this larger trough begins to amplify. There is good agreement that this shortwave will close off and dig south into the Deserts of AZ, leading to increasingly impressive mid-level divergence downstream. At the same time, a subtropical jet streak will intensify and rotate around the base of this amplifying closed low to place favorable LFQ ascent into the eastern Rockies, while additionally the cold front from D2 across the northern Rockies drops south across WY and CO. The overlap of this baroclinic gradient with the increasing synoptic ascent could result in an impressive area of expanding precipitation D3 and even moreso into D4. There is still uncertainty into the exact evolution of this event, and current WPC probabilities are modest (10-30%) for more than 6 inches of snow, but during D4 these could increase and expand more impressively. 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 $$