Extended Forecast Discussion...UPDATED NWS Weather Prediction Center College Park MD 300 PM EDT Thu Mar 21 2024 Valid 12Z Sun Mar 24 2024 - 12Z Thu Mar 28 2024 ...Late season winter storm for the Dakotas and into Minnesota and Wisconsin Sunday and into Monday... ...Heavy rain threat across the Deep South through early next week... ...General Overview... A strong low pressure system is forecast to intensify and track across the central Plains to the Upper Midwest, and will likely bring heavy snow from the northern Plains into the upper Midwest through early next week. On the warm side of the system, heavy rain associated with strong thunderstorms ahead of a relatively potent cold front will likely lead to flooding issues across the Deep South through early next week. A second surface low is forecast to develop over the Southeast U.S. by next Thursday and result in renewed prospects for additional enhanced rainfall spreading up the East Coast. Meanwhile, a low pressure system from the Pacific is forecast to move into the northwestern U.S., bringing additional rain and mountain snow into the region through mid-week. ...Guidance/Predictability Assessment... The 06Z and 12Z model guidance generally have halted the westward model trend of placing a trough/stationary front across the upper Midwest early next week ahead of the intensifying low pressure system over the central Plains. This front will likely be instrumental in placing and orienting an axis of heaviest snowfall associated with this winter weather event across the northern U.S. Models have also come into better agreement with the forward speed of the low pressure system, with the GFS slowing down versus the ECMWF speeding up the low, bolstering confidence that the actual track of the low will be somewhere between those two model solutions. Farther south, there are noticeable model discrepancies on the heavy rain area across the Deep South early next week, with the GFS/GEFS keeping the heaviest rainfall farther north than the ECMWF cluster. This discrepancy is likely due to the GFS' recent trend of developing a new low pressure wave upstream across the southern Plains toward the mid-Mississippi Valley on Tuesday in response to a slower progression of the winter storm up north and the resulting more amplified upper-air pattern. The ECMWF-AI model also has shown this tendency while the ECMWF and CMC are keeping this southern stream development minimal and progressive. The WPC forecast blend favored a combination of these two extremes, with the QPF based on the farther south solutions from the ECMWF early next week while the PMSL and 500 mb maps are based on 40% from 00Z EC/EC mean, 25% from 00Z GFS/GEFS, 15% from the 06Z GEFS/GFS, and 20% from the 00Z CMC. ...Weather/Hazards Highlights... On Sunday, a Marginal Risk area for excessive rainfall is adjusted northeastward from eastern Nebraska to Iowa in anticipation of some convective rainfall later on Sunday ahead of a warm front associated with the intensifying surface low over the central Plains. The low will likely track towards the upper Midwest by Monday morning and become the driver for a big late season winter storm. There continues to be an upward trend for significant snowfall accumulations (8"+) across northern South Dakota, southern North Dakota, central Minnesota, and northwestern Wisconsin, as this region will be on the colder side of the low with a deformation zone developing, and producing bands of heavier wet snow with gusty winds. There may also be a swath of potentially impactful mixed precipitation, including some freezing rain, most likely to the southeast of the heavy snow swath from eastern Nebraska to northwest Iowa and into southern Minnesota. Timing/track uncertainty may change the eventual location of the impactful winter weather, but the risk for disruptions to daily life and hazardous travel is likely. Multiple rounds of showers and thunderstorms, some of which could be strong to severe, can be expected in the warm sector of the system, beginning from the Southern Plains Sunday, and then spreading eastward to the Deep South on Monday where a Slight Risk area has been indroduced for Day 5 based on the latest QPF guidance. There are still question marks on the north-south placement of the heavy rainfall ahead of the front as the system progresses eastward, even though the kinematic environment will be more favorable for potential severe weather. Nonetheless, a quasi- linear convective system (QLCS) is evident on the latest GFS and ECMWF runs. The stormy weather then reaches the Florida Panhandle and portions of Alabama and Georgia on Tuesday with a secondary low likely developing over the northern Gulf. In terms of temperatures, it will feel more like January across the western High Plains from western Kansas to Montana and the Dakotas in the wake of the strong cold front. Highs will only be in the 20s and 30s for these areas on Monday, but a moderating trend will commence going into the middle of the week, even though Montana and North Dakota will still remain chilly by late March standards. Warmer weather likely makes a return to much of the south-central U.S. by next Wednesday and Thursday. Kong/Hamrick Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw