Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Tue Mar 19 2024 Valid 12Z Fri Mar 22 2024 - 12Z Tue Mar 26 2024 ***Late season winter storm becoming more likely for the Dakotas and into portions of the Upper Midwest... ...General Overview... A split upper level flow pattern is forecast to initially be in place across the continental U.S. for the end of the week, with a shortwave trough crossing the Gulf Coast region and then tracking off the East Coast, and broad cyclonic flow across the north- central states. The southern shortwave is expected to produce a surface low over the northern Gulf, and then the low tracks off the Southeast Coast going into the weekend. Looking ahead to the Sunday to Tuesday time period, a pattern change evolves across the western half of the U.S. as a larger synoptic scale trough develops across the Intermountain West and Rockies. This will lead to surface cyclogenesis across the Central Plains and Midwest bringing a late season winter storm to parts of the Northern Plains, and strong thunderstorms across portions of the South. ...Guidance/Predictability Assessment... The latest model guidance continues to show reasonably good agreement on the synoptic scale to close out the work week. There continue to be some amplitude and timing differences with the Southeast/Gulf Coast low, with the UKMET slower and farther inland, and the GFS continuing its trend of a more northerly track. The ensemble means still support the idea of a closed cut-off low meandering off the Southeast. For the larger scale trough developing across the Rockies Sunday into Monday, the GFS is slower than the rest of the guidance with the shortwave into the Southwest. The CMC is slightly faster with it during this time as it amplifies over the Four Corners region, and it has the surface low farther northwest over Minnesota. The WPC forecast blend incorporated a blend of the operational guidance for Friday possible across portions of the Northern Plains/Upper Midwest Sunday-Mondayinto Saturday afternoon, with less of the GFS over the weekend owing to the more northward track of the low off the East Coast. For the Sunday through Tuesday time period, the ensemble means were gradually increased to about 50%. Overall, this maintained good continuity with the previous WPC forecast. ...Weather/Hazards Highlights... There are still some uncertainties in the expected mesoscale evolution of the low developing in the vicinity of the Southeast U.S. coast on Friday, with model guidance varied regarding placement of heaviest QPF axes. However, it does appear more likely that heavier rain could fall more inland compared to earlier forecasts, and the Marginal Risk planned for Day 4 now encompasses most of the Florida Peninsula and extending north to central North Carolina. A Slight Risk area could eventually be needed near the coastal Carolinas and even parts of South Florida, but overall forecast confidence is not yet high enough in exact placement. For the Day 5 period Saturday, the core of heaviest rainfall lifts northeast and the best prospects for heavier rainfall would be from eastern North Carolina to the Delmarva, although some guidance suggests it could also be farther inland. There is also a Marginal Risk planned both days for coastal portions of northwestern California and southwestern Oregon with moisture flux from the Pacific producing 1-3 inches of QPF over this time period. Attention then turns to the central U.S. as a potentially strong surface low develops in the lee of the Rockies and then tracks towards the Midwest by Monday morning. There is an upward trend for snowfall accumulations from the Dakotas to Minnesota and into Wisconsin, as this region will likely be on the colder side of the low with a deformation zone likely developing, and producing bands of heavier wet snow with gusty winds. Multiple rounds of showers and thunderstorms, some of which could be strong to severe, can be expected in the warm sector of the low from Texas to the Ohio Valley. Snow showers are also expected to continue across many of the Western U.S. mountain ranges with the upper trough building in. There will likely be a stark temperature contrast from the Central Plains/Midwest to the Canadian border late in the week. Winter- like readings will continue across Montana, North Dakota, and into northern Minnesota with a strong arctic high situated over central Canada providing cold northerly flow. Even colder temperatures are possible from Montana to the Central Plains by next Monday behind the strong cold front with subfreezing high temperatures for Montana and most of the Dakotas. Meanwhile, a pleasant warm-up is likely ahead of the developing storm system from the Deep South to the Ohio Valley. 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