Extended Forecast Discussion NWS Weather Prediction Center College Park MD 301 AM EDT Sat Mar 26 2022 Valid 12Z Tue Mar 29 2022 - 12Z Sat Apr 02 2022 ...A deepening low pressure system presents a mid-late next week heavy rain/severe weather threat across the South and heavy snow/ice threat focus across the Upper Midwest/Great Lakes... ...Overview... The main weather focus across this fine nation will work from the Southwest to the south-central Rockies Tuesday. As the system lifts across the central U.S. mid-later week, guidance favors ample phasing with northern stream trough energies digging into the northern Plains that would promote solid intensification of a surface low and associated frontal systems. Overall, this will favor rather unsettled and wet pattern from the Southwest to the south-central Rockies (including mountain snows) that will emerge/expand in magnitude and spread from the Plains into midweek in an active severe weather pattern per SPC to a still active east-central and eastern/southeastern U.S. later next week as Gulf moisture/instability is increasingly fed into the deep low/dynamic system and fronts in a pattern with coupled upper jet support. ...Guidance Evaluation/Predictability Assessment... A composite of the 18 UTC GFS and 12 UTC ECMWF/UKMET/Canadian along with the 01 UTC NBM seems to offer a run to run consistent forecast days 3/4 (Tuesday-Wednesday) that enjoys good GEFS/NAEFS/ECMWF ensemble support. Forecast clustering has improved through medium range time scales. However, the 12 UTC ECMWF/ECMWF ensemble mean seems best in line best in line with WPC continuity days 5-7 (Thursday-next Saturday), so have adjusted NBM guidance strongly toward this guidance. This blend offers good product detail consistent with a pattern with gradually lowering but still above normal predictability. A lingering guidance difference in this time frame concerns upper trough/system amplification back over the West well upstream of the main lead central to eastern U.S. storm. Overall, the 12 UTC ECMWF/UKMET/Canadian and ECMWF/Canadian ensemble means and their latest 00 UTC versions develop a more amplified eastern Pacific upper ridge than the 18 UTC GFS/GEFS mean. This allows for deeper trough digging back into the West late next week. The 00 UTC GFS/GEFS mean has trended in this direction. ...Weather Highlights/Threats... A ejecting southern CA/Southwest upper low will support a spread of enhanced rain and higher elevation snow across the region to the south-central Intermountain West/Rockies Tuesday. As surface low pressure strengthens in the Plains and tracks northeast, increasingly widespread rain and the threat for severe weather with heavy downpours are forecast to develop over the southern Plains late Tuesday and then move across the South on Wednesday before reaching the Southeast on Thursday. The heaviest rains are forecast to move through the eastern southern Plains through the Mid-South/Gulf Coast states Tuesday night through Thursday where areas of flash flooding are possible. Meanwhile, light rain and some thunderstorms are also expected farther north from the central Plains through the Mid-Atlantic. On the northern side of the precipitation shield, the potential for a swath of heavy wintry mix and accumulating snows have increased across the upper Great Lakes into the upper Midwest Wednesday-Thursday. Depending on the strength and size of the intensifying cyclone, high winds could also impact a large portion of the northern U.S. during this time frame. Some wintry precipitation is also forecast for interior New England late Thursday/early Friday ahead of a warm front, while pockets of heavy rain are possible then down the East Coast ahead of a cold front. Over the central Rockies to the nearby High Plains, the trend toward a stronger surge of cold air down the High Plains has also increased the potential for heavier snowfall from the central Rockies to the central High Plains on Tuesday. By late next week, another upper trough is forecast to dig southeastward from the Pacific Northwest through the western U.S. and could provide another opportunity for an enhanced round of wintry mix from the northern to central Rockies to the nearby High Plains. Schichtel 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 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml