Extended Forecast Discussion NWS Weather Prediction Center College Park MD 331 PM EDT Fri Mar 25 2022 Valid 12Z Mon Mar 28 2022 - 12Z Fri Apr 01 2022 ...Wet weather moving through southern California early next week will be followed by low pressure system intensifying over the Plains mid-late week to bring heavy rain/severe weather across the South and increasing potential of heavy snow/ice across the upper Great Lakes to upper Midwest... ...Overview... An amplified upper trough and lingering wintry weather will exit the northeastern U.S. by early next week, followed by a gradual moderation of a polar airmass across the north-central through eastern states. The main weather focus across the nation will then shift to the West as a strong upper trough and embedded closed low progress into and through the southwestern states early next week. As the system lifts across the south-central Rockies/Plains midweek, model guidance continues to trend toward supporting additional phasing with northern stream trough energies digging into the northern Plains mid to late week that would promote more solid intensification of a surface low and associated frontal systems. Overall, this will favor rather unsettled and wet pattern from California and the Southwest to the south-central Rockies early next week (including mountain snows) that will emerge/expand in magnitude and spread from the Plains to the east-central and eastern/southeastern U.S. later next week as more Gulf moisture is fed into the system. ...Guidance Evaluation/Predictability Assessment... Since yesterday, model guidance has continued the trend of increasing interaction/phasing between a developing surface low over the southern Plains on Wednesday and a surge of colder air down the northern and central Plains. The GFS took the most decisive shift of tracking a rather robust cyclone into the upper Midwest by Thursday morning in recent runs. The 00Z ECMWF and, to the lesser extent, the 00Z CMC have trended toward a more robust cyclogenesis. The 12Z ECMWF, CMC, as well as the GFS have now agreed with this scenario. The ensemble means from earlier this morning have also indicated such a trend. In addition, this trend has also led to a better-defined reinforcing surge of cold air down the northern and central High Plains Tuesday-Wednesday compared with previous forecasts. The WPC medium-range forecast package was based on a blend of 40% from the 00Z ECMWF/EC mean, 40% from the 06Z GFS/GEFS, and 20% from the 00Z CMC and CMC mean. Only a minimal contribution from the 00Z CMC was included starting on Day 5, which favors the cyclogenesis scenario farther west over the upper Midwest as supported by the 00Z CMC mean as well as the 00Z EC/06Z GFS/GEFS consensus. ...Weather Highlights/Threats... The medium-range period will begin with a vigorous upper low moving onshore over the southwestern U.S. on Monday. The heaviest rain totals for southern California will likely be enhanced by higher terrain and could cause flooding issues if heavy rain falls over burn scar areas. Rain and higher elevation snow will spread across the Intermountain West and Rockies Monday and Tuesday. As surface low pressure strengthens in the Plains and tracks east, more widespread rain and possibly severe thunderstorms 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 eastern Oklahoma as well as the 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 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. Kong/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