Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Fri Apr 29 2022 Valid 12Z Mon May 02 2022 - 12Z Fri May 06 2022 ...Overview... Expect an active weather pattern next week with a series of Pacific systems (each supported by an upper trough that may contain a closed low for a period of time) entering and progressing across the lower 48. These systems will spread rain and high elevation snow across the Pacific Northwest and north-central Rockies/High Plains, and then mostly rain over a large part of the central/eastern U.S. Some areas of precipitation may be heavy and SPC indicates a threat of severe weather over the southern Plains and vicinity Monday into Tuesday. WPC has also issued an experimental medium range "slight" risk for excessive rainfall then from the eastern southern Plains into the mid-Mississippi Valley. Upstream this pattern will likely leave the southern half or third of the West, the northern Plains near the Canadian border, and the Gulf Coast as the relatively drier areas during the forecast period. As for individual features, a leading system will weaken as it tracks northeast from the Upper Mississippi Valley Sunday onward while another over the West by early Sunday should reach the Midwest/Great Lakes by Tuesday and the next one entering the West by Monday may reach as far east as the Mississippi Valley by next Thursday. A larger scale upper trough approaching the West Coast next Thursday may also bring some moisture into the Northwest. ...Model Guidance Evaluation... The WPC medium range product suite was primarily derived from best clustered guidance from the 18 UTC GFS and 12 UTC ECMWF along with a compatible 01 UTC National Blend of Models (NBM) Days 3-5 (Monday into Wednesday). This solution maintains good WPC continuity and has strong ensemble support in a pattern with seemingly above normal forecast predictability. Increasing forecast spread, particularly with embedded system progression variance, portends near average predictability into days 6/7 (Thursday/next Friday). Opted to embrace a transition to a composite blend of the still compatible 18 UTC GEFS mean and the 12 UTC ECMWF ensemble mean along with the 01 UTC NBM that seem to offer a reasonable flow evolution into these longer time frames. Latest 00 UTC guidance remains in line. ...Sensible Weather/Threats... Over the West, yet another system will spread moisture from the Pacific Northwest through the Rockies into early to mid next week. Depending on exact system details, this could produce some enhanced totals, including accumulating snows into the north-central Rockies and adjacent High Plains. Subsequently, an amplified upper trough and surface frontal system still expected to breach the West Coast Thursday into next Friday should bring a renewed precipitation focus into the Pacific Northwest and increasingly inland. Over the central/eastern U.S., the leading surface low tracking out of the Great Lakes on Monday and associated fronts will spread precipitation across much of the eastern U.S. with generally light to moderate rain. Potential exists for pockets of locally heavier activity though. The trailing cold front will tend to stall over the southern Plains while the next system emerges from the West, with this system currently expected to track through the Plains/Midwest early next week. Currently there remains decent potential for areas of moderate to heavy rainfall from portions of the central/southern Plains northeastward to include a focus for a "slight" risk of excessive rainfall into Monday/Tuesday over the south-central U.S. Some severe weather is also possible, with the Storm Prediction Center currently indicating the best potential for severe thunderstorms across the southern Plains Sunday and Monday. The guidance signal is also growing that the next system in the series out from the West may produce yet another area of significant rainfall over and out from the central U.S. again mid-late next week. Confidence is fairly low for details of coverage and timing. A system on the deepest side of the spread could produce some snow in the northern periphery, but this has fairly low probability at the moment. Some areas over the central U.S. need to monitor forecasts of these systems given the potential to produce significant weather and sensitivity to additional rainfall. At least for the time being, the majority of forecasts produce most precipitation to the south of the far northern Plains where soil conditions are the wettest. 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 WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, experimental excessive rainfall outlook, winter weather outlook probabilities and heat indices are at: 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