Extended Forecast Discussion NWS Weather Prediction Center College Park MD 407 PM EDT Thu Apr 14 2022 Valid 12Z Sun Apr 17 2022 - 12Z Thu Apr 21 2022 ...Overview and Guidance Evaluation/Predictability Assessment.. It remains evident that compared to what has been a pretty amplified and active weather pattern the past few days, relatively low amplitude mean flow should continue through about Sunday or Monday across much of the lower 48. This features shortwave energy through the Northeast, with a possible closed low development over the Canadian Maritimes, while a shortwave and associated surface low pressure system moves over the northern tier. Chances are increasing that this may bring another round of spring snow to parts of the Northern Plains on Sunday into Monday. After this, the pattern is expected to transition to a more amplified flow, as an upper trough/closed low reaching the West Coast by Tuesday should act to build a downstream ridge and amplify the northern tier shortwave as it digs through the Great Lakes and Northeast by mid next week. Meanwhile, as the Western U.S. trough energy progresses through the Northwest, it could again face amplification in response to yet another upper low/amplified trough towards the West Coast next Wednesday-Thursday. The WPC medium range product suite was primarily derived from a blend of the GFS/ECMWF/UKMET/Canadian, the GEFS/ECMWF ensemble means and WPC continuity along with the 13 UTC NBM. While guidance clustering has improved from the past few days through medium range time scales, bolstering forecast confidence, multiple system differences remain with the amplitude of systems and QPF. NBM 4.0 QPF remains particularly light with QPF across the east-central U.S., and WPC corrected upwards given support. Overall, this blend plan seems to adaquately mitigate the blending process while still maintaining decent detail consistent with predictability. ...Weather Highlights/Threats... It remains the case that moisture and instability interacting with a warm front lifting through the South/Southeast this weekend and approach of a cold front from the north should bring areas of moderate to locally heavy rainfall to parts of those areas, but with lower confidence in exact placement of heaviest totals. Farther north, a low pressure system into the Northern Plains on Sunday may again bring a round of accumulating spring snow to northern locations, with rainfall farther south along the attendent cold front into the Midwest. Moisture reaches the East early next week, with some potential over the Southeast as well as precipitation north and west of a surface low to affect New England. This will include a threat of higher terrain enhanced snow over the interior Northeast. Some gusty winds are also possible across the Northeast Tuesday into Wednesday. Out West, expect another episode of precipitation from the Pacific Northwest/northern California into the northern Rockies through early next week, with some enhanced totals possible over favored coastal/terrain areas. Precipitation potential may increase again into next Wed/Thu with approach of another amplified upper trough and associated and slowed frontal progression. The core of below normal temperatures across the northern Plains and vicinity will likely persist into early next week, with daytime highs generally 20-30F below normal, and moderating slowly with time. The system reaching the Midwest/East early next week could draw some of the chilly northern Plains air southward and eastward behind it, with expanding coverage of minus 10-20F anomalies Sunday-Tuesday. Warm anomalies across the Southern Plains and Southwest on Sunday should progress slowly north and eastward as upper level ridging builds and moves through. Schichtel/Santorelli 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 Hazards: - Heavy precipitation across portions of California, the Pacific Northwest, and the Northern Great Basin, Wed-Thu, Apr 20-Apr 21. - Heavy precipitation across portions of the Northeast, Tue, Apr 19. - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Wed, Apr 20. - Heavy rain across portions of the Southeast, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Sun, Apr 17. - Heavy rain across portions of the Mid-Atlantic, Mon, Apr 18. - Heavy snow across portions of the Upper Mississippi Valley and the Northern Plains, Sun, Apr 17. - Flooding possible across portions of the Northern Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, the Southeast, the Great Lakes, and the Ohio Valley. - Flooding occurring or imminent across portions of the Southeast, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains. - High winds across portions of the Central Rockies, the Central Plains, the Central Great Basin, and the Northern Plains, Sun, Apr 17. - Much below normal temperatures across portions of the Central Rockies, the Central Plains, the Northern Plains, and the Northern Rockies, Sun, Apr 17. - Much below normal temperatures across portions of the Upper Mississippi Valley and the Northern Plains, Sun-Tue, Apr 17-Apr 19. 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