Extended Forecast Discussion NWS Weather Prediction Center College Park MD 314 PM EDT Thu Apr 07 2022 Valid 12Z Sun Apr 10 2022 - 12Z Thu Apr 14 2022 ...Active weather is likely next week, with heavy snow spreading from higher elevations of the West into the north-central U.S. and heavy rain and severe thunderstorm chances in the south-central CONUS... ...Overview... Latest guidance continues to show an amplified pattern in which one upper trough departs from the East after Sunday while energy digging in from the northeastern Pacific reinforces western U.S. mean troughing that should finally emerge into the Plains by around midweek. There is a decent signal in the guidance that this pattern should produce active weather over a significant portion of the lower 48 next week--including rain/snow over the West, eventually a vigorous low pressure system over the Plains/Upper Midwest with some snow to the northwest of its track, and a threat for areas of heavy rainfall plus strong to severe convection over some southern areas of the central U.S. However within this broad theme there are a number of uncertainties for details that temper confidence in specifics of the forecast, not only for the main area of focus over the western-central U.S. but also frontal position over the East due to differences in how leading shortwave energy initially ejecting across the Plains ultimately evolves. ...Guidance Evaluation/Predictability Assessment... Model guidance remains consistent with the upper trough departing from the East early in the period. And fortunately, the 00/06Z model cycle and the new 12Z cycle is showing better agreement compared to the last few cycles with the western trough as well, though with typical lingering differences in the details. One such detail is leading shortwave energy in the base of the trough over the northern Rockies/High Plains early Sunday that shows differences in its ejection across the northern tier and its effects on frontal position in the north-central and northeastern U.S. by Monday-Tuesday. The 00Z UKMET and GFS were among the stronger solutions with this shortwave and pushed the front farther south compared to the 06Z GFS/00Z ECMWF and CMC that deflected the shortwave on the northern side of the ridge. The WPC forecast leaned toward the latter cluster given continuity and not much support for the southward extent of the UKMET especially for Great Lakes shortwave in individual ensemble members. The next shortwave with notable differences stems from energy in the Gulf of Alaska in the short term, and is forecast to drop south across the northeastern Pacific/western Canada coast to form possibly a potent shortwave near the Pacific Northwest on Monday. This feature varies somewhat with its position but particularly varies in strength, which affects a surface low underneath as well. Most guidance is now indicating a small closed upper low but the 00Z and new 12Z ECMWF are persistent in showing an open shortwave farther east in the northwest and a weaker, displaced surface low. The ensemble spaghetti plots are extremely messy over the eastern Pacific and western U.S. so detail confidence remains quite low. The WPC forecast continued with a solution stronger than the ECMWF but not as strong as the other guidance. By Tuesday-Thursday, model agreement has improved regarding the evolution of the trough and its movement, with the 00Z ECMWF a bit weaker than its previous runs but clustering better with other guidance. GFS runs since 00Z have been consistent in showing a solution similar to what the ECMWF has had, namely a upper low that closes off in the northern Plains Wednesday and moves into the Midwest Thursday, and the CMC is similar as well. The track of the associated surface low is also fairly well clustered for the late medium range period. Thus models all indicate an impactful storm system across the central U.S. despite differences in the exact details. Trailing flow could bring another system toward the Pacific Northwest by Wednesday-Thursday, which is now advertised by the bulk of guidance after previous cycles of the GFS did not show this feature. Despite better agreement now for a system, timing of the shortwave track remains questionable. Better agreement between GFS/ECMWF/CMC deterministic guidance led to the WPC forecast utilizing a blend of these early in the period, and even maintained a majority of operational models through the latter part of the period though phased in some EC and GEFS ensemble means to temper individual model differences. ...Weather Highlights/Threats... Early in the period expect the best rain/mountain snow focus to be over the Pacific Northwest and central West Coast. However the details of location and intensity are unusually uncertain for a forecast only 3-4 days out in time as guidance varies widely for the strength and track of arriving low pressure. Lighter activity should prevail eastward through the northern Rockies. Then some moisture should extend southward into the Sierra Nevada, with rain and mountain snow extending across central and possibly some southern parts of the West. By Tuesday the southern Montana into Colorado Rockies and north-central High Plains should begin to see a favorable combination of upper trough dynamics and low level upslope flow that would increase precipitation over those areas, with the High Plains possibly seeing some springtime snow in addition to the Rockies. Potentially strong low pressure that may track from the Plains into the Upper Midwest would extend snow farther northeast across the northern tier along with strong winds. Meanwhile in the warm sector, there will be increasing coverage and intensity of rainfall over the eastern Plains/Mississippi Valley with the establishment of moist low level flow from the Gulf of Mexico. Persistence of the Gulf inflow could lead to a couple days or so with a heavy rain threat over or near the Lower Mississippi Valley. Also the Storm Prediction Center is monitoring the potential for severe weather over some southern areas in the central U.S. Check their latest outlooks for more information. Farther north, a front draped over the Midwest could also provide a focus for rainfall though likely with lower totals given less moisture/instability. Lack of confidence in some specifics of eastern Pacific/western U.S. flow maintains the potential for some changes in the above most likely scenario. Colder air moving into the West will initially bring highs down to as much as 10-20F below normal over the Northwest/northern Rockies as of Sunday. An area of minus 10-25F anomalies for highs should then reach into the Intermountain West, Rockies, and northern-central Plains by next Tuesday-Wednesday. The northern half of the Plains should still see highs around 15-20F below normal on Thursday. Sunday should provide the best potential for some locations in the Northwest to see max temperatures near or below current record cold highs but Monday could still produce a few lingering records. Meanwhile most of the eastern half of the country should trend from mostly below normal temperatures (minus 5-15F anomalies) on Sunday, and potential for a late frost across parts of the southeastern quadrant of the country, to mostly above normal readings (plus 5-15F anomalies for highs and perhaps slightly warmer for morning lows) spreading from west to east after the weekend. However confidence is lower for exact temperatures over the northern half of the East due to uncertain position of a front during the first half of next week. Tate/Rausch 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 rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Southeast, the Southern Plains, and the Ohio Valley, Mon-Thu, Apr 11-Apr 14. - Heavy snow across portions of California, the Central Great Basin, and the Pacific Northwest, Mon, Apr 11. - Heavy snow across portions of the Pacific Northwest and the Northern Great Basin, Sun-Mon, Apr 10-Apr 11. - Heavy snow across portions of the Central Rockies, the Central Plains, the Central Great Basin, the Northern Plains, and the Northern Rockies, Mon-Wed, Apr 11-Apr 13. - Heavy snow across portions of the Central Plains, the Upper Mississippi Valley, and the Northern Plains, Tue-Thu, Apr 12-Apr 14. - Severe weather across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains, Mon-Wed, Apr 11-Apr 13. - Flooding possible across portions of the Southeast. - Flooding occurring or imminent across portions of the Southeast and the Middle Mississippi Valley. - High winds across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Southern Rockies, the Southern Plains, and the Southwest, Sun-Wed, Apr 10-Apr 13. - Much below normal temperatures across portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Ohio Valley, Sun, Apr 10. - Much below normal temperatures across portions of the Southern Appalachians, the Mid-Atlantic, the Central Appalachians, and the Ohio Valley, Sun-Mon, Apr 10-Apr 11. - Enhanced wildfire risk across portions of the Southern Rockies, the Southern Plains, and the Southwest, Sun-Tue, Apr 10-Apr 12. 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