Extended Forecast Discussion NWS Weather Prediction Center College Park MD 306 AM EDT Fri Apr 08 2022 Valid 12Z Mon Apr 11 2022 - 12Z Fri Apr 15 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 across the South... ...Overview... The latest guidance continues to support an amplified and active weather pattern across the lower 48 next week. A reinforced western U.S. trough should finally emerge into the Plains by around midweek and a vigorous low pressure system developing over the Plains/Upper Midwest. This is likely to bring an array of significant weather across the CONUS... including rain/snow in the West, and a leading heavy rainfall/severe weather threat across the South/Midwest, with late season snow possible to the north and west of the low track later next week. Amplified ridging off the East Coast should drive this system more northward into eastern Canada, as the next (likely less amplified) trough enters the West around Friday/day 7. ...Guidance Evaluation/Predictability Assessment... The main system of concern in the medium range period surrounds an upper low dropping out of the Gulf of Alaska in the short range, reaching the Pacific Northwest by day 3/Monday. Right off the bat, models struggle with the details of the energy as it moves across the West days 3-4. Differences really begin to show by day 5 and beyond as the trough sharpens and moves out into the Plains. The last few runs of the GFS have been consistently much quicker with the developing low as it lifts into the Upper Midwest. The CMC, ECMWF, and the UKMET are slower, but with latitudinal differences in placement. The ensemble means generally side with their deterministic counterparts, but do seems to more support a slower solution for now. Despite significant timing questions, there is good agreement on a closed low forming over the Plains by Wednesday-Thursday and majority of the guidance suggests a decent storm system traversing the central part of the country. The blend for the overnight WPC progs weighted the slower solutions more, with increasing ensemble means by the latter half of the period. This afforded a good middle ground solution for low placement and also good continuity with the previous forecast as well. By next Friday, the next system should near/enter the West Coast. Again, plenty of timing/strength differences and given the late period, a blend towards the ensemble means seemed best at this point. ...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 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 should 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. The pattern certainly suggests a heavy rain/severe weather/wintry weather threat, but details on where these hazards occur and when remains very uncertain still with plenty of forecast refinements to come. Western U.S. should see several days of below normal tempeatures, with daytime highs 20+ degrees below normal shifting eastward Mon-Wed. Some moderation likely by later in the week across the West, though still below normal with additional troughing moving in. By next Thursday-Friday, core of the cold should be over the northern Plains with anomalies 10-20F below normal. Meanwhile, ahead of the big storm, expect temperatures from the south-central U.S. to the East to be above normal, but trending back towards normal following passage of the cold front. Santorelli/Tate 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