Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Sun Apr 10 2022 Valid 12Z Wed Apr 13 2022 - 12Z Sun Apr 17 2022 ...Potent storm system to bring heavy snow/blizzard conditions across the Northern Plains with heavy rainfall and severe weather from the Gulf Coast to the Mid-Mississippi Valley... ...Overview... The latest guidance continues to support an active weather pattern across the lower 48 into next weekend. The main system of interest is an amplified trough/developing closed low over the northern U.S./Upper Midwest which should spin up a rather impressive looking spring storm system. This system brings a full array of weather hazards mid to later next week... including heavy snow and possible blizzard conditions to the north and west of the low track across the Northern Plains and severe weather and heavy to excessive rainfall in the warm sector. Upstream, uncertainty is high regarding flow into the Western U.S. but changes are that another trough may kick out into the West next weekend. ...Guidance Evaluation/Predictability Assessment... Models continue to show higher than avearge uncertainty surrounding an amplified trough in the central U.S. which eventually develops into a deep closed upper low tracking across the Northern Plains and Upper Midwest. While all models now suggest a rather significant storm system, there remains a lot of questions on track and timing of the surface low and attendent cold front across the South and Midwest. The 18z/Apr 9 GFS is the fastest with closed low development, but is actually not too far out of line with location of surface low pressure at day 3-4 in the Upper Midwest. After this, likely a result of a much blockier Western Atlantic ridge, the GFS gets much faster with steering this low quickly northward, while the ECMWF and CMC suggest the upper system is sheared/redevelops over the Great Lakes/eastern Canada next weekend. Ensemble means do not really give a clear answer here as they generally continue to follow their deterministic counterparts. In the interest of continuity, continued to favor the ECMWF over the GFS, with increasing weighting towards the ECENS/GEFS means late period. Beyond Wednesday/Thursday, flow upstream across the West becomes very uncertain with some significant model variability especially by the day 6-7 time frame. There is increased consensus on some kind of open shortwave (or closed low) into the Pacific Northwest on Friday. Models suggest another trough into the West next weekend, but the details on embedded energy within that trough and amplifcation become very murky next weekend with very poor model run to run continuity. A blend heavily weighted towards the ensemble means gets some weak troughing across the West with a hint at low pressure once again moving into the Plains next Sunday. ...Weather Highlights/Threats... Some lingering snowfall is likely as the period begins Wednesday across the West, but by then a well developed storm should be tracking across the northern Plains/Upper Midwest with a significant snow storm likely to the north and west of the surface low across the Dakotas and northwest Minnesota. Heavy snowfall, possibly exceeding a foot in some locations, with gusty winds could create blizzard conditions leading to hazardous travel and power outages in many areas. Meanwhile in the warm sector, there will be increasing coverage and intensity of rain and thunderstorms ahead of the attendant cold front given persistent Gulf moisture and instability. The Storm Prediction Center's extended outlook indicates severe potential across the lower and middle Mississippi Valley on Wednesday, with more uncertain potential farther east into the Southeast on Thursday. Heavy to excessive rainfall concerns may focus on the southern side across the Lower Mississippi and Tennessee Valley, but farther north, dynamics wrapping around the low may support an additional area of modest rainfall across the Upper Mississippi Valley. This may cause localized flooding and flash flooding issues there as well particularly if rain falls over frozen or snow covered ground. Rainfall may linger through Friday across the Southeast as the western part of the boundary stalls across the region. Out West, moderate to heavy rain/mountain snows are possible across parts of California/Oregon with the next low pressure system moving in late this week. Moisture looks to spread east into the intermountain West, with more uncertainty by next Sunday regarding precipitation into the Plains. Much below normal temperatures (with anomalies 20+ degrees below average) will shift eastward with time into the northern Plains into next weekend. Some moderation is likely by later in the week across the West, though still below normal with additional troughing moving in. 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 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