Extended Forecast Discussion NWS Weather Prediction Center College Park MD 307 AM EDT Sat Apr 09 2022 Valid 12Z Tue Apr 12 2022 - 12Z Sat Apr 16 2022 ...Active weather is likely next week, with heavy snow spreading from higher elevations of the West into the Northern Plains 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 looks to emerge into the Plains by around midweek as a vigorous closed low and associated surface low develop over the Plains/Upper Midwest. Initially, this should bring heavy mountain snows out west, with heavy snow and possible blizzard conditions spreading north and west of the low track into the northern Plains. In the warm sector of the system, severe weather and heavy to excessive rain is likely across parts of the Deep South and potentially eastward. By late week, a blocky ridge in the western Atlantic should steer the closed upper low in a more northerly direction into eastern Canada as the next trough moves into the West. ...Guidance Evaluation/Predictability Assessment... Though model guidance is united in showing the developing western trough becoming a deep closed upper low as it tracks into the central U.S., ample differences remain with the timing and track of the upper and surface low features. For a few days now, the GFS has been and continues to be a fast and north outlier, with the ECMWF and CMC the farthest west/south with the surface low Wednesday into Thursday. The last couple of runs of the ECMWF however, including tonights new 00z run, seem to be trending faster with the system. Not quite as fast still as the GFS, but the two may be coming into somewhat better agreement and this warrants watching. The ensemble means generally follow their deterministic counterparts, which does not increase confidence in one solution over the other. All of this seems to be related to strength and interactions of pieces of energy embedded within the larger Western U.S. trough as early as day 3/Tuesday. So perhaps, once these details get resolved, models may start converging on a solution as it moves farther downstream. WPC continuity has been favoring the more southerly/slower track and so with no clear indication to shift that thinking, tonights forecast also leaned heavily on the ECMWF/CMC and respective ensemble means. Also considerable differences late period regarding the next system into the West. GFS runs much weaker/faster with energy dropping out of the Gulf of Alaska into the Pacific Northwest. ECMWF much stronger, with another compact closed low over the Pacific Northwest by next Friday. Ensembles also show considerable spread, so seems prudent to stick close to the ensemble means at this point, especially given the late period timing. ...Weather Highlights/Threats... Beginning Tuesday, mountain snow will be ongoing across the Washington/Oregon Cascades as well as farther inland across the intermountain West. Meanwhile, the low pressure system should really begin to ramp up and so a favorable combination of upper trough dynamics and low level upslope flow should increase precipitation and a springtime heavy snow threat into the Rockies and especially the northern High Plains. Strong low pressure looks to track from the Plains into the Upper Midwest Wednesday into Thursday with snow spreading into the northern Plains along with strong winds, possibly creating blizzard conditions. Meanwhile in the warm sector, there will be increasing coverage and intensity of rainfall ahead of the attendent cold front from the Mississippi Valley eastward. The greatest threat for heavy to excessive rains and severe weather looks to converge over or near the lower Mississippi Valley/Tennessee Valley with several days of persistent gulf moisture and instability. Farther north, dynamics wrapping around the low may support an additional area of modest rainfall across the Upper Mississippi Valley. While this overall pattern certainly suggests a heavy rain/severe weather/wintry weather threat, but details on where these hazards occur and when remains uncertain still, with plenty of forecast refinements to come. The western U.S. should see several days of below normal temperatures, with daytime highs 20+ degrees below normal shifting eastward with time. Some moderation is likely by later in the week across the West, though still below normal with additional troughing moving in. By next Thursday-Saturday, the core of the cold should be over the northern Plains with low temperatures 10-20F below normal and highs even approaching 30F below average. 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