Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM 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 Mississippi Valley... ...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 expected, with the biggest threat across the Mississippi Valley but potentially spreading eastward ahead of the cold front. By late week, at least some energy from the closed low should shear off to the northeast due to a blocky ridge in the western Atlantic, while the flow upstream is uncertain but chances are another weaker trough will move into the West. ...Guidance Evaluation/Predictability Assessment... Recent model guidance continues to indicate a developing western trough becoming a deep closed upper low as it tracks into the central U.S., though timing and track differences between models continue to be an issue. For a few days now, the GFS has been a fast and north outlier, with the ECMWF and CMC the farthest west/south with the surface low Wednesday into Thursday. While this continues to be the case, the 00Z ECMWF and the newer 12Z run is slightly faster than it was a day or so ago, and shows a more west-east oblong than circular height pattern (so not indicating troughing as far south through the Plains/Mississippi Valley) that would push the cold front faster than in previous runs. Meanwhile, the 06Z and 12Z GFS runs were still fast with the closed low to develop and not as amplified farther south compared to other guidance, but generally closer to consensus than the 00Z and previous runs, as upstream energy spilling into the Pacific Northwest around Wednesday shows a more favorable track in the more recent GFS runs. So overall it seems the guidance is at least converging a bit even though the differences remain. Individual ensemble members and thus the ensemble means cluster with their deterministic counterparts, which does not increase confidence in one solution over the other. The WPC forecasts have been favoring a slower track of the upper/surface lows compared to the GFS. For this cycle, stuck with that with a deterministic model blend favoring the ECMWF for the first part of the period, leading to a forecast a bit faster than continuity with the surface low and associated fronts, particularly given the ECMWF adjustment. Beyond Wednesday/Thursday, flow upstream of that main upper low feature is quite uncertain with significant model variability. As noted the 06Z and 12Z GFS runs did look closer to consensus with an initial bout of energy spinning near the Pacific Northwest Wednesday/Thursday, but the track of that feature varies from serving to enhance and elongate the upper low (00Z ECMWF) or maintaining a troughing in the West into late week (06Z GFS and newer 12Z GFS and ECMWF and the EC ensemble mean). The latter seems more likely now that most 12Z guidance is in. For the WPC forecast created with the 00Z/06Z cycle, heavily favored the ECMWF ensemble mean amid rapidly increasing model discrepancies. ...Weather Highlights/Threats... Beginning Tuesday, mountain snow will be ongoing across particularly the Oregon Cascades as well as farther inland across the Intermountain West. Meanwhile, the surface low pressure system should be consolidating and so a favorable combination of upper trough dynamics and low level upslope flow should increase precipitation, yielding a springtime heavy snow threat into the Rockies and the northern Plains. As the strong low pressure looks to track from the Plains into the Upper Midwest Wednesday into Thursday, high winds are expected along with the snow, possibly creating blizzard conditions. 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 from eastern parts of the southern/central Plains into the Mississippi Valley eastward. Heavy to excessive rainfall concerns may focus on the southern side across the Lower Mississippi 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. While these wintry weather/heavy rain/severe weather threats are generally coming into better focus, continue to monitor forecasts for additional changes in timing and location of these impacts. The western U.S. should see several days of below normal temperatures, with daytime highs 20+ degrees below normal shifting eastward with time into the north-central CONUS. 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. Tate/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