Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 PM EDT Sun Apr 17 2022 Valid 12Z Wed Apr 20 2022 - 12Z Sun Apr 24 2022 ...Wintry Storm threat from the West to the North-Central U.S. late week/next weekend... ...Weather Pattern Overview... The departure of the strong low pressure system from New England will leave a surface high in its wake across the eastern U.S. on Wednesday. At the same time, an organizing storm system just north of the Canadian border will bring a cold front eastward across the north-central U.S. with a weakening low farther south across the central Plains. Attention then turns to the western U.S. by Friday with advent of an amplified upper level trough/frontal system with an enhanced precipitation focus. The cooling/unsettling system then works inland over the Intermountain West and leads into later next weekend development of a potentially strong surface low over the cooled central/northern Plains to include the threat for heavy wrapping winds/snow/ice on the northern periphery of the system and an emerging pre-frontal rainfall/strong convection area broadly underneath and into the warming/moistening east-central U.S. Meanwhile, a building downstream upper ridge axis over the Appalachians may allow closed trough development cut underneath over southern FL and Cuba to increase/focus next weekend rainfall. ...Model Guidance Evaluation... The 00/06 UTC model guidance suite appears to have above average agreement on the main synoptic scale features through Thursday night. By Friday, the GFS remains more progressive with the axis of the main trough axis across the western U.S., and this difference is even more apparent going into Saturday/Sunday across the High Plains. Meanwhile, the 00 UTC CMC and ECMWF are in close agreement and depict a closed low evolving over the Southwest by Friday night, and this also has support from the 00 UTC UKMET. This amplified and less progressive trend continues through next weekend, leading into deepening trends with cyclogenesis over the Plains. This would result in an increased and less progressive QPF swath compared to the 13 UTC NBM 4.0. Elements of this deepening system can be traced back to former Pacific Typhoon Malakas that is currently a deep extratropical low slamming into the Aleutians. Another deep Pacific low expected track into the Aleutians then the Gulf of Alaska later week/next weekend also portends a solution on the more amplified side of the full guidance envelope downstream over the lower 48. Accordingly, model preference for the later half of the forecast period for the WPC medium range product suite was a CMC/ECMWF/ECENS mean blend as a starting point. 12 UTC models overall remain consistent with this plan. The GFS trended less progressive and the ECMWF/Canadian slightly more progressive next weekend, a bit more into common alignment. This seems to bolster forecast confidence in the threat, albeit with slightly more progression. ...Sensible Weather/Threats... In the precipitation department, the West Coast region is expected to remain active with a strong cold front and onshore flow directed inland across the mountainous terrain of central and northern California. This spring event will deliver some highly beneficial precipitation to drought-stricken areas of California, with the potential for several inches of rain in some areas next week, and several feet of snow for the Sierra. Elsewhere across the continental U.S., improving weather can be expected for the Northeast as the strong storm system moves out of the region. Deep warming over the East into next weekend may be tempered from the Northeast down into the Mid-Atlantic by frontal damming that may prove slower to erode than shown in the models. Another round of organized showers and storms are expected to develop across the central U.S. and extending northward to the Great Lakes through late week as Gulf moisture is advected northward ahead of the organizing storm system over the central Plains. Additional moderate to heavy snow is also expected for portions of the northern Rockies for Friday and into the weekend, with an increasing threat for heavy snow to spread and intensify in particular across the northern High Plains and Dakotas/vicinity next weekend. Schichtel/Hamrick 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