Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1151 AM EDT Sun Apr 14 2019 Valid 12Z Wed Apr 17 2019 - 12Z Sun Apr 21 2019 ...Yet another major spring storm mid-late week will pack a heavy rainfall and severe weather threat for the central to eastern U.S... ...Overview... Potent upper level low will exit the Four Corners region Wednesday and work its way eastward/northeastward as ridging builds in the western Atlantic. This will lead to a dynamic spring storm again for the central states with rain, severe weather, and some northern fringe snow. Ridging will also push into the West Coast,to be partially replaced by an upper low tracking into Southern CA into Saturday and shearing over the Southwest to the southern Plains next Sunday with little fanfare. The system is kicked out as more unsettling/wetter Pacific trough energies and height falls dig back upstream and inland across the West Coast. ...Guidance Preferences... 06 UTC GFS/GEFS and 00 UTC ECMWF/ECMWF ensemble forecasts now cluster extremely well and maintain good continuity days 3-7. WPC progs were mainly derived from a composite blend of these guidance pieces. Greater weighting was applied to the deterministic models for extra detail consistent with a pattern with seemingly above normal predictability. However, it remains a bit less certain the extent the southern portion of the upper trough remains separated from the flow to the north. The 00 UTC UKMET and especially the 00 UTC Canadian delay stream phasing compared to the GFS/ECMWF, perhaps slowing the system down more by the weekend. ...Weather Highlights/Threats... Significant precipitation will again increase into Wednesday and spread from the Mississippi/Missouri Valleys through the East as low pressure strengthens over the Plains and Corn Belt. Multi-inch rainfall totals with local flooding are probable (enhanced in embedded convection) both along/ahead of the front and to the north/northeast of the surface low. Consult SPC for the latest on the severe weather risk. Mild temperatures will precede the front (10-15F above average) to be replaced by cooler than average temperatures after its passage. Upstream, the Northwest will see a front with modest precipitation push through the region Friday and the weekend, reaching the Upper Midwest and stretched back to CA. Fracasso/Schichtel Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml