Extended Forecast Discussion NWS Weather Prediction Center College Park MD 225 AM EDT Sun Apr 14 2019 Valid 12Z Wed Apr 17 2019 - 12Z Sun Apr 21 2019 ...Yet another major spring storm mid-late next 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 but be replaced by an upper low late Friday coming into Southern California with little fanfare. ...Guidance Preferences... Ensemble spread continued to decrease markedly in the Rockies to start the period with the ECMWF ensembles largely shifting slower like the GEFS members have been. Blend of the guidance sufficed to start, though the Canadian was perhaps too strong with northern stream flow. Favored a mean position between the ECMWF/GFS and their ensemble means which differed in how the system evolved east of the Mississippi. Unclear how much the southern portion of the upper trough remains separated from the flow to the north, perhaps slowing the system down even more by the weekend. Pacific Northwest will see a front push through the region Friday through the weekend, reaching the Upper Midwest and stretched back to California. Timing via a consensus has been fairly steady but deterministic runs have been wavering. ...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. The 12Z GEFS mean was forecasting 24h precipitation amounts much higher than typical for this lead time over parts of MN/WI/MI. 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. Fracasso 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