Extended Forecast Discussion NWS Weather Prediction Center College Park MD 110 PM EDT Sun Apr 12 2020 Valid 12Z Wed Apr 15 2020 - 12Z Sun Apr 19 2020 ...Overview and Guidance/Predictability Assessment... Latest models and ensembles paint a similar picture in showing a stable longwave pattern aloft over the lower 48 states Wed-Fri downstream of an amplified northeast Pacific/AK mean ridge. In this period, a lead shortwave energy slides across the Great Lakes as upstream impulses dig into the Northwest and over the Rockies into broad troughing across the Central and Eastern states. This pattern also favors the spilling of cold lower atmospheric Canadian air down over much of the nation. A lingering forecast question continues to be with the handling of shortwave energy undercutting the Pacific/AK Ridge later next week. By Thu/Fri, models mostly agree this energy may close off into an upper low and slide southward along or just offshore California before progressing inland across the U.S. southwest and southern tier next weekend. Deterministic models continue to show variability both with respect to timing and intensity, but forecast spread/forecast confidence is gradually improving. Ensemble means are in line, but by nature are not as detailed consistent with average predictability. Meanwhile, a still active northern stream flow across the mid-higher latitudes of the central and eastern U.S. is expected to provide upper support favorable for development and progression of several developing frontal waves, The models now seem to be keying in a low lifting from the Midwest Fri to the Northeast Sat whose moderately expanding precipitation shield could include some risk of organized snows in the more deeply cooled airmass on the northwest periphery. Overall, the WPC medium range product suite was mainly derived from a composite of best clustered 00 UTC GFS/GEFS mean, 00 UTC ECMWF/ECMWF ensemble mean and 13 UTC National Blend of Models guidance. ...Weather/Hazard Highlights... There is potential for lingering convective rains along a wavy trailing frontal boundary settled over the Southeast U.S. that will continue to focus deeper moisture mid-later week. Out West, additional shortwave energy digging southward through the Intermountain West will again support snow in parts of the northern/central Rockies Wed-Thu. As an unsettling eastern Pacific closed low/trough enters the Southwest/Four Corners region next weekend, it should also begin to tap a return of downstream Gulf of Mexico moisture to fuel showers and thunderstorms back into the forecast over the South. This occurs as a developing frontal wave/precipitation lifts overtop from the Midwest to the Northeast. 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