Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1212 AM EDT Sat Mar 23 2019 Valid 12Z Tue Mar 26 2019 - 12Z Sat Mar 30 2019 ...Guidance Assessment/Preferences... Models and ensembles seem reasonably compatable into Days 3-4/Tue-Wed and a favored composite solution de-emphasizes the less predictable smaller scale features. While guidance overall continues to offers a fairly similar larger scale CONUS and vicinity pattern evolution over for much of next week, run-run variance with a multitude of mid-smaller scale embedded systems and stream interactions do grow quickly with time. This is especially evident with recent GFS and to a lesser extent FV3 runs that do not cluster as well with latest GEFS/ECMWF ensembles as the ECMWF. Variance seems to mainly stem from differences in the handling of east-Pacific trough energies. Prefer to maintain WPC and guidance continuity better with a 18 UTC GEFS mean and 12 UTC ECMWF/ECMWF ensemble mean blended forecast approach day 5-7. ...Weather Highlights and Hazards... A southern stream front with moisture and enhanced precipitation focusing waves ejects across the Southeast into Tuesday. The frontal low/coastal wave will cut underneath and interact with a cooling northern stream frontal drape overtop whose deepened post-frontal high pressure then settles down through the central and eastern U.S. Meanwhile, a protracted series of Pacific systems with associated height falls and enhanced precipitation swaths are slated to track onshore and across much of the West through next midweek ahead of an mean closed low/trough reinforced just off West Coast. Heaviest precipitation/heavy mountain snows threaten northern California/Oregon through the northern Rockies. It is expected that the bulk of Pacific trough energy will eject through the West Wed/Thu to emerge over the Plains into later next week to induce cyclo/frontogenesis. This may occur just as a renewed northern stream may force cool air down into the unsettled n-central states. This airmass would prove to be in stark contrast to a rapidly warming airmass spreading from the east-central U.S. to eastern U.S. into next weekend. Deepening return flow from the Gulf of Mexico would fuel an expanding risk of enhancing rains/convection to channel between the approaching fronts and slowly retreating eastern U.S. high pressure. The emerging heavy rain area threatens areas of the Mississippi Valley/Midwest (where flooding is ongoing) heading into next weekend. Uncertainty remains regarding heaviest rainfall amounts/placement, but the guidance signal for developent continues to grow. 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