Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1210 PM EDT Tue May 14 2019 Valid 12Z Fri May 17 2019 - 12Z Tue May 21 2019 ...Overview and Weather Highlights/Threats... Overall, amplified mean troughing aloft will bring a wet period to a large portion of the western U.S. and Plains states during the weekend to early next week. Much of the western US to the northern high Plains will turn colder, with much of the mid-lower MS Valley eastward turning more summerlike. Guidance is steadily trending toward resolving the leading strong trough progressing from the West and Rockies Fri/Sat and in ernest over the central then east-central states from the weekend into early next week. This neg-tilt system will spawn surface system genesis and offers rounds of locally heavy convection/severe weather as per SPC. Underneath, a gradually weakening closed low is expected to meander from the northern to eastern Gulf of Mexico and offer some heavy rain potential for southern Florida. There is some agreement that upstream flow will bring another round of strong height falls and widespread precipitation/terrain enhanced snows to the western states Fri into this weekend, continuing inland early week across the Great Basin to the High Plains. Upstream, there is a still uncertain guidance signal to develop a deeper low in the eastern Pacific early next week that offers potential to reach CA and the Great Basin/Southwest by Tuesday 21 May along with renewed unsettled weather/precipitation. Meanwhile, model and ensemble solutions continue to show above normal forecast spread with respect to downstream northeastern U.S./Mid-Atlantic flow through the medium range period as a series of potent Canadian upper systems progress within an energetic northern stream. These upper systems and surface system reflections have trended stronger into the weekend. Teleconnections relative to the negative height anomaly center associated with the West Coast mean trough then favor modest cyclonic flow aloft into early next week. ...Guidance Assessemnt and Preference... The latest deterministic models (06 UTC GFS/FV3 and 00 UTC ECMWF/UKMET/Canadian) seem to offer better than expected forecast clustering Fri into Sun morning, but confidence remains somewhat muted due to less than stellar continuity issues. Even so, the WPC product suite primarily was derived from a composite model solution during this period that seems increasingly reasonable before quickly transitioning to the much more compatable ensemble means (06 UTC GEFS/00 UTC ECMWF ensemble mean) into early next week amid growing forecast spread. 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